Are you getting enough sunlight? Recent data suggests you may not be. According to the Cleveland Clinic, vitamin D deficiency is a widespread issue: over one billion people globally and approximately 35% of U.S. adults lack this essential vitamin, which provides numerous health benefits (including some that can be life-saving!).
If you’re not receiving enough regular sunlight, consider increasing your intake of vitamin D-rich foods or selecting an appropriate vitamin D supplement based on your dietary needs. Additionally, you can obtain vitamin D directly from sunlight. As discussed in an article by Harvard Health, “The sunlight transforms a chemical in your skin into vitamin D3, which travels to your liver and kidneys to convert it into its active form.”
While basking in the sun can be a pleasant experience, a common query arises: Can you obtain vitamin D through a window, or must you be outdoors?
Can you get vitamin D through a window?
“Ultraviolet B (UVB) radiation is the type of sunlight that initiates vitamin D production in the body,” explains Grant Radermacher, DC, a chiropractor in Wisconsin. Unfortunately, UVB radiation is mostly filtered out by standard window glass. Therefore, you cannot obtain vitamin D through a window.
There are two concerning points to consider: Firstly, you cannot synthesize vitamin D through a window, and secondly, there remains a risk of skin damage.
Carly King, ND, a naturopath based in Ontario, CA, adds, “Regular glass absorbs all UVB radiation, rendering sun exposure through glass, plexiglass, or plastic ineffective for vitamin D production. However, glass does not block UVA rays, which means that sun damage is still a risk when exposed to sunlight through windows.” (For instance, car windows may contribute to the higher risk of skin cancer around the eye area, among the most vulnerable body parts.)
Are all windows the same?
Not all glass is identical in terms of its UV filtering properties. “While conventional glass blocks most UVB rays, specialized glass like low-E glass permits more UVB rays to penetrate,” Dr. Radermacher explains. However, you should not expect substantial vitamin D synthesis from sunlight that passes through any window.
How your body gets vitamin D from the sun
It is crucial to understand that we do not actually “receive” vitamin D from sunlight in the same way we absorb it from supplements or foods like tuna, salmon, or eggs. Rather, the body synthesizes vitamin D upon exposure to UVB rays.
BreAnna Guan, ND, a naturopathic physician from Boston, explains, “Most UVB radiation (290 to 320 nm) is absorbed by the ozone layer and is most plentiful when the sun is overhead during summer, typically between 10 a.m. to 2 p.m.”
Fortunately, you do not need to spend excessive time in the sun (Guan recommends about 10 to 15 minutes at most). It’s also advisable to use sunscreen to still get the vital exposure needed for vitamin D production.
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