A group of genes could be common to both depression and heart disease, a finding that researchers said could explain why having one of them increases risk of developing the other.
The "puzzling" link between the diseases has been known to exist since the 1990s, they said.
Studies have found that people with depression run a greater risk of cardiovascular disease, with early and effective treatment of the mental illness lowering the risk of developing heart-related conditions. Conversely, studies have also shown that people having cardiovascular disease tend to have depression as well.
The researchers, including those from the Tampere University, Finland, said that the link between the two conditions could be partly explained by lifestyle commonly observed in depression patients such as poor diet and lack of exercise.
However, they said, it is also possible that the two diseases could be related on a "deeper level" by sharing biological processes such as inflammation, which are important to developing these conditions. The findings are published in the journal Frontiers in Psychiatry.
The researchers collected blood samples from close to 900 men and women aged between 34 and 49 years, who were participants in the Young Finns study. The study, examining cardiovascular risk factors in children and adolescents as they grow into adults, started in 1980. The participants were followed-up since then.
The blood samples were analysed for gene expression, which is the process by which information in a gene eventually translates into observable traits in an individual.
The researchers identified a specific group of genes that expressed themselves in a similar manner across both the conditions -- depression and cardiovascular health. This group of genes, or gene module, was found to be associated with a high score for depressive symptoms as well as a low score for cardiovascular health.
"We looked at gene expression profile in the blood of people with depression and CVD and found 256 genes in a single gene module (group of genes) whose expression at levels higher or lower than average puts people at greater risk of both diseases," first author Binisha H. Mishra, a postdoctoral researcher at Tampere University, said.
The genes forming the module are involved in biological processes such as inflammation known to play a role in the development of both depression and cardiovascular disease, the researchers said.
This helps explain why both diseases often occur together, they said.
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