Adequate levels of vitamin D, which the body synthesises with the help of sunlight, are needed to maintain our bones and overall health. During the summer, when the sun is directly overhead, it’s easier to make enough vitamin D. For example, the New York Times reports that as little as ten minutes of sun exposure a day may be enough for people with light skin. People with darker skin may need two to three times more than that, and older people may need even more since aging tends to slow down vitamin D synthesis. In contrast, during the winter, the low angle of the sun and the short time it appears above the horizon each day can make it harder to maintain healthy vitamin D levels. Here’s what you need to know to keep your levels up when it’s cold outside:

• Who’s at risk of low vitamin D in the winter? Anyone with low sun exposure is at risk, but living at latitudes above around 37 degrees north puts you at a particular risk. In the US, this includes people living in Northern California and north of Arizona, New Mexico, Texas, Oklahoma, Arkansas, Tennessee, and North Carolina. In these areas, the sun is lower during the winter and colder temperatures cause people to bundle up, covering skin and blocking the sun.
• Will using sunscreen reduce sun exposure? Sun safety precautions like sunscreen, hats, and protective clothing are important but do limit our ability to make vitamin D. Although the degree to which sunscreen affects vitamin D levels is still not precisely known, according to the National Institutes of Health, most of us don’t use enough sunscreen to completely block vitamin D production.
• How much vitamin D do you need? Regardless of sun exposure, the recommended dietary allowance (RDA) for vitamin D is 600 IU per day in healthy adults. If you’re 70 or older, that bumps up to 800 IU per day.
• What are dietary sources of vitamin D? You can get almost 450 IU from three ounces of cooked salmon and about 120 IU from a cup of vitamin D-fortified milk. Fortified orange juice, yoghurt, and cereal are other sources. Your doctor may also recommend you take a vitamin D supplement.

Source: New York Times