On Nutrition

There’s been a lot of interest in vitamin D for several years due to the possibility that deficiency increases the risk of developing osteoporosis, heart disease, diabetes, high blood pressure and several other health conditions. But it’s vitamin D’s role in immune health that’s currently grabbing our attention, thanks to research suggesting that low vitamin D levels may increase COVID-19 risk. But here’s why you should hold up before loading your shopping cart with vitamin D supplements.

It’s worth noting that the only vitamin-D-related health claim allowed by the Food and Drug Administration is that adequate calcium and vitamin D — technically a hormone that promotes absorption of calcium into the body — may reduce the risk of osteoporosis. This is the only allowed claim because this is the only claim supported by robust evidence. Recent research funded by the National Institutes of Health found little value in using supplemental vitamin D to lower risk of cancer or cardiovascular disease, and the validity of multiple vitamin D research papers from one research group at an Iranian university — many of which suggested a role in diabetes prevention — is currently under suspicion.

What about immune health? Well, two scientific groups in the United Kingdom concluded last month that evidence does not support taking vitamin D solely to prevent or treat COVID-19. Rather, they recommend taking a modest daily dose (400-1,000 IU) in the fall and winter months to protect bone and muscle health, noting that this might also slightly reduce the risk of acute respiratory tract infections, such as cold and flu.

The bottom line is that vitamin D isn’t a magic panacea — we need enough for good health, but that doesn’t mean that getting more than what we need to correct or prevent deficiency makes us any healthier.

You have two main ways to get vitamin D — exposing your bare skin to sunlight or taking vitamin D supplements. While few Americans experience severe vitamin D deficiency, about four in 10 are mildly deficient — not surprising when you consider that modern life mostly takes place indoors, and we use sun protection when we’re outdoors. This lack of sun means your body may not be able to manufacture enough vitamin D on its own. Washingtonians are at even higher risk of deficiency thanks to our northern climate. Other factors that increase risk of deficiency include:

  • Dark skin. The darker your skin, the more sun it takes to make vitamin D.
  • BMI (body mass index) over 30. Vitamin D can become sequestered in body fat instead of making its way to the bloodstream.
  • Diseases that may interfere with absorption of dietary fat and vitamin D — which is a fat-soluble vitamin — including celiac disease, Crohn’s disease and ulcerative colitis.
  • Previous gastric bypass surgery, which can also prevent adequate absorption.

It’s almost impossible to meet your body’s vitamin D needs with food alone, but many dairy products are fortified with vitamin D — read the label to be sure. Fatty fish such as salmon and sardines, egg yolks, fortified orange juice and cereals, mushrooms and beef liver also contain some D.

If you’re concerned about your vitamin D status, talk to your doctor. A simple blood test can measure your levels of 25-hydroxyvitamin D, although it isn’t always covered by insurance. If you don’t know your numbers and don’t want to get tested right now, a modest daily dose — 600 IU for ages 1 to 70, 800 IU from age 71 onward — can cover your bases. Just don’t expect any miracles.