Siblings of people with mental illness are more likely to suffer episodes of depression at some point in their lives, according to researchers.
After analysing four decades of data, the researchers also found that people with a sibling with low IQ are more likely to live near that brother or sister, but had a tendency to be somewhat emotionally detached from that sibling.
"So little is known about the impact that a person with low IQ or mental illness has on the psychological and social development of his or her siblings, especially beyond childhood. Our findings highlight the need for families of the mentally ill, specifically siblings, to be more aware of their own mental health needs throughout their lifetimes," said the study's lead author, Julie Lounds Taylor, PhD.
In their study, the researchers at University of Wisconsin-Madison identified 351 people from a 46-year longitudinal study who had at least one sibling with a mental disability. They then divided the disabled siblings into two categories: those with a low IQ and those who had been diagnosed with a mental illness, specifically a depressive or anxiety disorder.
Overall, there were 268 who had siblings with low IQs - defined as 85 or below - and 83 who had siblings with mental illnesses. The researchers also looked at results from a comparison group of 791 people who did not have a mentally disabled sibling.
It was found that people who had siblings with mental illnesses were 63 percent more likely to report having a depressive episode during their lifetime.
A depressive episode was described as lasting for at least two weeks and could include a variety of symptoms such as feeling lonely, crying and losing appetite.
They also found the brothers and sisters of the people with low IQs were 18 percent more likely to live in the same state as the disabled brother or sister than those in the comparison group. However, they were significantly less likely to have contact with the disabled sibling. Also, they reported feeling less emotionally close to their siblings.
"These findings suggest siblings of those with low IQs tend to live closer to their families. But we found, in the end, their physical proximity is often offset by a lower level of emotional attachment," said Taylor.
Also, it was found that those having a brother with a mental illness had lower levels of psychological well being than those in the comparison group, but the same didn't hold true for those who had a sister with a mental illness.
The result above indicated that genetics may not be the only link to poor mental health among siblings of the mentally ill, but the social relationship is also important.
"Our study suggests environmental and social factors also play a role in why these siblings may be at a greater risk for poor mental health. The good news is we found having a mentally disabled sibling did not seem to have an effect on whether the person got married or had children," said Taylor.
The findings were reported in the latest issue of the Journal of Family Psychology, published by the American Psychological Association.