Should you take Vitamin D for your bones?

About a year ago a team member started jogging.  After just a few weeks of vigorous workouts she found herself with ankle pain that just wouldn't go away, so she went to the doctor and found out that she'd developed an incipient stress fracture in her ankle. Fortunately the treatment for this is simply rest, but the doctor she saw told her to take vitamin D supplements "to help strengthen her bones." This made sense, as back in 2009 we recalled reporting on a study that showed that those taking vitamin D were as much as 20% less likely to break a bone than those who did not.

Since that study, however, meta-analyses of multiple smaller studies have shown mixed results with respect to Vitamin D's effects on actual bone mineral density and not just the risk of fracture.

With that in mind, researchers in New Zealand devised a meta-analysis designed to see if vitamin D alone - not in combination with calcium - would affect bone mineral density (Lancet 2014;383(9912):146-55). They limited the selected studies to those that measured bone density in at least one (and as many as six) different locations; where participants' baseline vitamin D levels were low enough that taking a supplement would have a measurable effect; and the study had to administer a high enough dose of vitamin D, without calcium, to affect the bones.

Twenty-three studies including over 4,000 people, over 90% of whom were female, were included in the meta-analysis. In addition to the criteria above, none of the participants had conditions that might affect their bone mineral density, such as pregnancy, corticosteroid use, or kidney problems.

Briefly, they found that those studies showing positive effects were more likely to be due to random chance rather than taking Vitamin D. Other studies showed bone mineral density decreasing, while yet others showed no effects at all. In short, they concluded, "the use of vitamin D supplements for skeletal protection in adults without specific risk factors for vitamin D deficiency is not justified."

What this means for you

Unless you are told that you have a vitamin D deficiency, taking vitamin D supplements is unnecessary. The sun is our biggest source of vitamin D, but with more attention being paid to the risk of skin cancer, we've actually heard people express concern that they weren't getting enough Vitamin D because they wore sunscreen on a daily basis. Don't worry about it - between 5 and 30 minutes of sun exposure twice a week on your arms, legs, face or back, without sunscreen, is thought to be enough, so you may well get all the vitamin D you need walking to your car or the bus stop. Further, many foods are fortified with vitamin D, including orange juice, milk, and many commercial cereals. Fatty fish such as mackerel or salmon are also good sources of vitamin D.

First posted: January 15, 2014