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Chinese Studies Confirm Antioxidants Protect Against Cancer...and Stroke
A large-scale study of Chinese villagers has demonstrated that supplements of beta-carotene, vitamin E, and selenium can reduce the incidence of esophageal and stomach cancers, as well as the overall death rate.
Meanwhile, a second study found that a common, low-dose multivitamin-multimineral formula only slightly benefited people with pre-cancerous changes of the esophagus. However, the vitamin-mineral formula did significantly lower the risk of death by stroke.
In the first study, researchers from the US National Cancer Institute and the Chinese Academy of Medical Sciences tracked almost 30,000 men and women who took one of several vitamin and mineral combinations of a placebo. The different supplements included one to two times the Recommended Daily Allowance of beta carotene, vitamin E and selenium; retinol (synthetic vitamin A) and zinc; vitamin B2 and B3; and vitamin C and molybdenum.
The researchers focused on residents of rural Linxian County in the Henan province of north-central China. The residents had one of the world's highest rates of cancers of the esophagus and gastric cardia (where the stomach joins the esophagus). Death rates from these cancers are about 10 times higher in Linxian County than elsewhere in China and 100 times higher than in the United States.
Supplements were provided on a regular basis from 1986 through 1991, and patient compliance was assessed by counting unused pills and randomly taking of blood samples.
"If vitamins work to help prevent cancer, then they should work in this population," William Blot, Ph.D., a principal investigator, was quoted in a news article in the Journal of the National Cancer Institute (Sept. 15, 1993;85:1448-50). "These people have had a consistently poor intake of several vitamins and minerals, and the cancers we were trying to prevent are known to be diet-related."
In fact, benefits from the beta carotene, vitamin E and selenium supplements were noticeable in less than two years.
"This trial revealed a significant reduction in total mortality, due mostly to a lowered risk of cancer, among those receiving the combination of beta carotene, vitamin E, and selenium. There was a differential effect between mortality from stomach cancer (21% reduction) and other cancers (20% reduction) versus esophageal cancer (4% reduction)," wrote Blot in the Journal of the National Cancer Institute (Sept. 15, 1993;85:1483-92).
"Several reports have suggested that antioxidant nutrients may reduce the risk or progression of cerebrovascular disease (stroke), a common cause of death in Linxian...mortality from cerebrovascular disease was 10% lower among those receiving supplements with the antioxidants beta carotene, vitamin E, and selenium," the researchers wrote.
They also speculated that the failure of other vitamins and minerals to prevent cancer might have been related to the short duration of the study.
The second study, led by Dr. Jun-Yao Li of the Chinese Academy of Medical Sciences, followed about 3,300 Linxian residents diagnosed with precancerous esophageal dysplasia, which often becomes malignant, Participates were given a standard multivitamin-multimineral supplement and extra beta carotene. The incidence of stroke dropped by 38%, according to the researchers' report in the Journal of the National Cancer Institute (April 1993;12:138-46).
Source: The Special Edition Nutrition Reporter, 1994.
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