The Paleo Diet - Loren Cordain [52]
Skin Cancers
Skin cancers come in three basic varieties:
• Squamous cell cancers, which form on the top layers of the skin
• Basal cell cancers, which form on the bottom layers of the skin
• Melanomas, which form within the skin’s pigment-producing cells, the melanocytes
The American Cancer Society estimated that 2 million Americans would develop the first two types of skin cancer in the year 2010. These cancers grow slowly, rarely spread to other areas of the body, and are easily curable by early removal. An estimated 69,000 Americans were expected to develop melanoma in 2009. If detected early and surgically removed before they spread to other parts of the body, melanomas are highly curable, with 95 out of 100 people alive five years after diagnosis. But if melanomas spread to the rest of the body, they can be deadly; the five-year survival rate drops drastically, to 16 out of 100.
Scientists know that excessive sunlight exposure is linked to all three cancers. But this does not mean you should avoid sunlight in any amount. Here again, the experience of our hunter-gatherer ancestors proves helpful. Ironically, many studies have shown that people with high lifetime sunlight exposure (similar to that of hunter-gatherers) have lower rates of melanoma than those with low sunlight exposure. Also, indoor workers have a greater risk of developing melanoma than outdoor workers do. Even more puzzling, melanomas often arise in body areas that are infrequently or intermittently exposed to the sun. These unexpected findings have led researchers to believe that severe sunburn during childhood, or intense burns in body areas that are infrequently or intermittently exposed to the sun, may be more important in the development of melanoma than cumulative exposure during adulthood.
When your exposure to sunlight is gradual, moderate, and continuous—if you don’t get excessive sunburn—your body responds in a manner guided by evolutionary wisdom. The skin begins to tan from increased production of melanin, and the darkened skin provides protection from the sunlight’s damaging ultraviolet rays. Also, vitamin D levels in the blood begin to rise as ultraviolet light strikes the skin, causing it to convert cholesterol into vitamin D.
Vitamin D is a potent inhibitor of the cancer-causing process. In fact, vitamin D has been shown to prevent the growth of melanomas in experimental animals and cultured tissue lines.
An unexpected bonus of vitamin D is that it may also be one of our most important allies in the war against prostate, breast, and colon cancers. Evidence from population studies confirms that people with the greatest lifetime sun exposures have the lowest rates of these cancers.
Skin cancer is a complex disease, with several factors influencing its ultimate course. In laboratory animals, scientists have found that excessive omega 6 fats promote the development of skin cancer—but omega 3 fats slow it down. Furthermore, antioxidants like beta-carotene, vitamin C, and vitamin E tend to prevent the sun’s ultraviolet damage to the skin. You can get these same dietary advantages when you adopt the dietary principles I have laid out in the Paleo Diet. (Note: As with many of the diseases we have discussed, proper diet reduces your risk of developing some types of skin cancer, but it cannot completely prevent it.)
Exposure to sunlight is natural for human beings. It is part of our evolutionary heritage. Without sunlight, it is virtually impossible to achieve an adequate intake of vitamin D from the natural foods that were available to our hunter-gatherer ancestors. Our food supply has been a significant source of vitamin D for a very short time—less than a century, when dairy producers began adding it to milk and, later, margarine. Sunlight exposure is healthy as long as it occurs in a slow, gradual, and limited dose over the course of a lifetime.
As you have seen, the Paleo Diet will not only help you get thin; it will also help prevent and treat a broad range of diseases. The Paleo Diet is good