Feeling lonely? Blame it on your genes, say scientists who have found that loneliness - a trait linked to poor health and early death - is partially heritable.
Loneliness is linked to poor physical and mental health, and is an even more accurate predictor of early death than obesity, researchers said.
To better understand who is at risk, researchers at University of California San Diego conducted the first genome-wide association study for loneliness - as a life-long trait, not a temporary state.
They discovered that risk for feeling lonely is partially due to genetics, but environment plays a bigger role.
The study of more than 10,000 people also found that genetic risk for loneliness is associated with neuroticism and depressive symptoms.
Evidence suggested links between heritable loneliness and schizophrenia, bipolar disorder and major depressive disorder.
"For two people with the same number of close friends and family, one might see their social structure as adequate while the other doesn't," said Abraham Palmer, professor at UC San Diego, who led the study.
"And that's what we mean by 'genetic predisposition to loneliness' - we want to know why, genetically speaking, one person is more likely than another to feel lonely, even in the same situation," he said.
The heritability of loneliness has been examined before, in twins and other studies of both children and adults.
From these, researchers estimated that 37 to 55 per cent of loneliness is determined by genetics.
Previous studies also to pinpoint genes that contribute to loneliness, focusing on genes related to neurotransmitters, such as dopamine and serotonin, or other cellular systems associated with human attachment, such as oxytocin.
However, these studies mostly relied on small sample sizes, Palmer said.
Researchers examined genetic and health information from 10,760 people aged 50 years and older that was collected by the Health and Retirement Study.
As part of this study, participants answered three questions that measure loneliness.
The study accounted for gender, age and marital status, as married people tend to be less lonely than unmarried people.
Researchers found that loneliness - the tendency to feel lonely over a lifetime, rather than just occasionally due to circumstance - is a modestly heritable trait.
It is 14 to 27 per cent genetic, as compared to the previous estimates of 37 to 55 per cent.
This new estimate of the genetic contribution to loneliness could be lower than previous estimates because the team relied on chip heritability, a method that only captures common genetic variations and not rare genetic variation. The study was published in the journal Neuropsychopharmacology.