The study, published in Nature Communications, analysed data from 32,000 adults aged 50 or over from 14 European countries who responded to surveys over 10 years.

The researchers investigated how rates of cognitive decline might differ among cognitively-healthy older adults with different combinations of health-related behaviours, including smoking, physical activity, alcohol consumption and social contact.

Cognitive function was assessed according to participants’ performance in memory and verbal fluency tests. Participants were grouped into lifestyles based on whether they smoked or not, whether they did both moderate and vigorous physical activity at least once per week, whether they saw friends and family at least weekly, and whether they drank more or the same/less than two alcoholic drinks per day (men) or one drink per day (women).

They found that cognitive decline was faster for lifestyles that included smoking, while cognitive decline was generally similar for all non-smoking lifestyles. Smoking lifestyles had cognitive scores that declined up to 85% more over 10 years than non-smoking lifestyles.

The exception was smokers who had a healthy lifestyle in all other areas – that is, they did regular exercise, drank alcohol in moderation, and socialised regularly. This group had a rate of cognitive decline similar to non-smokers.

Lead author Dr Mikaela Bloomberg (UCL Behavioural Science & Health) said: “Our study is observational so cannot definitively establish cause and effect, but it suggests smoking might be a particularly important factor influencing the rate of cognitive ageing.

“Previous evidence suggests individuals who engage in more healthy behaviours have slower cognitive decline; however, it was unclear whether all behaviours contributed equally to cognitive decline, or if there were specific behaviours driving these results.

“Our findings suggest that among the healthy behaviours we examined, not smoking may be among the most important in terms of maintaining cognitive function.

“For people who aren’t able to stop smoking, our results suggest that engaging in other healthy behaviours such as regular exercise, moderate alcohol consumption and being socially active may help offset adverse cognitive effects associated with smoking.”

The researchers accounted for a range of factors that might have influenced the findings, including age, gender, country, education, wealth, and chronic conditions.