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UCLA News release May 29, 2008.
Tobacco smokers who eat three servings of fruits and vegetables
per day and drink green or black tea may be protecting themselves from
lung cancer, according to a first-of-its-kind study by UCLA cancer
researchers.
UCLA researchers found that smokers who ingested high levels of
natural chemicals called flavonoids in their diet had a lower risk of
developing lung cancer — an important finding, since more than 90
percent of lung cancers are caused by tobacco smoking.
The study appeared this month in the peer-reviewed journal CANCER, published by the American Cancer Society.
"What we found was extremely interesting, that several types of
flavonoids are associated with a reduced risk of lung cancer among
smokers," said Dr. Zuo-Feng Zhang, a researcher at UCLA's Jonsson
Cancer Center and a professor of public health and epidemiology at the
UCLA School of Public Health. "The findings were especially interesting
because tobacco smoking is the major risk factor for lung cancer."
Flavonoids are water-soluble plant pigments that have antioxidant
and anti-inflammatory properties, both of which can counteract damage
to tissues. For the UCLA study, researchers looked at 558 people with
lung cancer and 837 people who did not have lung cancer and analyzed
their dietary history.
Researchers found that study participants who ate foods containing
certain flavonoids seemed to be protected from developing lung cancer.
Zhang said the flavonoids that appeared to be the most protective
included catechin, found in strawberries and green and black teas;
kaempferol, found in Brussels sprouts and apples; and quercetin, found
in beans, onions and apples.
So should smokers run out and stock up on the teas, apples, beans
and strawberries? Quitting smoking is the best course of action, Zhang
said, but eating more fruits and vegetables and drinking more black and
green teas won'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," Zhang
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."
Zhang said flavonoids may protect against lung cancer by blocking
the formation of blood vessels that tumors develop so they can grow and
spread, a process called angiogenesis. They also may stop cancer cells
from growing, allowing for naturally programmed cell death, or
apoptosis, to occur.
The antioxidant properties found in the flavonoids also may work
to counteract the DNA-damaging effects of tobacco smoking, Zhang said,
explaining why they affected the development of lung cancer in smokers
but not in nonsmokers.
"The naturally occurring chemicals may be working to reduce the damage caused by smoking," Zhang said.
The next step in research, Zhang said, involves laboratory-based
studies of flavonoids on cell lines and animal models to determine how
they are protecting smokers from developing lung cancer. And in
addition to larger studies to confirm these findings, other studies
need to be done to see if the protective effects of flavonoids extend
to other smoking-related cancers, such as bladder, head and neck, and
kidney cancers.
Zhang and his team also plan to study which types of fruits and
vegetables have the highest levels of the flavonoids found to be
helpful in this study and what the optimal number of servings per day
might be to provide the greatest protection.
Source: UCLA press release, by Kim Irvin.
Article abstract: Yan Cui, Hal Morgenstern, Sander Greenland, Donald P. Tashkin, Jenny T. Mao, Lin Cai, MD, Wendy Cozen, Thomas M. Mack, Qing-Yi Lu, Zuo-Feng Zhang. Dietary flavonoid intake and lung cancer - A population-based case-control study. Cancer, 112(10): 2241;2248. March 2008 .
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