People who stop smoking in middle age can reduce their cognitive decline so dramatically that within 10 years their chances of developing dementia are the same as someone who has never smoked, research has found.
Kicking the habit halves the rate of decline in verbal fluency and slows the loss of memory by 20%, according to a study of 9,436 people in England, the US and 10 other European countries.
The findings add to a growing body of evidence that quitting smoking can slow the rate of mental deterioration that ageing brings and thus help prevent the onset of dementia.
“Our study suggests that quitting smoking may help people to maintain better cognitive health over the long term even when we are in our 50s or older when we quit”, said Dr Mikaela Bloomberg of University College London, the lead researcher.
“We already know that quitting smoking, even later in life, is often followed by improvements in physical health and wellbeing. It seems that for our cognitive health too it is never too late to quit, she added.
Bloomberg and her colleagues from UCL reached their conclusions by comparing the cognitive functioning of adults aged at least 40 in the 12 countries who quit with those who kept smoking. While their performance was the same at the start, the quitters had gained substantial advantages over the smokers when their cognitive capacities were assessed over the next six years.
“Individuals who quite smoking had more favourable [cognitive] trajectories following smoking cessation than continuing smokers”, they write in The Lancet Healthy Longevity. “The rate of cognitive decline was slower for smokers who quit than for continuing smokers in the period after smoking cessation.
“The results suggest the importance of smoking cessation, even in later life, for long-term cognitive health.”
Although the findings do not prove cause and effect, they could provide “compelling motivation” for older smokers – who are less likely than younger age groups to try to give up – to do so, the authors added.
Smoking is one of the 14 risk factors for dementia which a commission of experts assembled by The Lancet medical journal identified last year. There is growing evidence that tackling them, which include depression, drinking too much, hearing loss and high cholesterol, reduce the risk of developing dementia in the first place, they added.
“The findings strengthen existing evidence that changing to a healthier lifestyle can have a measurable impact on your brain health,” said Dr Richard Oakley, the associate director of research and innovation at Alzheimer’s Society. “We know that quitting smoking, keeping physically active, eating a healthy balanced diet and drinking less alcohol can all help reduce the risk of dementia.”
The paper explains that smoking is thought to contribute to neurodegeneration by both harming cardiovascular health, by affecting blood vessels that supply oxygen to the brain, and also by causing chronic inflammation and directly damaging brain cells through oxidative stress.
However, Dr Julia Dudley, the head of research at Alzheimer’s Research UK, cautioned that “the greater cognitive decline seen in smokers doesn’t mean that these people will go on to develop dementia”. Differences between the two groups in their socioeconomic background or alcohol intake may have influenced the results, she said.
Caroline Cerny, the deputy chief executive at Action on Smoking and Health (ASH), said: “We’ve known for some time that smoking increases the risk of dementia and cognitive decline, but this important evidence shows that the harms can be slowed by quitting.
“It illustrates just why it is so important to stop smoking at any age, but particularly in middle age before many of the symptoms of cognitive decline will have emerged and highlights the need for sustained investment in stop smoking services.”
Last month, 35% of smokers in England tried to quit and 29% of them succeeded, almost double the rate seen when records began in 2007.
