Vitamin D

Have you ever wondered why we have such a range of skin colors in the world? Our African ancestors had dark skins because the melanin helped to protect them from ultraviolet light – up to an SPF 15. This UV protection, however, meant that it slowed down vitamin D synthesis. Not a problem when you live in an area that has so much sunshine.

But, as humans migrated northwards, exposure to the sun diminished. Skins became lighter because protection wasn’t as important as being able to synthesize vitamin D. (The lighter the skin the more efficient is the chemical reaction between the skin and UVB.) White skin synthesizes vitamin D six times faster than dark skin. This is why I found my sun-phobic dermatologist the other day standing in the parking lot wearing his ski jacket and holding his face to the sun.

How important is vitamin D? For years, we have known about its role in bone building and how it acts in the kidneys, intestines and the skeleton to help control the flow of calcium into and out of bones from the bloodstream. However, in an article entitled Sunshine Vitamin by Luz E. Tavera-Mendoza and John H. Shite for Scientific American, they point out that studies of vitamin D’s function have broadened, revealing that the so-called sunshine vitamin does far more than build bones. Extensive evidence now shows that D has potent anticancer actions and also serves as an important regulator of immune system responses. Moreover, many of D’s newly recognized benefits are maximized when it is present in the bloodstream at levels considerably higher than those found in many populations. These findings, together with epidemiological data linking low vitamin D levels to disease, support the possibility that widespread vitamin D deficiency is contributing to a number of serious illnesses.

The other source of vitamin D is through food, but food provides relatively small doses of D compared with amounts made by the skin. For example, one of the higher sources, cod-liver oil provides 1,360 IU in one tablespoon, whereas full-body exposure to UVB for 15 to 20 minutes at midday in summer provides 10,000 IU.

So, where are we with all this? Clearly some sun exposure is necessary. No more than 20 minutes though because UVB light will end up degrading vitamin D to prevent too much of it from building up in the skin. (Don’t get confused with exposure in tanning beds. This does not synthesize vitamin D. Tanning beds emit UVA rays which go deeper into the skin and destroy our collagen and elastin. No one has yet found anything good to say about UVA!)

If you don’t see the sun for weeks, then make sure you incorporate food sources of vitamin D such as cod-liver oil, cooked tuna, sardines, mackerel or salmon, shiitake mushrooms and organic eggs.

I’ve always noticed that my nails grow longer and stronger when I’m in the sun for a while, so I know there must be something to this!