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ORIGINAL RESEARCH COMMUNICATION |
1 From the Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY (SNR); the Departments of Epidemiology and Nutrition (EBR, WCW, and FBH) and Biostatistics (BR), Harvard School of Public Health, Boston, MA; and the Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA (EBR, WCW, and FBH)
2 Supported by NIH grants DK58845 and CA87969. FBH is partly supported by an American Heart Association Established Investigator Award. 3 Reprints not available. Address correspondence to S Rajpathak, Department of Epidemiology and Population Health, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Belfer 1308D, Bronx, NY 10461. E-mail: srajpath{at}aecom.yu.edu.
| ABSTRACT |
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Objective: We investigated the association between calcium and dairy intakes and 12-y weight change in US men.
Design: This study was conducted with the use of data from the Health Professionals Follow-up Study, a prospective cohort of men aged 4075 y in 1986. Data on lifestyle factors and diet were updated biennially with self-administered questionnaires. The participants reported their body weight in 1986 and in 1998. The outcome in our study was 12-y weight change. We used multivariate linear regression to examine how baseline calcium intake (n = 23 504) and change in calcium intake (n = 19 615) were associated with weight change. Because dairy foods are the predominant source of calcium in the diet, we also evaluated a similar association with dairy intake.
Results: In a multivariate analysis with adjustment for potential confounders, baseline or change in intake of total calcium was not significantly associated with weight change. In addition, we did not find any association with dietary, dairy, or supplemental calcium intake when evaluated separately. The men with the largest increase in total dairy intake gained slightly more weight than did the men who decreased intake the most (3.14 compared with 2.57 kg; P for trend = 0.001). This association was primarily due to an increase in high-fat dairy intake. Low-fat dairy intake was not significantly associated with weight change.
Conclusion: Our data do not support the hypothesis that an increase in calcium intake or dairy consumption is associated with lower long-term weight gain in men.
Key Words: Calcium dairy intake weight change
| INTRODUCTION |
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| SUBJECTS AND METHODS |
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6 servings/d. The FFQ has a standard portion size alongside the frequency of intake; hence, each person chooses the consumption frequency for the same serving size. We calculated nutrient intake by multiplying the frequency of consumption with the nutrient content and then adding the contributions from all foods and beverages. The food-composition database used to calculate the nutrient values is based primarily on US Department of Agriculture data (10) and was supplemented with the manufacturers' data. We collected additional information on the use of calcium and multivitamin supplements (including dose and frequency of use) from the participants. Total calcium intake was calculated as the sum of dietary and all supplemental intakes. All nutrient intakes (except supplemental calcium and alcohol) were energy-adjusted by the residual method (11). To determine dairy calcium intake, we summed the calcium intake from whole milk, skim milk, low-fat milk, ice cream, cheese, yogurt, and cream consumption. The Pearson correlation coefficient between calcium intake from the FFQ and the average intake of two 1-wk diet records from a subsample of 127 men from this study population was 0.53 (7). In the present study, we evaluated the role of change in calcium intake (19861998) as well as the role of baseline calcium intake (in 1986) on weight change. We calculated glycemic load (GL) by multiplying the carbohydrate content of each food by its glycemic index, then multiplied this value by the frequency of consumption and summed the values from all foods. Each unit of GL represents the equivalent of 1 g carbohydrate from white bread. In a validation study, a higher GL was strongly associated with increased triacylglycerol concentrations (12). In addition, GL was associated with an increased risk of diabetes in this cohort (13). Intake of trans-fat was estimated from the FFQ with the use of composition values that were based on analyses performed by Enig et al (14) and Slover et al (15). To assess the validity of our measure of trans-fat intake, the calculated intake was compared with its concentration in subcutaneous adipose tissue in 118 male participants of this cohort with the use of gas-liquid chromatography (16). The Spearman rank correlation between calculated intake as a proportion of fat and the proportion in subcutaneous adipose tissue was 0.34 (P < 0.001). To assess the reproducibility of the measurement of trans-fat intake, the same group of men was asked to complete a second FFQ 1 y after the first; the correlation between the 2 measurements was 0.63. The calculation and validity of trans-fat intake and its health effects in this cohort has been reported previously (1618).
Outcome assessment
Weight change was defined as the difference between the 1986 and 1998 self-reported body weights. We previously evaluated the reproducibility and validity of self-reported body weight in a subset of the cohort (19). Self-reported weight and the average of 2 technician measures were highly correlated (Pearson's correlation coefficient = 0.97), and there was no significant linear trend in the accuracy of reported weight across quartiles of age or body mass index (BMI).
