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.
"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.
"These findings suggest siblings of those with low IQs tend to live closer to their families," said Taylor, who is now an assistant professor of pediatrics at Vanderbilt University. "But we found, in the end, their physical proximity is often offset by a lower level of emotional attachment."
The researchers also found those who had a brother with a mental illness had lower levels of psychological well-being than those in the comparison group. They did not see this effect when looking at those who had a sister with a mental illness. This suggests 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," said Taylor. "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."
The data for this study were obtained from the Wisconsin Longitudinal Study. The study includes approximately 10,000 people who were first surveyed after they graduated from high schools in Wisconsin in the mid-1950s. These men and women were periodically surveyed throughout their lifetime. The participants were surveyed most recently in 2005 when they were in their mid-60s.
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