Cancer Causesand Control, 1, 1 6 9 - 1 7 2
Anthropometric measures and breast cancer in young w o m e n
Eiliv L u n d , H a n s - O l o v A d a m i , R e i n h o l d BergstrOm, O l a v Meirik
(Received 5 July 1990; accepted 9July 1990) Body height and weight in reladon to breast cancer in women younger than 45 years were investigated in a case-control study in Sweden and Norway. The study included 317 Swedish and 105 Norwegian cases diagnosed in 1984 - 85 with 317 Swedish and 210 Norwegian age-matched population controls. Neither height nor body size, measured as body mass index, was associated with breast cancer. Change in body mass from the age of 20 years to 18 months before the time of diagnosis (cases) or interview (controls) had no effect on breast cancer risk. The study provides no evidence that anthropometric measures are risk factors for breast cancer in young women, indicating that the postulated inverse relationship between body mass index and pre-menopausal breast cancer could be limited to peri-menopausal women.
Key words: Breast cancer, body mass index, case-control study, height, premenopausal. Introduction Different anthropometric measures have been investigated as determinants of breast cancer risk under the assumption that these variables are indicators or proxy variables for other factors more directly related to the carcinogenesis of breast cancer. I'2 Height has been interpreted as an indicator of childhood nutritional status, and body mass index or relative weight as a measure of adult diet, total energy, or energy expenditure. The most consistent finding has been an increased risk for post-menopausal breast cancer according to increased body size. 1 For pre-menopausal breast cancer, a less consistent pattern for adult body mass index has emerged. Several large cohort studies show lower relative risk for pre-menopausal women with a high body mass index,3- 5 while case-control studies show decreased risk in obese women 6'7 or no association. 8- ~2 Increased body height in cohort studies was either associated with increased risk of about 30 percent 4 or no excess risk. 3 In a population-based national case-control study in Sweden and Norway, data were collected for further examinations of possible associations between anthropometric measures- i.e. height, body mass index, and
change in body mass index - and breast cancer among young women. Methods The study was a national, population-based case-control study in Sweden and Norway. The two countries share many common features regarding language, national registers of the total population based on individually unique national registration numbers, population-based medical services and mandatory cancer registration. Detailed information on the subjects and methods has been published previously. 13 The study aimed to include all newly diagnosed cases of a histologically verified adenocarcinoma of the breast among Swedish women younger than 45 years and Norwegian women younger than 40 years, over a period of one year (1984 - 85). Complete ascertainment of all cases was achieved through cooperation with all six regional cancer registries in Sweden and all 71 surgical departments in Norway and the Cancer Registry of Norway. Altogether, 317 (88.3 percent) of the 359
Dr Lund is at the Institute of Community Medicine, University of Troms¢, Troms¢, Norway. Dr Adami is with the Unit of CancerEpidemiology, University Hopsital, Uppsala, Sweden. Dr Bergstr~m is in the Department of Statistics, University of Uppsala, Uppsala, Sweden. Dr Meirik is with the Special Programme of Research, Development and Research Training in Human Reproduction, lVorld Health Organization, Geneva, Switzerland. Reprint requests should be addressed to Dr Lund, lnstitutt for Samfunnsmedisin, Postuttak, Universitetet i Troms¢, 9000 Troms¢, Norway. The study wasfinanced by the Swedish CancerSodety, the Swedish National Board of Health and Welfare and the Norwegian CancerSociety. © 1990 Rapid Communications of Oxford Ltd
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E. Lund et al. eligible cases were interviewed in Sweden and 105 (92.1 percent) of 114 eligible cases in Norway. Population controls in both countries were chosen randomly from the central population registers; in Sweden, one control was selected for each case, matched on m o n t h and year of birth and country of residence; in Norway, two controls were matched on day and year of birth. In Sweden, a total of 85.2 percent of all eligible controls sampled, 88.1 percent of those contacted, were interviewed; in Norway, 71.2 percent of those sampled, 84.7 percent of those contacted, were interviewed. The study design, data collection, and analysis were coordinated between Sweden and Norway. The interview followed a questionnaire which was identical in the two countries. All cases and controls were interviewed by professional interviewers (Sweden) or health professionals (Norway). All women were asked about their weight at age 20, and at 18 months prior to diagnosis of breast cancer, or pseudo-diagnosis-time for the matched controls. The question on height referred to present height. As a measure of relative weight, we used body mass index (Quetelet's index) given as weight (kg)/height (m) 2. The basic measure used for the relative risk (RR) was the odds ratio. O d d ratios with 95 percent confidence interval (CI) were obtained in the matched analysis by the conditional maximum-likelihood method.14
