STUDIES O N SELENIUM The principal sources o f selenium in the human diet are cereals, followed b y meat, poultry, and fish, and then the dairy products. Selenium is incorporated into the teeth either from inorganic or organic compounds with the major amount being found in the protein matrix o f the enamel and dentin. Key Words: selenium, h u m a n foods, tooth develo p m e n t , dental caries
Current interest in selenium varies from c:oncern about the adequacy of human dietaries for all age groups to the desire to know whether slightly elevated levels of selenium ingestion may alter the formation of the teeth to cause them to be more susceptible to dental caries. In an effort to evaluate the amount of selenium available for consumption, J. N. Thompson and co-workers determined the selenium content of food groups and composite diets based on the average distribution of foods consumed by Canadians.' Samples of 86 individual foods in Winnipeg and in Halifax and two samples of each in Toronto were purchased in proportion to their per capita rate of disappearance from the market place on a nationwide basis. The foods were trimmed, cooked in typical ways, and pooled in the appropriate proportions into the following 11 groups: dairy products; meat, poultry, and fish; cereal products; potatoes; leafy vegetables; legumes; root vegetables; garden fruits; other fruits; oil and fats; and sugar and adjuncts. The daily selenium contribution to the diet was determined for each of these food groups. In addition, a composite diet vvas prepared by mixing the 11 groups in the appropriate amounts for Winnipeg and Halifax and two composite diets in the same way for Toronto. The four composite diets were also analyzed for selenium. The authors also calculated the selenium content of the "average" Canadian diet from published values of selenium concentration in Canadian foods and the per capita rate of disappearance of fresh foods. Water and 138 NUTRITION REVIEWSIVOL. 33,NO. 5IMAY 7975
other drinks were omitted from all of these comparisons on the basis that the authors considered these fluids to supply negligible amounts of selenium. This decision may be entirely appropriate, presuming that the water supplies in Winnipeg, Halifax, and Toronto are known to contain negligible amounts of selenium. However, in areas where com muna I water cont a ins sel enium in appreciable amounts, the amount from this source in the human dietary would also need to be calculated. The calculations based on previously available data yielded food consumption of 1,646 g per person per day, providing 196.6 p g selenium per day. The four composite diets weighed 1,570 to 1,659 g per person per day. Analyses of the selenium contents of the 11 food groups used to make the composite diets from Winnipeg, Halifax, and Toronto #1 and #2 indicated 180.8, 224.2, 98.3, and 148.5 p g selenium per daily portion, respectively. The variation from diet to diet, especially between the two Toronto diets, was surprisingly high since they were composite diets. These selenium values vary from 0.06 to 0.14 p g per gram of fresh diet. The largest amount of selenium in all four diets was provided by the cereal products in Group 3, next by the meat, poultry, and fish in Group 2, and then by the dairy products in Group 1. The dairy products in the Winnipeg and Halifax diets provided four to five times the amount of selenium as in the two Toronto diets. In addition, the meat, poultry, and fish in the Winnipeg and Halifax diets contained two to three times as much selenium as the Toronto diets. The other eight food group-
ings provided rather trivial amounts of selenium. The total values for the composite diets compared fairly well with the average daily selenium intake in the northeastern United States of 60 t o 150 p g which was reported by H. A. Schroeder and co-workers.' The possibility of a selenium deficiency in Canadian adults was considered by these authors to be remote. They expressed concern, however, that deprivation in infancy was possible due t o the low amounts of selenium in milk and other dairy products. Shearer studied the uptake of inorganic and organic selenium from drinking water by the fully developed molar teeth and the developing incisor teeth of pregnant rats and by the developing molar and incisor teeth of their ~ f f s p r i n g .Selenium ~ was provided from the tenth day of pregnancy to parturition either as an 0.2 ppm solution of selenomethionine t o ten rats or of sodium selenite to nine rats tagged in both instances with Se. Distilled water was provided to the rats from parturition for 13 days a t which time the dams and their offspring were sacrificed and samples prepared for selenium analyses. The time of sacrifice was determined so that the first and second molars of the offspring would not have erupted. For the rats provided with selenomethionine, 22.1 percent of the ingested dose was retained with one-half in the carcasses of the mothers and one-half in the offspring; for the rats fed sodium selenite, only 14.1 percent of the ingested dose was retained with slightly more than half in the bodies of the mothers. In the rats provided with selenomethionine, the developing molars of the offspring incorporated almost eight times as much selenium on a weight basis as the fully-formed molars of the mothers. This ratio is not surprising due t o the rapid development of molars in the offspring of this age and the lack of molar development in the mothers. The developing incisors of the offspring had incorporated almost identical amounts of selenium t o the molars; the ratio of selenium in the offspring's incisors to that in their mothers' incisors was 1:6.
