Breast and colon cancer are rampant in the industrial world. In the United States, where the average adult gets less than half the recommended daily allowance of vitamin D, nearly a third of all cancers involve the breast or colon. Could a simple vitamin pill help control these common killers? It’s still too early to say. “The epidemiologic studies are all there,” says Dr. William Harlan, associate director for disease prevention at the National Institutes of Health. “But you need to do an interventional trial before you make clinical recommendations.” The NIH is now planning a huge clinical trial that should yield definitive answers over the next decade. And Frank Garland, for one, is optimistic. “I think we’ll find that colon and breast cancer are essentially vitamin-deficiency diseases of adulthood,” he says.
Medical researchers have long regarded high-fat diets and delayed childbearing as key risk factors for colon and breast cancer. But those factors don’t seem to account for the striking geographic patterns these diseases exhibit. The Garlands started puzzling over the patterns in the late 1970s, when a colleague showed them a map of the world color-coded to reflect the prevalence of colon cancer in different countries. The map suggested the disease was virtually unknown at the equator and that its prevalence mounted as the latitude grew higher. One of the few exceptions to this rule was Japan, a country that has traditionally enjoyed low rates of breast and colon cancer despite its northern geography.
What did the lucky populations have in common? They all seemed to be getting plenty of vitamin D, whether from sunshine or (like Japan) from diets rich in fish oil, so the Garlands started exploring the possibility. In a 1980 study, they compared colon-cancer death rates for different regions of the United States. As they’d predicted, the rates were lowest in the sunny South and West and highest in the gray Northeast–even though Northeasterners ate more vegetables, and roughly the same amount of meat, as the other groups.
In subsequent studies, the Garlands and other researchers have put the vitamin D hypothesis to a range of other tests, and it has held up well. In 1985, a team led by Cedric Garland examined the health records of nearly 2,000 Chicago utility workers who recorded everything they ate for 28 days back in the late ‘5Os. Over the next 19 years, the workers who’d consumed at least 150 iu (international units) of vitamin D each day suffered only half as much colon cancer as those who’d consumed lesser amounts (200 iu is the recommended daily allowance for adults). A similar pattern turned up in a study of 101 blood samples drawn from volunteers in Maryland in 1974. The volunteers with the lowest vitamin D levels went on to develop colon cancer at three times the rate of other subjects.
More recently, the Garlands and their San Diego colleague Edward Gorham have concentrated on showing that breast cancer follows the same pattern as colon cancer. In 1990, they analyzed breast-cancer incidence in the Soviet Union and discovered a threefold discrepancy between the northern and southern republics. Back in the United States, a similar study revealed that breast-cancer death rates were more than 1.5 times as high in New York and Boston as in Phoenix or Honolulu (chart). Sunshine isn’t the only amenity the South offers and the North lacks, but still other studies suggest it’s the crucial one. Gorham has compared communities at similar latitudes and shown that breast and colon cancer are most common in the communities with the most light-blocking air pollution.
No one knows exactly how vitamin D might ward off these diseases. The molecule–which is found in egg yolks, liver and fortified milk as well as in tuna, salmon and other fatty fish–helps the body absorb calcium. Calcium, in turn, can help prevent uncontrolled cell growth. However the vitamin works, its potential benefits are immense. As part of the Women’s Health Initiative, the massive NIH research project scheduled to begin in 1992, some 60,000 postmenopausal women will receive either a twice-daily calcium and vitamin D supplement or a placebo for up to nine years. The trial’s formal goal is to reduce colon cancer and bone fractures by 25 percent, says Dr. Harlan of the NIH. But investigators will monitor the participants for breast cancer and other conditions as well. If the evidence to date is any indication, they could be in for pleasant surprises.
