9 Things That Prevent Sunlight from Making Vitamin D in Your Skin

Where You Live Matters During the Winter


Vitamin D is unique among the vitamins because we can make some of it ourselves — if we get enough sunlight on our skin. All the other vitamins we obtain entirely from food or from the bacteria in our intestinal tract.

It’s important to have enough vitamin D because it’s essential for calcium absorption and helps keep our bones healthy, no matter what our age. Researchers are discovering that vitamin D may also be important for healthy muscles and a strong immune system, though that’s still under investigation.


Vitamin D production in the skin drops during the winter in most areas of the United States and so do the levels in our blood. Is there anything you can do about that?

Yes! Get your vitamin D from the right foods or from supplements.

Here are the major factors that can lower or even block the vitamin D that your skin can make with the help of sunlight:

  • Northern latitudes (unless you live in the South or Southwest United States, you don’t make much D during the winter)
  • Lower altitudes (your body makes more D at higher altitudes where sun rays are stronger)
  • Cloud cover
  • Shade
  • Hats
  • Clothing
  • Sunscreen
  • Window glass
  • Darker skin


Vitamin D in food

Other than salmon and other fatty fish, most foods aren’t naturally rich in vitamin D. Some foods such as milk, most cereals, and margarine are fortified with some D, so check the labels. They list D as a percent of the Daily Value, which is 400 IU.

How much vitamin D do adults need every day? People 70 and younger need 600 IU, those over 70 need 800 IU. The safest maximum daily intake: 4,500 IU.

There are two forms of vitamin D in supplements and fortified foods: D3 is manufactured from the lanolin in sheep’s wool, and D2 comes from plants. In food and in multivitamins, they’re basically equal in potency, according to the National Institutes of Health. At very high levels in supplements, D3 may be more potent.

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