'
The incisors of the mothers, however, contained over five times the selenium of their molars. The latter observation is an interesting confirmation that the incisor of the adult rat is continuously erupting as enamel and dentin are being formed throughout life a t the germinative center. Among the rats provided with sodium selenite the incorporation of selenium into the molars of the offspring was only half that observed with sel enometh ioni ne; the amount incorporated into molars of the mothers was about half that in the offspring. The ratio of selenium in the incisors was about 2.0 times in the offspring for the amount in the mothers. Both values were substantially higher for incisors than for molars in the same rats, but were a little lower than for incisors in the rats provided with selenomethionine. Among both the mothers and their offspring provided with either selenomethionine or sodium selenite, the highest percent of the ingested dose per 100 g of tissue was found in the liver and kidney, followed by spleen, heart, blood, and lungs. The authors stated that the selenium levels in milk in the stomachs of the offspring were routinely low, suggesting that the selenium had come from placental rather than mammary transfer. Except for teeth and bone, more selenium was present in all maternal tissues than in those of the offspring. Both enamel and dentin from developing and developed teeth incorporated selenium either from selenomethionine or from sodium selenite. In all comparisons dentin values were higher than enamel. The incorporation of selenium into both enamel and dentin of developing molars was significantly higher from selenomethionine than from sodium selenite, while the reverse was true postdevelopmentally. When selenium was provided as selenomethionine, over 79 percent of the total selenium in the developing enamel was located in the protein fraction, which is only about 2 percent by weight of the enamel; almost 95 percent of the selenium in dentin of these developing teeth was in the protein NUTRITION RNIEWS/VOL. 33,NO. SIMAY 1975 139
fraction. In developed molars of the mothers, almost as high a percent of selenium was incorporated from selenomethionine into the protein fraction. When selenium was provided as sodium selenite, comparable amounts were incorporated into the protein fractions of enamel and dentin from developing teeth as was observed with selenomethionine. However, postdevelopmentally much less selenium was incorporated into the protein fraction of either enamel or dentin when sodium selenite was the source. The selenium in the protein fraction was present either in the form of selenotrisulfides ( R-S-Se-S-R ) which were removed by treatment with dilute sodium hydroxide and mercaptoethanol, or in a more stable form which could not be removed from the enamel and dentin proteins under the conditions of the experiment. In developing enamel and dentin, 41 and 66 percent of the total selenium was in this stable form when selenomethionine was fed and 40 and 55 percent when sodium selenite was provided. Postdevelopmentally the values were similar for enamel and dentin after selenomethionine administration but were much lower when sodium selenite was given. The results in this paper for sodium selenite in drinking water are very similar to those obtained by Shearer and Hadjimarkos when sodium selenite was injected subcutaneously four times during the last 12 days of pregnan~y.~ The author did not study mineralization of the teeth in the offspring in this experiment or carry any of the offspring to an age when their caries susceptibility could have been determined. These areas need further careful investigation. He draws a t tention to the three epidemiological surveys in the western United and
140
NUTRITION REVIEWSfVOL. 33. NO. 5fMAY 1975
the additional one in Russia' where an association between either the selenium concentration in drinking water or in urine or in teeth and dental caries was reported. In addition, an experiment with monkeys supplemented with selenium indicated an ~ postulated increased caries a ~ t i v i t y . He that increased selenium, in the protein fraction of enamel especially, may alter the quality of mineralization and therefore the caries susceptibility of the teeth. 0
1. J. N. Thompson, P. Erdody, and D. C. Smith:
2.
