Vitamin D & the Races of Man

The very existence of the essential vitamin D, or "sunshine vitamin," was not established until the present century, but its imprint upon history goes back a million years or more. According to a theory now elaborated by Brandeis University Biochemist W. Farnsworth Loomis, it is because of the human body's need to take in a certain amount of vitamin D, but not too much, that the human species has developed into three principal racial groups distinguished by skin color and loosely called black, yellow and white.

Loomis points out in the journal Science that vitamin D is no ordinary vitamin. Unlike the others, it occurs in virtually no natural foods.* It is synthesized in the skin under the influence of ultraviolet rays. The body needs vitamin D if it is to process calcium from food to make bone. Consequently, children need proportionately more vitamin D for their growing bones, and a D deficiency causes rickets.

D differs from most other vitamins in a second important respect: too much of it is as bad as too little. Severe or long-term excess causes chalky calcium deposits in arteries, notably the aorta, and in the kidneys, with stone formation and loss of kidney function. Eventually, this can be fatal. To guard the

U.S. child against rickets, health authorities recommend a daily vitamin D intake of 400 international units (ten micrograms), which is easily obtained from milk. If the youngster's system makes more vitamin D as he plays in the sun, it is usually not enough to be dangerous. If he is given more than 20,000 units, a child becomes severely ill. In northern climes, most white adults make all the vitamin D they need from casual exposure of their face and hands to the sun and need no dietary supplement. They get ill on 100,000 units a day. But in the tropics, Loomis figures, the white man's unpigmented skin could make a deadly dose of D: up to 800,000 units, he calculates, in a six-hour exposure of his whole body to the equatorial sun.

Origin on the Equator. The control of skin color over vitamin D synthesis, says Loomis, explains the distribution of the races of man in prehistoric and early historic times. As far as anthropologists can tell, "human beings" originated in Africa near the equator. Almost certainly, they had black skins. Many anthropologists have argued that dark skin evolved as a protection against sunburn and skin cancer. On the contrary, says Loomis: dark skin came first, and light skin evolved as a protection against a deficiency of vitamin D. Black skin allows only 3% to 36% of ultraviolet rays to pass, while white skin passes 53% to 72%. As early man moved north from the equatorial region, beyond the 40th parallel (roughly, the latitude of Madrid and Naples), Loomis argues, he got into a zone where black skin filters out too much ultraviolet.

He encountered rickets. The darkest-skinned young male hunters were so crippled that they could not keep up; the darkest-skinned females died in childbirth because of pelvic deformities. Those who happened to be lighter skinned, of both sexes, survived.

Thus, by the classic Darwinian process of evolution by natural selection, the farther north man went, the more completely did the light-skinned survive and the dark-skinned die out.

The layers of the skin involved in the sun-screening process are visible under a microscope. Below the skin's outermost horny layer, or stratum corneum (see diagram), lies a germinative layer where, on exposure to sunlight, the pigment-producing cells are stimulated to produce more melanin--and a suntan. The black races (Negro, Bushman-Hottentot and Australoid), with a more abundant supply of melanin, are in effect, perpetually tanned. Members of the white race are transparent-skinned in winter, when they must make the most of the limited ultraviolet avail able to synthesize vitamin D, but they take a tan in summer, when they might suffer from an excess. There are other bits of confirmatory evidence: the only relatively dark-skinned people in high latitudes are the Eskimos, who get all the vitamin D they need from fish-liver oils. Until the 1930s, when irradiation of milk to enrich its vitamin D content became prevalent, U.S. Negro children suffered far more commonly from rickets than white children.

Reverse Selection. There remains the question of why the Mongols and related peoples are "yellow." Biochemist Loomis explains this on the basis of additional keratin (horny material) in the outer skin layers--though dermatologists deny this and say that the Mongol's sun screen is melanin, like the Negro's, but in smaller amounts. Loomis surmises that the yellow races may have developed their coloration after having gone through the white-race depigmentation phase. If migration away from the equator produces lighter skins, says Loomis, reverse migration could have the opposite effect. In the mere 10,000 to 20,000 years since relatively light-skinned Mongols crossed from Siberia to Alaska and spread southward to Tierra del Fuego, there has been a natural selection in favor of the darker-skinned Amerindians between 40DEG north and 40DEG south latitude. Outside these boundaries, and in most of the dark rain forests of Brazil, the Indians are not appreciably darker than most Asiatic Mongols.

Loomis' theory is not entirely new, but he has honed it to a greater sharpness than have previous investigators. Every human being of every race lives through a cycle of supporting evidence for at least part of it and carries some in his hand throughout life. Babies of all races are lighter than adults, presumably reflecting nature's provision for early vitamin D needs. And people of all races have pale, unpigmented palms and soles. Since these parts have extra keratin and are not exposed to ultraviolet, they need no melanin protection against excess vitamin D synthesis.

* Exceptions: the liver oils of some fish, notably cod and halibut; egg yolks (small quantities) and milk (minute amounts). Milk and many other foods are now "vitamin D enriched" by ultraviolet irradiation.

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