Dairy-Food and Vitamin D Intake in Endometriosis
Dairy-Food and Vitamin D Intake in Endometriosis
During 737,712 person-years of follow-up contributed by 70,556 women, 1,385 incident cases of laparoscopically confirmed endometriosis with no past infertility were reported. Of these cases, 1,129 women never reported infertility and 235 reported undergoing an infertility evaluation during the same follow-up period as their laparoscopic confirmation of endometriosis. Women with the greatest intake of total dairy foods were slightly younger, more likely to be Caucasian and to have had a recent gynecological examination, and less likely to be current smokers and nulliparous than those with lower total dairy-food intake (Table 1).
Intake of total dairy foods was associated with a lower risk of endometriosis (Table 2). After adjustment for covariates, an increase in total dairy-food intake of 1 serving per day was associated with a 5% reduction in the risk of endometriosis (rate ratio (RR) = 0.95, 95% confidence interval (CI): 0.91, 1.00). When low-fat dairy foods were considered separately, a similar association was observed. High-fat dairy foods were not associated with endometriosis. The relationships between dairy-food intake and endometriosis were similar in women who had never reported infertility and women who reported a concurrent laparoscopic endometriosis diagnosis and infertility (Table 2). When the association between specific dairy foods and endometriosis risk was examined (Table 3), the relationship between dairy-food intake and endometriosis appeared to be driven primarily by the association of skim/low-fat milk with the disease.
Predicted plasma 25(OH)D level was inversely associated with endometriosis (Table 4). Women in the highest quintile of predicted vitamin D level had a 24% lower risk of endometriosis than women in the lowest quintile, and there was no evidence of heterogeneity according to case definition. Total intakes of calcium and vitamin D (including intake from supplements) were not associated with endometriosis. However, calcium and vitamin D intakes from food were inversely related to endometriosis. Women in the highest quintile of calcium intake from food had a multivariable adjusted rate ratio of 0.79 (95% CI: 0.66, 0.94; Ptrend = 0.001). The corresponding figure for vitamin D intake from foods was 0.79 (95% CI: 0.66, 0.94; Ptrend = 0.003). The associations between both calcium and vitamin D intakes from foods and endometriosis were attenuated after adjustment for milk consumption. Calcium and vitamin D intakes from dairy-food sources only were unrelated to endometriosis. When the relationships of calcium and vitamin D intake with endometriosis were evaluated separately by case status, these associations were more pronounced in women who had never reported infertility; the test for heterogeneity between the two case types reached statistical significance for calcium intake from foods and vitamin D intake from dairy foods.
Total magnesium intake and total phosphorus intake had inverse relationships with endometriosis risk that approached statistical significance (Table 4). When intake from food sources was examined, there was a statistically significant inverse relationship between magnesium intake and endometriosis (RR = 0.86, 95% CI: 0.73, 1.01; Ptrend = 0.007). The association of phosphorus intake from foods with endometriosis was similar to the association for total phosphorus intake. When intakes of magnesium and phosphorus from foods were mutually adjusted for each other, the association between phosphorus and endometriosis was attenuated and the association between magnesium and endometriosis did not materially change. The association between magnesium intake from foods and endometriosis was not altered by adjustment for milk consumption. The associations of these two nutrients with endometriosis appeared to be more pronounced in the never-infertile group. However, none of the tests for heterogeneity reached statistical significance.
Next, we examined dairy protein, dairy fat, and lactose to explore what component of dairy foods might explain the association between milk intake and endometriosis. Adjustment for dairy protein and lactose strengthened the inverse association between milk intake and endometriosis, while adjustment for dairy fat did not materially alter the association. None of the dairy components (dairy protein, dairy fat, and lactose) were associated with endometriosis in these models (results not shown).
Finally, we assessed whether the associations between dairy-food intake and other nutrients were modified by BMI, parity, or cigarette smoking. The association between high-fat dairy-food intake and endometriosis differed by BMI (Pinteraction = 0.0004). Among women who had a BMI less than 25, the risk of endometriosis was lowest among those in the highest intake category. In these women, we observed a multivariable rate ratio of 0.69 (95% CI: 0.53, 0.90) compared with women in the lowest quintile (Ptrend = 0.004). No association was observed in women who were overweight (BMI ≥25) (RR = 1.25, 95% CI: 0.90, 1.75; Ptrend = 0.11).
