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Supplement use drives rising vitamin D levels among midlife women
The percentage of midlife women with vitamin D insufficiency and deficiency fell by approximately 50% between 1998 and 2011, in part due to a rise in the use of vitamin D supplements, according to an analysis of data from the Study of Women’s Health Across the Nation.
“Our data suggest that increased awareness of the importance of vitamin D among both physicians and patients has dramatically decreased the number of women at high risk of complications of low vitamin D,” Deborah Mitchell, MD, a clinical investigator in the endocrine division and a clinician in the pediatric endocrine and endocrine units at Massachusetts General Hospital in Boston, told Endocrine Today. “However, the number of women at high risk is still substantial. In particular, 23% of women in our cohort who did not take vitamin supplements had a 25-hydroxyvitamin D level less than 12 ng/mL. Among black women not taking supplements, the prevalence was 46%.”
Mitchell and colleagues analyzed data from 1,585 women aged 45 to 52 years at baseline who attended at least two visits as part of the Study of Women’s Health Across the Nation (SWAN), a longitudinal, community-based cohort study initiated in 1996. Women provided blood samples at baseline and follow-up visits to assess levels of 25-(OH)D. The use of supplemental vitamins was assessed in interview-administered questionnaires and on a worksheet recording medication use. Researchers measured serum 25-(OH)D levels at the second study visit (between 1998 and 2000) and again at visit 12 (between 2009 and 2011) and assessed between-visit changes in the whole cohort and in socioeconomic and demographic subgroups. Researchers also evaluated the determinants of persistent vitamin D deficiency at follow-up among women with vitamin D deficiency at baseline.
At the second study visit (1998-2000), researchers found that 43.1% of women had vitamin D insufficiency ( 50 nmol/L) and 20.4% had vitamin D deficiency (30 nmol/L); mean 25-(OH)D level for the cohort was 53.8 nmol/L. Researchers found that baseline vitamin D level varied by race, household income, education level, vitamin use, season of blood draw and BMI category.
Between visits 2 and 12, mean serum 25-(OH)D level increased by 16.2 nmol/L to 70 nmol/L (P < .001), with changes similar among all subgroups, according to researchers. The percentage of women with vitamin D deficiency decreased to 9.7% between visits. The proportion of women reporting dietary supplement use rose from 40.8% at the second visit to 67.1% (P < .001).
“The absolute increase in 25-(OH)D was very similar among women of differing race and ethnicity, educational attainment and socioeconomic status,” Mitchell said. “Increasing prevalence of the use of vitamin supplements appeared to underlie the observed increases.”
Researchers also found that, among 324 women with vitamin D deficiency at baseline, 89 (27.5%) remained vitamin D deficient at visit 12. In univariate analyses, higher BMI at baseline (P = .046), black race (P = .001), low household income (P = .049) and no supplement use (P < .001) were all predictors of remaining vitamin D deficient over follow-up, according to researchers.
Compared with women who reported never taking vitamin supplements and were vitamin D deficient at visit 2, those who started supplementation after visit 2 were 78% less likely to remain vitamin D deficient at visit 12 (OR = 0.22; 95% CI, 0.1-0.49), whereas those who reported taking supplements throughout were 83% less likely to remain deficient at visit 12 (OR = 0.17; 95% CI, 0.05-0.66), according to researchers.
“Accumulating evidence suggests that women with a 25-(OH)D less than 30 nmol/L are at increased risk of osteoporosis and may benefit from vitamin D supplementation,” Mitchell said.
Mitchell said that further educational outreach efforts as well as clinical trials studying the effects of vitamin D supplementation should target patients at highest risk for complications of vitamin D deficiency.
“Our data help to identify some of the risk factors among midlife women; future studies to replicate and extend these findings are warranted,” Mitchell said. – by Regina Schaffer
For more information:
Deborah M. Mitchell, MD, can be reached at Massachusetts General Hospital, Pediatric Endocrine Unit, 55 Fruit St., Boston, MA 02114; email: dmmitchell@mgh.harvard.edu.
Disclosures: The authors report no relevant financial disclosures.