Do Vitamin D Supplements Improve Bone Health?

Long dark Minnesota winters raise concerns about whether we get enough sun to supply the vitamin D our bones need. A new study measured the effectiveness of vitamin D supplements to improve bone mineral density.

Our bodies need vitamin D to maintain healthy bones and teeth. Because few unfortified foods contain vitamin D, our best source of this nutrient is sunlight—which can be in short supply for those of us who stay indoors through the cold winter months. When we don’t get enough vitamin D, our bones can’t absorb as much calcium, and the risk of osteoporosis rises. Can supplements replace sunlight during the winter to keep bones strong? In light of recent research, the answer remains unclear.

Experts are not in agreement about the amount of vitamin D we need to maintain skeletal health. The Institute of Medicine recommends levels of 20 ng/mL or greater, but others believe that the minimum level should be higher: at least 30 ng/mL.

Researchers at the University of Wisconsin School of Medicine and Public Health in Madison, led by Dr. Karen E. Hansen, wanted to address this question with a study focused on the needs of postmenopausal women. Getting enough vitamin D is a particular concern for this demographic. It is estimated that 75 percent of postmenopausal women in the United States are vitamin D deficient. We know that nearly half of women sustain an osteoporotic fracture during their postmenopausal years.

Hansen and her colleagues recruited 230 postmenopausal women age 75 or younger with vitamin D insufficiency—defined as a vitamin D level of between 14 and 27 ng/mL—and divided them into three groups. For a period of one year, one group was given a high-dose vitamin D supplement to maintain vitamin D levels at 30 ng/mL or higher, one group was given a low-dose vitamin D supplement, and the third group received a placebo.

During the study, researchers tracked calcium absorption, bone mineral density, muscle mass, and sit-to-stand test results of the participants. They wanted to answer two questions: did high-dose supplementation increase calcium absorption, and could the supplements reduce the number of falls suffered by participants?

Within the parameters of this study, vitamin D supplements were not helpful. Researchers did not find any significant increase in bone mineral density in the groups and there was no difference in the number of falls between the three groups. Although this study does not support the effectiveness of higher-dose vitamin D supplements to improve bone health, researchers note that the study was limited to one year. It’s possible that factors such as a different demographic of participants or continued treatment beyond one year might affect bone health outcomes.

Until further research provides a more definitive answer, your physician can help you evaluate your bone health and your vitamin D needs based on your age, lifestyle, and overall health picture. You can always chose to boost your vitamin D with fortified foods or by spending short periods of time (10 to 15 minutes) outside each day between the hours of 11 a.m. and 3 p.m.