Vitamin D: What does it do and why do we need it?

We all know people who have walked outside on a rare, sunny winter day and said, “I need all the vitamin D I can get!” But before we all go sunbathing in 40-degree weather, let’s take a look at what’s going on.

What does Vitamin D do?

Vitamin D helps the body absorb calcium from our food, which in turn builds strong bones; it may also help with other body functions. Mild vitamin D deficiency can have no symptoms. Although severe deficiency — which can cause rickets in children and osteomalacia (softening of the bones, typically through a deficiency in Vitamin D) in adults — is uncommon today, moderate vitamin D deficiency can be associated with decreased calcium absorption and low bone density, and possibly with a higher likelihood of broken bones.

How do we get Vitamin D?

We get vitamin D in 2 ways — through sun exposure and through foods that contain or are supplemented with vitamin D.

It is hard to get enough light from the sun, especially in the winter, to make enough vitamin D. Those of us in the Pacific Northwest know far too well that our UV light exposure can vary with season, latitude, time of day, cloud cover, and air pollution. How much sun exposure you need also depends on your skin tone and how much skin you’re exposing, so there’s no set amount of time recommended. We are in the dark days of winter now and with our sun exposure so limited, it takes considerably longer to get what we need. And unless they are specifically labeled as providing it, those high-powered seasonal affective disorder lamps don’t supply the right kind of light to cause your body to produce vitamin D.

Given the difficulty of getting good sunlight this far north, it is all the more important to be sure you are getting enough vitamin D through food. Some foods like oily fish naturally contain vitamin D, while many foods in the United States have added vitamin D to prevent vitamin D deficiency and rickets. Those include foods like milk, orange juice, cereals, and yogurt.

How much Vitamin D do we need?

How much and whether kids need vitamin D supplements depend on their age and diet. Formula-fed babies usually don’t need supplementation if they’re taking at least 32 ounces each day of formula, but exclusively breastfed babies do need supplementation from a few days of life until they are transitioned to whole milk at one year. The American Academy of Pediatrics recommends 600 IU of vitamin D for children 1 to 18 years old. Picky eaters and unpredictable eaters may also need supplements. If you’re not sure, consult your physician.

It is possible to plan to get all the vitamin D you need — 600 IU — without supplements. But at this time of year, we need to plan to get it from our food rather than that elusive sun. Time outside for us and our kids is good for our health in so many other ways, but vitamin D is one benefit of outside time that we can’t count on in winter.
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Dr. Susanna Block, MD is a pediatrics specialist at the Kaiser Permanente Capitol Hill Campus.

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