Statistical analysis
All statistical analyses were performed with SAS software version 8 (Cary, NC). We used age-adjusted and multivariate linear regression to examine the association between 12-y weight change (in kg) and baseline and change in calcium intake. In all analyses, we modeled the main exposure variable in quintiles to avoid a linearity assumption and to reduce the effect of outliers. To evaluate the association of dairy and dietary calcium intake with weight change, we excluded men who reported the use of calcium supplements anytime during the 12-y period (n = 6255). We calculated the least-squares means for changes in body weight across quintiles of baseline calcium intake or change in calcium intake after adjustment for age (<50, 5054, 5559, 6064, or
65 y), smoking (past, current, or never), alcohol consumption (nondrinker, 0.14.9, 5.09.9, 10.014.9, or
15.0 g/d), physical activity (MET-h/d), caloric intake (kcal/d), GL, and intakes of caffeine (mg/d), cereal fiber (g/d), whole grains (g/d), fruit and vegetables (servings/d), soft drinks (servings/d), and trans fat (% of calories). We included these nutrients and food variables in the multivariate models either because they are likely to be associated with a healthy lifestyle or because they were shown to predict weight gain in the present cohort or in other cohorts (2023).
In the analysis of change in calcium intake, we controlled for both change and baseline levels of covariates, including baseline calcium intake because it was a potential confounder. Because weight change can be dependent on attained weight at baseline, we adjusted for this variable in all models. Such adjustment can also control for bias due to regression to the mean (24). We conducted stratified analyses to evaluate a potential effect modification by age (<65 or
65 y) and intakes of vitamin D and protein using median intake as the cutoffs. Because the predominant source of dietary calcium intake was from dairy product consumption, we conducted similar analyses to evaluate whether baseline or change in dairy product intake (servings/d) was associated with weight change. For all analyses of dietary and dairy intake, we excluded the men who reported calcium supplement use to avoid confounding by supplement use. Tests of linear trend across quintiles of calcium or dairy intake were performed by assigning the median values for the categories and fitting this continuous variable in the model. All statistical tests conducted were two-sided with a type I error (
) of 0.05, and P values < 0.05 were considered statistically significant.
| RESULTS |
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3 kg. During this time, the median intake of total calcium increased from 791 to 899 mg/d; the median dietary calcium intake increased from 736 to 765 mg/d, and calcium supplement use increased from 16.1% to 22.5%. The age-standardized characteristics are shown in Table 1
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Baseline intake analyses
Mean weight gain did not differ significantly by quintile of total, dietary, dairy, or supplemental calcium intake assessed at baseline in 1986 (Table 2
). Similarly, we did not find a significant association between total dairy intake and weight gain (Table 3
). In the multivariate model, the difference in mean weight gain between extreme quintiles of high-fat dairy intake was small (3.24 kg for the highest quintile compared with 2.86 kg for the lowest quintile; P for trend = 0.03), which indicated that the participants who consumed more high-fat dairy at baseline had a slightly lower 12-y weight gain than the participants who consumed less high-fat dairy. Although this difference for low-fat dairy intake between extreme quintiles was similar (2.83 compared with 3.18 kg), it showed a reverse trend that was not significant (P = 0.17).
