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Aug 31, 2023

How to Get Enough Vitamin D During the Winter

Ask Well If you live in certain parts of the country, you’ll need a lot more

Ask Well

If you live in certain parts of the country, you’ll need a lot more than sunlight to maintain adequate levels this season. Here's what the experts recommend.

Credit...Joyce Lee for The New York Times

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By Rachel Rabkin Peachman

Q: I spend most of my winter days indoors, and when I’m outdoors, I’m covered from head to toe. If I only get a few minutes of sun exposure on my face and hands each day, is that enough to get adequate vitamin D? And if not, what should I do?

If you live in a part of the country where winters are cold and gray, it's smart to think about how you’ll get vitamin D — often called the sunshine vitamin — over the next several months.

Vitamin D is synthesized in the skin after exposure to the sun's ultraviolet B rays, and is crucial for calcium absorption and the maintenance of strong, healthy bones, said Julie Stefanski, a registered dietitian nutritionist and spokeswoman for the Academy of Nutrition and Dietetics. Deficiencies, which are common worldwide, can cause soft, weak and brittle bones, leading to fractures. Your vitamin D status can also play a role in other aspects of health including inflammation, autoimmune disease risk, heart health and cognitive function.

Most healthy people with fair skin can typically produce enough vitamin D during the summer by exposing their faces, arms and legs to sunlight for about five to 10 minutes several times per week during midday, when the sun is highest and its UVB rays are most powerful, said Antony Young, an emeritus professor of experimental photobiology at the St. John's Institute of Dermatology at King's College London, via email. People who have more melanin, or darker pigmentation, in their skin need longer periods in the sun (in some cases two-and-a-half to three times as much, though it depends on your skin tone) because melanin reduces vitamin D synthesis.

The winter sun, however, does not have the same effect if you live in regions north of the 37th parallel (in the United States, this border runs from around central California to the southern borders of Utah, Colorado, Kansas, Missouri, Kentucky and Virginia). In these places during the cold-weather months (around October or November through April or March), the sun is lower and its UVB rays are weak.

"Winter sunlight does not have enough of the UVB component that is essential for vitamin D synthesis," Dr. Young said. "For all practical purposes, one cannot make vitamin D in cold climates in winter."

That doesn't mean, however, that you can't meet your vitamin D needs during the chillier months. "You don't need to get it from sunshine," said Dr. Deborah S. Sarnoff, president of The Skin Cancer Foundation and a clinical professor of dermatology at the NYU Grossman School of Medicine.

There is a lot of controversy about how much vitamin D you should have in your blood for optimal health, Dr. Young said. But in general, he added, most major medical organizations recommend at least 20 nanograms per milliliter as measured by a simple blood test.

How much vitamin D you should get from foods or supplements is also debated, Ms. Stefanski said, noting that it's difficult to suggest one blanket recommendation for everyone. Your skin color, age, health conditions and sun exposure during warmer months, among other things, will influence how much vitamin D you need each day.

Still, federal guidelines recommend that in general, to maintain good bone health and normal calcium metabolism, people between 1 and 70 years of age should get 600 international units (or 15 micrograms) each day — from foods, supplements or both. Those over 70 should get 800 I.U. (or 20 micrograms), according to the guidelines, and infants up to 12 months need 400 I.U. (or 10 micrograms).

"But many organizations don't feel those numbers are high enough," Ms. Stefanski said. For example, the Endocrine Society — which recommends a blood level of 40 to 60 nanograms per milliliter — says that most adults can safely take between 1,000 to 2,000 I.U. (or 25 to 50 micrograms) of vitamin D per day from either supplements or a combination of food and supplements.

If you’re concerned about a deficiency, are at risk for osteoporosis or have a condition that affects how you absorb nutrients, talk with a health care provider about getting your vitamin D level tested.

While winter's chill is in the air, you’ll likely need to look beyond the sun to satisfy your vitamin D needs, Dr. Young said.

Foods that supply the highest amounts of naturally occurring vitamin D include fatty fish (like salmon, tuna and sardines), cod liver oil, beef liver, egg yolks and some mushrooms. But because the typical American diet tends not to include many or enough of those foods, manufacturers have been fortifying foods with vitamin D since the 1930s. Good sources of vitamin-D-fortified foods are cow's milk, soy milk, cereal and orange juice. Keep in mind, though, that it can be challenging to get enough vitamin D from food sources alone, Ms. Stefanski said. And not all dairy products are fortified with vitamin D, so make sure to check the nutrition facts label.

"Especially as we’re entering the winter months," Ms. Stefanski said, "most people would benefit from taking a supplement."

When looking for a supplement, choose vitamin D3 over vitamin D2, Ms. Stefanski said, since research suggests you can absorb it more effectively. Also, look for a supplement that has the U.S.P. Verified Mark on the bottle, which indicates that the product contains the ingredients listed on the label and does not contain harmful contaminants.

Just don't take more vitamin D than is recommended by the packaging or your health care provider, Ms. Stefanski added. In excess, vitamin D can build up in the body and lead to toxicity, which can result in symptoms like fatigue, weakness, confusion, vomiting, dehydration, constipation and pain.

Another thing to avoid in your pursuit of vitamin D, Dr. Sarnoff said: the tanning salon. Not only do the machines increase your risk of skin cancer, they also emit primarily ultraviolet A rays, which don't spur the skin to make vitamin D. So stick with supplements and foods as your vitamin D sources in the winter, and consider adjusting your strategy when the summer sun returns.

Rachel Rabkin Peachman is a regular contributor to The Times, where she frequently writes about health, science and family. @RachelPeachman

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