Can You Get Vitamin D Through a Window? Doctors Explain
There are health benefits to soaking in vitamin D through sunlight...but do you even have to step outside?
Are you getting enough sunlight? The data suggest maybe not. The Cleveland Clinic reports that vitamin D deficiency is a global problem: One billion people worldwide and approximately 35% of U.S. adults are deficient in this critical vitamin which has many health benefits, including some that save lives.
If you don’t get enough regular exposure to sunlight, you can eat more vitamin D-rich foods or find the right vitamin D supplement based on your nutritional needs. You can also get vitamin D from the sun—as Harvard Health‘s blog explains: “The sun’s energy turns a chemical in your skin into vitamin D3, which is carried to your liver and then your kidneys to transform it to active vitamin D.”
Enjoying the sun’s warmth can be soothing—but can you get vitamin D through a window, or do you have to be outside?
Can you get vitamin D through a window?
“Ultraviolet B radiation (UVB) radiation is the type of radiation from the sun that triggers vitamin D production in the body and turns it into the active form of vitamin D,” explains Grant Radermacher, DC, a chiropractor in Wisconsin. But as it turns out, UVB radiation is mostly blocked by ordinary window glass.
So, there are two pieces of unfortunate news here: First, you can’t get vitamin D through a window—and second, you can get sun damage. Says Carly King, ND, a naturopath in Ontario, CA: “Since glass absorbs all UVB radiation, exposure of the skin to sunlight that passes through glass, plexiglass, and plastic will not result in any production of vitamin D in the skin. But glass doesn’t block UVA rays, so sun damage from exposure through windows is still a concern,” Dr. King says. (Just take car windows as an example: That may be a reason the area around the eyes is one of the body parts most at risk for skin cancer.)
It’s important to note that we don’t actually “get” vitamin D from the sun in the same way that we get vitamin D through supplements or from eating foods like tuna, salmon or eggs. What happens is that the body produces vitamin D when exposed to UVB rays, which triggers vitamin D synthesis.
Says BreAnna Guan, ND, a Boston-based naturopathic physician. “Most of the UVB radiation (290 to 320) nm [nanometer] is absorbed by the ozone layer,” Dr. Guan says, “and is most abundant when the sun is overhead in summer months between the hours of 10 a.m. and 2 p.m.”
You don’t need to spend much time out there (Guan suggests 10 to 15 minutes, max). Also, apply sunblock. You’ll still get the exposure your body needs to make vitamin D.
Are all windows the same?
Not all types of glass are created equal, though. “While ordinary glass blocks most UVB rays, specialized glass, such as low-E glass, allows more UVB rays to pass through,” Dr. Radermacher says…but you still shouldn’t expect to synthesize much vitamin D from sunlight exposure through a window.