Current issues of ACP Journal Club are published in Annals of Internal Medicine


Etiology

Coffee intake was inversely associated with suicide in women

ACP J Club. 1996 Sept-Oct;125:47. doi:10.7326/ACPJC-1996-125-2-047


Source Citation

Kawachi I, Willett WC, Colditz GA, Stampfer MJ, Speizer FE. A prospective study of coffee drinking and suicide in women. Arch Intern Med. 1996 Mar 11;156:521-5.


Abstract

Objective

To study the association between long-term coffee consumption and the risk for suicide in women.

Design

10-year cohort analysis of women in the Nurses' Health Study.

Setting

Community-based study of registered nurses in the United States.

Participants

86 626 women who were 34 to 59 years of age in 1980 and who responded to mailed questionnaires every 2 years until 1990. Questionnaire items included medical history and food intake. Women were excluded who left ≥ 10 food items blank; had implausibly high or low food intake scores; did not address coffee consumption; or had a history of cancer, coronary heart disease, or stroke.

Assessment of risk factors

Consumption of caffeinated coffee was categorized as almost never, 1 to 3 cups/mo to 2 to 4 cups/wk, 5 to 6 cups/wk to 1 cup/d, 2 to 3 cups/d, and 4 to ≥ 6 cups/d. Risk factors included smoking status; alcohol intake; body mass index; marital status; history of angina, hypertension, diabetes mellitus, and hypercholesterolemia; tranquilizer use; stress at home and at work; and current work status.

Main outcome measure

Relative risk (RR) for suicide in relation to coffee consumption.

Main results

During 10 years of follow-up, 56 suicides occurred. Coffee drinkers, especially those with higher intake, had a lower risk for suicide than non-coffee drinkers. The age-adjusted RR for 2 to 3 cups/d was 0.34 (95% CI 0.17 to 0.68) and for 4 to ≥ 6 cups/d was 0.42 (CI 0.21 to 0.86, P for trend = 0.002). After adjustment for other risk factors, the inverse relation was maintained (RR for 4 to ≥ 6 cups/d was 0.28, CI 0.12 to 0.69, P for trend = 0.006). The multivariate RR for caffeine intake 3 690 mg/d was 0.33 (CI 0.13 to 0.87, P for trend = 0.002). No association was seen between tea intake and risk for suicide.

Conclusion

An inverse association existed between coffee intake and the risk for suicide in women.

Source of funding: National Institutes of Health.

For article reprint: Dr. I. Kawachi, The Channing Laboratory, 180 Longwood Avenue, Boston, MA 02115, USA. FAX 617-432-3755.


Commentary

Should we advise our patients to drink more coffee? This study by Kawachi and colleagues confirms the strong inverse association between coffee intake and suicide risk that was shown by Klatsky and colleagues (1), who also identified a trend toward fewer deaths among coffee drinkers from motor vehicle accidents. 22% of the nurses in the current study did not drink coffee, whereas 58% drank 2 or more cups per day.

Is the reduced risk for suicide directly related to the effects of caffeine in producing mood enhancement or, as Klatsky and colleagues suggest, do depressed adults drink less coffee? Perhaps abstinence from coffee is associated with other factors that increase the risk for suicide. The design of this study precludes a valid answer to this question.

Cultural and religious factors, which were not measured in the study, also influence coffee consumption. For example, Seventh Day Adventists and Mormons abstain from coffee; in some cultures tea is a more common drink.

Do such personality factors as introversion or extroversion, anxiety, or obsessive behavior influence coffee consumption? Suicide is not only related to depressive illness, it is also associated with other mental and personality disorders, substance abuse, and failed interpersonal relationships. Women with eating disorders are at high risk for suicide and may be over-represented among non-coffee drinkers. Although the authors excluded "implausible" dietary histories, were the records accurate representations of intake? No direct information about these risk factors or the use of antidepressants is reported in the study.

The correlation between coffee drinking patterns in nurses and those of the general population is unknown. Further rigorous studies are clearly required. Until such studies are done, no evidence-based clinical policy about coffee intake is warranted.

Alyson Hall, MBBS
Royal London HospitalLondon, England, UK


Reference

1. Klatsky AL, Armstrong MA, Friedman GD. Coffee, tea, and mortality. Ann Epidemiol. 1993;3:375-81.