Even moderate drinking affects women's cancer risk

Drinking just a glass of wine a day increases women's risk of breast cancer, as well as several other types of the disease, a new study concludes. The research, carried out among more than a million UK women, says that alcohol accounts for 5,000 cases of breast cancer every year. Now researchers have examined the results from a very big study of women aged around 55, to see exactly how the amount of alcohol they drank related to their risk of getting different types of cancer. The women were recruited when they attended breast cancer screening and followed for the next 7 to 8 years, to see if they were diagnosed with any type of cancer.

Compared to women who said they drank only 1 or 2 units of alcohol a week, women who regularly drank the equivalent of 1 unit a day had an increased risk of getting seven types of cancer: breast, liver, rectum (part of the bowel), mouth, pharynx (a space at the back of the mouth), oesophagus (the tube that takes food from the mouth to the stomach) and larynx (voicebox).

The risk was most increased for breast cancer. In developed countries like the UK, the chance of having had breast cancer by the age of 75 is 9.5 in 100. According to the study, for every extra daily unit of alcohol (over 2 a week), that risk increases by 1.1 per 100. So if you had a roughly 9.5 percent chance of getting breast cancer by the age of 75, but you drank one glass of wine a day, that risk would go up to 10.6 percent. If you drank two glasses of wine a day, that would increase to 11.7 percent.

These might sound like quite small increases in risk. But because many women drink alcohol at these sorts of levels, it means a lot of women are affected overall. The researchers estimate that alcohol accounts for 11 percent of all breast cancers in the UK. That means that every year, 5,000 women get breast cancer who wouldn't have got it without drinking alcohol.

The risk for cancers of the mouth, oesophagus, pharynx and larynx only increased for women who also smoked. Researchers think that alcohol may dissolve some of the toxins in cigarette smoke, making drinking and smoking together more risky than doing either alone. There was no increased risk of these cancers for women who drank alcohol but didn't smoke.

The increased risks for rectum and liver cancer were relatively small, with an increased risk of 1 per 1000 and 0.7 per 1000 respectively.

Most of the women in the study were moderate drinkers. A quarter didn't drink at all, and of those who drank, only 2 percent drank more than 21 units a week. The average woman in the study who drank alcohol had 7 units a week, or about one drink a day. That reflects previous studies of women in this age group (the average age was 55 at the start of the study).

The findings are likely to be fairly reliable. The study followed 1.28 million women, for an average 7 years. The women filled in questionnaires at the start of the study, and then again 3 years later, saying how much alcohol they drank. The researchers were also able to take account of other things that affect women's cancer risk, such as whether they'd taken the contraceptive pill, HRT, whether they smoked or took exercise, and how much they weighed.

The researchers didn't use the women who drank no alcohol at all as their comparison group. That's because women who don't drink at all may have quit alcohol because of serious health problems. So they're not a healthy group to compare to. Instead, the researchers used women who drank only one or two alcoholic drinks a week as their comparison group. That's likely to make the results more reliable.

It helps to know how much you're drinking. One unit is 10 millilitres (ml) or 8 grams of pure alcohol, which is the amount of pure alcohol in a 25 ml single measure of spirits (ABV 40%), a third of a pint of beer (ABV 5-6%) or half a standard (175 ml) glass of red wine (ABV 12%).

The government's recommendations are not to drink more than 2 to 3 units a day for women or 3 to 4 units a day for men. Journal of the National Cancer Institute. 2009; 101: 296-305. 

Moderate Alcohol Intake and Cancer Incidence in Women

Naomi E. Allen, Valerie Beral, Delphine Casabonne, Sau Wan Kan, Gillian K. Reeves, Anna Brown, Jane Green
on behalf of the Million Women Study Collaborators

Background: With the exception of breast cancer, little is known about the effect of moderate intakes of alcohol, or of particular types of alcohol, on cancer risk in women.  Methods: A total of 1 280 296 middle-aged women in the United Kingdom enrolled in the Million Women Study were routinely followed for incident cancer.

Results: A quarter of the cohort reported drinking no alcohol; 98% of drinkers consumed fewer than 21 drinks per week, with drinkers consuming an average of 10 g alcohol (1 drink) per day. During an average 7.2 years of follow-up per woman 68 775 invasive cancers occurred. Increasing alcohol consumption was associated with increased risks of cancers of the oral cavity and pharynx (increase per 10 g/d = 29%), esophagus (22%), larynx (44%), rectum (10%), liver (24%), breast (12%), and total cancer (6%). The trends were similar in women who drank wine exclusively and other consumers of alcohol. For cancers of the upper aerodigestive tract, the alcohol-associated risk was confined to current smokers, with little or no effect of alcohol among never and past smokers . Increasing levels of alcohol consumption were associated with a decreased risk of thyroid cancer, non–Hodgkin lymphoma, and renal cell carcinoma.

Conclusions: Low to moderate alcohol consumption in women increases the risk of certain cancers. For every additional drink regularly consumed per day, the increase in incidence up to age 75 years per 1000 for women in developed countries is estimated to be about 11 for breast cancer, 1 for cancers of the oral cavity and pharynx, 1 for cancer of the rectum, and 0.7 each for cancers of the esophagus, larynx and liver, giving a total excess of about 15 cancers per 1000 women up to age 75.

