People who stayed married to one person for many years in mid-life had a lower risk of developing dementia in old age, according to a recent study published in the Journal of Aging and Health.

“Being married can have an influence on risk factors for dementia,” said lead author Vegard Skirbekk, PhD, at the Norwegian Institute of Public Health (NIPH-FHI), in a press release. The group that stayed married continuously had the lowest incidence of dementia, while those who were divorced or single were the most likely to develop mild cognitive impairment or dementia. Among singles, though, people with children had lower rates of dementia than people without.

Risk of Cognitive Decline May Be Highest Among the Single and Divorced

To explore how marital status may impact brain health, investigators used data from 8,706 people who were enrolled in the HUNT Study, a large, ongoing population-based health survey from the former Nord-Trøndelag County in Norway.

The researchers looked at marital status in people over a period of 24 years — from the age of 44 until 68 — to see if there was a relationship to a clinical diagnosis of dementia or mild cognitive impairment (MCI) after the age of 70.

Dementia is considered a serious impairment to memory, language, and thinking that disrupts day-to-day functioning, whereas MCI is milder, and symptoms may not impact daily living. People with MCI may eventually develop dementia, but in some cases do not, according to the Alzheimer’s Association.

Participants were placed into one of six groups:

• Unmarried
• Continuously married
• Continuously divorced (divorced throughout the study period)
• Intermittently divorced (divorced and remarried during the study period)
• Intermittently married (married and divorced more than once)
• Widowed

Researchers accounted for age, sex, and education level, and looked at how factors such as health conditions, number of children, mental distress, and having no close friends influenced the likelihood of developing dementia and MCI.

At the end of the 24-year study period, 11.6 percent of participants were diagnosed with dementia, and 35.3 percent were diagnosed with MCI.

Key findings included:

• The prevalence of dementia was higher among the unmarried (14.1 percent) than the continuously married (11.2 percent).
• The risk of dementia was higher for the unmarried, continuously divorced, and intermittently divorced. The widowed and intermittently married groups had the same risk for dementia and MCI as the continuously married.
• In general, marital history was less associated with MCI than with dementia. The risk of MCI was only higher among the unmarried relative to the continuously married.

Social Isolation Might Raise Dementia Risk

“Exactly what causes dementia is a mystery. This survey indicates that being married and a lower risk of dementia are linked, but we don't know why,” said coauthor Asta Håberg, MD, PhD, a doctor at St. Olav's Hospital and a professor at the Norwegian University of Science and Technology in Trondheim, in the press release.

Social isolation may be one possible explanation. Social isolation is a lack of human connections or support. Social isolation can lead to loneliness in some people, while others can feel lonely without being socially isolated.

Research suggests that social isolation significantly increases a person’s risk of premature death from all causes and is associated with about a 50 percent increased risk of dementia, according to the Centers for Disease Control and Prevention (CDC).

Another theory has been that people who are married live healthier lives, and that this explains differences in the risk of various diseases, said Dr. Håberg. To check out that theory, investigators looked at the incidence of dementia relative to health factors such as smoking, high blood pressure, obesity, physical inactivity, diabetes, psychological problems, and having close friends.

“We thought that these factors would mean something, but they didn’t explain anything,” said Håberg. “In this survey, we found no support for health differences between married and unmarried people that would explain the difference in dementia risk.”

Good Marriages May Help Our Brain — Bad Ones, Not So Much

These findings support previous research, including a study published in 2019 in The Journals of Gerontology, which found that people who are divorced are twice as likely as married people to experience the cognitive dysfunction associated with dementia, with divorced men having the highest risk.

But other research suggests that an unhappy marriage may have the opposite effect. A study published in August 2021 in Social Science & Medicine found that marital quality was significantly associated with men’s cognitive health but not women’s. Among men, an increase in positive marital quality was associated with a slower rate of cognitive decline, whereas an increase in negative marital quality was associated with a faster rate of cognitive decline.

The authors concluded that older men who are in a bad relationship may be vulnerable to cognitive decline and that improving their marriage may protect their cognitive health in later life.

For Single Parents, Having Children Lowered Dementia Risk

The Norwegian researchers also found that having children reduced the risk of dementia by 60 percent among the unmarried group in the study.

“Some people have theorized that if you have children, you stay more cognitively engaged. For example, you have to deal with people and participate in activities that you wouldn’t otherwise have to. This stimulates your brain so that it possibly works better. That way you build up a kind of cognitive reserve,” said Håberg.

What Is Cognitive Reserve and How Can It Help Protect the Brain?

Cognitive reserve is the brain’s ability to be agile, solve problems, take on challenges, and resist injury due to trauma, stroke, or aging.

The concept first came about in the 1980s, when researchers examined people’s brains after they died, according to Harvard Health Publishing. Some individuals had evidence of brain changes consistent with Alzheimer’s disease, yet these people had shown no signs of memory loss or other symptoms of dementia while they were alive.

The scientists believed that those people were able to stay mentally sharp due to cognitive reserve — in other words, they were able to compensate for the damage and continue to function normally.

How a person develops or improves “brain resilience” isn’t totally clear. It seems to be a combination of the brain we were born with and how we do or don’t use it, according to Bright Focus, an Alzheimer’s disease research and advocacy organization.

Trauma and poor nutrition may lower cognitive reserve, while factors like good relationships, education, sleep, exercise, and staying curious may help build it.

Håberg hopes that the findings from her study might lead to a better understanding of the mystery of cognitive reserve. “We don’t know whether it’s being married or having children that protects against dementia, or if it’s a case of preselection, for example. This would mean that people who have a lower probability of developing dementia also have a higher probability of finding a partner and having children,” she said.