Dementia is often thought of as a disease of old age, and for good reason: the vast majority of cases occur after age 65. As a result, most studies of the disease have focused on understanding the risk factors associated with late-onset dementia—generally classified as dementia that occurs after age 65—while far less is known about what contributes to cases that develop earlier in life.

A new University of Minnesota School of Public Health (SPH) study helps fill that gap, finding that several common health conditions and lifestyle factors, including diabetes, depression, smoking, obesity, and physical inactivity, are associated with a substantially higher risk of developing dementia before age 65.

To conduct the study, researchers combined data from five, large community-based studies in the United States and the United Kingdom, creating a dataset of more than 544,000 adults. They analyzed a range of demographic, health, and lifestyle factors and followed participants for nearly 14 years on average to identify cases of dementia diagnosed before and after age 65.

The study, published in The Lancet Healthy Longevity, found:

• Several health and lifestyle factors were strongly associated with early-onset dementia. People with depression, diabetes, obesity, physical inactivity, current smoking habits, or excessive alcohol consumption faced a higher risk of developing dementia before age 65.
• Depression, diabetes, and smoking emerged as particularly important risk factors. People with depression had nearly three times the risk of early-onset dementia, while people with diabetes and those who currently smoked doubled their risk of early-onset dementia compared with people without those risk factors.
• Many of the strongest risk factors are potentially modifiable. While early-onset dementia is relatively uncommon, the study identified a number of potentially modifiable risk factors, indicating that improving cardiovascular health, mental health, and lifestyle factors such as physical inactivity earlier in life could help reduce the risk of developing dementia before age 65.

“Early-onset dementia is relatively rare, but when it occurs, it can have an especially profound impact on people and families because it often develops during the prime of adulthood, when people are building careers, raising children, and planning for the future,” said Katherine Giorgio, lead author and SPH researcher. “Our findings suggest that dementia is not simply an inevitable consequence of aging. Many of the same health and lifestyle factors associated with dementia later in life are also linked to dementia before age 65, highlighting the importance of prevention efforts that support brain and cardiovascular health for people of all ages.”

The study’s findings suggest that public health efforts to improve cardiovascular health, diabetes prevention, smoking cessation, physical activity, and mental health could play an important role in reducing dementia risk.