"These findings suggest that vitamin D supplements over the recommended dietary allowance do not protect bone health, whereas calcium supplements do have an effect," study lead author Dr John Aloia, of Winthrop University Hospital in Mineola, NY, said in a news release from the Endocrine Society.
For the study, published on 24 September in the Journal of Clinical Endocrinology & Metabolism, the researchers examined bone turnover in 159 postmenopausal women. Bone turnover is the body's natural process for breaking down old bone. Young people produce enough new bone to replace what is lost, but bone mass in women begins to decline after age 30, and this loss speeds up after menopause.
The women in the study were divided into four groups: one group received a combination of vitamin D and calcium; one group took 1 200 milligrams of calcium daily; one group took 4 000 IU of vitamin D daily; and one group took an inactive placebo. Levels of bone turnover markers, such as parathyroid hormone levels in the blood, were assessed for six months.
Decline in bone turnover
There was a significant decline in bone turnover markers among women who took daily calcium supplements. The vitamin D supplements had no effect on bone turnover markers, the researchers reported.
"Vitamin D and calcium interact to suppress bone turnover by decreasing parathyroid hormone levels," said Aloia in the news release. "This can be beneficial in women who are vitamin D deficient. In women who already are receiving the recommended daily allowance of vitamin D, however, the study found there was no advantage to adding a vitamin D supplement."
Aloia added: "Women do need to be cautious about the possibility of vascular side effects from too much calcium and should consult their physicians about whether their diet is adequate or whether they should take supplements at all."
By 2020, half of all Americans over age 50 are expected to have low bone density or osteoporosis, according to the National Osteoporosis Foundation. This can lead to painful and debilitating fractures.
The U.S. National Institute of Arthritis and Musculoskeletal and Skin Diseases has more about bone health.