Friday, December 17, 2010

Life Lines 85


When I was a lanky child, growing up in the Depression, I heard myself referred to as being all skin and bones. I wasn’t starving; it was just my genetics and the modest diet that my father’s wages provided. When I saw the first photos of Holocaust survivors in the newspapers, I learned what that phrase really meant to those deprived of food. We use up our stored fats and then go after our own muscles when we starve. Skin and bones are also connected by vitamin D. We make vitamin D from the cholesterol in our skin. Not all cholesterol is bad for us. To do this our skin uses ultraviolet light which we get from the sun. Where sunlight is meager, as in the winters of those who live in northern latitudes, not enough vitamin D is made through sunlight entering the skin. Those people have to get vitamin D from the food they eat and that’s usually seafood. Inland people in the past did not have access to such foods and when I was a child it was supplied by parents in the form of cod liver oil, a disgusting tasting fishy and oily substance.

Infants and children deprived of vitamin D cannot produce enough bone. Their bones become rubbery and deformed in shape. Such children had rickets. During the 1930s concern for children deprived of vitamin D led to federal requirements that milk be supplied with vitamin D. In those days the bottle caps used to boast that the dairy provided irradiated milk (the ultraviolet to convert cholesterol in milk being supplied by technology).

Much later, scientists learned that there is a relation between vitamin D synthesis and the amount of melanin pigment in the skin. The more melanin deposited in the skin, the less ultra violet enters. This makes good sense if people live in tropical areas near the equator where sunlight is abundant and intense all year round. Too much ultraviolet causes sunburn to people with light skin color. It also leads to skin cancers and melanomas which can be fatal. Dark skin is thus adaptive to those who live in equatorial regions. People who live in northern latitudes, however, found dark skin a disadvantage because it led to rickets which can be fatal in a world where physical skills determined survival. As humans moved out of their ancestral home in Africa some 200,000 years ago, their skin color was selected for more efficient ultraviolet absorption. Skin colors became lighter and normal bone growth followed. Thus both dark skin and light skin served their purposes over the millennia as humans settled the earth.

Life is filled with agents and substances that are both necessary for health and damaging to health. Fatalists take it on the chin and just ride their fates hoping for miracles to spare them harm. Scientists try to understand why things work the way they do and thus we can take charge of our lives and enjoy the benefits of vitamin D produced in our skins, the ultraviolet induced protective tanning, the natural skin color adaptive to our latitude, or a variety of sun screens to prevent those chromosome-snapping thymine dimers formed in our DNA whenever ultraviolet penetrates the barriers of our melanin and enters deep within our cells. Today dark skinned people living in the north are protected by diet from rickets and light skinned people living in the south are protected, if they use good sense while outdoors, from sunburn and skin cancers.

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