Vitamin D is made in your body when your skin is exposed to sunlight. According to VeryWellFit.com, people who live north of an imaginary line drawn from the northern border of California in the west, to Boston in the east, can't even get vitamin D from the sun during the winter months. This is because the sun’s rays aren't strong enough to give us the UV exposure we need. For these people, vitamin D supplementation is important during the colder months.
What we think:
Your body will make vitamin D when the skin is exposed to UVB radiation (note: UVB won’t travel through glass, so sitting by a window does not qualify). How long you need this exposure depends on the time of the year and your location, but your skin would need to be sunscreen free to get the main benefits. Obviously, that is a cancer risk, so you may decide to eat food rich in vitamin D. Milk is often fortified with vitamin D. Vitamin D is not available in fruits or vegetables although you juicers out there can get it from juicing sunflower sprouts. The best sources of vitamin D are cold-water fish, sunflower seeds and mushroom.