Finding foods and nutritional supplements that can help prevent cancer is one of those one-step-forward, two-steps-back areas of research: frequently, when researchers think they've hit upon something that works, a new study comes along that finds that, no, eating that actually doesn't help prevent cancer--or worse, that eating too much of that might actually increase your odds of developing cancer.
Lung cancer, which in 2009 was diagnosed 220,000 times and killed 160,000, is a good example: Researchers have gone through the alphabet looking for vitamins that may help drive down cancer risk. They thought for awhile that beta-carotene might help. But in 2004, a large study found that for smokers, beta-carotene supplementation appeared to boost lung cancer risk.
With such reversals fresh in their mind, cancer researchers these days are at pains to hold their enthusiasm in check over new studies that seem to offer new hope in the prevention of lung cancer. But this week, there have been two new ones, and they have found some striking cancer-prevention properties in green tea and green vegetables.
In the first, a study of 1,100 current and former smokers found that those whose diets had been high in folic acid, leafy-green vegetables and those currently taking multivitamins rich in phytochemicals (vitamins A, C, K, folate, carotenoids and lutein) showed lower levels of genetic changes known to give rise to lung cancer in smokers.
The second found that compared with Taiwanese smokers who drank at least one cup of green tea a day, smokers who did not drink green tea were 12.7 times more likely to develop lung cancer. Smokers who had genetic variations that put them at greater risk of developing lung cancer didn't get quite as much protection from green tea as those who didn't have those genetic variations. But they still benefited.
The polyphenols found in tea, and especially in green tea, have drawn lots of attention as potential cancer-blockers. This study was presented at a conference being held this week in Coronado, Calif., on lung cancer and its molecular origins. It's sponsored by the American Assn. for Cancer Research.
The leafy-greens study, published in the journal Cancer Research, appeared online Tuesday. Officials of the National Cancer Institute, which funded the study, lauded the study as "well designed." But in a statement, NCI's biomarkers research group chief Sudhir Srivastava cautioned that more research would need to strengthen the evidence--even for leafy greens--before it could serve as the basis for dietary recommendations.
OK, so we don't know for sure what specific nutrients to avoid or eat more of to avoid cancer. But there's lots of evidence that a diet with lots of vegetables is generally good for your health. Want some advice on what to eat? Check the American Cancer Society's website for lots of ideas.
-- Melissa Healy