Results The median age of the women was 39 years. Only 14 percent of the control w o m e n had a body mass index of 24 or higher at the age of 20 years; the corresponding proportion was 31 percent at adult age. The association between both body mass index at age 20 years and relative risk of developing breast cancer before the age of 45, was non-significant with a slightly decreasing risk with increasing body mass index (Table 1). Adjustment for age at menarche, age at first birth, parity, history of breast cancer in mother, and menopausal status, did not materially alter the estimates (Table 1). Analysis with exclusion of the small n u m b e r of post-menopausal women (n = 10) gave similar results (data not shown). For body mass index at the age of 20 years, additional adjustment for oral contraceptive use, smoking, or alcohol consumption, respectively, left the estimates of relative risk mostly unchanged (figures not shown). Adult body mass - 18 months before diagnosis or interview of controls - showed no significant associations with breast cancer. The estimates were slightly elevated for obese women (Table 1). The change in body mass between the two periods in life, age 20 years and 18 months before interview, had no significant effect on risk for pre-menopausal breast 170
cancer and there was no evidence of a trend (Table 2). W e examined further the relationship between change in body mass index in adult life and pattern of childbearing (Table 3). The body mass index at age 20 years was similar for women regardless of later fertility. Nulliparous women had less subequent increase in average body mass than parous women. Parous women with a first birth before the age of 20 years had more children and a greater increase in body mass index compared to w o m e n with first birth after the age of 20 years. However, no difference in the estimates of relative risk of breast cancer was found for models with interaction terms between change in body mass index and different fertility patterns (Table 4). Height was not associated with the occurrence of breast cancer in this study (Table 5). In a model which adjusted for several potential confounding factors, relative risk was Table 1. Relative risk with 95 percent confidence interval (CI) for breast cancer according to body mass index at age 20 years, and 18 months before diagnosis Casesa
Controlsa
Body mass index at age 20 years 23 50 73
Relative risk (95 % CI) Unadjusted Adjustedb 1.0 reference 1.0(0.7-1.4) 0.9(0.6-1.3) 0.9 (0.6-1.5)
1.0 reference 1.0 (0.7-1.4) 0.9(0.6-1.3) 0.9 (0.6-1.3)
Body mass index 18 months before diagnosis < 20 36 59 1.0 reference 20-21 124 151 1.3 (0.8-2.0) 22-23 133 154 1.3 (0.8-2.1) >23 127 160 1.2 (0.8-2.0)
1.0 reference 1.1 (0.7-1.9) 1.3 (0.8-2.1) 1.1 (0.6-1.8)
~Number of cases and controls differ from 422 and 527 due to some missing values. bAdjusted for age at menarche, age at first birth, parity, history of breast cancer in mother, menopausal status. Table 2. Relative risk for breast cancer according to change in body mass index between age of 20 years and 18 months before diagnosis or interview Change in body mass index
Anthropometric measures and breast cancer in young w o m e n
Eiliv L u n d , H a n s - O l o v A d a m i , R e i n h o l d BergstrOm, O l a v Meirik
(Received 5 July 1990; accepted 9July 1990) Body height and weight in reladon to breast cancer in women younger than 45 years were investigated in a case-control study in Sweden and Norway. The study included 317 Swedish and 105 Norwegian cases diagnosed in 1984 - 85 with 317 Swedish and 210 Norwegian age-matched population controls. Neither height nor body size, measured as body mass index, was associated with breast cancer. Change in body mass from the age of 20 years to 18 months before the time of diagnosis (cases) or interview (controls) had no effect on breast cancer risk. The study provides no evidence that anthropometric measures are risk factors for breast cancer in young women, indicating that the postulated inverse relationship between body mass index and pre-menopausal breast cancer could be limited to peri-menopausal women.
Key words: Breast cancer, body mass index, case-control study, height, premenopausal. Introduction Different anthropometric measures have been investigated as determinants of breast cancer risk under the assumption that these variables are indicators or proxy variables for other factors more directly related to the carcinogenesis of breast cancer. I'2 Height has been interpreted as an indicator of childhood nutritional status, and body mass index or relative weight as a measure of adult diet, total energy, or energy expenditure. The most consistent finding has been an increased risk for post-menopausal breast cancer according to increased body size. 1 For pre-menopausal breast cancer, a less consistent pattern for adult body mass index has emerged. Several large cohort studies show lower relative risk for pre-menopausal women with a high body mass index,3- 5 while case-control studies show decreased risk in obese women 6'7 or no association. 8- ~2 Increased body height in cohort studies was either associated with increased risk of about 30 percent 4 or no excess risk. 3 In a population-based national case-control study in Sweden and Norway, data were collected for further examinations of possible associations between anthropometric measures- i.e. height, body mass index, and
change in body mass index - and breast cancer among young women. Methods The study was a national, population-based case-control study in Sweden and Norway. The two countries share many common features regarding language, national registers of the total population based on individually unique national registration numbers, population-based medical services and mandatory cancer registration. Detailed information on the subjects and methods has been published previously. 13 The study aimed to include all newly diagnosed cases of a histologically verified adenocarcinoma of the breast among Swedish women younger than 45 years and Norwegian women younger than 40 years, over a period of one year (1984 - 85). Complete ascertainment of all cases was achieved through cooperation with all six regional cancer registries in Sweden and all 71 surgical departments in Norway and the Cancer Registry of Norway. Altogether, 317 (88.3 percent) of the 359
