Can You Get Vitamin D Through a Window? Doctors Explain Whether You Can Absorb Any of the Sunshine Vitamin Through Glass

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It’s long been advised that soaking up the sun is the best way to get enough vitamin D (while still wearing sunscreen, of course). But that’s not exactly easy to do during the winter months when even a short walk requires bundling up.

It’s not as if we’re all collectively living in total darkness for months on end, though. Most people are still getting plenty of indirect sunlight through windows, whether it’s by sitting at a strategically placed work-from-home desk or while driving in the car. But if you're relying on sunny windows to get your vitamin D, your nutrient needs aren't exactly made in the shade.

Doctors say you likely aren't getting enough—which is important intel, since being deficient in the nutrient is linked to a wide range of health problems, including potentially being more at-risk for COVID-19. Here's what doctors want you to know about how to get enough.

Why Is Vitamin D Important?

Before getting into the best ways to get vitamin D, it’s first important to know why we need it at all. According to Dr. Natasha Bhuyan, MD, a primary care physician at One Medical, scientific research keeps unearthing more reasons why vitamin D is crucial for the body, adding to an already long list. “We know with certainty that vitamin D supports bone health as well as reducing the risk of falls in older adults,” she says, citing one major benefit.

Dr. Sophia Tolliver, MD, an assistant professor of family medicine at Ohio State University College of Medicine, says that vitamin D is also connected to our mood: Scientific studies have shown a link between depression and being deficient in the nutrient. Vitamin D is also connected to protecting against cardiovascular disease, lowering the risk of breast cancer, and, as mentioned above, may even help protect against COVID-19.

“There’s good evidence that the higher your blood level of vitamin D, the lower your risk of getting infected with COVID-19,” says Dr. Michael Holick, MD, a leading vitamin D expert and a professor of medicine at Boston University School of Medicine. Unfortunately, he adds, the vast majority of people in the U.S. don’t get enough.

Related: This is the Number One Way to Know if You Are Deficient in Vitamin D

How to Get Enough Vitamin D

Dr. Tolliver says it’s recommended that adults get 600 international units of vitamin D a day, and there are some foods that are an excellent source of it. “Fatty fish like salmon, sardines, and herring all have vitamin D,” she says. One serving of salmon, for example, has 526 international units of vitamin D — almost all of what you need for a whole day. “Egg yolks, cheese, and beef liver are other foods with smaller amounts of vitamin D,” Dr. Tolliver says. Unfortunately, it’s extremely difficult to get vitamin D from plant-based foods, although fungi does contain small amounts.

The other way to get your vitamin D filled is through the sun. Dr. Andrew Ordon, MD, host of the Emmy Award-winning show The Doctors, explains that the body produces vitamin D when the skin is exposed to the sun’s ultraviolet rays.

“It only takes 15 to 20 minutes of direct sun exposure a day to get enough exposure to ultraviolet rays to spur vitamin D production,” Dr. Ordon says. But Dr. Holick says being out in the sun during the winter months won’t get you there. “If you live in a state above 35-degree latitude — above the border of Tennessee and Nevada — your body will not synthesize enough vitamin D during the winter months because of the angle of the sun,” he says. Scientific studies back him up, proving the sun’s angle does affect how much vitamin D someone can synthesize. Dr. Tolliver adds that people with darker skin need three times as much vitamin D as those with lighter skin because they synthesize the nutrient at a lower amount.

Related: 13 Foods High In Vitamin D

Can You Get Vitamin D Through a Window?

Unfortunately, all four experts also say that it’s impossible to get enough vitamin D through a sunny window; the glass quite literally blocks it. Dr. Tolliver explains that there are two types of ultraviolet rays: UVA and UVB. UVB rays are what lead to vitamin D synthesis. UVA rays are what can lead to premature aging and can be a cause of skin cancer. “Glass 100% blocks UVB rays — which is what you need to make vitamin D — while allowing in UVA rays,” Dr. Tolliver says. This means that if you are sitting near a sunny window all day, you’re getting no vitamin D benefits and you’re actually exposing your body to harmful UV rays. Take away tip: Anytime you’re exposed to sunlight you should be wearing sunscreen — even if you’re indoors.

Dr. Tolliver says this holds true whether the sun is shining through a window in your car or in your house; you are not getting any vitamin D benefits if a window is involved, period. Dr. Ordon reiterates that direct sun exposure — a.k.a. being outside in the sun — can help the body produce enough vitamin D, but for the vast majority of people in the U.S., this is only possible during part of the year. For this reason, all the experts say it’s a smart idea to consider a vitamin D supplement.

Related: How Many Americans Are Vitamin Deficient?

What Are Signs of Vitamin D Deficiency?

Something else that’s tricky about vitamin D is that even though it’s linked to a long list of health benefits, it can be difficult to know when you aren’t getting enough. Signs of vitamin D deficiency include fatigue, depression, and bone weakness. Dr. Tolliver says the best way to know if you’re deficient is through a blood test at your doctor’s office.

Getting enough vitamin D is important year-round, but it’s especially important to be mindful of it during the winter months since, for most people, the sun isn’t providing enough UVB ways to ignite its production in the body. And if you thought strategically placing your WFH desk by a sunny window would do the trick, think again: Now you know it’s one vitamin D myth you can see right through.

Next, 15 Foods That Can Boost Your Immune System

Sources:

• Dr. Natasha Bhuyan, MD, primary care physician at One Medical

• Dr. Sophia Tolliver, MD, assistant professor of family medicine at Ohio State University College of Medicine

• Dr. Andrew Ordon, MD, host of the Emmy Award-winning show The Doctors

• Dr. Michael Holick, MD, a leading vitamin D expert and a professor of medicine at Boston University School of Medicine