The combination of both heavy drinking and smoking in midlife can accelerate cognitive decline.
Problems with cognitive function affects mental abilities such as thinking, knowing, judging and remembering things. Impairment can range from mild to severe issues caused by conditions such as dementia.
We already know that an overall decline in our cognitive abilities is evident from about the age of 45 and that smoking is associated with faster cognitive decline and a risk of developing dementia. Evidence for a link between just alcohol and a decline is more mixed.
But a study we carried out of 6473 adults suggested that the combined effect of smoking and drinking more than 21 units a week for men and 14 units of a week for women - the official recommended limit - had a stronger effect on cognitive decline compared to people who drank moderately and didn’t smoke.
Participants in the study - 4,635 men and 1,838 women aged between 45 and 69 - were enrolled in the Whitehall II cohort study of British civil servants. They were all asked about their cigarette and alcohol consumption and their cognitive function (including verbal and mathematical reasoning, short-term verbal memory and verbal fluency) was then assessed three times over ten years.
Smokers who drank alcohol heavily had a 36% faster cognitive decline compared to non-smoking moderate drinkers over the ten years of follow-up. This meant that for every ten years that they aged, their brains aged the equivalent of 12 years.
Among smokers, we also found cognitive decline to be faster as the number of alcohol units consumed per week increased.
Heavy drinking and smoking often go together, perhaps as a comforting habit, and particularly in certain groups of the population. In the UK, it’s common in many older adults. Our results, published in the British Journal of Psychiatry, were adjusted for age, sex, educational attainment and chronic disease.
The reason that a link between alcohol and cognitive decline is more mixed could be because of the apparent protective effects of drinking moderate amounts of alcohol, for example when it comes to reducing heart attack and stroke risk.
However, the results of our study don’t necessarily mean that it’s completely healthy. Non-drinkers included people who may have been heavy drinkers in the past and stopped drinking for health reasons - so-called “sick quitters”.
It is also possible that the signs of early cognitive decline may have motivated participants to stop drinking. People should not drink more alcohol than they do already, in the mistaken belief that this will prevent cognitive decline.
Although we know that the combination of heavy drinking and smoking leads to faster cognitive decline, we don’t yet know why.
But as drinking and smoking are changeable habits people can reduce their risk and improve their health. Existing advice is that smokers should stop, or cut down if they feel unable to stop. And men and women should avoid drinking more than 21/14 units of alcohol per week.
The results from this study suggest there may be additional benefits to cognitive health if people avoid combining smoking with heavy drinking - particularly from midlife onwards. We should choose our vices with care.