Also, reaching older ages is associated with a higher risk of Alzheimer's. So, although a healthier lifestyle may delay the onset of Alzheimer's dementia, it may increase the years spent with the disease.
To investigate this lesser-known issue further, a team of US and Swiss researchers have analysed the potential impact of a healthy lifestyle on the number of years spent living with and without Alzheimer's.
The study analyses data from 2449 participants aged 65 years and older (average age 76), with no history of dementia, within the Chicago Health and Aging Project (CHAP).
Participants completed detailed diet and lifestyle questionnaires and a healthy lifestyle score was developed based on: a hybrid Mediterranean-DASH Diet (a diet rich in whole grains, green leafy vegetables and berries and low in fast/fried food, and red meats); late-life cognitively stimulating activities; at least 150 minutes a week of physical activity; not smoking; low to moderate alcohol consumption.
Cognitive activities included reading, visiting a museum or doing crosswords.
For each lifestyle factor, participants received a score of 1 if they met the criteria for healthy, and 0 if they did not. Scores from five lifestyle factors were summed to yield a final score ranging from 0 to 5. A higher score indicated a healthier lifestyle.
After taking into account other potentially influential factors, including age, sex, ethnicity and education, the researchers found that, on average, the total life expectancy at age 65 in women and men with a healthy lifestyle was 24.2 and 23.1 years, respectively. But for women and men with a less healthy lifestyle, life expectancy was shorter- 21.1 and 17.4 years, the study shows.
For women and men with a healthy lifestyle, 10.8 per cent (2.6 years) and 6.1 per cent (1.4 years) of the remaining years were lived with Alzheimer's respectively, compared to 19.3 per cent (4.1 years) and 12.0 per cent (2.1 years) for study participants with a less healthy lifestyle.
At age 85, these differences were even more notable.
While the study was population-based with long-term follow-up, this was an observational study, and as such, cannot establish cause.
The researchers point to some other limitations, for example, lifestyles were self-reported, possibly leading to measurement error, and the estimates provided in this study should not be generalized to other populations without additional research and validation.
However, the researchers conclude: "This investigation suggests that a prolonged life expectancy owing to a healthy lifestyle is not accompanied by an increased number of years living with Alzheimer's dementia."
The life expectancy estimates presented here "could help health professionals, policymakers, and stakeholders to plan future healthcare services, costs, and needs," they add.
In a linked editorial, a University of Michigan researcher highlights the study's "important implications for the wellbeing of ageing populations and for related public health policies and programmes."
She argues that the development and implementation of intervention programmes to reduce the risk of Alzheimer's disease and other dementias is critically important in global efforts to reduce pressure on stressed healthcare systems, healthcare workers, and both paid and unpaid carers.
"Promoting greater engagement in healthy lifestyles may increase dementia-free life years- by delaying the onset of dementia without extending life years spent with dementia," she concluded.