…Until recently.  Now, scientists are starting to discover that all this sun blocking has had an unintended effect.  SPF blocks the ultraviolet rays that can age skin and lead to skin cancer (benefits that are certainly important), but it also prevents epidermal cells from making vitamin D.  And sun exposure is the most effective way to obtain the nutrient—technically not a vitamin, but a fat-soluble prohormone that’s intimately involved in every bodily process.  Sunlight also supplies the most readily available form—cholecalciferol (known as D3). 

Most of us know vitamin D as calcium’s little helper.   Since the1930’s, it’s been added to milk to help prevent rickets, a now-rare disease in which bones fail to mineralize properly.  But D has far-reaching effects beyond building stronger bones.   There are vitamin D receptors in nearly every cell in the human body.   We need it to moderate the inflammatory response, to normalize blood pressure, to encourage healthy cell division.   Evolutionarily speaking, it is incredibly important to have an adequate intake.  When we don’t, we’re at risk.    And many of us don’t get enough, particularly African-Americans and women and men over age 50.  Emerging studies are linking vitamin D deficiency with cardiovascular disease, diabetes, rheumatoid arthritis, and various cancers of the colon, breast and prostate.  Researchers are also exploring connections between low levels and Alzheimer’s disease and dementia, as well as thyroid disorder, asthma, and allergies.  It’s no exaggeration to say that some of the best minds in medicine are on the case. 

So how much D do we need?  The answer isn’t yet clear.  An Institute of Medicine report released last year recommends at least 2,000 IUs per day for adults.  Some research suggests the need is more like 5,000 IUs.  Why the confusion?  Our new sun screened reality is less than 20 years old, and we simply haven’t had the time to produce the kind of randomized, double-blind studies that are the gold standard for determining exactly what is needed and what will work.  Also vitamin D needs vary widely, making one-size-fits-all recommendations very difficult, if not impossible.  You need more if you live in the Northeast because sunlight is weaker in northern latitudes.  Darker skin tones make it harder to synthesize vitamin D, so African-Americans may need more.  Because vitamin D is stored in fatty tissue, people who are overweight may already have enough, but it is locked away in body fat and not available to the rest of the body.

Further complicating matters, food sources of D are scarce.  The most significant natural food source is fatty fish (something that’s food for your heart health anyway).  Salmon, mackerel, canned tuna and sardines contain 150-450 IUs of the D3 form per 3 oz serving.  But several independent tests have shown that vitamin D levels in fortified foods are spotty.  And fortification is most often a less effective plant-based form (yeast) of the vitamin.  Mushrooms can be a source, particularly if they’re briefly treated with UV rays when growing.  

Which brings us back to sunlight—and calls conventional wisdom into question.  It’s a classic double-edged sword that you want enough exposure to meet your health needs without raising your risk of cancer.  How much is enough?  If you know how much sunshine causes a slight redness in your skin, then one-fourth that amount, provided 2-3 times per week is more than enough.  In that small amount of time, the skin on your face, arms and legs can produce as much as 10,000 IUs or more of vitamin D.  When we don’t get enough sunshine (for example during the winter months), it may be helpful to not only try to eat foods naturally rich in vitamin D, but to use a D3 supplement in a gel cap form.

Perhaps it’s time for a new mantra: Shun the sun, yes, but just a little less.

Sources: Hillari Dowdle and Dr. T. Colin Cambell (The China Study)