Vitamin D is the hottest vitamin in both medical studies and the press. In the last few years, an explosion of publications has linked vitamin-D deficiency to cancer, heart disease, metabolic syndrome, hypertension, heart failure, and autoimmune diseases. We also know that insufficient levels of vitamin D may be at epidemic levels in the U.S. Given the many vital functions served by vitamin D (which I explore over the next few articles), if left untreated, the dire health consequences are disastrous indeed. So let’s look at where we get this all-important nutrient and how to best absorb it.
Vitamin D is the “sunshine vitamin.” Ultraviolet-B radiation can stimulate vitamin D production in your skin. Even slight exposure to sun, the amount required to cause some pinkness in the skin, is equivalent to 20,000 international units (IU) of vitamin D. But most children and adults in the U.S. do not get enough sun exposure to maintain healthy levels of vitamin D.
About 90% of your vitamin D requirement comes from casual exposure to sunlight. But how much sun exposure do you need for this? Here are the factors that play a role:
— Where do you live? People who live further north from the equator (northeastern U.S. and Canada) make less vitamin D from the sun.
— What season and time of day is it? More vitamin D is made in your skin during the summer months. Light-skinned individuals can get as little as five to 10 minutes of sun exposure on the face, arms or legs three times a week between 11 a.m. and 2 p.m. during spring, summer and fall.
— Do you use sunscreen? SPF 8 or 15 or more reduces the capacity of your skin to make vitamin D by more than 90% and 99%, respectively. We’re not recommending that you don’t use sunscreen; just that you attempt to get that minimum amount of sun exposure before putting on the sunscreen. Don’t forget that your skin will burn after 20 minutes in the sun at peak times.
— What is your age? Older adults’ skin and kidneys are less able to make vitamin D, at about 25% the capacity of a younger person. So, older adults must increase their time in the sun to make up that difference.
— What is your skin color? The darker your skin is, the less vitamin D is made in your body. Compared to Caucasians, African Americans need a 10-fold increase in sun exposure to get the same amount of vitamin D made from their skin.
The second source of vitamin D consists of natural foods, but it is far more minimal than the sun. Besides, only a limited number of foods contain substantial amount of vitamin D, as listed here:
— Salmon, cooked (3.5 ounces): 360 IU
–Mackerel, cooked (3.5 ounces): 345 IU
–Canned tuna (3.0 ounces): 200 IU
–Sardines canned in oil, drained (1.75 ounces): 250 IU
–Fortified milk, one cup (8.0 ounces): 100 IU
–Fortified orange juice, one cup (8.0 ounces): 100 IU
–Raw Shiitake mushrooms (10 ounces): 76 IU
Farmed fish has less vitamin D than fish caught in the wild. Most cereals sold in the U.S. are fortified with vitamin D containing approximately 40 to 80 IU per serving. However, not all cheese and yogurt is fortified with vitamin D. The amount of vitamin D in vegetables is negligible.
Maintaining healthy levels of vitamin D begins with understanding how to best absorb it. Now you’re all set!