DEAR DOCTOR K:
I’ve read several articles about the negative effects of a low blood level of vitamin D, but my doctor said I didn’t need to have my level checked. Why not?
Many of my patients are asking me the same question. Vitamin D has been in the news a lot in recent years, but we still don’t have solid answers to many questions, including yours.
There is strong evidence that people with a low blood level of vitamin D have higher rates of osteoporosis (thin bones). There is less strong, but still worrisome, evidence that they have higher rates of various autoimmune diseases (including Type 1 diabetes and multiple sclerosis), atherosclerosis and associated heart attacks and strokes.
The linking of a low blood level of vitamin D to these and other diseases has led many doctors to routinely test the vitamin D levels in their healthy patients.
But an authoritative group, the U.S. Preventive Services Task Force (USPSTF), points out that even if you have a low vitamin D level, there’s little evidence that taking a vitamin D supplement will do you any good.
There are exceptions. People who might need testing include those who:
- have osteoporosis or other bone-health problems;
- have circumstances that affect fat absorption, including celiac disease or weight-loss surgery. Such conditions lower the amount of vitamin D your gut can digest;
- routinely take medications that interfere with vitamin D activity, including anticonvulsants and glucocorticoids.
Another approach many experts recommend is not to get a blood test: Just take a vitamin D pill daily. If your blood level is low, it may help. And if it’s not low, it won’t hurt. The recommended daily intake of vitamin D is 600 international units (IU) for everyone aged 14 to 70 and 800 IU for those age 71 and above. Some experts recommend 1,000 to 2,000 IU a day.
There are large studies underway here at Harvard and elsewhere to test whether there are health benefits from taking daily vitamin D supplements. Results are likely to be published in four to six years. Until then, what’s the right thing to do? I think it’s reasonable for people to take regular vitamin D supplements.
For people who are at risk for diseases linked to a low vitamin D level, I get their blood tested. If their level is low (below 30 ng/dL), I recommend taking a daily vitamin D supplement. And I retest their blood level, because in my experience the supplements don’t raise the level very much in some people. Some of my colleagues disagree with me on this.
What if the studies that are underway show that I’m wrong — that the blood tests and the daily pills achieve nothing and are just a waste of money? I’d be sorry. But what if I did no blood testing and did not recommend pills until the studies were completed — and the studies showed that, by waiting, I had put my patients at higher risk for various diseases? I’d be even sorrier.