People who have a sibling with a mental illness are more likely to suffer episodes of depression at some point in their lives, say researchers who analyzed four decades of data.
Additionally, they found people with a sibling with low IQ are more likely to live near that brother or sister – but be somewhat emotionally detached from that sibling.
The findings were reported in the December issue of the Journal of Family Psychology, published by the American Psychological Association.
"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," said the study's lead author, Julie Lounds Taylor, PhD. "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."
University of Wisconsin–Madison researchers identified 351 people from a 46-year longitudinal study who had at least one sibling with a mental disability. These disabled siblings were divided into two categories: those with a low IQ and those who had been diagnosed with a mental illness, specifically a depressive or anxiety disorder. In all, 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.
The researchers found 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, reporting an average of 13 fewer contacts a year with their disabled sibling than the comparison group. In addition, they reported feeling less emotionally close to their siblings.