9 1985 by The Humana Press Inc. All rights of any nature whatsoever reserved. 0163-4984/8510811-0157502.00
Calcium, Magnesium, and Zinc Status of Young Adult Females on an Adequate Protein and Calorie Intake TOLA A T I N M O ~ A N D M A R J O R I E FRIDAY Department of Human Nutrition, College of Medicine, University of Ibadan, Ibadan, Nigeria Received D e c e m b e r 18, 1984; Accepted February 1985
ABSTRACT Calcium, magnesium, and zinc balances were determined in eleven young adult college females (mean age, 24.9 + 2.35) during a 39-d metabolic study when the subjects were fed an adequate calorie and protein diet based on habitually consumed foods. Analysis showed that the dietary contribution of calcium, magnesium, and zinc to the RDA were 53.6, 26.4, and 57.9%, respectively. Mean fecal losses of calcium and magnesium were low, while fecal zinc losses were higher than the daily intake. Mean urinary excretion of calcium was within the normal range, but was low for magnesium whereas urinary zinc was higher than normal. Mean daily apparent retentions of calcium and magnesium were positive, whereas positive apparent retention for zinc were observed in four of the subjects. Plasma calcium and magnesium remained normal, but mean plasma zinc declined at the end of the study. Significant correlations were observed between the fecal losses of calcium and magnesium and calcium and zinc. Urinary calcium also correlated significantly (P < 0.05) with urinary magnesium, but not with zinc. It appears that adequate protein and calorie intake in the presence of low dietary intake of calcium, magnesium, and zinc has no significant effect on calcium and magnesium status whereas a lowering effect on plasma zinc and apparent zinc retention was observed in the subjects studied. *Author to whom all correspondence and reprint requests should be addressed. Biological Trace Element Research
15 7
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Index Entries: Calcium, status in young adult females; magnesium, status in young adult females; zinc, status in young adult females; protein intake, and trace-metal status of young adult females; calorie intake, and trace metal status of young adult females.
INTRODUCTION The adequacy of a diet in terms of minerals is influenced not only by the quantity but also by the variety of dietary components, as well as the interaction between the minerals themselves. The level of dietary protein has been shown to affect the absorption, retention, and excretion of calcium (1), magnesium (2), and zinc (3,4). Mineral utilization is also affected by the interactions of these elements. A diet consisting of milk and cheese with a high calcium content, and whole meal bread with high phytic acid content, resulted in positive zinc absorption. Subsequently, Greger and Snedeker (3) and Greger et al. (5) observed that high calcium intake had no effect on fecal or urinary zinc, nor on its apparent retention in adult males. Calcium and magnesium metabolism have been shown to be interrelated, and they both affect each other depending on the level present in the diet (6). High calcium intake increases the loss of magnesium from the body, particularly in the urine. Increasing the dietary level of magnesium, especially during adequate calcium intake, improves calcium utilization (6). Previous studies from this laboratory indicate that low dietary zinc intake and the subsequently low plasma zinc levels are associated with the generally low protein content of the habitual diet (9). Therefore, the purpose of the present study was to investigate the calcium, magnesium, and zinc status of young adult college females when their protein and calorie intakes were satisfactory.
MATERIALS AND METHODS
Subject and Study Design Eleven young adult students of 21-30 yr from the University of Ibadan population participated in a study that lasted 39 d. The subjects were studied under close supervision. Daily body weights were recorded between 7:00 and 8:00 am throughout the entire study period under standardized conditions (preprandial, post-voiding, and with light indoor clothing). All subjects engaged in their normal routine daily activities while maintaining a reasonably constant level of physical activity during the study period. Each subject kept activity records in which they were required to record their physical activity, waking hours, menstrual Biological Trace Element Research
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Ca, Alg, a n d Z n S t a t u s o f Y o u n g F e m a l e s
flow, a n d p h y s i c a l a n d e m o t i o n a l stress. There w e r e t w o 5-d b a l a n c e periods d u r i n g the s t u d y , o n the 15th-19th a n d on the 3 5 t h - 3 9 t h days.
Diet The diet w a s b a s e d on f o o d s habitually c o n s u m e d a n d w a s pres e n t e d in a g i v e n meal p a t t e r n that w a s similar to that w h i c h the subjects w e r e a c c u s t o m e d to. Tables la a n d b s h o w the c o m p o n e n t of the diet that w a s c o n s t r u c t e d to p r o v i d e 40 kcal/kg b o d y w t a n d 0.6 g/kg b o d y w t of protein.
