Researcher Links Sunlight With Loss of Vital Nutrient
Research at Cornell University suggests that too much exposure to the sun may destroy a nutrient in the body that is believed to fight certain types of cancer.
The nutrient is beta-carotene and earlier studies have suggested it might help protect the body against skin, lung, bladder and other cancers, says nutrition professor Daphne A. Roe.
Beta-carotene is found in red and yellow vegetables and is converted into vitamin A in the body.
“There is a variety of evidence that people with higher carotenoid levels have a lower risk with certain types of cancer,” she said in a telephone interview.
Concluded Two Studies
Roe recently concluded two studies that have shown people who are repeatedly exposed to ultraviolet light lose “highly significant” amounts of beta-carotene from their blood plasma.
In the first study, a dozen Caucasian women volunteers were exposed to ultraviolet-A light rays 11 times in a two-week period. The rays are identical to those used in many tanning salons and the repeated exposures were enough to give some of the volunteers mild sunburns, Roe said.
She repeated the experiment in her second study, using 12 Caucasian and Oriental men instead of women.
In both study groups, the levels of carotenoids, of which beta-carotene is the most important, dropped significantly--in some cases by more than half, Roe said. In addition, the volunteers received the recommended daily allowances of vitamin A, carotenoids, folate and riboflavin during the two-week experiments.
‘Significant Finding’
“We knew before that if you gave people beta-carotene they would be less sensitive to the light,” she said. “Now we have a significant finding that light exposure can change carotenoid levels in the blood.
“That means that people in sunny climates and those who do not protect themselves from the harsh summer sun could lose much of beta-carotene’s protective benefits against many kinds of cancer,” she said.
But Roe said her research may be more significant to nutrition research than to cancer research. The reduction of beta-carotene also means a corresponding reduction in vitamin A, necessary for the formation of healthy hair, skin, bones and teeth.
She said previous studies at Cornell have shown sunlight can destroy significant quantities of vitamin A in milk stored in clear containers and that sunlight may affect the amount of the vitamin in other foods as well.
Will Examine New Link
Vitamin A deficiencies in sunny countries in parts of Africa and the Far East are common and have led in many cases to permanent blindness, she said.
“Our research raises the question of whether some of these deficiencies may be caused by sun exposure,” she said. “We have to examine the relationship, but I think a link is clear.”
Roe said dosing up on vitamin A pills before sunbathing will not help the process of beta-carotene deterioration, “but the answer may be to eat plenty of carotenoid vegetables. We’re not sure at this point.”
Good sources of carotenoids include spinach, broccoli, squash, carrots, pumpkin, peas and cantaloupe, she said.
Roe plans to continue her research by studying the effects of sun exposure on people with dark skin and on blacks to determine if they also lose carotenoids.
