From The March 2001 Issue of Nutrition Science News

Vitamin D Less Effective in Older Women

One reason older women are prone to osteoporosis may be that as a woman ages, vitamin D becomes less able to fulfill its functions in the body. In fact, a study by researchers at the Mayo Clinic in Rochester, Minn., has found that 1,25-dihydroxy vitamin D supplements are less effective at promoting calcium absorption in older women.

In this study, 20 young women (mean age 29) and 20 older women (mean age 72.5) were given various doses of calcium citrate and vitamin D supplements in a standardized diet during a weeklong stay at a metabolic study unit. The subgroups received either 1 or 2 mg per day of vitamin D with 200 mg of calcium or no vitamin D and 200 to 3,000 mg of calcium. Isotopes of calcium were used to determine how much calcium was absorbed and present in the women's serum.

The researchers plotted fractional calcium absorption against the amount of free vitamin D present in subjects' blood. For the young women, there was a direct correlation—the more vitamin D in the body, the more calcium they absorbed. For the elderly women, however, there was no connection. Increasing vitamin D intake did not aid in calcium absorption. The women in this study were not on estrogen replacement therapy, so researchers were unable to distinguish whether the lack of responsiveness to vitamin D was due to aging or estrogen deficiency. The fact that older women do not respond adequately to vitamin D may contribute to their negative calcium balance and bone loss.

—The Journal of Clinical Endocrinology and Metabolism
2000 Nov:85(11);4023-7.