Vitamin D deficiency in a subfertility population and the impact of COVID-19 lockdowns.

Objective: To evaluate the burden of vitamin D deficiency in female patients attending a fertility clinic in a tertiary referral center, assess temporal trends-including the potential impact of COVID-19 lockdowns-and explore socioeconomic disparities in vitamin D levels.

Methods: This retrospective cohort study analyzed vitamin D measurements from 765 female patients (mean age 35.7 ± 5.8 years) attending a fertility clinic between March 2010 and May 2022. Vitamin D status was categorized as deficient (<30 nmol/L), insufficient (30-50 nmol/L), or normal (>50 nmol/L). Comparative analyses examined pre- and post-COVID periods and healthcare funding status.

Results: Overall, 39.9% (n = 305) of patients exhibited suboptimal vitamin D levels, with 8.8% (n = 67) deficient and 31.1% (n = 238) insufficient. Mean serum 25(OH)D was 62.8 ± 27.4 nmol/L. No statistically significant difference was observed between pre-COVID (44.2% suboptimal) and post-COVID (38.1% suboptimal) periods (OR 0.78, 95% CI: 0.57-1.06, P = 0.110). However, marked seasonal variation was identified, with winter values significantly lower than summer values (45.3 ± 24.6 vs. 72.1 ± 28.3 nmol/L, P < 0.001). Furthermore, state-funded patients had a significantly higher rate of suboptimal vitamin D status (50.2%, n = 107) compared to self-funded patients (35.9%, n = 198, P < 0.001).

Conclusion: Our findings demonstrate a high prevalence of suboptimal vitamin D levels in a subfertility population, with significant seasonal fluctuations and notable socioeconomic disparities. Despite initial concerns, COVID-19 lockdown measures did not appear to adversely affect overall vitamin D status. These results support the incorporation of routine vitamin D screening in infertility evaluations and the implementation of targeted supplementation, particularly in economically vulnerable groups and during winter months.