Results
During 737,712 person-years of follow-up contributed by 70,556 women, 1,385 incident cases of laparoscopically confirmed endometriosis with no past infertility were reported. Of these cases, 1,129 women never reported infertility and 235 reported undergoing an infertility evaluation during the same follow-up period as their laparoscopic confirmation of endometriosis. Women with the greatest intake of total dairy foods were slightly younger, more likely to be Caucasian and to have had a recent gynecological examination, and less likely to be current smokers and nulliparous than those with lower total dairy-food intake (Table 1).
Intake of total dairy foods was associated with a lower risk of endometriosis (Table 2). After adjustment for covariates, an increase in total dairy-food intake of 1 serving per day was associated with a 5% reduction in the risk of endometriosis (rate ratio (RR) = 0.95, 95% confidence interval (CI): 0.91, 1.00). When low-fat dairy foods were considered separately, a similar association was observed. High-fat dairy foods were not associated with endometriosis. The relationships between dairy-food intake and endometriosis were similar in women who had never reported infertility and women who reported a concurrent laparoscopic endometriosis diagnosis and infertility (Table 2). When the association between specific dairy foods and endometriosis risk was examined (Table 3), the relationship between dairy-food intake and endometriosis appeared to be driven primarily by the association of skim/low-fat milk with the disease.
Predicted plasma 25(OH)D level was inversely associated with endometriosis (Table 4). Women in the highest quintile of predicted vitamin D level had a 24% lower risk of endometriosis than women in the lowest quintile, and there was no evidence of heterogeneity according to case definition. Total intakes of calcium and vitamin D (including intake from supplements) were not associated with endometriosis. However, calcium and vitamin D intakes from food were inversely related to endometriosis. Women in the highest quintile of calcium intake from food had a multivariable adjusted rate ratio of 0.79 (95% CI: 0.66, 0.94; Ptrend = 0.001). The corresponding figure for vitamin D intake from foods was 0.79 (95% CI: 0.66, 0.94; Ptrend = 0.003). The associations between both calcium and vitamin D intakes from foods and endometriosis were attenuated after adjustment for milk consumption. Calcium and vitamin D intakes from dairy-food sources only were unrelated to endometriosis. When the relationships of calcium and vitamin D intake with endometriosis were evaluated separately by case status, these associations were more pronounced in women who had never reported infertility; the test for heterogeneity between the two case types reached statistical significance for calcium intake from foods and vitamin D intake from dairy foods.
Total magnesium intake and total phosphorus intake had inverse relationships with endometriosis risk that approached statistical significance (Table 4). When intake from food sources was examined, there was a statistically significant inverse relationship between magnesium intake and endometriosis (RR = 0.86, 95% CI: 0.73, 1.01; Ptrend = 0.007). The association of phosphorus intake from foods with endometriosis was similar to the association for total phosphorus intake. When intakes of magnesium and phosphorus from foods were mutually adjusted for each other, the association between phosphorus and endometriosis was attenuated and the association between magnesium and endometriosis did not materially change. The association between magnesium intake from foods and endometriosis was not altered by adjustment for milk consumption. The associations of these two nutrients with endometriosis appeared to be more pronounced in the never-infertile group. However, none of the tests for heterogeneity reached statistical significance.
Next, we examined dairy protein, dairy fat, and lactose to explore what component of dairy foods might explain the association between milk intake and endometriosis. Adjustment for dairy protein and lactose strengthened the inverse association between milk intake and endometriosis, while adjustment for dairy fat did not materially alter the association. None of the dairy components (dairy protein, dairy fat, and lactose) were associated with endometriosis in these models (results not shown).
Finally, we assessed whether the associations between dairy-food intake and other nutrients were modified by BMI, parity, or cigarette smoking. The association between high-fat dairy-food intake and endometriosis differed by BMI (Pinteraction = 0.0004). Among women who had a BMI less than 25, the risk of endometriosis was lowest among those in the highest intake category. In these women, we observed a multivariable rate ratio of 0.69 (95% CI: 0.53, 0.90) compared with women in the lowest quintile (Ptrend = 0.004). No association was observed in women who were overweight (BMI ≥25) (RR = 1.25, 95% CI: 0.90, 1.75; Ptrend = 0.11).
