Background: Studies comparing serum 25-hydroxyvitamin D concentrations in women with and without polycystic ovary syndrome (PCOS) have produced inconsistent results. Additionally, no previous studies have evaluated associations between vitamin D and specific PCOS phenotypes.
Methods: This case-control study was conducted among women undergoing intrauterine insemination. Cases (N.=137) were diagnosed with PCOS and then further classified into 3 diagnostic phenotypes based on combinations of the Rotterdam criteria (ovulatory dysfunction+polycystic ovaries [N.=55]; ovulatory dysfunction +androgen excess [N.=15]; and ovulatory dysfunction, +polycystic ovaries, +androgen excess [N.=67]). Controls (N.=103) were ovulatory women without PCOS who were undergoing IUI. Serum total 25-hydroxyvitamin D concentrations were categorized as deficient (≤20 ng/mL), insufficient (21-29 ng/mL), and sufficient (≥30 ng/mL). Prevalence odds ratios (PORs) were calculated using logistic regression.
Results: A higher proportion (59.9%) of PCOS cases lacked sufficient vitamin D levels compared to controls (47.6%; P value=0.06). The odds of vitamin D deficiency in all PCOS cases were twice that of controls (POR=2.03, 95% CI 0.97-4.26); however, the association was attenuated after adjusting for Body Mass Index (BMI) and race/ethnicity (adjPOR=1.43, 95% CI 0.62, 3.26). When examining PCOS phenotypes exhibiting androgen excess, crude associations were observed for deficient vitamin D levels (unadjPOR=2.93, 95% CI: 1.27, 6.77); however, the association decreased after adjustment for BMI and race/ethnicity (adjPOR=2.03, 95% CI: 0.79, 5.19).
Conclusions: Vitamin D deficiency occurred more frequently in PCOS cases with androgen excess, but associations were attenuated after adjusting for BMI and race/ethnicity. Combining etiologically distinct PCOS subgroups may obscure associations with lower vitamin D levels and other potential risk factors.