Prophylaxis against vitamin D deficiency in the elderly by regular sunlight exposure.

The effects of regular sunlight exposure on levels of vitamin D metabolites and on other indices of calcium metabolism have been studied in elderly rest-home residents. Fifteen subjects who formerly went outdoors very infrequently were studied over a 4-week period while spending 0, 15 or 30 minutes daily sitting on the rest-home verandah. During this time, levels of 25-hydroxyvitamin D [25(OH)D] rose by 7.4 +/- 1.2 (s.e.m.) microgram/1 in the group spending 30 minutes per day outdoors (P less than 0.005) and there was a smaller but nonsignificant increase in the 15 minutes per day group also. Serum 1,25 (OH)2D levels did not change during the study but serum ionized calcium and alkaline phosphatase showed small, but significant, decreases. Intestinal strontium absorption increased in both treatment groups (P less than 0.05), indicating a similar change in calcium absorption. It is concluded that 30 minutes spent outdoors each day leads to a substantial increase in 25(OH)D levels in elderly subjects and that this has significant effects upon other indices of calcium metabolism. This regimen provides a safe and inexpensive method for the prevention of osteomalacia in frail elderly subjects.