Your body breaks down old bone in a process called bone turnover. Younger women make enough bone to replace the bone that is lost in this process. Bone mass decreases after the age of 30 in most women, and menopause accelerates the rate of bone loss.

Osteoporosis develops when the body is unable to replace bone as fast as it is broken down. To offset bone loss and prevent osteoporosis, many postmenopausal women rely on calcium and vitamin D supplements which are supposed to increase the absorption of calcium.

Women, however, may want to reconsider their choices. Calcium supplements or a combination of calcium and vitamin D do reduce the rate of bone turnover and the risk of osteoporosis in postmenopausal women. But vitamin D alone does little for bone health, according to a new study.

Markers of bone turnover declined significantly among women who were given daily calcium supplements.

“Vitamin D and calcium interact to suppress bone turnover by decreasing parathyroid hormone levels,” John Aloia, MD, lead author on the study, said in a statement. He added that women who are deficient in vitamin D may still benefit from a combination of calcium and vitamin D, but for those who already get the recommended daily allowance of vitamin D through their diet, the study findings suggest that no advantage exists to adding a vitamin D supplement.

Aloia and his team divided postmenopausal women into four groups. One group received a combination of vitamin D and calcium; one was given 1,200 milligrams of calcium daily and a placebo; one took 4,000 IU of vitamin D daily and a placebo; and a control group received two placebos. In all, 120 women completed the six-month study.

The investigators found that markers of bone turnover declined significantly among women who were given daily calcium supplements. And vitamin D supplements had no effect on the markers.

“The findings suggest that vitamin D supplements over the recommended dietary allowance do not protect bone health, whereas calcium supplements do have an effect,” Aloia said. Women also need to be aware of the increased risk of heart attacks from too much calcium, and should ask their doctor about their diet and their need for supplements.

The study is published in The Journal of Clinical endocrinology & Metabolism.