Can couples really share dementia risk? Here's what a new study found

Most couples start finishing each other's sentences at some point. They begin ordering the same food, watching the same shows and settling into routines that become second nature. Over the years, they often end up sharing more than just a home.

Research has long shown that partners can develop similar health conditions, including obesity, diabetes and heart disease. Now, a large study from Taiwan suggests dementia may also be something that appears more often within couples. That doesn't mean dementia is contagious. Instead, it highlights just how much our shared lives can shape our health.

What the study found

Researchers analysed health records from nearly one million married adults enrolled in Taiwan's national health insurance programme between 1998 and 2022.

They focused on more than 190,000 people whose husband or wife had recently been diagnosed with dementia. Their health outcomes were compared with over 760,000 people whose spouses had not developed the condition.

To make the comparison fair, participants were matched according to age, sex, income and where they lived. The researchers also considered factors such as existing medical conditions, healthcare use and family size before tracking who later developed dementia.

Even after taking these differences into account, one clear pattern remained.

People were more likely to be diagnosed with dementia if their spouse had already received the diagnosis.

What do the numbers actually mean?

The study found that women whose partner developed dementia had a 74 percent higher relative risk of receiving the same diagnosis. For men, the increase was 69 per cent.

Those figures sound dramatic, but they don't tell the whole story.

Looking at the actual number of people affected gives a clearer picture.

Over five years, about 6.5 percent of women whose spouse had dementia were diagnosed themselves. Among women whose partner did not have dementia, the figure was 3.7 percent.

For men, 9.2 percent developed dementia if their spouse had the condition, compared with 5.8 percent if their partner did not.

Put another way, a spouse's diagnosis was linked to roughly three extra dementia cases for every 100 people over a five-year period.

No, dementia doesn't spread between couples

It's important not to misunderstand these findings. The study does not suggest dementia passes from one person to another. Instead, researchers believe couples often have similar risk factors long before dementia becomes part of the picture.

People frequently choose partners with backgrounds and lifestyles similar to their own. They may have comparable levels of education, income, eating habits and overall health. Researchers call this assortative mating, where people tend to partner with those who share similar characteristics.

Then comes the shared life itself.

Years of living together usually mean eating similar meals, breathing the same air, spending time in the same neighbourhoods and following similar daily routines. These experiences can influence brain health over decades.

Caring changes lives too

Another possible piece of the puzzle is caregiving.

Looking after a partner with dementia can be emotionally and physically demanding. Many carers experience ongoing stress, interrupted sleep and social isolation. Exercise may become less frequent, meals can become less balanced and personal health often takes a back seat.

All of these changes have been linked to poorer cognitive health in previous research.

Scientists are also exploring whether factors such as oral health and the gut microbiome play a role in brain ageing. While these areas are attracting growing interest, they were not directly examined in this Taiwanese study and require more research.

Healthy habits still matter

While researchers continue to understand exactly why dementia risk appears to cluster within couples, one message remains unchanged.

Looking after your overall health is still one of the best ways to support your brain as you age.

The World Health Organisation recommends several lifestyle habits that may help reduce the risk of cognitive decline, including:

• Staying physically active
• Eating a balanced, healthy diet
• Keeping blood pressure under control
• Not smoking
• Using hearing aids if hearing loss is present
• Continuing to learn and stay mentally engaged throughout life

These habits benefit far more than just the brain. They support heart health, mobility and overall wellbeing too.

It's not just about personal choices

At the same time, experts say it's important not to place the entire responsibility on individuals.

Healthy living is influenced by much more than willpower. Where people live, how much they earn, their access to healthcare, education, housing and safe places to exercise all shape the choices available to them.

In other words, brain health isn't built in isolation. It grows out of the environments we live in and the opportunities we have throughout life.

One of the most interesting takeaways from this study is not that couples develop dementia together, but that our lives become deeply connected over time.

Partners share routines, responsibilities, meals, worries and milestones for decades. It's perhaps no surprise that their health journeys can begin to look similar too.