A major new study indicates that people -- even cigarette smokers--who eat a lot of carrots, peaches, tomatoes, spinach and other deep red, green or yellow fruits and vegetables are less likely than others to get lung cancer.
This relationship has been reported by scientists from four major institutions --Rush-Presbyterian-St. Luke's Medical Center, Chicago; Harvard and Northwestern University Medical Schools and the University of Michigan -- in a lead article in the British medical journal, Lancet.
All these foods are high in vitamin A and particularly in carotene, a natural coloring matter that is converted to vitamin A in the body.
A 19-year study of 1,954 Chicago men, all Western Electric Co. employes, found far less lung cancer than expected in men, even smokers, whose diets were high in carotene.
Among cigarette users of 30 years' standing, those who consumed the least carotene had eight times the risk of those who consumed the most carotene, that is, those who consumed more carotene than three quarters of the other smokers.
More studies are needed, the scientists say, to prove whether carotene or any vitamin A intake will reduce lung cancer risk. Meanwhile, they add, "it seems prudent" to include carotene-rich foods in daily diets.
"I'd suggest one or two helpings a day," the study's chief author, Dr. Richard Shekelle of Rush-Presbyterian-St. Luke's, said yesterday. "I've increased my carrot intake," Shekelle, an ex-smoker, added.
Carotene abounds in vividly red, green or yellow fruits and vegetables, Linda Smith of the Community Nutrition Institute in Washington reported. Among others: dark salad greens (like endive, bibb lettuce and collard greens), beets, broccoli, green and yellow squash, sweet potatoes, grapes (especially red grapes), apples (especially in the skin) and persimmons.
But no one, said another scientist, should try to augment vitamin A intake by taking large numbers of vitamin A pills. These contain forms of the chemical that can cause liver damage in excess doses.
The Rush-Presbyterian scientists have been studying the Western Electric employes since the late 1950s. They recently showed that those who ate diets low in fats and cholesterol tended to have less cholesterol buildup in their blood vessels and also less heart disease.
In recent years studies in several countries have seemed to show that persons who consume foods high in vitamin A have less lung cancer. But these foods may be richest in either "pre-formed vitamin A" or retinol, or "pro-vitamin A," the carotene which can become the vitamin in the body.
The Chicago study found no correlation with retinol intake, but a strong correlation with carotene.
Thirty-three of the Western Electric men developed lung cancer over the 19-year observation period. Twenty-five of these 33 ate less than average amounts of carotene; 14 were in the lowest 25 percent for carotene intake.
Though most lung cancer occurs in cigarette smokers, nonsmokers apparently benefited too.
Dr. Michael Sporn of the National Cancer Institute has shown that various vitamin A compounds can prevent cancerous transformation of human and animal cells in the test tube. It's still not sure just which vitamin A or pre-vitamin A compounds might help prevent cancer, he said.
But there is good reason, he said, to test such compounds against a variety of human cancers. And tests in various human populations have recently started or are now being planned.