Is it true that like attracts like? When it comes to mental health, it seems the answer is yes.

A study published in JAMA Psychiatry this week sheds light on the influence of psychiatric disorders on relationships and mating.

The study from the famous Karolinska Insitute in Sweden examined over 700,000 men and women with psychiatric diagnoses and compared them to over three million people without psychiatric diagnoses.

They measured marital resemblance for psychiatric disorders. Marital resemblance is the degree to which we marry people who resemble us in some characteristic or another.

For instance, marital resemblance is positively correlated for personality, height and weight – so we have a positive tendency to marry people who are similar to us on these characteristics.

Debate has raged for years around the influence of psychiatric disorders on relationships, and the genetic risks for offspring, but no one has ever collected data on such a large number of people.

Partnering up

The Swedish study had a number of key findings. First up, people with a psychiatric diagnosis were less likely to be married. When they did marry, the chance of them marrying someone else with a psychiatric diagnosis was two to three times higher than for people without a psychiatric diagnosis.

There was also a correlation between specific diagnoses. People with disorders that developed at a young age, like autism spectrum disorder and attention deficit hyperactivity disorder, had a tendency to marry people with the same diagnosis. As did people with disorders that had particularly severe symptoms, such as schizophrenia.

People with depression and generalised anxiety disorder were also more likely to partner with people with psychiatric disorders, but the correlation between diagnoses for these was lower.

The results held for men and women. Similar correlations weren’t found for people with non-psychiatric medical disorders, such as Crohn’s disease, diabetes (types 1 and 2) and rheumatoid arthritis. People with these disorders showed little or no increase in the chances of being married to someone else with a medical disorder of the same, or any sort.

As with most good science, the study raises more questions than it answers.

Laws of attraction

The laws of attraction are complex.

Evolutionary theory says we mate with those who give us the highest chances of surviving and reproducing. Social theories tell us we tend to marry people we are exposed to and familiar with. Most people marry someone who lives in close proximity to them. Most are introduced through friends or shared experiences. Work, school or university are the commonest places people meet their spouses. We mate who we meet.

We also have a strong tendency to marry people who are similar to us – marital resemblance holds to some degree for religious beliefs, politics and other characteristics.

Physical attraction is complex and affects us consciously and unconsciously in many ways. In terms of influencing relationship choices, as the saying goes beauty is in the eye of the beholder, but it’s also a bit like the market economy. We marry those who we can “afford”, not necessary the most “expensive”.

In terms of helping us understand the laws of attraction, this study probably doesn’t add much.

What this tells us

It might be that the correlations are simply due to mixing in similar circles. So people with a psychiatric diagnosis are far more likely to meet others in the same boat, either in hospital, via support groups or online communities.

It might be related to reduced stigma; perhaps people with mental illness are more accepting of others with mental illness. They understand the problems and so might be less judgemental.

There might also be an element of contagion; where one partner influences the other. If one spouse drinks alcohol excessively, this might have an impact on their partner’s drinking, or their partner’s mental health in other domains.

The possible explanations are endless, and as the authors point out, the limitations of a study such as this are significant.

If anything, this study highlights the complexity of mental illness. Psychiatric disorders result from a mix of our biology, our past experiences and our current circumstances. They are not simply the result of pathology.

They affect most aspects of our lives including our personality, how we live, whom we meet, how we work, how we respond to others…and who we marry.

High quality studies such as this give us a tiny glimpse into our lives, but rather than answering some of the great existential questions, they mostly just add to the list of things we want to understand.