Flavonoids linked to lung cancer protection amongst smokers: study

Increasing intakes of epicatechin, catechins, and quercetin, found in tea and vegetables were associated with significant risk reductions, according to a study involving 558 patients with lung cancer and 837 healthy people for comparison published in Cancer .

"What we found was extremely interesting, that several types of flavonoids are associated with a reduced risk of lung cancer among smokers," said lead researcher Zuo-Feng Zhang from UCLA's Jonsson Cancer Center.

"The findings were especially interesting because tobacco smoking is the major risk factor for lung cancer."

Although expert advice is clearly to avoid tobacco smoke altogether, the results suggest smokers could benefit from upping their intake of flavonoid-rich foods.

One in three Europeans are smokers, while the US figure is one in five.

Tobacco smoke contains over 4,000 compounds, of which 60 are known carcinogens.

The oxidative stress levels of smokers are significantly greater than non-smokers, and as such there is a bigger drain on the levels of antioxidants in the body.

The UCLA researchers conducted a population-based case-control study, and used food frequency questionnaires to estimated flavonoid intakes.

Flavonoids, a class of antioxidants found in tea, red wine, soybeans, fruit and vegetables, are the focus of increasing study since oxidative stress has been linked to an increased risk of various diseases including cancer, Alzheimer's, and cardiovascular disease.

After adjusting the results to account for potential confounding factors, such as age, sex, smoking status and pack-years of tobacco smoking, and race-ethnicity, for example, a significant protective effect was observed for increased intake of epicatechin, catechins, quercetin, and kaempferol.

Specifically, a 10 mg per day increase in epicatechin intake reduced the risk by 36 per cent, a four mg increase in catechin intake reduced the risk by 51 per cent, a nine mg increase in quercetin intake reduced the risk by 35 per cent, a two mg increase in kaempferol intake reduced the risk by 32 per cent.

Catechin is found in strawberries and green and black teas, kaempferol is found in Brussels sprouts and apples, and quercetin is found in beans, onions and apples.

On the other hand, no association between flavonoid intake and lung cancer risk among non-smokers was observed, said Zhang and co-workers.

Zhang said that stopping smoking was the best course of action to reduce the risk of developing lung cancer, but added that eating more fruits and vegetables and drinking more black and green teas wouldn't hurt.

"Since this study is the first of its type, I would usually be hesitant to make any recommendations to people about their diet," he said.

"We really need to have several larger studies with similar results to confirm our finding.

However, it's not a bad idea for everyone to eat more fruits and vegetables and drink more tea."

Mechanism Commenting on the potential mechanism, the UCLA-based researcher said that flavonoids may act by blocking the formation of blood vessels that tumors develop so they can grow and spread, a process called angiogenesis.

A potential role in apoptosis, or naturally programmed cell death, may also be occurring.

Next step The subject warrants further study, he said, and noted that laboratory-based studies of flavonoids on cell lines and animal models will determine the mechanism, while larger studies are necessary to confirm these observations Interest in flavonoids is growing rapidly and a mounting body of science, including epidemiological, laboratory-based and randomised clinical trials, continues to report the cancer-fighting potential of a number of different flavonoids, such as isoflavones, anthocyanidins and flavonols.

According to Business Insights, the market potential for flavonoids in the dietetic and nutritional supplement market is in excess of €670m ($862m) for 2007, with annual increases of 12 per cent.

Source: Cancer 15 May 2008, Volume 112, Issue 10, Pages 2241-2248 "Dietary flavonoid intake and lung cancer - a population-based case-control study" Authors: Y. Cui, H. Morgenstern, S. Greenland, D.P. Tashkin, J.T. Mao, L. Cai, W. Cozen, T.M. Mack, Q.Y. Lu, Z.F. Zhang