Consumption and lifestyle key to link between alcohol and cancer
R. Curtis Ellison reviews the scientific data surrounding the link between alcohol consumption and cancer.
With alcohol consumption increasingly under the spotlight at EU level, it's perhaps fitting to review some of the lifestyle factors that may affect our risk of developing cancer.
And a common question is, "Does drinking alcohol cause cancer?" Current scientific data give a clear answer: it depends on how much you drink.
Heavy alcohol consumption, especially among alcoholics and other alcohol-dependent people, increases the risk of a number of types of cancer, especially the upper aero-digestive cancers such as cancer of the mouth, throat, and oesophagus.
In fact, these are known as 'alcohol-related cancers'. An important feature of these cancers is that they occur primarily among heavy drinkers who are also heavy smokers; they are unusual among life-time non-smokers.
What about people who consume alcohol moderately? In particular, are people who have a drink or two per day increasing their risk of cancer? In most instances, the answer is no. We appreciate that many epidemiologic studies have reported that even light drinking may be associated with a slightly increased risk of breast cancer among women.
"Scientific data clearly show a relation between heavy drinking and certain types of cancer"
On the other hand, we know that other factors modify this association: a woman's risk is increased if she is a binge-drinker, if she is also taking hormone replacement therapy (HRT), and/or if she has an inadequate intake of the vitamin folic acid.
For women who have a drink a day who have an adequate folate intake and are not on HRT, any increase in risk would be minimal.
A key limitation in epidemiologic studies relating alcohol to cancer is knowing how much a person is actually drinking, and the pattern of drinking (small amounts on a regular basis versus binge drinking).
Estimates of alcohol consumption are based on what subjects tell the researchers, their self-report of drinking. But researchers have often wondered how truthful such reports are - if someone under reports their intake, we may attribute a cancer or other disease to light drinking when the subject may have been exposed to much more alcohol.
Luckily, investigators in a recent study in California of more than 100,000 subjects (a large number that strengthens the results) have developed a reasonable approach to judge which subjects are underreporting their alcohol intake and which are not.
This is done by reviewing the person's medical records for other diseases and conditions (such as liver cirrhosis, alcoholic neuropathy, or alcoholism) that are known to occur only in very heavy drinkers.
In the California study, the 18 per cent of their subjects who reported light or moderate drinking but had such diagnoses elsewhere in their medical records were considered to be "likely under reporters" of their alcohol intake.
Among these subjects, even the reported light intake of alcohol was associated with an increase in their risk of cancer.
On the other hand, among subjects reporting light drinking who had extensive other medical records with no evidence of these alcohol-related diagnoses, who were considered "unlikely to be underreporting their intake," there was no increase in cancer when their risk was compared with that among abstainers or occasional drinkers.
In summary, scientific data clearly show a relation between heavy drinking and certain types of cancer. For even light-to-moderate drinking, many studies have shown a slight increase in the risk of certain cancers, especially breast cancer.
However, when subjects likely to be underreporting their intake are removed from that pool, new data indicate that light to moderate drinking is not associated with an increased risk for breast cancer or for other types of cancer.
The question of alcohol and cancer boils down to dose: heavy consumption increases risk but light to moderate consumption is unlikely to increase risk.
The data upon which these views are based come especially from reviews by the international scientific forum on alcohol research, a group of 40 international scientists who are experts in the field of alcohol consumption and health; they volunteer their services in the review of emerging papers on the topic.
I serve as the co-director of this organisation, which has a goal of presenting unbiased, scientifically accurate information on research relating alcohol to health.
Since 2010, the Forum has reviewed more than 135 emerging scientific papers on the topic and published our critiques on the free Boston University web-site: www.bu.edu/alcohol-forum.
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