Serum levels of 25-hydroxyvitamin D in adults and elderly humans after a prophylactic dose of vitamin D2.

Vitamin D2 was administered orally as a single dose (2 mg) to 19 elderly subjects and 17 young adults. The maximum elevation of serum 25-hydroxyvitamin D was significantly greater in young than in elderly subjects. To evaluate intestinal absorption we also measured serum levels of vitamin D2 5 h after the given dose. A vitamin A absorption test was also performed simultaneously. Small differences between young and old subjects were seen with respect to serum vitamin D2 or vitamin A increments. In both groups the serum level of 25-hydroxyvitamin D was still elevated above initial level 60 days after a dose was given. No side effects, nor any change in serum calcium ion activity were noted during this period. These results speak in favour of the use of intermittent large doses of vitamin D2 as a prophylaxis against vitamin D deficiency in the elderly.