Alcohol and cancer risk: What is the connection?

Issue: April 25, 2016

Alcoholic drinks — a 5-ounce glass of wine, a 12-ounce beer or a 1.5-ounce glass of 80-proof liquor — all contain ethanol.

Data suggest ethanol increases a person’s risk for cancer, according to the American Cancer Society. Still, the exact mechanism that affects this risk is not clear, and the risk varies depending upon the cancer type.

Edward Giovannucci

Although heavy alcohol consumption has been known to be associated with an increased risk for several cancer types, the association between light to moderate alcohol consumption and a person’s overall risk for cancer is not quite as clear.

HemOnc Today asked Edward Giovannucci, MD, ScD, professor of nutrition and epidemiology at Harvard T.H. Chan School of Public Health, about the association between moderate alcohol consumption and cancer risk, as well as whether alcohol should be avoided completely during cancer treatment.

Question: You led a study published in BMJ about light to moderate intake of alcohol and cancer risk. What did you find?

Answer: Most of our previous knowledge on alcohol and cancer has been focused on higher consumption of alcohol and in smokers. We set out to determine whether light to moderate drinking is associated with an increased risk for cancer, especially among nonsmokers. We used data from two large U.S. studies that tracked the health of 88,084 women and 47,881 men for up to 30 years.

We assessed the risk for total cancer as well as known alcohol-associated cancers, including cancer of the colorectum, female breast cancer, liver, oral cavity, pharynx, larynx and esophagus.

Light to moderate drinking was defined as up to one standard drink or 15 g of alcohol per day for women, and up to two standard drinks or 30 g of alcohol per day for men. One standard drink is roughly equivalent to a small (118 ml) glass of wine or a 355ml bottle of beer.

Influential factors — such as age, ethnicity, BMI, family history of cancer, history of cancer screening, smoking, physical activity and diet — also were taken into account.

During the follow-up period, 19,269 cancers were diagnosed in women and 7,571 cancers were diagnosed in men. We found that, overall, light to moderate drinking was associated with a small and nonsignificant increased risk for total cancer in both men and women, regardless of smoking history. For alcohol-related cancers, the risk was increased among light and moderate drinking men who had ever smoked, but not among men who never smoked. However, even in women who never smoked, risk for alcohol-related cancers — primarily breast cancer — increased even within the range of up to one drink per day.

Q: Can you speculate on why alcohol increases the risk for breast cancer?

A: Many studies have shown this, and our study just confirmed this. Although the percentage of increased risk is not significantly high (less than 10%), because breast cancer is so common, even a small increase in risk is important. We do not yet know the mechanism for why alcohol increases the risk for breast cancer.

Q: What should future research on alcohol intake and cancer risk assess?

A: Important topics are to understand why alcohol increases the risk for breast cancer and if any factors can modify this risk. Also, it is important to better understand the benefits and risks of moderate alcohol consumption — for example, the effects on cardiovascular disease. In addition, personalizing risk assessment may be important. For example, the pros and cons of moderate drinking may differ for a man at high risk for heart disease and for a woman at low risk for heart disease but increased risk for breast cancer.

Q: How much is too much alcohol in terms of increasing the risk for cancer?

A: For nonsmokers, it seems that a general rule can be up to two drinks for men and one drink for women. It is important to note that to optimally reduce the risk for cancer, zero alcohol is best because there can be a very small risk even at low levels of alcohol. I say up to two drinks for men and one drink for women as a general rule because, above these levels — especially substantially above these levels — the cons are likely to outweigh the pros. However, in the moderate range we define for men and women, the risk for cancer is real but relatively low so there could be benefit overall, at least for some individuals. Even still, for a woman with a strong family history of breast and colorectal cancer, perhaps alcohol should be limited as much as possible.

Q: A cancer diagnosis is incredibly stressful, and some patients may choose to have a glass of wine or beer each day to relax. Is it wise to consume alcohol while undergoing treatment for cancer?

A: It is important for the patient to discuss consumption of alcohol with his or her treating physicians, especially to make sure there are not any contraindications with any specific treatment. I would definitely avoid high alcohol consumption, but one drink may be OK under certain circumstances, unless the physician states otherwise. Alcohol is a powerful substance. We do not consider it technically as a drug, but it has many features of a drug. Physicians should know their patients’ drinking habits.

Q: Can alcohol contribute to cancer’s growth, or can alcohol consumption after remission increase risk for recurrence?

A: There is no definitive evidence for this at this time. The studies to date, although limited in number, do not show moderate drinking worsens prognosis of cancer. More study is needed, but the evidence to date is reassuring. The evidence to date also does not suggest that moderate drinking has a big influence on cancer recurrence. I would just like to emphasize that we are talking moderate drinking, defined as up to two drinks per day for men and one per day for women. High alcohol intake definitely increases risk for cancer. It might also be useful to note that although the evidence is not definitive at this point, it is likely that drinking with a meal is better than drinking with an empty stomach. – by Jennifer Southall

For more information:

Edward Giovannucci, MD, ScD, can be reached at Harvard T.H. Chan School of Public Health, 677 Huntington Avenue, Boston, MA 02115; email: egiovann@hsph.harvard.edu.

Disclosure: Giovannucci reports no relevant financial disclosures.