Vitamin D types affect serum levels

Madison, Wis. - A recently published study suggests that mean serum levels of 25-hydroxyvitamin D, or 25(OH)D, are somewhat higher in older adults after a year of taking vitamin D3 (cholecalciferol) compared with taking vitamin D2 (ergocalciferol), Reuters Health reports.

Furthermore, the University of Wisconsin researchers write that the effect is the same whether dosing occurs daily or monthly.

The study was designed to determine whether the two vitamin D types raise 25(OH)D serum levels to the same degree, as is widely assumed. The researchers had 64 adults over age 65 take either vitamin D2 or D3 at daily doses of 1600 IU or monthly doses of 50,000 IU. Daily or monthly placebos were administered for blinding purposes.

“Total 25(OH)D increased from baseline to the 12-month follow-up with all regimens,” the researchers report. The specific increases were 32 percent with D3 daily, 29 percent with D3 monthly, 21 percent with D2 daily and 11 percent with D2 monthly.

Moreover, the researchers write, “The absolute increase at 12 months with D3 was greater than with D2 for both daily and monthly dosing.”

Compliance rates in the four arms of the study ranged from 91.6 percent to 98.9 percent, the study notes.

“Vitamin D3 is slightly, but significantly, more effective than vitamin D2 at increasing circulating 25(OH)D,” the study concludes, adding that “the physiological importance of this, if any, remains to be determined.”

The study results were published online Feb. 2 in Journal of Clinical Endocrinology and Metabolism.