Analyses Blood, f o o d , urine, a n d fecal s a m p l e s w e r e collected u s i n g p r e c a u tions to a v o i d trace mineral c o n t a m i n a t i o n . Blood s a m p l e s w e r e collected TABLE la Composition of the Experimental Diet Ingredients Bread Tea Sugar Margarine Gari (dried fermented cassava) Pepper (dried) Tomato stew (fresh) Onion (fresh) Palm oil Rice Beef Soft drinks
Quantity, g
Protein, g
Energy, kcal
100
7.8
232.22
Ad libitum
20 30 300 4 80 40 40 350 80 3 Bottles Total:
--
--0.75 0.48 0.80 0.48 -6.9 16.0 -33.21
--
120 219 263.25 13.2 17.6 16.4 360.0 420.0 213.4 360.0 2235.07
TABLE lb Daily Menu Breakfast Bread Tea Sugar Margarine
Quantity, g 100 Ad libitum
20 30
Biological Trace Element Research
Lunch
Quantity, g
Gari (cassava) Cooked meat Stew Okra soup Soft drinks 2
300 34.29 66.2 47 Bottles
Supper
Quantity, g
Rice Meat Stew Soft drinks
350 34.2 66.2 1 Bottle
VoL 8, 1985
160
Atinmo and Friday
at the beginning, midday, and end of the study period. Other samples were collected during the two 5-d balance periods and w e r e composited for determination of nutrients. A 1-g food sample was digested with 4 mL of 70% perchloric acid, heated at 150~ until the digest became colorless, and 50 mL glass distilled water were added. The mixture was filtered and m a d e up to 100 mL using deionized water. An aliquot was then read for calcium, magnesium, and zinc on AAS (Perkin Elmer) Model 3058 using appropriate standards. Fecal samples were precisioned and dissolved in 3N HC1 and m a d e to 100 mL volume in a volumetric flask. Zinc concentration was determined without any further treatment. Concentrations of calcium and m a g n e s i u m w e r e determined on 5 mL aliquots to which 5 mL of 0.5% l a n t h a n u m chloride solution was added. Frozen samples of urine w e r e thawed and 1:4 dilutions were m a d e with deionized water for zinc determination. For calcium and magnesium, 1:100 dilutions were m a d e using 0.5 l a n t h a n u m chloride solution (0.1 mL + 10 mL 5% LaC12). Frozen plasma samples were thawed and 0.5 mL of samples was diluted with 2 mL of deionized water for zinc determination for calcium and magnesium, 0.2 mL of plasma was diluted 50 times with 0.1% lant h a n u m chloride solution.
RESULTS There was a 0.9 kg decrease in the body weight of subjects at the end of the study compared to the beginning of study (55.3 vs 56.2 kg). This was not significant. Dietary intake of calcium, magnesium, and zinc were 268.15, 79.17, and 8.89 mg, respectively. These values represented 53.6% of the 500 mg/d r e c o m m e n d e d by the FAO/WHO Committee (7) and 33.5% of the RDA set by the US Food and Nutrition Board for calcium, 26.39% for magnesium, and 57.93% for zinc (8). Table 2 shows the group balance data for the three minerals studied. There was no significant difference between the fecal excretion of calcium, magnesium, and zinc during the first and second metabolic periods (P < 0.05). There were more variations in fecal calcium and magnesium during the first metabolic period compared to the second. A significant positive correlation (r = 0.642) was observed b e t w e e n fecal calcium and fecal zinc and also between fecal calcium and fecal magnesium (r = 0.97) (P < 0.05). Average urinary calcium/24 h was significantly higher during the first metabolic period than the second (P < 0.05). The differences between the urinary m a g n e s i u m and zinc for the first and second metabolic phases were not statistically significant. Urinary calcium was positively correlated with urinary magnesium.
Biological Trace Element Research
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Ca, ~g, and Zn Status of Young Females
161
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Biological Trace Element Research
Vol. 8, 1985
Atinrno and Friday
162
The a p p a r e n t absorptions for calcium a n d m a g n e s i u m w e r e 98 a n d 99%, a n d 86.77 a n d 90%, for the first a n d s e c o n d metabolic phases, respectively, w h e r e a s negative a p p a r e n t absorption was obtained for zinc. Table 2 s h o w s that a p p a r e n t retentions for calcium a n d m a g n e s i u m were positive, w h e r e a s that for zinc was negative. Table 3 s h o w s that the m i d p h a s e concentration of p l a s m a calcium was h i g h e r t h a n the others, but that difference was not significant (P > 0.05). Plasma concentration was h i g h e s t at the e n d of the s t u d y , compared to the other two phases, w h e r e a s plasma zinc was h i g h e s t at the b e g i n n i n g of the s t u d y a n d lowest at the end.
