The study, published in the Journal of Clinical Endocrinology & Metabolism (JCEM), evaluated whether calcium and vitamin D3 supplementation had benefits for bone health in postmenopausal women as measured by levels of serum parathyroid hormone (PTH) and bone turnover.
The US-based researchers reported that while calcium supplements noticeably improved bone health, vitamin D supplements did not reduce bone turnover.
"Vitamin D and calcium interact to suppress bone turnover by decreasing parathyroid hormone levels," explained the study's lead author Dr John Aloia of Winthrop University Hospital in Mineola, USA. "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."
"These findings suggest that vitamin D supplements over the recommended dietary allowance (RDA) do not protect bone health, whereas calcium supplements do have an effect," he said.
The study - a double-blind, placebo-controlled, parallel group, longitudinal factorial design study - divided 159 postmenopausal women into four groups. One group was given 1,200 milligrams of calcium daily, one took 4,000 IU of vitamin D daily, a third group received a combination of vitamin D and calcium, while a final group were given placebos.
Aloia and his team then measured bone turnover markers, including PTH levels in the blood, over the course of six months. In all, 120 women completed the study.
The team found a significant decline in bone turnover markers among women who were given daily calcium supplements, however it was shown that vitamin D supplements did not have any effect on bone turnover markers - even though the supplements did decrease parathyroid hormone levels.
Source: The Journal of Clinical Endocrinology & Metabolism
Published online before print, doi:10.1210/jc.2013-2121
"Calcium and Vitamin D Supplementation in Postmenopausal Women"
Authors: John F. Aloia, Ruban Dhaliwal, Albert Shieh, et al