Effects of sun exposure on 25(OH) vitamin D concentration in urban and rural women in Malaysia

Ultraviolet B sunlight exposure is a primary source of vitamin D. There have been reports of low vitamin D status amongst the Malaysian population despite it being a tropical country. This study was conducted to determine the influence of sun exposure on 25(OH)D concentrations in urban and rural women in Malaysia and factors predicting 25(OH)D concentrations. Women aged above 45 years were recruited from urban (n=107) and rural areas (n=293). Subjects were interviewed regarding their outdoor activities and usual outdoor attire over the previous week. 25(OH)D concentrations were analyzed using the vitamin D3 (25-OH) electrochemiluminescence immunoassay. Median (Q1-Q3) age of the participants was 57 (53-61) years old. Median (Q1-Q3) 25(OH)D concentration of rural women was significantly higher [69.5 (59.0-79.1) nmol/L] compared to urban women [31.9 (26.1- 45.5) nmol/L] (p<0.001). Rural women spent more time in the sun compared to urban women (7.83 (3.67-14.7) vs 2.92 (1.17-4.92) hours, p<0.001), although the fraction of body surface area (BSA) exposed to sunlight was significantly higher in the urban group [0.21 (0.21-0.43) vs 0.12 (0.07-0.17), p<0.001]. The calculated sun index (hours of sun exposure per week × fraction of BSA) was significantly higher in rural [0.89 (0.42-1.83)] compared to urban women [0.72 (0.26-1.28)], p=0.018. In the stepwise linear regression, rural dwelling increased the serum 25(OH)D by 31.74 nmol/L and 25(OH)D concentrations increased by 1.93 nmol/L for every unit increment in sun index. Urban women in Malaysia had significantly lower vitamin D status compared to rural women. Rural dwelling and sun index were key factors influencing vitamin D status in Malaysian women.