DISCUSSION The daily dietary intakes of the minerals were low c o m p a r e d to the US Food a n d Nutrition Board r e c o m m e n d a t i o n (8). This finding confirms the general observation that mineral intake in Nigeria is low c o m p a r e d to the r e c o m m e n d e d dietary allowance (9). Fecal excretion values of calcium, m a g n e s i u m , and zinc w e r e lower than values r e p o r t e d in the literature. These r e d u c e d values can be attribu t e d to the fact that the dietary intakes of the minerals were low. Fecal calcium a c c o u n t e d for less t h a n 2% of the intake for the two balance periods, indicating that almost the entire dietary intake of 265.15 m g was being absorbed in addition to the complete reabsorption of the secreted calcium. This finding is in a g r e e m e n t with that of H e a n e y et al. (10), Mazuoli et al. (11), a n d Allen (12) that an inverse relationship exists bet w e e n calcium absorption a n d calcium intake. At lower levels of calcium intake, the a m o u n t that is absorbed far exceeds that absorbed on h i g h e r intakes. Studies have also s h o w n that absorption efficiency c h a n g e s over a period of 1 w k with a c h a n g e from a high intake to a lower calcium intake (12,13). The p r o p o r t i o n of m a g n e s i u m absorbed is d e p e n d e n t on the dietary intake (14). The high p e r c e n t a g e of absorption of m a g n e s i u m o b s e r v e d in the p r e s e n t s t u d y came about as a result of the low dietary intake. This finding is also s u p p o r t e d by Barnes et al. (14), w h o reported a striking a n d p r o m p t reduction in the m a g n e s i u m content of the stool of his subjects following the institution of a low m a g n e s i u m diet after a transition TABLE 3 Mean Plasma Concentration of Ca, Mg, and Zn for the Two Balance Periods Ca,
Beginning Midway End
mg/lO0
mL
11.43 + 3.84 12.30 __ 3.26 10.03 _+ 1.5
Biological Trace Element Research
Mg,
mg/lO0
mL Zn,
2.33 _+ 0.14 2.44 _ 0.35 2.65 _+ 0.72
~g/lO0 mL
87.75 _+ 16.1 75.75 _+ 2.6 74.7 _+ 39.42 VoL 8, I98.5
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163
period. The high correlation b e t w e e n fecal calcium and fecal m a g n e s i u m suggests an interrelationship b e t w e e n their absorption. Fecal zinc excretion was higher than the dietary intake. The increase in the fecal zinc can be attributed to zinc of e n d o g e n o u s origin. The same observation was made w h e n Greger and Snedeker (3) fed two levels of protein and phosphorus to subjects. Fecal zinc was higher than dietary zinc intake w h e n subjects were fed low protein. Urinary calcium was 61 and 56% of the intake for the two metabolic periods, respectively. The low intake in this study is possibly the reason for the higher urinary levels recorded. This agrees with the finding of Knapp (15) that the proportion of calcium intake excreted is not constant at all levels of intake, but is highest on the low intake, decreasing rapidly as the intake increases. It was further suggested that this was particularly evident w h e n the intake was less than 5 mg/kg body weight. In this study the average intake/kg body wt was 4.76 mg. The level of dietary protein has also been repeatedly s h o w n to affect the amount of calcium excreted in urine (1,16). These workers, as well as others such as Kim and Linskwiler (17), have s h o w n that an increase in the protein content of the diet at any calcium level results in an increase in urinary calcium loss because of a reduction in the a m o u n t of filtered calcium absorbed by the kidneys. Mahalko (18) also s h o w e d that a less positive calcium balance results w h e n the diet provides increased protein. In the present study, both the calcium and the protein intakes were held constant for a long time. This could possibly explain the significantly lower urinary calcium loss observed. The low urinary m a g n e s i u m observed in this study can be attributed to the low dietary intake of the mineral. This finding is in agreement with that of Shroeder et al. (14), which indicated that urinary excretion of m a g n e s i u m is a close function of intestinal absorption and dietary intake. Urinary m a g n e s i u m , expressed as a percentage of intake, correlated significantly with the individual intake/kg body wt. The correlation was more significant than that for calcium, suggesting that the level of dietary intake affects the urinary excretion of m a g n e s i u m more than it does that of calcium. It has been shown that a relationship also exists between calcium and m a g n e s i u m in the renal tubule; that w h e n the calcium/ m a g n e s i u m ratio is high, more calcium will be excreted and more magnesium reabsorbed (19). The m e a n values for urinary zinc were higher than the reported normal range by McCance and W i d d o w s o n (20). Fell et al. (21) suggested that zinc was being w i t h d r a w n mainly from the skeletal muscle. The increase in the urinary zinc can thus be attributed to zinc of e n d o g e n o u s origin. Greger and Snedeker (3) observed an increase in urinary zinc with incresing dietary nirogen from 8.1 to 24.1 g/d, whereas dietary zinc levels remained constant. The dietary nitrogen fed in this study was about 5 g/d. This a m o u n t is less than the low protein fed by Greger and Snedeker (3). Since the only source of e n d o g e n o u s zinc is the muscle protein (21), it Biological Trace Element Research
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can therefore be suggested that muscle b r e a k d o w n has probably occurred to provide the zinc required for tissue metabolism in the presence of low dietary zinc intake. Apparent retentions of the minerals were higher during the second metabolic phase. This observation might occur because the subjects had fully adjusted and adapted to the diet by the second phase of the experimental period. Apparent m e a n retention of calcium was positive for both metabolic periods, except for one subject w h o was in negative balance during the first metabolic period. It was observed that her urinary calcium loss was greater than her daily intake. She, however, s h o w e d a positive balance during the second period w h e n she gained weight and excreted less calcium in urine. The positive balances observed were the result of the low excretion of calcium in both feces and urine. Low fecal calcium was primarily a result of the adaptation of the body to a constant low dietary intake, whereas the urinary loss was a result of the individual intake per kilogram body weight, plus the adequate protein intake. Spencer et al. (22) s h o w e d that calcium balance could be maintained by 200 mg calcium/d and 0.5 w/kg body wt of protein for meat. Begun and Periera (23) also carried out balance studies on normal children w h o were on a low calcium intake of 200 mg/d and found that all subjects were in positive balance, which became greater w h e n the intake was increased to 280 mg/d. The a m o u n t is only 11.8 mg higher than the content of diet in the present study. M a g n e s i u m balance was positive for the two balance periods. This indicates that these healthy y o u n g female adults had the ability to conserve m a g n e s i u m while on an adequate protein and calorie intake and at a comparatively low calcium intake. These findings are consistent with those of Barnes et al. (14), w h o conducted a short-term study with y o u n g adult females w h o were placed on a low magnesium diet with adequate calorie and protein. A p p a r e n t zinc retentions were negative for both metabolic periods because of an increase in both fecal and urinary losses. A l t h o u g h the overall retention was negative, some individuals were in positive balance. This could be attributed to their prior zinc status. The negativity in the apparent retention can also be the result of low dietary intake. It has been s h o w n that by increasing the zinc intake, retention also increased (24). Therefore, if the requirements of all subjects were to be met, a higher dietary zinc content was required. The m e a n concentration of plasma calcium at the end of the study fell within the normal range of 9.0-11.0 ~g/100 mL for adults (14). Plasma calcium is usually maintained at a constant level of approximately 10 mg/d by parathyroid h o r m o n e , calcitonin, and vitamin D (25). This level is not affected by intake (26).
