Prevalence of low vitamin D status in an urban district in Sri Lanka: a population-based study

Vitamin D deficiency (VDD) is conventionally associated with inadequate sunlight exposure. Ironically, recent evidence suggests a rising prevalence in urban areas of tropical regions like Sri Lanka, where comprehensive data are unavailable. This study aimed to estimate the prevalence of low vitamin D status in urban adults and its impact on serum calcium.

A population-based cross-sectional study was conducted among 1260 adults aged 35-74 years, living in Colombo, the most urban district in Sri Lanka. They were recruited from 63 administrative divisions, using multi-stage, probability-proportionate-to-size, cluster sampling. Non-fasting venous blood was collected without tourniquet. Low vitamin D (< 30.0 ng/mL), VDD (< 20 ng/mL) and vitamin D insufficiency (20.0-29.9 ng/mL) were determined using chemiluminescence assay method, and serum calcium using Calcium Gen2 reagent.

Among the population (53.3% females; mean age = 51.8 years), the prevalence of low vitamin D was 93.9% (95% CI: 92.5-95.2). This was primarily due to VDD (67.5%; 95% CI: 64.9.0-70.1%), with some insufficiency (26.4%; 95% CI: 24.0-28.9%). Most VDD cases (53.9.0%) were 'mild' (10.0- < 20.0 ng/mL) in severity, with fewer 'moderate' (12.8%) and 'severe' (0.8%) cases. Prevalence of VDD was highest in females, aged 35-44-years, living in 'highly urban' areas and of Tamil ethnicity. Further, VDD showed a decreasing trend with older age groups, while it was significantly more prevalent in females than males (72.6% vs. 61.7%; p < 0.01), across all age groups. Low serum calcium levels were observed in 9.8% of adults with low vitamin D, compared to 22.4% with normal vitamin D, implying that there could be factors other than vitamin D in maintaining serum calcium levels.

Colombo District, representing urban settings in Sri Lanka faces a high prevalence of low vitamin D, primarily VDD, with higher rates in females, younger individuals and highly urban areas. These findings challenge assumptions about tropical regions being guaranteed of optimal vitamin D levels; and underscore the need for national vitamin D supplementation and food fortification programs, especially in high-risk urban settings in South Asian countries like Sri Lanka.