Three factors in midlife can delay the onset of dementia by 13 years

People who steer clear of smoking in their mid-50s, while also maintaining healthy habits that stave off diabetes and high blood pressure, can expect to gain an additional 13 dementia-free years compared with those who live less healthily during midlife.

We already knew that smoking, diabetes and high blood pressure damage blood vessels and stir up inflammation in the brain, both of which can damage neurons involved in memory and learning, raising the risk of dementia.

But few studies have looked at how avoiding these risks in the 50s affects how long you live dementia-free later in life, says Josef Coresh at New York University. “We thought focusing on time gained may help get across the benefits of averting dementia risks.”

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Coresh and his colleagues analysed data from a cohort of more than 12,000 adults living in the US, who were tracked for 26 years, on average. When the adults were 56 years old, on average, and free from dementia, they reported whether they smoked, had diabetes or had high blood pressure. 

About a quarter of the participants later went on to develop dementia. The researchers found that the risk of this happening was highest for those who, during midlife, had reported that they had diabetes and high blood pressure, and also smoked. These participants were 2.7 times more likely to develop dementia than those who avoided all three risks during midlife.

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Crucially, participants who avoided those risk factors gained 12.6 dementia-free years, on average, compared with those who experienced all three. “By avoiding a few risks in midlife [when brain changes linked to dementia begin], you get more than a decade free of both dementia and death,” says Coresh.

Avoiding just one or two of the risks was also beneficial. Coresh says participants who did so gained roughly four and eight dementia-free years, respectively, compared with those who experienced all three risks. 

Regular exercise and avoiding too many sugary foods are good ways to cut your likelihood of getting diabetes or high blood pressure, he says. 

The researchers controlled for other factors known to influence dementia risk, including sex, level of education, physical activity level, body mass index and which variant of a gene called APOE people had – which is the main genetic risk factor for Alzheimer’s disease, the most common form of dementia. 

But they didn’t account for all of the additional factors that are known to affect dementia risk, says Richard Siow at King’s College London. These include hearing loss and how socially isolated people are. Because of this, the benefits of avoiding the three midlife risks the study focused on may be greater or smaller than the results suggest, he says. 

Another limitation is that the study focuses on the population level, rather than individuals, and included only people living in the US. Individuals in other countries may gain a different number of dementia-free years by adopting a healthy lifestyle in their 50s, due to differences in their genetics or exposure to environmental factors known to influence dementia, such as air pollution, says Coresh.

Neurology Open Access DOI: 10.1212/WN9.0000000000000152