Sunlight and vitamin D status in normal Saudi subjects.

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 less than 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 2 1/2-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.