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The m a i n t e n a n c e of n o r m a l p l a s m a m a g n e s i u m t h r o u g h o u t the s t u d y suggests that, despite the low dietary intake of the mineral, the m a g n e s i u m status was not a d v e r s e l y affected. The d e c r e a s i n g m e a n p l a s m a zinc levels o b s e r v e d d u r i n g the s t u d y w e r e p r o b a b l y a result of the low d i e t a r y zinc intake. Hess et al. (27) rep o r t e d a similar decline in the s e r u m zinc levels in y o u n g w o m e n o n a low zinc intake. In s u m m a r y , it appears that a d e q u a t e protein a n d calorie intake in the p r e s e n c e of low dietary intake of calcium, m a g n e s i u m , a n d zinc has no significant effect on calcium a n d m a g n e s i u m status, but has a lowering effect o n the plasma zinc levels a n d zinc retention of the subjects studied. The m e c h a n i s m by w h i c h this occurs n e e d s to be f u r t h e r studied.
REFERENCES 1. M. Hegsted and H. Linkswiller, J. Nutr. 111, 241 (1981). 2. R. Schwartz, M. A. Woodcock, S. D. Blakely, and I. Mackellar, Am. ]. Cdin. Nutr. 26, 510, 519 (1973). 3. J. L. Greger and S. M. Snedeker, J. Nutr. 110, 2243 (1980). 4. M. A. Colin, L. T. Taper, and S. T. Richey, Br. J. Nutr. 113, 1480 (1983). 5. J. L. Greger, P. Baligan, R. F. Abernathy, O. A. Bennett, and T. Peterson, Amer. J. Clin. Nutr. 31, 117 (1978). 6. M. Seelig, Am. J. Clin. Nutr. 14, 342 (1964). 7. FAO/WHO: Report of a FAL/WHO Expert Committee on Calcium Requirements, Rome, FAO Tech. Rep. Ser. 230 (1962). 8. US Food and Nutrition Board, Recommended Dietary Allowances, 9th ed., National Academy of Sciences, Washington, DC, 1980. 9. C. M. F. Mbofung and T. Atinmo, Nig. ]. Nutr. Sci. 1, 14 (1980). 10. R. R. Heaney, P. D. Saville, and R. R. Pecker, J. Lab. Clin. Med. 88 (1975). 11. G. Mazzuoci, J. Samchson, and D. Lazsi, J. Lab. Clin. Med. 52, 522 (1978). 12. L. H. Allen, Am. J. Clin. Nutr. 35, 783 (1982). 13. A. P. P. Walker, S. Aft. Med. ]. 40, 814 (1966). 14. H. A. Shroeder, A. P. Mason, and I. H. Tipton, J. Chronic Dis. 21,815 (1969). 15. E. L. Knapp, 1. Clin, Inv. 26, 182 (1947). 16. L. H. Allen, R. S. Bartbett, and S. D. Block, J. Nutr. 109, 1345 (1979). 17. V. Kim and M. G. Linskwiller, J. Nutr. 109, 1399 (1979). 18. J. R. Nahatko, H. H. Sandstead, L. K. Johnson, and D. B. Milne, Amer. J. Clin. Nutr. 37, 8 (1983). 19. F. W. Heaton, A. Hodginson, and G. A. Rose, J. Clin. Sci. 27, 31 (1964). 20. R. A. McCance and B. M. Widdowson, Biochem. ]. 36, 692 (1942). 21. G. S. Fell, A. Fleck, D. P.Cuthberson, K. Queen, C. Morrison, R. Bessert, and Grand Hussain, Lancet 280 (1973). 22. H. Spencer, L. Kramer, D. Osis, and C. Morris, Am. J. Clin. Nutr. 31, 2167 (1978). 23. C. Begun and S. Periera, Br. J. Nutr. 23, 905 (1969).
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24. S.J. Richey, M. K. Korslund, L. M. Gilbert, D. C. Fay, and M. F. Robinson, Am. J. Clin. Nutr. 32, 799 (1979). 25. S. K. Czarnecki, Trace Elements in Nutrition and the Adult Micronutrients, Vol. 38, R. A. Slater and D. Kritchevsky, eds., Plenum Press, N e w York, 1980. 26. S. E. Miller, Textbook of Clinical Pathology, 6th ed., William and Wilkins, Baltimore, 1960. 27. F. M. Hess, J. C. King, and S. Margen, J. Nutr. 107, 1610 (1977).