3.
4.
5.
Selenium Content of Food Consumed by Canadians. J. Nutrition 105: 274-277, 1975 H. A. Schroeder, D. V. Frost, and J. J. Balassa: Essential Trace Elements in Man: Selenium. J. Chron. Diseases 23: 227-243, 1970 T. R. Shearer: Developmental and Postdevelopmental Uptake of Dietary Organic and Inorganic Selenium into the Molar Teeth of Rats. J. Nutrition 105: 338-347, 1975 T. R. Shearer and D. M. Hadjimarkos: Comparative Distribution of 75Se in the Hard and Soft Tissues of Mother Rats and Their Pups. J. Nutrition 103: 553-559, 1973 D. M. Hadjimarkos: Effect of Selenium on Dental Caries. Arch. Environ. Health 10:
893-899, 1965 6. G. Tank and C. A. Storvick: Effect of Naturally Occurring Selenium and Vanadium on Dental Caries. J. Dent. Res. 39: 473-488,
1960 7. T. G. Ludwig and B. G. Bibby: Geographic Variations in the Prevalence of Dental Caries in the United States of America. Caries Res. 3: 32-43, 1969 8. 6 . P. Suchkov, I. M. Katsan, and A. I. Gulg'asenko: A Study of the Influence of Selenium on t h e Dental Caries of the Population of the Chernovitsi Region. Stomatologia (Moskow) 52: 21-2, 1973 9. W. H. Bowen: The Effects of Selenium and Vanadium on Caries Activity in Monkeys (M. irus). J. Irish Dent. Assn. 18: 83-88, 1972
Current interest in selenium varies from c:oncern about the adequacy of human dietaries for all age groups to the desire to know whether slightly elevated levels of selenium ingestion may alter the formation of the teeth to cause them to be more susceptible to dental caries. In an effort to evaluate the amount of selenium available for consumption, J. N. Thompson and co-workers determined the selenium content of food groups and composite diets based on the average distribution of foods consumed by Canadians.' Samples of 86 individual foods in Winnipeg and in Halifax and two samples of each in Toronto were purchased in proportion to their per capita rate of disappearance from the market place on a nationwide basis. The foods were trimmed, cooked in typical ways, and pooled in the appropriate proportions into the following 11 groups: dairy products; meat, poultry, and fish; cereal products; potatoes; leafy vegetables; legumes; root vegetables; garden fruits; other fruits; oil and fats; and sugar and adjuncts. The daily selenium contribution to the diet was determined for each of these food groups. In addition, a composite diet vvas prepared by mixing the 11 groups in the appropriate amounts for Winnipeg and Halifax and two composite diets in the same way for Toronto. The four composite diets were also analyzed for selenium. The authors also calculated the selenium content of the "average" Canadian diet from published values of selenium concentration in Canadian foods and the per capita rate of disappearance of fresh foods. Water and 138 NUTRITION REVIEWSIVOL. 33,NO. 5IMAY 7975
other drinks were omitted from all of these comparisons on the basis that the authors considered these fluids to supply negligible amounts of selenium. This decision may be entirely appropriate, presuming that the water supplies in Winnipeg, Halifax, and Toronto are known to contain negligible amounts of selenium. However, in areas where com muna I water cont a ins sel enium in appreciable amounts, the amount from this source in the human dietary would also need to be calculated. The calculations based on previously available data yielded food consumption of 1,646 g per person per day, providing 196.6 p g selenium per day. The four composite diets weighed 1,570 to 1,659 g per person per day. Analyses of the selenium contents of the 11 food groups used to make the composite diets from Winnipeg, Halifax, and Toronto #1 and #2 indicated 180.8, 224.2, 98.3, and 148.5 p g selenium per daily portion, respectively. The variation from diet to diet, especially between the two Toronto diets, was surprisingly high since they were composite diets. These selenium values vary from 0.06 to 0.14 p g per gram of fresh diet. The largest amount of selenium in all four diets was provided by the cereal products in Group 3, next by the meat, poultry, and fish in Group 2, and then by the dairy products in Group 1. The dairy products in the Winnipeg and Halifax diets provided four to five times the amount of selenium as in the two Toronto diets. In addition, the meat, poultry, and fish in the Winnipeg and Halifax diets contained two to three times as much selenium as the Toronto diets. The other eight food group-
