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Alcohol consumption and the risk of dementia

THE LANCET Neurology Vol 2 June 2003 http://neurology.thelancet.com 333

Reflection & Reaction

The possibility that alcohol mayprotect against age-related cognitivedecline and neurodegenerative diseasehas been debated for more than twodecades. Mild to moderate alcoholconsumption—defined as one to threeglasses per day—is associated withlower mortality, reduced risk of coronary heart disease, and fewer white-matter lesions.1 Becausevascular disease is implicated in thecause of both vascular and Alzheimertype dementia, there has been renewedinterest in the role of alcohol, eventhough previous studies have beeninconclusive.

Studies done in the 1980s were cross-sectional in design, did not include possible confoundingcomorbid disorders, and producedconflicting results (odds ratios rangedfrom 0·5 to 2·3). Meta-analyses of these case control studies found nosignificant association between alcoholconsumption and dementia. However,the exclusion of individuals with ahistory of alcoholism or cardiovasculardisease was an important source ofbias in many of these studies. The factthat abstinence from alcohol iscommonly the result of poor health isanother potential source of bias. Inaddition, some studies did notdifferentiate between the type orquantity of alcohol consumed.

Several large-scale population-based studies, which accounted forboth confounding and interacting riskfactors in a longitudinal design, havenow been done. Most of these studieshave found an association of alcoholconsumption with a low risk ofincident dementia. More recentstudies have shown that risk is highboth in people who abstain fromdrinking and in those who consume alot of alcohol. The Rotterdamlongitudinal study2—which used“never drinkers” rather than recentabstainers as a reference group—concluded that risk was lowest inpeople who consumed one to threedrinks per day.

Non-health related variables mustalso be considered. Leibovici and co-workers3 reported a decrease risk of dementia (odds ratio=0·26)

associated with alcohol consumption.However, when place of residence wasincluded in the model used, this effectdisappeared. This is because elderlypeople with mild cognitive impair-ment or dementia commonly live innursing homes where alcohol isprohibited. Studies that do not takenon-alcohol related risk factors intoaccount are therefore at risk ofmisclassifying participants.

In a recent prospective nestedcohort study, Mukamal and co-workers4 have tried to avoid the biasesof previous studies. They tookrepeated measurements of alcoholconsumption, separated formerdrinkers from long-term abstainers,and tried to establish drinkingbehaviour up to 5 years before the startof the study. Mukamal and colleaguesalso attempted to obtain proxyassessment of deceased or unavailableparticipants.

The results of the study supportprevious findings of a small protectiveeffect of mild to moderate alcoholconsumption on the risk of dementia.However, out of 5888 participants inthe initial study, 842 were notexamined, 1386 did not have an MRIexamination, 52 did not complete acognitive examination, and 107 of 480incident cases of dementia wereeliminated. People with cognitiveimpairment and early dementia aremore likely to refuse cognitiveexaminations, to have difficulties intravelling to examination centres, andto drop out of community studies dueto change of residence. The authorsnoted, for example, that individualswho completed an MRI examinationwere significantly healthier andconsumed significantly more alcoholthan those who did not. Therefore, thisstudy may still have been open to bias.

The study by Mukamal and co-workers is an improvement onprevious studies for two reasons: first,the retrospective assessment ofcognitive function in deceasedindividuals by proxy questionnaire,although such a global assessmentwould cover all causes of terminalcognitive decline; and second, theassessment of drinking behaviour up

to 5 years before the start of the studyfor the identification of individualswho may have recently stoppeddrinking due to cognitive or otherhealth problems.

But is a 5 year time periodsufficient? Because dementia in laterlife has been associated with highblood pressure in early adulthood,5 doyounger adults who are at a high riskof developing dementia reduce theiralcohol consumption at an early agebecause of hypertension?

Although most population-basedstudies have found that consumptionof one to three glasses of alcohol perday decreases the risk of dementia inlater life, these findings should be interpreted with great caution.Population-based studies are flawed byvarious problems: the diagnosis ofincident dementia, the reliability ofself-reports of alcohol consumption,fluctuating patterns of drinkingbehaviour throughout life, mortality,and drop-out bias. More importantly,if alcohol is protective, at what age is it protective? Researchers haveassumed that alcohol is protectiveimmediately before the potential onsetof dementia. However, considering the adverse effects of alcoholconsumption—such as stroke, corticalatrophy, driving accidents, and falls—clinicians should think carefully beforeprescribing several glasses of alcoholper day in the absence of a clearbenefit.

Karen Ritchie

Institut National de la Santé et de laRecherché Médicale, E0361Epidemiology of Nervous SystemPathologies, Hôpital La Colombière,Montpellier, France. Email ritchie@montp.inserm.fr

References1 Scherr PA, LaCroix AZ, Wallace RB. Light to

moderate alcohol consumption and mortality in theelderly. J Am Geriatr Soc 1992; 40: 651–57.

2 Ruitenberg A, van Swieten JC, Witteman JC, et al.Alcohol consumption and risk of dementia: theRotterdam study. Lancet 2002; 359: 281–86.

3 Leibovici D, Ritchie K, Ledésert B, Touchon J. The effects of wine and tobacco consumption oncognitive performance in the elderly: a longitudinalstudy of relative risk. Int J Epidemiol 1999; 28:77–81.

4 Mukamal KJ, Kuller LH, Fitzpatrick AL, LongstrethWT, Mittleman MA, Siscovick DS. Prospectivestudy of alcohol consumption and risk of dementiain older adults. JAMA 2003; 289: 1405–13.

5 Skoog I, Lernfelt B, Landahl S, et al. 15 yearlongitudinal study of blood pressure and dementia.Lancet 1996; 347: 1141–45.