Biological Trace Element Research
Vol. 8, 1985
Calcium, Magnesium, and Zinc Status of Young Adult Females on an Adequate Protein and Calorie Intake TOLA A T I N M O ~ A N D M A R J O R I E FRIDAY Department of Human Nutrition, College of Medicine, University of Ibadan, Ibadan, Nigeria Received D e c e m b e r 18, 1984; Accepted February 1985
ABSTRACT Calcium, magnesium, and zinc balances were determined in eleven young adult college females (mean age, 24.9 + 2.35) during a 39-d metabolic study when the subjects were fed an adequate calorie and protein diet based on habitually consumed foods. Analysis showed that the dietary contribution of calcium, magnesium, and zinc to the RDA were 53.6, 26.4, and 57.9%, respectively. Mean fecal losses of calcium and magnesium were low, while fecal zinc losses were higher than the daily intake. Mean urinary excretion of calcium was within the normal range, but was low for magnesium whereas urinary zinc was higher than normal. Mean daily apparent retentions of calcium and magnesium were positive, whereas positive apparent retention for zinc were observed in four of the subjects. Plasma calcium and magnesium remained normal, but mean plasma zinc declined at the end of the study. Significant correlations were observed between the fecal losses of calcium and magnesium and calcium and zinc. Urinary calcium also correlated significantly (P < 0.05) with urinary magnesium, but not with zinc. It appears that adequate protein and calorie intake in the presence of low dietary intake of calcium, magnesium, and zinc has no significant effect on calcium and magnesium status whereas a lowering effect on plasma zinc and apparent zinc retention was observed in the subjects studied. *Author to whom all correspondence and reprint requests should be addressed. Biological Trace Element Research
15 7
VoL 8, ] 985
Atinmo and Friday
158
Index Entries: Calcium, status in young adult females; magnesium, status in young adult females; zinc, status in young adult females; protein intake, and trace-metal status of young adult females; calorie intake, and trace metal status of young adult females.
INTRODUCTION The adequacy of a diet in terms of minerals is influenced not only by the quantity but also by the variety of dietary components, as well as the interaction between the minerals themselves. The level of dietary protein has been shown to affect the absorption, retention, and excretion of calcium (1), magnesium (2), and zinc (3,4). Mineral utilization is also affected by the interactions of these elements. A diet consisting of milk and cheese with a high calcium content, and whole meal bread with high phytic acid content, resulted in positive zinc absorption. Subsequently, Greger and Snedeker (3) and Greger et al. (5) observed that high calcium intake had no effect on fecal or urinary zinc, nor on its apparent retention in adult males. Calcium and magnesium metabolism have been shown to be interrelated, and they both affect each other depending on the level present in the diet (6). High calcium intake increases the loss of magnesium from the body, particularly in the urine. Increasing the dietary level of magnesium, especially during adequate calcium intake, improves calcium utilization (6). Previous studies from this laboratory indicate that low dietary zinc intake and the subsequently low plasma zinc levels are associated with the generally low protein content of the habitual diet (9). Therefore, the purpose of the present study was to investigate the calcium, magnesium, and zinc status of young adult college females when their protein and calorie intakes were satisfactory.
MATERIALS AND METHODS
Subject and Study Design Eleven young adult students of 21-30 yr from the University of Ibadan population participated in a study that lasted 39 d. The subjects were studied under close supervision. Daily body weights were recorded between 7:00 and 8:00 am throughout the entire study period under standardized conditions (preprandial, post-voiding, and with light indoor clothing). All subjects engaged in their normal routine daily activities while maintaining a reasonably constant level of physical activity during the study period. Each subject kept activity records in which they were required to record their physical activity, waking hours, menstrual Biological Trace Element Research
VoL 8, 1985
159
Ca, Alg, a n d Z n S t a t u s o f Y o u n g F e m a l e s
flow, a n d p h y s i c a l a n d e m o t i o n a l stress. There w e r e t w o 5-d b a l a n c e periods d u r i n g the s t u d y , o n the 15th-19th a n d on the 3 5 t h - 3 9 t h days.
Diet The diet w a s b a s e d on f o o d s habitually c o n s u m e d a n d w a s pres e n t e d in a g i v e n meal p a t t e r n that w a s similar to that w h i c h the subjects w e r e a c c u s t o m e d to. Tables la a n d b s h o w the c o m p o n e n t of the diet that w a s c o n s t r u c t e d to p r o v i d e 40 kcal/kg b o d y w t a n d 0.6 g/kg b o d y w t of protein.
