Abstract
The relationship between plasma 25-OHD and exposure to ultraviolet B (UVB) radiation in natural sunlight was measured in elderly long-stay patients from April to July 1984. Polysulphone film badges, calibrated in energy units, were worn by all subjects to measure accumulated UVB dose, and plasma 25-OHD was measured fortnightly by a competitive protein binding assay. A linear relationship between changes in plasma 25-OHD and UVB exposure was found. The result shows that exposure to sunlight for a few hours each week is sufficient to improve the vitamin D status of the elderly.