Sunlight and vitamin D status in normal Saudi subjects

Abstract

Serum levels of the circulating form of vitamin D₃, 25-hydroxycholecalciferol [25-(OH)D₃], were determined in 59 university students, 26 males and 33 females, aged 18 to 26 yr and in 24 elderly subjects, 13 males and 11 females, with a mean age of 62 ± 13 yr. The level of 25-(OH)D₃ was significantly lower in the elderly persons (p < 0.001) than in young students of both sexes, and was significantly higher in females than in males. Serum levels of 1, 25- and 24, 25-dihydroxycholecalciferol were measured in adult males and found to be within the normal range. A group of elderly patients were exposed to natural uv light, and the circulating levels of 25-(OH)D₃, serum phosphorus, and alkaline phosphatase were determined both before and 1 day after the last exposure. The exposure to natural uv light resulted in a 2½-fold increase in the level of 25-(OH)D₃ and a significant decrease in the activity of alkaline phosphatase, but no significant change in serum phosphorus concentrations was observed. It is concluded that the low vitamin D₃ status in Saudis is mainly due to avoidance of sunlight exposure and other factors discussed below.