Spouses of people with dementia face higher risk of developing the condition, study finds

Spouses of people with dementia face a significantly higher risk of developing the condition themselves, according to a large study published in JAMA Network Open, with the level of risk varying according to household income and family size.

The study, titled "Spousal Dementia Exposure and Risk of Dementia", followed almost one million married people in Taiwan from 1998 to 2022. It was led by Wang Shi-heng (王世亨), an associate researcher at the National Health Research Institutes' National Center for Geriatrics and Welfare Research, with Wu Chi-shin (吳其炘), a senior attending physician and researcher at the institutes, as corresponding author.

The researchers used Taiwan's National Health Insurance Research Database, which covers close to 99 per cent of the population, to analyse data from 955,000 married individuals and identify dementia diagnoses among them.

They compared spouses of people who developed dementia against a matched group of unaffected couples, accounting for age, income, place of residence and pre-existing health conditions.

The study found female spouses had a 74 per cent higher risk of developing all-cause dementia if their partner had the condition, while male spouses faced a 69 per cent higher risk.

Similar patterns emerged when researchers examined Alzheimer's disease and vascular dementia separately, according to the study.

Absolute risk increase modest but significant

Among spouses whose partners did not have dementia, about six in every 100 men and three in every 100 women were diagnosed with dementia over a five-year period, the data showed.

However, those figures rose to nine in 100 men and six in 100 women over the same period if their spouse had developed dementia, the researchers said. This corresponds to an increase of roughly 2.75 percentage points for women and 3.49 percentage points for men, once other risk factors were taken into account.

Relative risks were more prevalent among younger spouses, while the absolute increase in dementia cases was greater among older spouses, the researchers said.

Wu said the study addressed limitations in earlier, smaller research that had assumed every spouse was a primary caregiver.

"Many were based on relatively small or regional samples. Our study included spouses in general and did not assume that every spouse was the primary caregiver," Wu said, according to a statement carried by the Australian Broadcasting Corporation (ABC).

Wu said this approach allowed researchers to examine dementia risk at the household level, rather than attributing the association solely to the burden of caregiving.

Three possible explanations

The researchers pointed to several overlapping factors that may explain the association: assortative mating, in which people tend to select a spouse with a similar educational background, socioeconomic status and health behaviours, alongside shared environmental and lifestyle exposures accumulated over their lives.

The link might also be due to caregiver distress, depression, sleep disturbance, social isolation, metabolic dysregulation, inflammation and adverse health behaviours arising from living with a spouse with cognitive decline, they said.

Emerging evidence also suggests couples may share similar oral health outcomes, which some research links to cognitive decline, the study noted.

Simone Reppermund, an expert in cognitive disorders at the Centre for Healthy Brain Ageing at the University of New South Wales (UNSW), who was not involved in the research, said the study strengthened the evidence base.

"The researchers controlled for a lot of factors that are important to control for, which is a real strength of this study, and still the risk of dementia was a lot higher," Reppermund said, according to the ABC.

Income and family size linked to lower risk

Lower-income households and those with fewer children showed larger absolute risk differences, the researchers said.

Wu suggested this may be because lower-income households have fewer resources to pay for support, increasing caregiving stress on the spouse, while people with fewer children may have less family support available.

"Because we did not directly measure caregiving responsibilities, intensity or stress, this interpretation remains suggestive rather than conclusive," he said.

Reppermund said income may also serve as a proxy for education levels, noting higher education is a recognised protective factor against dementia. She cautioned against assuming more children automatically lowers risk.

"The present study showed that number of children played a modifying role, but it depends on the quality of the relationship. The children might be overseas, or there might be no relationship whatsoever," she said.

Not a cause, but a high-risk group

Wang said the study does not suggest that caring for a spouse with dementia causes dementia, but rather that people in that situation belong to a statistically high-risk group requiring more attention.

Wu echoed this, saying the link likely reflects shared lifestyle factors, overall health status and the long-term stresses associated with dementia caregiving, rather than a direct causal effect.

The study's authors also acknowledged several limitations, including an inability to measure spouses' lifestyle factors such as diet, exercise, smoking, social isolation or hearing loss, all of which are established dementia risk factors.

The World Health Organization (WHO) has identified 17 modifiable risk factors, which it says account for 45 per cent of dementia cases worldwide, including hearing loss, air pollution, obesity and poor sleep.

Wu said spouses should be aware of the elevated risk but not alarmed by it, and should prioritise their own sleep, mood, social connections and management of cardiovascular conditions such as hypertension and diabetes, while accessing respite care where possible.

Policy response

The researchers said that once a person is diagnosed with dementia, healthcare support should extend to their spouse, including assessments of cognitive function, depression and sleep quality, alongside chronic disease management.

Priority should be given to low-income families, households with fewer children and families lacking alternative caregivers, they added.