Study of 3 million Swedes links women’s suicide risk to female relatives’ attempts

A woman’s suicide risk may be influenced by the suicidal intention of her female first degree relatives, with sex-specific effects of a shared familial environment and possibly other social factors having a key role, finds a large population study published in the online journal BMJ Mental Health.

While genetic factors strongly influence a person’s risk of suicide, they don’t fully explain the observed sex differences in suicidal behaviors, whereby males die by suicide more often than females, but females attempt suicide around twice as often as males, say the researchers.

Worldwide, around 700,000 lives are lost to suicide every year, with notable sex differences in suicide attempts and deaths. But how much of these differences are influenced by genetic factors isn’t clear, they add.

To explore this further, the researchers drew on data from Swedish population registers, covering hospital admissions, specialist diagnoses, and cause of death for over 3 million people born between 1963 and 1998 (and their parents, full, and half siblings).

Their mental health and any suicide attempts were tracked from the age of 10 until the end of 2019, when they would have been at least 21.

At the end of this period, almost half of the birth cohort were women (49%) and the ages of the entire cohort ranged from 21 to 57, with minimal difference between the sexes.

Patterns in suicide attempts and self-harm

In all, 89,278 (3%) people had made at least one suicide attempt, over half (55%) of whom were women; and 126,411 (just over 4%) had self-harmed, half (50%) of whom were women.

More women than men attempted suicide: 3.3% vs. 2.6%. But the sex difference in the proportion of those who self-harmed was minimal at just over 4%.

Suicide attempts were more common among those with psychiatric disorders than among those without: 76% vs. 15%. Psychiatric disorders were also more common among women who attempted suicide than among men who did so.

How suicide risk clusters in families

To gauge familial clustering, the researchers focused on five types of familial relationships: mother-child; father–child; full siblings; maternal half siblings; and paternal half siblings.

In all, 3,653,013 mother–child pairs, 3,477,548 father–child pairs, 4,992,249 full sibling pairs, 908,740 maternal half sibling pairs and 1,164,125 paternal half sibling pairs were included in familial risk analyses.

In both sexes, suicide attempt risk clustered within families. It was higher among relatives of people who had attempted suicide themselves than it was among relatives of those who hadn’t. This was particularly evident in mother–child pairs where the risk was more than three times higher.

It was also higher among first degree relatives than among second degree relatives (half siblings).

The highest risk (nearly four times higher) was observed in sisters. And risks were generally higher in mother–daughter pairs and sisters than among father–son pairs and brothers.

A greater degree of clustering of suicide attempts was observed among same-sex relatives than among different-sex relatives.

Genetic heritability and shared environment

To gauge the influence of genetic factors, the researchers included 2,143,644 unique full sibling pairs and 343,075 unique maternal half sibling pairs in their analysis.

This showed that a sizable proportion (42%) of suicide attempt risk was heritable, which didn’t differ significantly between the sexes. Shared environmental factors were associated with a small but statistically significant proportion of the risk (around 4%).

There was a moderate to strong genetic risk associated with psychiatric disorders, with the strongest association observed for substance misuse.

Study limits and broader implications

This is an observational study, and as such, no firm conclusions can be drawn about cause and effect. And the researchers acknowledge that their study included relatively young people born in, and/or migrating to, Sweden in childhood, so may not be more widely applicable to other groupings.

“These findings reveal complex genetic and environmental influences on suicide attempt,” they suggest.

“Taken together, our findings do not support the hypothesis that genetic factors explain the higher incidence of suicide attempts in females. Non-genetic factors—such as hormonal, neurobiological and environmental interactions—may underlie sex-specific vulnerabilities to suicide attempt,” they add.

They conclude, “We observed stronger familial aggregation among females and same-sex first-degree relatives, even though overall heritability of suicide attempts did not differ by sex, suggesting potential sex-specific effects of shared familial environment and possibly other social factors.

“While genetic factors significantly influence suicide attempt risk, they do not fully account for observed sex differences—underscoring the need to investigate non-genetic factors and gene–environment interactions.”