ings provided rather trivial amounts of selenium. The total values for the composite diets compared fairly well with the average daily selenium intake in the northeastern United States of 60 t o 150 p g which was reported by H. A. Schroeder and co-workers.' The possibility of a selenium deficiency in Canadian adults was considered by these authors to be remote. They expressed concern, however, that deprivation in infancy was possible due t o the low amounts of selenium in milk and other dairy products. Shearer studied the uptake of inorganic and organic selenium from drinking water by the fully developed molar teeth and the developing incisor teeth of pregnant rats and by the developing molar and incisor teeth of their ~ f f s p r i n g .Selenium ~ was provided from the tenth day of pregnancy to parturition either as an 0.2 ppm solution of selenomethionine t o ten rats or of sodium selenite to nine rats tagged in both instances with Se. Distilled water was provided to the rats from parturition for 13 days a t which time the dams and their offspring were sacrificed and samples prepared for selenium analyses. The time of sacrifice was determined so that the first and second molars of the offspring would not have erupted. For the rats provided with selenomethionine, 22.1 percent of the ingested dose was retained with one-half in the carcasses of the mothers and one-half in the offspring; for the rats fed sodium selenite, only 14.1 percent of the ingested dose was retained with slightly more than half in the bodies of the mothers. In the rats provided with selenomethionine, the developing molars of the offspring incorporated almost eight times as much selenium on a weight basis as the fully-formed molars of the mothers. This ratio is not surprising due t o the rapid development of molars in the offspring of this age and the lack of molar development in the mothers. The developing incisors of the offspring had incorporated almost identical amounts of selenium t o the molars; the ratio of selenium in the offspring's incisors to that in their mothers' incisors was 1:6.
'
The incisors of the mothers, however, contained over five times the selenium of their molars. The latter observation is an interesting confirmation that the incisor of the adult rat is continuously erupting as enamel and dentin are being formed throughout life a t the germinative center. Among the rats provided with sodium selenite the incorporation of selenium into the molars of the offspring was only half that observed with sel enometh ioni ne; the amount incorporated into molars of the mothers was about half that in the offspring. The ratio of selenium in the incisors was about 2.0 times in the offspring for the amount in the mothers. Both values were substantially higher for incisors than for molars in the same rats, but were a little lower than for incisors in the rats provided with selenomethionine. Among both the mothers and their offspring provided with either selenomethionine or sodium selenite, the highest percent of the ingested dose per 100 g of tissue was found in the liver and kidney, followed by spleen, heart, blood, and lungs. The authors stated that the selenium levels in milk in the stomachs of the offspring were routinely low, suggesting that the selenium had come from placental rather than mammary transfer. Except for teeth and bone, more selenium was present in all maternal tissues than in those of the offspring. Both enamel and dentin from developing and developed teeth incorporated selenium either from selenomethionine or from sodium selenite. In all comparisons dentin values were higher than enamel. The incorporation of selenium into both enamel and dentin of developing molars was significantly higher from selenomethionine than from sodium selenite, while the reverse was true postdevelopmentally. When selenium was provided as selenomethionine, over 79 percent of the total selenium in the developing enamel was located in the protein fraction, which is only about 2 percent by weight of the enamel; almost 95 percent of the selenium in dentin of these developing teeth was in the protein NUTRITION RNIEWS/VOL. 33,NO. SIMAY 1975 139