Dr Lund is at the Institute of Community Medicine, University of Troms¢, Troms¢, Norway. Dr Adami is with the Unit of CancerEpidemiology, University Hopsital, Uppsala, Sweden. Dr Bergstr~m is in the Department of Statistics, University of Uppsala, Uppsala, Sweden. Dr Meirik is with the Special Programme of Research, Development and Research Training in Human Reproduction, lVorld Health Organization, Geneva, Switzerland. Reprint requests should be addressed to Dr Lund, lnstitutt for Samfunnsmedisin, Postuttak, Universitetet i Troms¢, 9000 Troms¢, Norway. The study wasfinanced by the Swedish CancerSodety, the Swedish National Board of Health and Welfare and the Norwegian CancerSociety. © 1990 Rapid Communications of Oxford Ltd
169
E. Lund et al. eligible cases were interviewed in Sweden and 105 (92.1 percent) of 114 eligible cases in Norway. Population controls in both countries were chosen randomly from the central population registers; in Sweden, one control was selected for each case, matched on m o n t h and year of birth and country of residence; in Norway, two controls were matched on day and year of birth. In Sweden, a total of 85.2 percent of all eligible controls sampled, 88.1 percent of those contacted, were interviewed; in Norway, 71.2 percent of those sampled, 84.7 percent of those contacted, were interviewed. The study design, data collection, and analysis were coordinated between Sweden and Norway. The interview followed a questionnaire which was identical in the two countries. All cases and controls were interviewed by professional interviewers (Sweden) or health professionals (Norway). All women were asked about their weight at age 20, and at 18 months prior to diagnosis of breast cancer, or pseudo-diagnosis-time for the matched controls. The question on height referred to present height. As a measure of relative weight, we used body mass index (Quetelet's index) given as weight (kg)/height (m) 2. The basic measure used for the relative risk (RR) was the odds ratio. O d d ratios with 95 percent confidence interval (CI) were obtained in the matched analysis by the conditional maximum-likelihood method.14
Results The median age of the women was 39 years. Only 14 percent of the control w o m e n had a body mass index of 24 or higher at the age of 20 years; the corresponding proportion was 31 percent at adult age. The association between both body mass index at age 20 years and relative risk of developing breast cancer before the age of 45, was non-significant with a slightly decreasing risk with increasing body mass index (Table 1). Adjustment for age at menarche, age at first birth, parity, history of breast cancer in mother, and menopausal status, did not materially alter the estimates (Table 1). Analysis with exclusion of the small n u m b e r of post-menopausal women (n = 10) gave similar results (data not shown). For body mass index at the age of 20 years, additional adjustment for oral contraceptive use, smoking, or alcohol consumption, respectively, left the estimates of relative risk mostly unchanged (figures not shown). Adult body mass - 18 months before diagnosis or interview of controls - showed no significant associations with breast cancer. The estimates were slightly elevated for obese women (Table 1). The change in body mass between the two periods in life, age 20 years and 18 months before interview, had no significant effect on risk for pre-menopausal breast 170
cancer and there was no evidence of a trend (Table 2). W e examined further the relationship between change in body mass index in adult life and pattern of childbearing (Table 3). The body mass index at age 20 years was similar for women regardless of later fertility. Nulliparous women had less subequent increase in average body mass than parous women. Parous women with a first birth before the age of 20 years had more children and a greater increase in body mass index compared to w o m e n with first birth after the age of 20 years. However, no difference in the estimates of relative risk of breast cancer was found for models with interaction terms between change in body mass index and different fertility patterns (Table 4). Height was not associated with the occurrence of breast cancer in this study (Table 5). In a model which adjusted for several potential confounding factors, relative risk was Table 1. Relative risk with 95 percent confidence interval (CI) for breast cancer according to body mass index at age 20 years, and 18 months before diagnosis Casesa
Controlsa
Body mass index at age 20 years 23 50 73
Relative risk (95 % CI) Unadjusted Adjustedb 1.0 reference 1.0(0.7-1.4) 0.9(0.6-1.3) 0.9 (0.6-1.5)
1.0 reference 1.0 (0.7-1.4) 0.9(0.6-1.3) 0.9 (0.6-1.3)
Body mass index 18 months before diagnosis < 20 36 59 1.0 reference 20-21 124 151 1.3 (0.8-2.0) 22-23 133 154 1.3 (0.8-2.1) >23 127 160 1.2 (0.8-2.0)
1.0 reference 1.1 (0.7-1.9) 1.3 (0.8-2.1) 1.1 (0.6-1.8)
~Number of cases and controls differ from 422 and 527 due to some missing values. bAdjusted for age at menarche, age at first birth, parity, history of breast cancer in mother, menopausal status. Table 2. Relative risk for breast cancer according to change in body mass index between age of 20 years and 18 months before diagnosis or interview Change in body mass index