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4.5 kg (10 lbs) during the follow-up (based on a supplementary questionnaire in 1992; n = 2619) did not change our results. | DISCUSSION |
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The potential effect of calcium intake on body weight was first suggested by Zemel et al (4) in a clinical trial that investigated the antihypertensive effect of calcium in obese African-Americans. In that study, the investigators reported that increasing calcium intake from 400 to 1000 mg/d (2 cups of yogurt/d) for 1 y resulted in a 4.9 kg reduction in body fat. A subsequent review of multiple clinical trials that retrospectively evaluated the role of calcium or dairy on body weight concluded that there was not enough evidence to support the benefits of calcium or dairy intake on weight loss (25). However, most of the studies in the review were not designed or powered to study weight change as the outcome variable. Two recent weight-loss trials evaluated the role of calcium or dairy supplementation on weight as the primary outcome. In a 24-wk randomized clinical trial of 32 obese adults (27 women and 5 men) who were maintained on a 500 kcal/d deficit diet for 6 mo, the patients who received a standard diet (400500 mg dietary calcium/d) lost a mean (±SD) 6.4 ± 2.5% of their body weight, those who received a high-calcium diet (standard diet supplemented with 800 mg calcium/d) lost 8.6 ± 1.1%, and those who received a high-dairy diet (12001300 mg dietary calcium/d) lost 10.9 ± 1.6% (P < 0.01) (26). Thus, that small trial suggested that dietary calcium intake may enhance weight loss secondary to caloric restriction, and this effect was greater for dairy product intake. However, in another 25-wk double-blind, randomized clinical trial on weight loss in 100 overweight and obese women, Shapses et al (27) reported no effect of 1 g calcium supplementation/d on body weight (
± SD: 6.2 ± 0.7 kg for the placebo group and 5.5 ± 0.6 kg for the calcium group). Similar to the randomized trials, observational studies that examined the relation between calcium intake and body weight have yielded mixed results (2833). In a recent cross-sectional analysis within the Heritage Family Study (32), the authors reported a strong inverse association between calcium intake and BMI in black men and white women. Black men in the high-calcium intake group were leaner than were those in the low-intake group [BMI (in kg/m2): 23.4 ± 0.9 compared with 26.7 ± 1.1; P = 0.01]. Most observational studies that assessed this association were cross-sectional in design and may have been affected by a reverse causation bias, ie, weight gain may have modified dietary intake. In a longitudinal study of healthy perimenopausal women, however, dietary calcium was not associated with a 5- to 7-y weight change (30).
Several studies have suggested the beneficial role of dairy consumption on insulin resistance syndrome (34, 35) and type 2 diabetes (36). In the Coronary Artery Risk Development in Young Adults study, dairy consumption was inversely associated with the incidence of
2 components of the metabolic syndrome only in overweight persons aged 1830 y (odds ratio between extreme quintiles: 0.28; 95% CI: 0.14, 0.58) (34). In our previous analysis, a high consumption of low-fat dairy products was associated with a lower risk of diabetes, independent of BMI (36). These findings suggest that some components of dairy, such as vitamin D, calcium, and protein, may have a direct role in insulin sensitivity. It is also possible that the healthy eating pattern associated with low-fat dairy consumption accounts for its benefits on diabetes.
In our study, we examined both baseline and changes in calcium and diary intake on weight change. Our analysis suggested that the men who consumed more high-fat dairy products at baseline had slightly less weight gain over time than did the men who consumed less high-fat dairy products. However, high-fat dairy intake decreased over time, on average, in the whole population, and we found that the participants who reduced their dairy intake had less weight gain than did those who increased their intake (Table 5
). In addition, this finding may be simply due to chance. Although we found that an increase in total and high-fat dairy intake was associated with greater weight gain, we did not detect a similar association with low-fat dairy intake. This suggests that the weight change associated with increased dairy intake may represent changes in other dietary and lifestyle factors. It is also possible that any weight-reducing effect of calcium obtained from dairy products is compensated for by the caloric content of the dairy products. Some may argue that adjusting for caloric intake in all statistical models may be an overadjustment. However, excluding calories from all models or using non-energy-adjusted calcium intake yielded similar results (data not shown). Dairy foods contain trans fat that may have detrimental health effects; however, in this cohort, dairy intake accounted for <1% of the total trans fat intake. In addition, we adjusted for trans-fat intake in the multivariable analysis.
Because of the observational nature of the present study, our findings need to be interpreted with caution. A potential limitation of our study is that changes in body weight may have been due to changes in either fat mass or lean mass, but we could not differentiate between these 2 components. However, any increase in weight is most likely due to an increase in adiposity in middle-aged men, because lean body mass declines with age (37). Also, measurement error related to dietary assessment may bias the results toward the null and lead to wider CIs of the estimates. However, in our study, the 95% CIs were relatively narrow. In addition, we had the statistical power to detect small differences in weight change because of the large sample size of our study population. Residual confounding is another potential concern, but such confounding is unlikely to explain our results because most age and multivariate associations were similar and we found comparable results for dietary, supplemental, and dairy calcium intakes. Note that in our previous analyses of the same cohort, physical activity, whole grain intake, cereal fiber intake, trans-fat intake, and smoking cessation were significantly associated with weight change (38, 39).
In conclusion, our study does not support the hypothesis that increasing calcium or dairy consumption is associated with lower long-term weight gain in men. Whether calcium supplementation or increased dairy intake is beneficial in preventing weight gain needs to be further studied in long-term randomized trials.
| ACKNOWLEDGMENTS |
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