Sunshine Through the Window: Skin Cancer Risk and Vitamin D

by Amy Hendel, P.A. Health Writer

Being bathed by rays of sunshine through home windows or while driving can be mood boosting or even relaxing. However, we may often falsely believe that we are getting healthy doses of vitamin D from rays through the window. More so, we may also overlook the harmful risks of sun exposure, thinking that because we are indoors or behind glass we’re protected from UV rays.

Here’s a look at how to make sure you’re not only getting the proper amounts of vitamin D, but how and when to protect your skin to keep it at its healthiest.

Sunbathing and and vitamin D production

It’s important to understand that you don’t actually absorb vitamin D from the sun. Sunlight exposure helps your body to make vitamin D. Certain wavelengths of sunlight work to activate the 7-dehydrocholesterol compound in your skin. This reaction is what produces vitamin D within the body.

Specific UVB wavelengths of sun, or ultraviolet-B range wavelengths, happen to be the key to this process, but these wavelengths are also blocked by standard glass windows. Vitamin D can only be produced if the windows are open and direct sunlight is hitting your skin. Therefore, sunlight exposure through the window is not an effective way for your body to produce vitamin D.

When it comes to vitamin D production in the winter, most Northerners will not get enough sunshine exposure to produce adequate levels of vitamin D, even with prolonged time outdoors. That’s because the sun's rays hit the northern latitudes at a different angle in the winter time, changing the wavelength. UVB wavelengths that range from 290 – 320 nanometers are mainly available in the summer. With specific timed sun exposures to these rays, the body will be able make adequate amounts of vitamin D.

Specifically during winter months, while these wavelengths are unavailable, most people should focus on getting the vitamins from oily fish, fortified foods, or vitamin D supplements. A risk of insufficient sun exposure may also occur if you wear protective clothing or long sleeves in the summer, and use sunblock religiously. In cases like these, supplements may have to be taken year round.

Sunbathing through the glass and skin cancer risk

UVB rays, although involved with producing vitamin D, are associated with burning the skin. They also have the potential to instigate growth of cancerous cells. However, unlike UVB rays, Ultraviolet-A waves (UVA) rays can penetrate glass (and clouds) and they also penetrate the skin more deeply than UVB rays. UVA rays cause aging and wrinkling, both of which are also linked to risk of skin cancer. So it’s no wonder UVA rays are also known as the “tanning rays,” causing damage to the skin, aging it prematurely and damaging skin cells putting you at risk for skin cancer.

Vitamin D tips and reducing skin cancer risk

Some experts believe that 15 to 20 minutes of sun exposure several times a week, without protection (clothes or sunblock) is acceptable and safe, and will allow sufficient levels of vitamin D to be maintained. Other skin cancer experts worry that people won’t carefully “clock in” their minutes of exposure, putting them at risk of skin cancer for the sake of vitamin D.

Following these tips can help balance proper sun exposure and skin protection

  • If you do want some unprotected sun time, make sure you follow the formula of unprotected exposure to the sun two to three times a week for about 15 to 20 minutes maximum.

  • Understand that there is no “safe tan.”

  • Routinely wear sunblock on exposed skin, year round, especially during the warmer months, and especially during the hours of ten A.M. to 2 P.M. when ray wavelengths are strongest.

  • Discuss the viability of getting a baseline vitamin D level with your doctor.

  • Include several servings of oily fish daily including salmon, trout, herring, sardines, anchovies and orange roughy, all of which are also lower in mercury. Drink fortified milk and eat yogurt and other foods rich in vitamin D.

  • Use a vitamin D supplement that has USP seal, meaning it has undergone a vetting and certification process for levels of vitamin D in the product.


New York Times/Science

Amy Hendel, P.A.
Meet Our Writer
Amy Hendel, P.A.

Known as "The HealthGal", Amy Hendel P.A. is a medical and lifestyle reporter, nutrition and fitness expert, health coach and brand ambassador. Trained as a physician assistant, she maintains a health coach private practice in New York and Los Angeles. Author of The Four Habits of Healthy Families, find her on Twitter @Healthgal1103 and on Facebook @TheHealthGal. Check “Daily Health News” at Her personal mantra? “Fix it first with food, fitness, and lifestyle.”