Opposites may attract in fiction — but in real-life matters of mental health, it seems couples are more often cut from the same cloth.
A sweeping study of nearly 15 million people across Europe and Asia has shown that individuals with psychiatric disorders are far more likely to marry someone with a similar condition than to have a spouse without one.
The trend appears to have been remarkably consistent across generations and cultures — suggesting, potentially, that it is a stable feature of human relationships rather than a quirk of any single society.
The pattern may well have important consequences for the next generation
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The research, published in the journal Nature Human Behaviour, looked at conditions including schizophrenia, bipolar disorder, depression and anxiety and anorexia nervosa.
Drawing on data from more than 14.8 million individuals in Taiwan, Denmark and Sweden, it is one of the largest studies of its kind.
The findings were strikingly consistent. Across nearly all of the disorders, people with psychiatric conditions were significantly more likely than chance to marry someone who also had a psychiatric condition. Spouses were also more likely to share the same disorder than to have different ones.
This pattern looks to have had important consequences for the next generation: children with two parents affected by the same disorder were more than twice as likely to develop the condition as those with only one affected parent. This effect was especially pronounced for schizophrenia, depression, bipolar disorder and substance use disorders — conditions where genetics are thought to play a role.
Researchers said stigma around mental illness could reduce a person’s pool of potential partners
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Previous studies had hinted at this pattern in Nordic countries. The new analysis extends the observation across cultures, from east Asia to northern Europe, and across time, covering people born from the 1930s through the 1990s.
“The main result is that the pattern holds across countries, across cultures, and, of course, generations,” Chun Chieh Fan of the Laureate Institute for Brain Research in Tulsa, Oklahoma, who led the research, told the science journal Nature.
The study was observational, which means it could not definitively explain why people with psychiatric disorders often paired up. However, the researchers have suggested three plausible explanations.
People may be drawn to others who resemble themselves, perhaps because shared experience fosters understanding and empathy. Spouses may also grow more similar over time through shared environments, a process called convergence. Finally, lingering social stigma around psychiatric illness may narrow the pool of potential partners, subtly shaping marriage choices.
Couples might also grow more similar over time
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Even with large social changes in Taiwan, such as the beginning of universal healthcare in 1995, the patterns of spousal similarity remained consistent, and closely matched the Nordic data. This suggests that the phenomenon is not driven mainly by culture or a factor such as healthcare access.
Both genetics and environmental factors are thought to play a part in causing people to develop psychiatric disorders.
In the UK, the prevalence of psychiatric disorders varies, but they may be more common than many would guess. About 3 per cent of adults experience depression in any given week, while bipolar disorder affects about 2 per cent, or one in 50 people, over their lifetime.
The research found the same conclusions were true for obsessive compulsive disorder (OCD), attention-deficit hyperactivity disorder (ADHD) and autism.
ADHD is estimated to affect about 5 per cent of children, though only about a third have received a formal diagnosis. Obsessive-compulsive disorder (OCD) is thought to affect roughly 1 per cent of the population.