Philip J. Goscienski, M.D.
Humans or their predecessors have been around for at least a couple of million years and for roughly 97 percent of that time they lived in temperate, sunny areas. They built no shelters, wore no clothing and had little body hair, yet they had to contend with sun exposure for several hours a day. How did they avoid sunburn and skin cancer? Could there have been some evolutionary benefit from all that sun exposure?
The interaction between humans and sunlight is enormously complex. After thousands of generations, the human body has — until very recently — reached a near-perfect accommodation with the sun. Nature devised ways to protect us from its hazards and, simultaneously, to benefit from its energy.
From Africa to Australia, our distant ancestors evolved with darkly pigmented skin that would protect it from sun damage. Melanin gives dark skin its color, and is nature's sunscreen. When you remember how miserable you were after your last sunburn, consider how incapacitating that would be for a lifetime. Aboriginal people in Africa and Australia rarely get sunburn in the course of their daily activities. They also have a relatively low risk of skin cancer.
Dark skin can be a liability. When a form of cholesterol, acted upon by ultraviolet rays from the sun (UVB), undergoes chemical changes in the liver and kidney it becomes vitamin D. Dark-skinned persons who migrate to higher northern latitudes often become deficient in vitamin D. That's because UVB from the sun's rays does not penetrate the ozone layer for several months a year. Among elderly black persons in the Boston area, 84 percent were deficient in vitamin D even during the summer.
Barely a generation ago scientists thought that the only function of vitamin D was to maintain the skeleton and to prevent rickets, a bone-deforming disease of childhood. How wrong they were! Vitamin D has multiple roles that include preventing cancer, heart disease, high blood pressure and osteoporosis. Inadequate levels of vitamin D contribute to diseases of the immune system such as lupus, type 1 diabetes, multiple sclerosis and rheumatoid arthritis.
Almost all our vitamin D comes from sun exposure. Cod liver oil is a plentiful source, and dairy products provide a modest amount, but our Stone Age ancestors didn't have access to either of those. Some fish (salmon, sardines) and a few plant sources (mushrooms, sunflower seeds) may have provided them with a little more, but these were inconsequential.
A deficiency of vitamin D is so common, especially in certain population groups, and so often goes unrecognized that it is becoming a public health problem. Few physicians are aware that vitamin D deficiency mimics fibromyalgia, a chronic, painful and debilitating disease. Pediatricians encourage new mothers to breastfeed but not all of them are aware that nursing infants require vitamin D supplementation. As the rate of breastfeeding rises, so does the incidence of rickets, a disease that previous generations of physician saw rarely, if ever. Our aging population is the most seriously affected. Most persons over the age of 60 have some degree of vitamin D deficiency, and healthcare workers aren't aware of it.
(Next week: why we have become vitamin-D deficient, and what we can do about it)
Philip J. Goscienski, M.D. is the author of Health Secrets of the Stone Age, Better Life Publishers 2005. Contact him at firstname.lastname@example.org.