Analyses Blood, f o o d , urine, a n d fecal s a m p l e s w e r e collected u s i n g p r e c a u tions to a v o i d trace mineral c o n t a m i n a t i o n . Blood s a m p l e s w e r e collected TABLE la Composition of the Experimental Diet Ingredients Bread Tea Sugar Margarine Gari (dried fermented cassava) Pepper (dried) Tomato stew (fresh) Onion (fresh) Palm oil Rice Beef Soft drinks
Quantity, g
Protein, g
Energy, kcal
100
7.8
232.22
Ad libitum
20 30 300 4 80 40 40 350 80 3 Bottles Total:
--
--0.75 0.48 0.80 0.48 -6.9 16.0 -33.21
--
120 219 263.25 13.2 17.6 16.4 360.0 420.0 213.4 360.0 2235.07
TABLE lb Daily Menu Breakfast Bread Tea Sugar Margarine
Quantity, g 100 Ad libitum
20 30
Biological Trace Element Research
Lunch
Quantity, g
Gari (cassava) Cooked meat Stew Okra soup Soft drinks 2
300 34.29 66.2 47 Bottles
Supper
Quantity, g
Rice Meat Stew Soft drinks
350 34.2 66.2 1 Bottle
VoL 8, 1985
160
Atinmo and Friday
at the beginning, midday, and end of the study period. Other samples were collected during the two 5-d balance periods and w e r e composited for determination of nutrients. A 1-g food sample was digested with 4 mL of 70% perchloric acid, heated at 150~ until the digest became colorless, and 50 mL glass distilled water were added. The mixture was filtered and m a d e up to 100 mL using deionized water. An aliquot was then read for calcium, magnesium, and zinc on AAS (Perkin Elmer) Model 3058 using appropriate standards. Fecal samples were precisioned and dissolved in 3N HC1 and m a d e to 100 mL volume in a volumetric flask. Zinc concentration was determined without any further treatment. Concentrations of calcium and m a g n e s i u m w e r e determined on 5 mL aliquots to which 5 mL of 0.5% l a n t h a n u m chloride solution was added. Frozen samples of urine w e r e thawed and 1:4 dilutions were m a d e with deionized water for zinc determination. For calcium and magnesium, 1:100 dilutions were m a d e using 0.5 l a n t h a n u m chloride solution (0.1 mL + 10 mL 5% LaC12). Frozen plasma samples were thawed and 0.5 mL of samples was diluted with 2 mL of deionized water for zinc determination for calcium and magnesium, 0.2 mL of plasma was diluted 50 times with 0.1% lant h a n u m chloride solution.
RESULTS There was a 0.9 kg decrease in the body weight of subjects at the end of the study compared to the beginning of study (55.3 vs 56.2 kg). This was not significant. Dietary intake of calcium, magnesium, and zinc were 268.15, 79.17, and 8.89 mg, respectively. These values represented 53.6% of the 500 mg/d r e c o m m e n d e d by the FAO/WHO Committee (7) and 33.5% of the RDA set by the US Food and Nutrition Board for calcium, 26.39% for magnesium, and 57.93% for zinc (8). Table 2 shows the group balance data for the three minerals studied. There was no significant difference between the fecal excretion of calcium, magnesium, and zinc during the first and second metabolic periods (P < 0.05). There were more variations in fecal calcium and magnesium during the first metabolic period compared to the second. A significant positive correlation (r = 0.642) was observed b e t w e e n fecal calcium and fecal zinc and also between fecal calcium and fecal magnesium (r = 0.97) (P < 0.05). Average urinary calcium/24 h was significantly higher during the first metabolic period than the second (P < 0.05). The differences between the urinary m a g n e s i u m and zinc for the first and second metabolic phases were not statistically significant. Urinary calcium was positively correlated with urinary magnesium.
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Biological Trace Element Research
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Atinrno and Friday
162
The a p p a r e n t absorptions for calcium a n d m a g n e s i u m w e r e 98 a n d 99%, a n d 86.77 a n d 90%, for the first a n d s e c o n d metabolic phases, respectively, w h e r e a s negative a p p a r e n t absorption was obtained for zinc. Table 2 s h o w s that a p p a r e n t retentions for calcium a n d m a g n e s i u m were positive, w h e r e a s that for zinc was negative. Table 3 s h o w s that the m i d p h a s e concentration of p l a s m a calcium was h i g h e r t h a n the others, but that difference was not significant (P > 0.05). Plasma concentration was h i g h e s t at the e n d of the s t u d y , compared to the other two phases, w h e r e a s plasma zinc was h i g h e s t at the b e g i n n i n g of the s t u d y a n d lowest at the end.
