Combined impact of smoking and heavy alcohol use on cognitive decline in early old age: Whitehall II prospective cohort study

BACKGROUND: Identifying modifiable risk factors for cognitive decline may inform prevention of dementia. AIMS: To examine the combined impact of cigarette smoking and heavy alcohol consumption on cognitive decline from midlife. METHOD: Prospective cohort study (Whitehall II cohort) with three clinical examinations in 1997/99, 2002/04 and 2007/09. Participants were 6473 adults (72% men), mean age 55.76 years (s.d. = 6.02) in 1997/99. Four cognitive tests, assessed three times over 10 years, combined into a global z-score (mean 0, s.d. = 1). RESULTS: Age-related decline in the global cognitive score was faster in individuals who were smoking heavy drinkers than in non-smoking moderate alcohol drinkers (reference group). The interaction term (P = 0.04) suggested that the combined effects of smoking and alcohol consumption were greater than their individual effects. Adjusting for age, gender, education and chronic diseases, 10-year decline in global cognition was -0.42 z-scores (95% CI -0.45 to -0.39) for the reference group. In individuals who were heavy alcohol drinkers who also smoked the decline was -0.57 z-scores (95% CI -0.67 to -0.48); 36% faster than the reference group. CONCLUSIONS: Individuals who were smokers who drank alcohol heavily had a 36% faster cognitive decline, equivalent to an age-effect of 2 extra years over 10-year follow-up, compared with individuals who were non-smoking moderate drinkers.