Q Does one get any vitamin D benefits from the sun through window glass? How about through car windows?
A No. The type of sunlight that stimulates the body to produce vitamin D does not penetrate glass.
Although it's possible to meet vitamin D needs through exposure to sunlight, it can be difficult if not impossible:
• In northern climates, such as Minnesota, the sun is too low in the sky from October to April to stimulate vitamin D production.
• Complete cloud cover reduces UV energy by 50 percent; shade (including that produced by severe pollution) reduces it by 60 percent.
• Sunscreens appear to block vitamin D-producing UV rays, although in practice people generally do not apply sufficient amounts, cover all sun-exposed skin, or reapply sunscreen regularly.
• Those with dark skin need more light exposure to get their vitamin D.
• Fish, liver and egg yolk are the foods that naturally contain vitamin D; a few products such as milk contain vitamin D.