DISCUSSION The daily dietary intakes of the minerals were low c o m p a r e d to the US Food a n d Nutrition Board r e c o m m e n d a t i o n (8). This finding confirms the general observation that mineral intake in Nigeria is low c o m p a r e d to the r e c o m m e n d e d dietary allowance (9). Fecal excretion values of calcium, m a g n e s i u m , and zinc w e r e lower than values r e p o r t e d in the literature. These r e d u c e d values can be attribu t e d to the fact that the dietary intakes of the minerals were low. Fecal calcium a c c o u n t e d for less t h a n 2% of the intake for the two balance periods, indicating that almost the entire dietary intake of 265.15 m g was being absorbed in addition to the complete reabsorption of the secreted calcium. This finding is in a g r e e m e n t with that of H e a n e y et al. (10), Mazuoli et al. (11), a n d Allen (12) that an inverse relationship exists bet w e e n calcium absorption a n d calcium intake. At lower levels of calcium intake, the a m o u n t that is absorbed far exceeds that absorbed on h i g h e r intakes. Studies have also s h o w n that absorption efficiency c h a n g e s over a period of 1 w k with a c h a n g e from a high intake to a lower calcium intake (12,13). The p r o p o r t i o n of m a g n e s i u m absorbed is d e p e n d e n t on the dietary intake (14). The high p e r c e n t a g e of absorption of m a g n e s i u m o b s e r v e d in the p r e s e n t s t u d y came about as a result of the low dietary intake. This finding is also s u p p o r t e d by Barnes et al. (14), w h o reported a striking a n d p r o m p t reduction in the m a g n e s i u m content of the stool of his subjects following the institution of a low m a g n e s i u m diet after a transition TABLE 3 Mean Plasma Concentration of Ca, Mg, and Zn for the Two Balance Periods Ca,
Beginning Midway End
mg/lO0
mL
11.43 + 3.84 12.30 __ 3.26 10.03 _+ 1.5
Biological Trace Element Research
Mg,
mg/lO0
mL Zn,
2.33 _+ 0.14 2.44 _ 0.35 2.65 _+ 0.72
~g/lO0 mL
87.75 _+ 16.1 75.75 _+ 2.6 74.7 _+ 39.42 VoL 8, I98.5
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period. The high correlation b e t w e e n fecal calcium and fecal m a g n e s i u m suggests an interrelationship b e t w e e n their absorption. Fecal zinc excretion was higher than the dietary intake. The increase in the fecal zinc can be attributed to zinc of e n d o g e n o u s origin. The same observation was made w h e n Greger and Snedeker (3) fed two levels of protein and phosphorus to subjects. Fecal zinc was higher than dietary zinc intake w h e n subjects were fed low protein. Urinary calcium was 61 and 56% of the intake for the two metabolic periods, respectively. The low intake in this study is possibly the reason for the higher urinary levels recorded. This agrees with the finding of Knapp (15) that the proportion of calcium intake excreted is not constant at all levels of intake, but is highest on the low intake, decreasing rapidly as the intake increases. It was further suggested that this was particularly evident w h e n the intake was less than 5 mg/kg body weight. In this study the average intake/kg body wt was 4.76 mg. The level of dietary protein has also been repeatedly s h o w n to affect the amount of calcium excreted in urine (1,16). These workers, as well as others such as Kim and Linskwiler (17), have s h o w n that an increase in the protein content of the diet at any calcium level results in an increase in urinary calcium loss because of a reduction in the a m o u n t of filtered calcium absorbed by the kidneys. Mahalko (18) also s h o w e d that a less positive calcium balance results w h e n the diet provides increased protein. In the present study, both the calcium and the protein intakes were held constant for a long time. This could possibly explain the significantly lower urinary calcium loss observed. The low urinary m a g n e s i u m observed in this study can be attributed to the low dietary intake of the mineral. This finding is in agreement with that of Shroeder et al. (14), which indicated that urinary excretion of m a g n e s i u m is a close function of intestinal absorption and dietary intake. Urinary m a g n e s i u m , expressed as a percentage of intake, correlated significantly with the individual intake/kg body wt. The correlation was more significant than that for calcium, suggesting that the level of dietary intake affects the urinary excretion of m a g n e s i u m more than it does that of calcium. It has been shown that a relationship also exists between calcium and m a g n e s i u m in the renal tubule; that w h e n the calcium/ m a g n e s i u m ratio is high, more calcium will be excreted and more magnesium reabsorbed (19). The m e a n values for urinary zinc were higher than the reported normal range by McCance and W i d d o w s o n (20). Fell et al. (21) suggested that zinc was being w i t h d r a w n mainly from the skeletal muscle. The increase in the urinary zinc can thus be attributed to zinc of e n d o g e n o u s origin. Greger and Snedeker (3) observed an increase in urinary zinc with incresing dietary nirogen from 8.1 to 24.1 g/d, whereas dietary zinc levels remained constant. The dietary nitrogen fed in this study was about 5 g/d. This a m o u n t is less than the low protein fed by Greger and Snedeker (3). Since the only source of e n d o g e n o u s zinc is the muscle protein (21), it Biological Trace Element Research
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can therefore be suggested that muscle b r e a k d o w n has probably occurred to provide the zinc required for tissue metabolism in the presence of low dietary zinc intake. Apparent retentions of the minerals were higher during the second metabolic phase. This observation might occur because the subjects had fully adjusted and adapted to the diet by the second phase of the experimental period. Apparent m e a n retention of calcium was positive for both metabolic periods, except for one subject w h o was in negative balance during the first metabolic period. It was observed that her urinary calcium loss was greater than her daily intake. She, however, s h o w e d a positive balance during the second period w h e n she gained weight and excreted less calcium in urine. The positive balances observed were the result of the low excretion of calcium in both feces and urine. Low fecal calcium was primarily a result of the adaptation of the body to a constant low dietary intake, whereas the urinary loss was a result of the individual intake per kilogram body weight, plus the adequate protein intake. Spencer et al. (22) s h o w e d that calcium balance could be maintained by 200 mg calcium/d and 0.5 w/kg body wt of protein for meat. Begun and Periera (23) also carried out balance studies on normal children w h o were on a low calcium intake of 200 mg/d and found that all subjects were in positive balance, which became greater w h e n the intake was increased to 280 mg/d. The a m o u n t is only 11.8 mg higher than the content of diet in the present study. M a g n e s i u m balance was positive for the two balance periods. This indicates that these healthy y o u n g female adults had the ability to conserve m a g n e s i u m while on an adequate protein and calorie intake and at a comparatively low calcium intake. These findings are consistent with those of Barnes et al. (14), w h o conducted a short-term study with y o u n g adult females w h o were placed on a low magnesium diet with adequate calorie and protein. A p p a r e n t zinc retentions were negative for both metabolic periods because of an increase in both fecal and urinary losses. A l t h o u g h the overall retention was negative, some individuals were in positive balance. This could be attributed to their prior zinc status. The negativity in the apparent retention can also be the result of low dietary intake. It has been s h o w n that by increasing the zinc intake, retention also increased (24). Therefore, if the requirements of all subjects were to be met, a higher dietary zinc content was required. The m e a n concentration of plasma calcium at the end of the study fell within the normal range of 9.0-11.0 ~g/100 mL for adults (14). Plasma calcium is usually maintained at a constant level of approximately 10 mg/d by parathyroid h o r m o n e , calcitonin, and vitamin D (25). This level is not affected by intake (26).