EDITORIALS

Alcohol, Cardiovascular Disease, and Cancer: Treat With Caution

Michael S. Lauer, Paul Sorlie

Affiliation of authors: Division of Prevention and Population Sciences, National Heart, Lung, and Blood Institute, Bethesda, MD

Alcoholic beverages have been with us throughout the human history. During the last century, ill-advised efforts were made to eliminate its dangers by passing a constitutional amendment prohibiting its manufacture, sale, and distribution. As is well known, this created a social disaster and was later repealed. Beyond its social dangers, many of alcohol's medical dangers are well known and have been known for a long time, including acute intoxication; chronic destructive addiction; cirrhosis of the liver; dilated cardiomyopathy; fetal alcohol syndrome; and increased risks for hypertension, stroke, cardiac arrhythmias, and fatal motor vehicle accidents.

Over the past 20–30 years, the medical position on alcohol has become somewhat more nuanced. Investigations of large-scale observational cohorts have suggested that light to moderate drinking may be associated with decreased mortality rates and with decreased risk of cardiovascular disease. Some studies, but not all, have suggested that wine may provide additional benefits over and above the effects of alcohol, perhaps because of antioxidant or other types of effects of non-alcohol grape chemicals like resveratrol. Some investigators have been so intrigued by the possible benefits of low-dose alcohol that they have gone so far as to consider mechanisms by which alcohol can have salutary cardiovascular effects. These include increased levels of high-density lipoprotein cholesterol and a decreased tendency to thrombosis. Combining these reported biological benefits with epidemiological findings, some medical organizations have stated that low levels of alcohol consumption maybe considered safe or may be a legitimate "item of discussion between physician and patient".

In this issue of the Journal, Allen present fascinating findings that should give us pause. Allen et al. have systematically surveyed more than 1 million women who between 1996 and 2001 attended breast cancer screening clinics in the United Kingdom. They found that after 7 years of follow-up, even light to moderate levels of alcohol consumption were predictive of an increased risk of several common cancers, including those of the breast, rectum, liver, esophagus, and oropharynx. Taking into account the prevalence of alcohol consumption and its observed relative risks, the authors estimated that about 13% of cancers of the breast, aerodigestive tract, liver, and rectum could be attributed to alcohol.

Because of an enormous sample size, systematic survey methodology, and an ability to capture nearly all incident diagnoses of cancer, the authors could make a number of important, heretofore unappreciated, discoveries. Previous investigations have focused on the association between alcohol and mortality, including mortality due to cancer, but have not been able to so carefully assess the association of alcohol intake with the subsequent diagnosis of cancer. Allen et al. could estimate the association of different levels of alcohol intake with many different kinds of cancer. Perhaps more importantly, they could evaluate key interactions for specific cancer types; for example, they demonstrated that alcohol use was strongly predictive of cancer of the upper aerodigestive tract but only in current smokers. From a standpoint of cancer risk, the message of this report could not be clearer. There is no level of alcohol consumption that can be considered safe.

How are we to interpret the findings of Allen et al. given previous investigations suggesting that alcohol may be safe or even beneficial when taken in relatively low doses? Despite their study's many strengths, there are some important limitations that must be considered. The study was limited to women who were seen in breast cancer screening clinics; there is evidence that these women may be different in some respects from those of the general population. Nearly all the baseline clinical data were based on answers to a questionnaire, not direct measurement; this might be considered an acceptable sacrifice given the study's enormous sample size. This is also a limitation inherent to essentially all epidemiological investigations of alcohol use; it is doubtful that a systematic bias exists whereby women who are destined to develop cancer will misclassify their alcohol intake. Finally, the authors provide no information on all-cause mortality or incident cardiovascular disease events, despite the ability of their data to provide this information. We must hope that the authors plan to report on these outcomes in future publications.

Despite these limitations, the message from this report takes on a greater sense of urgency when considering the limitations of the many investigations suggesting beneficial cardiovascular effects of alcohol. Some have suggested that there is no real cardioprotective effect of alcohol. Epidemiological investigations are severely limited by failure to account for a number of important confounders, including socioeconomic status, social networks, mental health, reverse causality, and healthy cohort effects. The supposedly beneficial effects of alcohol seen in epidemiological studies may parallel the experience with hormone replacement therapy, where a number of observational reports suggested benefit, but definitive clinical trials showed harm. A major difference, however, is that a randomized trial of low-dose alcohol cannot happen.

Even if there are modest beneficial cardiovascular effects of alcohol, the current report of Allen et al. should remind us that we must consider these within a broader public health context. The current report, as well as a number of previous investigations, focused on middle-aged women. Among women, the major cause of death by far during the middle years is cancer Although it is true that cardiovascular disease is the leading cause of death among women overall, this primarily applies to women older than 75 years. It might be reasonable to suspect that many women in the lay public who are asking physicians about any possible safe effects of alcohol are middle aged; for this large group, the only reasonable recommendation we can make is that there is no clear evidence that alcohol has medical benefits.