The combination of smoking and heavy drinking accelerates cognitive decline more than either habit alone, new research shows.
A large, longitudinal study conducted by investigators from University College London in the United Kingdom showed that individuals who smoked and were also heavy drinkers had a 36% faster rate of cognitive decline than nonsmoking moderate drinkers.
“Our research shows that cognitive decline was 35% faster in those people who reported both cigarette smoking and drinking alcohol above the recommended limits (14 units per week for women, 21 units per week for men). When we looked at people who were heavy-drinking smokers, we found that for every 10 years that they aged, their brains aged the equivalent of 12 years,” lead investigator Gareth Hagger-Johnson, PhD, said in a statement.
The study was published online July 11 in theBritish Journal of Psychiatry.
Large, Prospective Study
Several studies have found a link between smoking and cognitive decline and dementia. On its own, moderate alcohol consumption has been associated with a lower risk for dementia, but not heavy drinking.
Smoking and heavy alcohol consumption frequently co-occur, and the combination of the 2 has been associated with an increased risk for all-cause mortality and aerodigestive cancer. However, the investigators note that few studies have examined the combined effect of smoking and alcohol use on cognitive decline.
The researchers also point out that evidence from studies in older populations looking at the combined effect of alcohol use and smoking on cognitive function, cognitive decline, or later Alzheimer’s disease has been inconsistent.
They note that the inconsistent findings from studies of elderly individuals can in part be attributed to selection bias because of the greater mortality among smokers, producing a selected group of older smokers.
To determine whether smoking and alcohol consumption interact to accelerate cognitive decline in the transition from midlife to early old age, the investigators assessed 6473 adults — 4635 men and 1838 women — between the ages of 45 and 69 years (mean age, 55.76 years) during a 10-year period. The individuals in the study were participants in the Whitehall II cohort study of British civil servants.
All participants underwent 3 clinical examinations in 1997/99, 2002/04 and 2007/09. Participants were asked about their cigarette smoking and alcohol consumption. Their cognitive function, including verbal and mathematic reasoning, short-term verbal memory, and verbal fluency, were assessed at each time point.
Modifying Risk
The study revealed that compared with the reference group of never-smokers/moderate alcohol users, individuals who smoked and drank heavily had a faster rate of age-related cognitive decline. Furthermore, the investigators report that the combined effects of smoking and alcohol consumption were greater than their individual effects.
After adjusting for age, sex, education, and chronic diseases, the 10-year decline in global cognition in the reference group was -0.42 z-scores (95% confidence interval [CI], -0.45 to -0.39). In comparison, the decline in individuals who were heavy alcohol users and who also smoked was -0.57 z-scores (95% CI, -0.67 to -0.48) — 36% faster than the reference group.
“Our findings, assuming the observed associations are causal, show that alcohol use and cigarette smoking do not appear to ‘cancel each other out.’ “
From a public health perspective, the investigators suggest that the burden associated with cognitive decline could be reduced through modification of lifestyle factors.
Furthermore, they add, individuals should not increase their alcohol consumption in the belief that it will guard against cognitive decline.
“Current advice is that smokers should stop or cut down, and people should avoid heavy alcohol drinking. Our study suggests that people should also be advised not to combine these 2 unhealthy behaviors, particularly from midlife onwards. Healthy behaviors in midlife may prevent cognitive decline into early old age,” said Dr. Hagger-Johnson.
The authors have disclosed no relevant financial relationships.
Br J Psychiatry. Published online July 11, 2013. Abstract