Stomach Cancer in Navajos Linked to Uranium Mines
CHICAGO (AP) _ Stomach cancer rates have soared to as high as 10 times the national average in recent years among some groups of Navajo Indians living near uranium mines in New Mexico, medical researchers report.
Meanwhile, other doctors studying cancers of the digestive system say new evidence exists that colon cancer is less likely to develop in people who increase their calcium intake and in women who smoke cigarettes, though the harmful effects of smoking still far outweigh benefits.
An unusually high number of stomach cancer cases began appearing among the Navajo in the 1970s, even though historically they had suffered the disease at one-tenth the rate of other Americans, said Dr. Richard Auld Jr., a specialist in digestive diseases at Kaiser-Permanente Medical Group in Santa Rosa, Calif.
Auld said he had noticed the trend among young Indians when he worked for the Indian Health Service in 1982-1984, and he and a colleague returned to the reservation to investigate.
″Tumors that were found were aggressive,″ said Auld, who studied records on 192 Navajo cases. ″The survival was very poor, averaging less than six months in men and approximately nine months in women.″
Victims were as young as 18, though stomach cancer usually strikes the elderly, Auld said in reporting his findings Wednesday at a joint meeting of the American Gastroenterological Association and several other groups.
Auld said mining operations exposed tons of uranium ore tailings, or waste rock, to erosion that enabled it to seep into soil and water.
In time, uranium entered the food chain and apparently caused the higher cancer rates, he said. The rate now is four times the national average, Auld said.
In some parts of the reservation, the rate reached 55 to 85 cases per 100,000 people per year, or eight to 10 times the national average, Auld said.
The risk continues, though the mines have been shut down for years, Auld said. The contamination also poses a threat to non-Indian residents in neighboring counties in New Mexico and Arizona, Auld said.
Some wells have been sealed off because they have been discovered to be contaminated, and state environmentalists have recommended that residents not depend on locally raised meat as their sole source of protein, he said.
In another study presented at the meeting, doctors reported that cigarette smoking was associated with a lowered risk of colon cancer among 25,369 women tracked over a 12-year period beginning in 1963.
Women over age 50 who smoked were found to have one-third the risk of cancer of the colon or rectum of women who didn’t smoke, said one of the researchers, Dr. Robert Sandler, assistant professor of medicine and epidemiology at the University of North Carolina at Chapel Hill.
There was no difference in risk among women under 50, said Sandler.
Colon cancer, like malignancies of the breast or womb lining, may grow partly with help from the female hormone estrogen, which smoking inhibits, Sandler said.
That would explain previous findings that women who smoke may have lower rates of breast and womb-lining cancers, he said.
But he added: ″Our findings in no way serve as an endorsement for cigarette smoking. The adverse health consequences of cigarette smoking are so pervasive and so widespread that the modest protective effect against colon cancer in no way justifies smoking.″
And in another report, doctors said the effect of calcium consumption on 35 subjects they studied added to evidence that supplements of the mineral may have a protective effect against colon cancer.
Dr. Paul Rozen, an associate professor of medicine at Tel Aviv University Medical School in Israel, said the study lends support to a finding reported last year that consuming 1,200 milligrams of calcium daily for three months instead of the usually recommended 800 milligrams seems to reduce cell proliferation in the colon lining that may precede cancer.
Rozen said it’s too early to make dietary recommendations based on the findings.