fraction. In developed molars of the mothers, almost as high a percent of selenium was incorporated from selenomethionine into the protein fraction. When selenium was provided as sodium selenite, comparable amounts were incorporated into the protein fractions of enamel and dentin from developing teeth as was observed with selenomethionine. However, postdevelopmentally much less selenium was incorporated into the protein fraction of either enamel or dentin when sodium selenite was the source. The selenium in the protein fraction was present either in the form of selenotrisulfides ( R-S-Se-S-R ) which were removed by treatment with dilute sodium hydroxide and mercaptoethanol, or in a more stable form which could not be removed from the enamel and dentin proteins under the conditions of the experiment. In developing enamel and dentin, 41 and 66 percent of the total selenium was in this stable form when selenomethionine was fed and 40 and 55 percent when sodium selenite was provided. Postdevelopmentally the values were similar for enamel and dentin after selenomethionine administration but were much lower when sodium selenite was given. The results in this paper for sodium selenite in drinking water are very similar to those obtained by Shearer and Hadjimarkos when sodium selenite was injected subcutaneously four times during the last 12 days of pregnan~y.~ The author did not study mineralization of the teeth in the offspring in this experiment or carry any of the offspring to an age when their caries susceptibility could have been determined. These areas need further careful investigation. He draws a t tention to the three epidemiological surveys in the western United and
140
NUTRITION REVIEWSfVOL. 33. NO. 5fMAY 1975
the additional one in Russia' where an association between either the selenium concentration in drinking water or in urine or in teeth and dental caries was reported. In addition, an experiment with monkeys supplemented with selenium indicated an ~ postulated increased caries a ~ t i v i t y . He that increased selenium, in the protein fraction of enamel especially, may alter the quality of mineralization and therefore the caries susceptibility of the teeth. 0
1. J. N. Thompson, P. Erdody, and D. C. Smith:
2.
3.
4.
5.
Selenium Content of Food Consumed by Canadians. J. Nutrition 105: 274-277, 1975 H. A. Schroeder, D. V. Frost, and J. J. Balassa: Essential Trace Elements in Man: Selenium. J. Chron. Diseases 23: 227-243, 1970 T. R. Shearer: Developmental and Postdevelopmental Uptake of Dietary Organic and Inorganic Selenium into the Molar Teeth of Rats. J. Nutrition 105: 338-347, 1975 T. R. Shearer and D. M. Hadjimarkos: Comparative Distribution of 75Se in the Hard and Soft Tissues of Mother Rats and Their Pups. J. Nutrition 103: 553-559, 1973 D. M. Hadjimarkos: Effect of Selenium on Dental Caries. Arch. Environ. Health 10:
893-899, 1965 6. G. Tank and C. A. Storvick: Effect of Naturally Occurring Selenium and Vanadium on Dental Caries. J. Dent. Res. 39: 473-488,
1960 7. T. G. Ludwig and B. G. Bibby: Geographic Variations in the Prevalence of Dental Caries in the United States of America. Caries Res. 3: 32-43, 1969 8. 6 . P. Suchkov, I. M. Katsan, and A. I. Gulg'asenko: A Study of the Influence of Selenium on t h e Dental Caries of the Population of the Chernovitsi Region. Stomatologia (Moskow) 52: 21-2, 1973 9. W. H. Bowen: The Effects of Selenium and Vanadium on Caries Activity in Monkeys (M. irus). J. Irish Dent. Assn. 18: 83-88, 1972
