Q. All I ever hear about the sun is how dangerous it is. But, when I was a kid, my mother used to tell me to get out in the sun and play. Did my mother give me bad advice?
(I've devoted a lot of space to the dangers of sun exposure. I believe I owe the sun a couple of columns to make up for this. Here's the first one.)
Most public health messages have focused on the hazards of too much sun exposure. Ultraviolet (UV) rays, an invisible component of sunlight, can cause skin damage, cataracts, wrinkles, age spots and skin cancer.
But there is some sunny news about the sun.
Sunlight increases the body's vitamin D supply. Most cases of vitamin D deficiency are caused by a lack of exposure to the sun.
If you don't have enough vitamin D, your bones will suffer. In children, vitamin D deficiency causes rickets, best known for creating bowed legs. Low vitamin D levels cause osteoporosis in adults. Osteoporosis is a disorder in which the bones become increasingly porous, brittle and subject to fracture.
Unlike other essential vitamins, which you must get from food, vitamin D can be synthesized in the skin through a reaction to ultraviolet radiation. How much vitamin D you produce depends upon how many units of ultraviolet light penetrate your skin.
The UV light can be blocked by skin pigment, sunscreen, clothing and body fat. Dark skin requires about five to six times more solar exposure than pale skin for equivalent amount of vitamin D production.
By the late 1800s, about 9 out of 10 children in industrialized Europe and North America had rickets symptoms. The medical community began promoting sunbathing for rickets. At the same time, doctors found that tuberculosis (TB) responded to sunlight.
Because of the results with rickets and TB, attitudes about the sun changed. Sunlight also became a popular medical treatment for rheumatic disorders, diabetes, gout, chronic ulcers, and wounds. From this, came the expression, "a healthy tan."
In the 1930s, the U.S. Public Health Service began issuing warnings about sun-related health risks. Subsequently, the hazards of skin cancer from too much sun were researched extensively.
However, too little sun exposure is associated with Hodgkin lymphoma and other cancers of the breast, ovaries, colon, pancreas and prostate. And, while the sun is a risk factor for melanoma the most dangerous form of skin cancer there is an increased survival rate in patients with early-stage melanoma who undergo high sun exposure.
Some studies have raised the possibility that vitamin D insufficiency is contributing to many major illnesses. For example, there is evidence that high levels of vitamin D may decrease the risk of developing multiple sclerosis (MS).
A recent Swedish study found that sufficient vitamin D in childhood was associated with a lower risk of developing type 1 diabetes.
There is also a connection between vitamin D and metabolic syndrome, a cluster of conditions that increases the risk for type 2 diabetes and cardiovascular disease.
(In our next column, we'll discuss other benefits of sunlight and how much sun is enough.)
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