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The m a i n t e n a n c e of n o r m a l p l a s m a m a g n e s i u m t h r o u g h o u t the s t u d y suggests that, despite the low dietary intake of the mineral, the m a g n e s i u m status was not a d v e r s e l y affected. The d e c r e a s i n g m e a n p l a s m a zinc levels o b s e r v e d d u r i n g the s t u d y w e r e p r o b a b l y a result of the low d i e t a r y zinc intake. Hess et al. (27) rep o r t e d a similar decline in the s e r u m zinc levels in y o u n g w o m e n o n a low zinc intake. In s u m m a r y , it appears that a d e q u a t e protein a n d calorie intake in the p r e s e n c e of low dietary intake of calcium, m a g n e s i u m , a n d zinc has no significant effect on calcium a n d m a g n e s i u m status, but has a lowering effect o n the plasma zinc levels a n d zinc retention of the subjects studied. The m e c h a n i s m by w h i c h this occurs n e e d s to be f u r t h e r studied.
REFERENCES 1. M. Hegsted and H. Linkswiller, J. Nutr. 111, 241 (1981). 2. R. Schwartz, M. A. Woodcock, S. D. Blakely, and I. Mackellar, Am. ]. Cdin. Nutr. 26, 510, 519 (1973). 3. J. L. Greger and S. M. Snedeker, J. Nutr. 110, 2243 (1980). 4. M. A. Colin, L. T. Taper, and S. T. Richey, Br. J. Nutr. 113, 1480 (1983). 5. J. L. Greger, P. Baligan, R. F. Abernathy, O. A. Bennett, and T. Peterson, Amer. J. Clin. Nutr. 31, 117 (1978). 6. M. Seelig, Am. J. Clin. Nutr. 14, 342 (1964). 7. FAO/WHO: Report of a FAL/WHO Expert Committee on Calcium Requirements, Rome, FAO Tech. Rep. Ser. 230 (1962). 8. US Food and Nutrition Board, Recommended Dietary Allowances, 9th ed., National Academy of Sciences, Washington, DC, 1980. 9. C. M. F. Mbofung and T. Atinmo, Nig. ]. Nutr. Sci. 1, 14 (1980). 10. R. R. Heaney, P. D. Saville, and R. R. Pecker, J. Lab. Clin. Med. 88 (1975). 11. G. Mazzuoci, J. Samchson, and D. Lazsi, J. Lab. Clin. Med. 52, 522 (1978). 12. L. H. Allen, Am. J. Clin. Nutr. 35, 783 (1982). 13. A. P. P. Walker, S. Aft. Med. ]. 40, 814 (1966). 14. H. A. Shroeder, A. P. Mason, and I. H. Tipton, J. Chronic Dis. 21,815 (1969). 15. E. L. Knapp, 1. Clin, Inv. 26, 182 (1947). 16. L. H. Allen, R. S. Bartbett, and S. D. Block, J. Nutr. 109, 1345 (1979). 17. V. Kim and M. G. Linskwiller, J. Nutr. 109, 1399 (1979). 18. J. R. Nahatko, H. H. Sandstead, L. K. Johnson, and D. B. Milne, Amer. J. Clin. Nutr. 37, 8 (1983). 19. F. W. Heaton, A. Hodginson, and G. A. Rose, J. Clin. Sci. 27, 31 (1964). 20. R. A. McCance and B. M. Widdowson, Biochem. ]. 36, 692 (1942). 21. G. S. Fell, A. Fleck, D. P.Cuthberson, K. Queen, C. Morrison, R. Bessert, and Grand Hussain, Lancet 280 (1973). 22. H. Spencer, L. Kramer, D. Osis, and C. Morris, Am. J. Clin. Nutr. 31, 2167 (1978). 23. C. Begun and S. Periera, Br. J. Nutr. 23, 905 (1969).
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24. S.J. Richey, M. K. Korslund, L. M. Gilbert, D. C. Fay, and M. F. Robinson, Am. J. Clin. Nutr. 32, 799 (1979). 25. S. K. Czarnecki, Trace Elements in Nutrition and the Adult Micronutrients, Vol. 38, R. A. Slater and D. Kritchevsky, eds., Plenum Press, N e w York, 1980. 26. S. E. Miller, Textbook of Clinical Pathology, 6th ed., William and Wilkins, Baltimore, 1960. 27. F. M. Hess, J. C. King, and S. Margen, J. Nutr. 107, 1610 (1977).
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