Ask Keri: Can You Get Vitamin D Through a Window?

By Keri Glassman, MS, RD, CDN

Ask Keri: My husband spends a lot of time driving from place to place for his job. Even though he’s deficient in vitamin D, he insists that he gets his ‘dose of D’ through the glass. Can you get vitamin D through a window?

Keri says:

If you live pretty much anywhere in the Northern Hemisphere, you already know that vitamin D deficiency is a thing. In fact, it’s a downright problem. 

In the United States, more than 40% of adults are considered deficient, according to this 2018 study from the National Library of Medicine. More recent data from Frontiers in Nutrition showed that there’s been a global vitamin D shortage as far back as 2002.

But why do we need the sunshine vitamin in the first place? And what are some of the ways we can get it? Unfortunately, sunning yourself through the window won’t work! 

Read on to find out why we need vitamin D, the causes of deficiency, and the best ways to get more vitamin D in our lives. 

What’s So Important About Vitamin D? 

Unlike other vitamins, vitamin D functions as a hormone. There are receptors for it throughout your body’s cells. Vitamin D is also fat soluble. This means your body can store it in the liver and fat cells and then use it when needed to help you absorb calcium and phosphorus—two minerals important for building stronger bones—from the food you eat. That’s why being deficient in vitamin D can lead to weak bones. 

Vitamin D is also critical for other aspects of good health. For example, it:

  • Helps support healthy immune function
  • Supports cardiovascular health 
  • Aids in neuromuscular function 
  • Helps to deter certain types of cancer
  • Protects against Type 1 and Type 2 diabetes 
  • Helps to regulate mood
  • Is linked to obesity 

RELATED: Healthy Eating for Diabetes: The Best Nutritious Snacks and Tasty Breakfast Ideas

“Sitting in front of a sunny window will not help increase your levels of vitamin D, but you might be exposed to the harmful radiation of UVA.”

Causes of Vitamin D Deficiency 

Whether you live in the northern latitudes, vitamin D deficiency can happen. You’re most at risk of deficiency if you’re elderly, have dark skin, are obese, eat a poor diet, or have a digestive disease, such as Crohn’s, celiac, or a food allergy, that affects your nutrient absorption. 

The factor that really comes into play in the high latitudes is lack of sun exposure. Whether it’s due to a family history of skin cancer or because we want to avoid wrinkles, many of us expose our skin to the sun far less than previous generations did. This is mostly because science has shown us in the last couple of decades how damaging the sun’s rays can be. We’re no longer slathering our skin in baby oil for that optimal tan, er, burn! Instead, we’re slathering up in sunscreen.

This can translate to too little vitamin D. While sunlight doesn’t actually give us the sunshine vitamin, our bodies produce it when our skin is exposed to the sun’s ultraviolet rays. Then our kidneys and liver work to convert the biologically inert form of vitamin D into an active form (D3) that the body can use. 

Here’s the catch—and this brings us back to the original question—sunlight contains two types of ultraviolet rays. Ultraviolet A, or UVA, are the rays that penetrate deep and can cause wrinkles and premature aging. Ultraviolet B, or UVB, are responsible for the redness that comes with a sunburn, and are the rays that trigger the synthesis of vitamin D. 

The thing is, most windows—whether on our cars, offices or homes—contain UVB blockers. This means that sitting in front of a sunny window will not help increase your levels of vitamin D, but you might be exposed to the harmful radiation of UVA.

 RELATED: The Surprising Truth About Vitamin D and Sunscreen

How to Boost Your Vitamin D

Now that we know how important vitamin D is and that you can’t get it simply by sitting next to a window, let’s talk about ways to get your sunny D fix.


OK, this one might be controversial, but let’s talk about it. Yes, overexposure to the sun is bad, and it can age us prematurely and lead to skin cancers in susceptible individuals. But that doesn’t mean that we should avoid the sun altogether. 

After all, the primary source of vitamin D3 is sunlight! Research has shown that as little as 10–30 minutes of midday sun, several times a week, will provide you with an adequate dose of D. If you have darker skin, you might need to increase your time in the sun a bit. The main rule here is to avoid a burn. This might mean exposing your skin in the morning or late afternoon, depending on where you live and, of course, liberally applying sunscreen when you no longer want exposure. 


At Nutritious Life, we always advocate for getting your nutrients first and foremost from whole, nutrient-dense foods. With vitamin D, that can get tricky because very few foods naturally contain vitamin D. 

Vitamin D-rich foods

Here’s a short list of the ones that do (including fortified ones): 

  • Beef liver
  • Butter
  • Cod-liver oil
  • Eggs (particularly the yolks)
  • Fortified cereals
  • Fortified milk (dairy and non-dairy varieties)
  • Fortified orange juice
  • Mushrooms
  • Salmon
  • Sardines
  • Swordfish
  • Tuna


If you are low in vitamin D, your doctor may prescribe a supplement. (The most accurate measure of vitamin D in your body is the 25-hydroxy vitamin D blood test. A serum level of 20–50 nanograms/milliliter is typically considered within the normal range. Anything under 20 ng/mL means you’re deficient.) 

To meet adequate levels of vitamin D, the National Institutes of Health (NIH), recommends that people ages 1–70 need about 15 micrograms or 600 IU (international units) of vitamin D daily.

The American Academy of Dermatology recommends that you get vitamin D from a healthy diet that includes foods rich in vitamin D and beverages and food fortified with it, and/or vitamin D supplements.  

Dr. Whitney Bowe, a superstar New York City-based dermatologist who is also a guest expert of the Nutritious Life Studio’s Become a Nutrition Coach Masterclass, takes a holistic approach to skincare (something we can definitely get behind!). She suggests supplementing with 1000 IU of vitamin D a day. But she cautions to not exceed 4000 IU daily. This is because overdoing vitamin D supplementation can be toxic to the liver. 

Dr. Bowe helps her patients and people around the country figure out how to get #thatboweglow. She shares some of her genius advice with Nutritious Life readers in a series on hot skin-care topics. For more insight from Dr. Bowe, check out her skincare posts.

More Advice from Dr. Whitney Bowe:

The Surprising Truth About Vitamin D and Sunscreen
Is This Summer Wellness Product Putting Your Health at Risk?
Why Your Skin Microbiome Matters, Too
Are These Hidden Ingredients Making You Break Out?

(Images: Shutterstock)

About Keri Glassman, MS, RD, CDN
Keri Glassman, MS, RD, CDN, is a renowned celebrity nutritionist, healthy cooking expert, and wellness thought-leader. She is the founder and CEO of Nutritious Life and The Nutritious Life Studio, an online certification that provides unparalleled, forward-thinking education to individuals of various backgrounds looking to establish successful careers in the health and wellness industry.

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