Vitamin D Alone Ineffective for Postmenopausal Osteoporosis

Laurie Barclay, MD

September 24, 2013

Calcium supplements significantly improved bone health in postmenopausal women in a double-blind, placebo-controlled, randomized trial, but vitamin D supplements alone did not reduce bone turnover or osteoporosis risk.

The trial results are published online September 24 in the Journal of Clinical Endocrinology and Metabolism.

"Vitamin D and calcium interact to suppress bone turnover by decreasing parathyroid hormone levels," lead author John Aloia, MD, from Winthrop University Hospital in Mineola, New York, said in a 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."

From December 2008 to April 2011, 159 postmenopausal healthy white women participated in this 6-month, longitudinal study at an ambulatory research center, and 120 completed the study. The 4 study regimens were: double placebo, calcium (1200 mg daily) plus placebo, vitamin D3 (100 μg; 4000 IU) plus placebo, and vitamin D3 and calcium. At baseline and 3 and 6 months, participants gave serum and urine samples after fasting and at 2 hours after a calcium load to measure markers of bone turnover.

When calcium load was given at baseline, serum parathyroid hormone (PTH) and cross-linked C-telopeptide levels fell and urinary calcium excretion rose. Over time, serum cross-linked C-telopeptide and procollagen type I N-terminal propeptide levels decreased with calcium supplementation but remained stable in participants receiving only vitamin D supplementation. The vitamin D groups had a decline in fasting PTH. Compared with the placebo groups, the vitamin D groups had greater suppression of PTH after a calcium load.

"Fasting PTH declines with vitamin D supplementation," the study authors write. "PTH declines after calcium intake. Supplementation of the diet with 1200 mg calcium/[day] reduces bone turnover markers, whereas supplementation with up to100 μg vitamin D3/[day] does not."

Clinical Implications

Limitations of this study include small sample size, lack of dose–response data or of 24-hour PTH measurement, and controversy regarding the most accurate assay for serum 25(OH)D.

Nonetheless, the investigators suggest that the findings support the benefit of high calcium intake in reducing bone turnover in postmenopausal white women. Although mean daily calcium intake in the placebo group was 946 mg, bone turnover was significantly reduced by the addition of 1200 mg/day of calcium supplements and further reduced by a calcium load.

"These findings suggest that vitamin D supplements over the recommended dietary allowance...do not protect bone health, whereas calcium supplements do have an effect," Dr. Aloia said in the news release. "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."

Merck and the Empire Clinical Research Investigator Program supported this study. The study authors have disclosed no relevant financial relationships.

J Clin Endocrinol Metabol. Published online September 24, 2013. Abstract

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