Impact of the COVID-19 lockdown on the vitamin D status of people in the West of Ireland

Objective: Identify the impact of COVID-19 lockdown restrictions on the vitamin D status of individuals in the west of Ireland. Design: Cross-sectional study. Setting: Adults who had wintertime serum 25(OH)D analysis completed in Galway University Hospital. Participants: A total of 16,725 participants (2015–2020 (n = 13,449) and 2020–2021 (n = 3276)). Baseline demographics; sex, age, origin of the sample and the date of sample collection. Results: Median serum vitamin D and serum vitamin D₃ concentrations were higher in the 5-month period from October–February 2020–2021 (61 nmol/L (± 36–85 nmol/L) and 60 nmol/L (± 34–85 nmol/L)) respectively, than for the corresponding 5-month period (October–February) in 2015–2020 (53 nmol/L (± 32–78 nmol/L) and 51 nmol/L (± 30–77 nmol/L)) respectively. These changes coincided with a decline in the prevalence of deficiency. In the 5-month period October–February 2020–2021, 19.2% of the population were vitamin D deficient (< 30 nmol/L) compared to 22.5% in the corresponding 5-month period in 2015–2020, and 38.1% were vitamin D deficient (< 50 nmol/L) in the 5-month period October–February 2020–2021 compared to 46.6% in the corresponding 5-month period in 2015–2020. Males were more likely to be deficient at both thresholds (p < 0.001). For the total cohort, at the < 30 nmol/L threshold, inpatients (25.5%) and nursing home residents (34.1%) had higher prevalence of deficiency. Conclusions: Vitamin D levels were higher in the 5-month period of October–February 2020–2021, and this precipitated a decline in deficiency at both thresholds, indicating that lockdown coincided with enhanced vitamin D status. We postulate that it may be attributable to changes in diet and/or supplementation, or increased sun exposure, but further confirmatory studies are required.