Alcohol and Colon Cancer - How Much is Too Much?

Summarized by Robert W. Griffith, MD
July 2, 2004

Introduction

We've heard (and we've been telling you for years) that one or two alcoholic drinks each day are positively good for you; a 'moderate' alcoholic intake is associated with decreased mortality, largely due to decreased likelihood of a heart attack. However, there are obvious dangers from drinking too much: cirrhosis of the liver, increased suicide risk, and increased likelihood of some cancer. A new report in the Archives of Internal Medicine has analyzed the results of 8 clinical studies of alcohol intake and colorectal cancer, and has found an association; more importantly, however, they have determined at what level of intake the association occurs.

What was done

The selected studies each had more than 50 cases of colorectal cancer, with an assessment of long-term dietary and alcohol intake at baseline.

Information collected included age, sex, smoking status, physical activity, education level, height, weight, multivitamin use, hormone replacement therapy, and contraceptive use.

For the purposes of this study, it was assumed that:

• 12 oz (335 mL) of beer contain 12.8 grams of alcohol
• 4 oz (118 mL) of wine contain 10.9 grams of alcohol
• 1.5 oz (44 mL) of 80-proof spirits contain 14.0 grams of alcohol

The average amount of alcohol for each participant was calculated, measured as grams per day (g/d). Subjects were assigned to one of 6 groups, according to their average intake: no alcohol, up to 5 g/d, 5 - 15 g/d, 15 - 30 g/d, 30 - 45 g/d, and over 45 g/d.

Cases of colon and rectal cancer were discovered from cancer and death registries, and follow-up questionnaires. The period of follow-up varied from 6 to 16 years, depending on the study.

Statistics were used to calculate the relative risk (RR) of someone who drank alcohol getting colorectal cancer during the follow-up period.

What was found

In the 8 different studies, 45% to 78% of women and 76% to 89% of men consumed alcohol. Among those who drank, the average intake was 3.5 to 10.9 g/d in women and 12.1 to 20.3 g/d in men.

There were roughly 490,000 participants, of whom over 4,650 (i.e. about 1 in 100) developed colorectal cancer. Examination of the association between alcohol intake and relative risk of cancer showed that an increased risk of colorectal cancer was limited to those people who drank 30 g/d or more of alcohol. This was roughly over two drinks a day (see the listing above), a level that was reported by 4% of the women and 13% of the men.

These results were similar for women and men, and the different types of alcohol consumed - beer, wine or spirits - and they weren't affected by the other factors assessed (smoking, diet, vitamins, exercise, etc).

What this means

The researchers admit the main flaw in their study - the results depend on a single self-report of alcohol intake at baseline, which may not be very reliable. Nevertheless, the numbers are very large (almost half a million subjects), which increases their reliability.

It seems clear that an intake of over 30 grams of alcohol a day is associated with a modest increase in colorectal cancer; 'modest' because only 1% of colorectal cancers in women and 5% of cases in men would have been avoided if heavier drinkers had limited their intake to two drinks a day or less.

The usefulness of this study is to reinforce the dangers of heavy drinking. We can still recognize the benefits of modest alcohol intake, but we need to remember the risks of excess, and tell ourselves: "Two's my limit!"

Source

• Alcohol intake and colorectal cancer: a pooled analysis of 8 cohort studies. E. Cho, SA. Smith-Warner, J. Ritz,  et al., Ann Intern Med, 2004, vol. 140, pp. 603--613

Related Links
Alcoholic Beverages: Health Benefit or Liability?
Regular Alcohol Intake Cuts the Heart Attack Risk
Is It the Grape, or the Wine?

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