The effects of dairy foods intakes on weight change and fracture risk during critical life stages in women
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Abstract
Menopause and pregnancy are crucial events in women’s lives because women experience a series of physical and psychological changes at these stages. One of the most critical challenges is excessive weight gain during both of these stages, which could contribute to various adverse health events in their later lives. In addition to weight gain, another critical health concern that women face is fragility-related factures. The rate of fragility fractures begins rising in women during their 40s and increases to the end of life. Fractures result in impaired mobility and hospitalization, which can decrease the life quality of women significantly. Identification of modifiable dietary risk factors for excessive weight gain and fracture risk is crucial. The objectives of this dissertation are to estimate the independent effects of total dairy and individual dairy foods (e.g., yogurt, milk, and cheese), alone and in combination with overall diet patterns, physical activity, and other lifestyle factors, on three outcomes among women: weight change during the menopausal transition, weight retention after pregnancy, and risk of fragility-related fractures throughout mid-life and older adult years.
Data from two prospective studies of nurses were used: Nurses’ Health Study I (NHS I) and Nurses’ Health Study II (NHS II). NHS II was used for both weight change analyses, while NHS was used for the fracture analyses. The first specific aim for the analysis of weight change during the menopausal transition was to investigate the effects of total dairy, yogurt, milk, and cheese intakes on menopausal weight change (N = 35,177) and risk of obesity (N = 38,892) among women in NHS II. Weights were self-reported in biennial questionnaires. Diet was assessed with food frequency questionnaires (FFQ) every 4 years. Generalized estimating equations were used to assess the adjusted mean weight change using repeated measures of weight change. Cox proportional hazards models were used to estimate risk of obesity, controlling for confounding.
The second specific aim relates to the postpartum weight change analyses and were to investigate the effects of total dairy, yogurt, milk, and cheese intakes on postpartum weight retention (N = 18,366) and risk of postpartum obesity (N = 17,126) among women in the NHS II. Generalized linear models were used to assess postpartum weight change as continuous outcomes and multivariable models with a Poisson distribution were used to estimate risk of postpartum obesity.
The third specific aim was for the fragility fracture analyses and included investigating the effects of total dairy, yogurt, milk, and cheese on fragility fractures of the hip, wrist, and vertebrae in women ages 40 years and older in NHS I. In total, there are 99,072 women included. Fractures at the wrist and hip were self-reported. For vertebral fractures, we relied on medical record confirmed cases. Proportional hazards models were used to estimate risk of first fracture (including wrist, hip, or vertebral fractures).
Results associated with the first aims suggested that more than 2 servings per week (s/w) of yogurt led to consistently less weight gain than that observed in women consuming less than 1 serving per month (s/m) throughout the menopausal transition. Further, this same yogurt intake was associated with a 31% reduced obesity risk (95% CI: 0.64 - 0.74) after adjusting for potential confounders and baseline body mass index (BMI). Higher total dairy intake was also associated with less obesity risk, but the effect was somewhat weaker than that for yogurt. There was a U-shaped relation between milk consumption and obesity risk during perimenopause. Moderate (0.5 s/d -< 1 s/d vs. < 0.5 s/d) milk consumption reduced obesity risk by 17% (95% CI: 0.78 - 0.89), while higher milk (≥1 s/d vs. < 0.5 s/d) consumption led to a marginally statistically significant 6% higher obesity risk. Cheese intake was not associated with obesity risk in perimenopausal women.
In the postpartum weight retention analyses, women who consumed moderate amounts of yogurt (1 s/m -< 2 s/w) and higher amounts of yogurt (≥ 2 s/w) had a 0.38 lb and 0.63 lb reduction in postpartum weight retention, respectively, than those who rarely consumed yogurt (< 1 s/m). Moderate and higher cheese intakes were associated with 0.30 lb and 0.64 lb less postpartum weight retention, respectively, than lower cheese intake (< 2 s/w). In the obesity analysis, moderate (1 s/m -< 2 s/w) and higher yogurt (≥ 2 s/w) intakes were associated with 20% (95%: 0.69 - 0.93) and 16% (95%: 0.69 - 1.02) reduced risks of postpartum obesity, but the association was weakened by adjusting for pre-pregnancy BMI. Women with higher levels of activity and higher yogurt intakes had a 39% (95%: 0.50 - 0.74) lower risk of obesity. Higher Alternative Healthy Eating Index 2010 (AHEI) scores alone were associated with a statistically significantly lower obesity risk.
Results from our fracture analyses found that women who consumed more than 2 s/d of total dairy had a 19% (95% CI: 0.67 - 0.98) lower fracture risk than those who consumed less than 1 s/w. In terms of individual dairy products, 2 s/d of milk were associated with a 14% (95% CI: 0.77 - 0.95) reduction in fracture risk compared with lower milk consumption (<1 s/w). Higher cheese (≥ 1 s/d vs. < 1 s/w) intake was associated with a non-statistically significant 9% (95% CI: 0.81 - 1.02) reduction in fracture risk. No association was found between yogurt consumption and fracture. In stratified analysis, the intakes of calcium, vitamin D, and protein from non-dietary sources did not modify the inverse association between total dairy or milk intake and fracture risk.
In summary, the findings of this dissertation suggested that greater yogurt consumption was inversely associated with weight change during menopausal transition and after pregnancy while intakes of total dairy and milk had beneficial effects on the risk of fragility fractures among women ages 40 years and older.