Around the world, the farther one gets from the equator, the more likely you are to find people with high blood pressure. Lack of exposure to ultraviolet light may actually contribute to the rise in blood pressure in higher latitudes, according to a new theory from an Alabama researcher. And the theory may explain why blacks in the U.S. and Europe have a greater risk of high blood pressure than whites in those countries or blacks who live in Africa.

Sunlight plays an important role in the synthesis of vitamin D. The farther away from the equator, the less ultraviolet exposure and the less vitamin D that is synthesized in the body. And those with greater amounts of pigment in the skin -- such as blacks -- require six times the amount of ultraviolet B (UVB) light to produce the same amount of vitamin D found in lighter-skinned people. While 20% to 30% of UVB radiation is transmitted through white skin, only 5% is transmitted through deeply pigmented skin.

Such observations are not limited to people of African origin, studies of Pakistani and Indian children living in the United States suggest that their capacity to produce vitamin D is the same as whites, but like blacks, they require longer exposure to UV light because of increased skin melanin content.

This is yet another compelling piece of information which clearly refutes the recommendations most of us receive to avoid any sun exposure. We all need sunlight to stay healthy. One should never get sunburned and probably limit exposure during the peak hour of the day. However an hour a day of sunshine is important to maintain optimal health. It is most likely the increased risk of melanoma is due to exposure to the chlorine in the drinking water, not just increased sun exposure.

Hypertension (1997;30:150-156)