Depression is associated with a molecular-level disturbance in the body's 24-hour clock, new research has suggested.
Scientists examined genes that regulate circadian rhythm in people with and without a history of depression. As a group, those with a history of depression had a higher level of activity of the so-called Clock gene, which has a role in regulating circadian rhythm, than did people with no mood disorders.
"If we look at people who have depression, they can have very different groups of symptoms. So if some of them have a biological profile that shows circadian dysfunction, there is a chance that a circadian type of treatment might be more helpful for them than for others," said Jean-Philippe Gouin, a graduate student in psychology at Ohio State University.
The researchers collected blood samples from, and conducted interviews with, 60 people: 25 who were providing at least five hours of care per week for a family member with dementia and 35 non-caregiving controls with similar demographic characteristics. Thirty participants had a lifetime history of depression, while the other 30 had never been clinically depressed.
All blood samples were drawn between 9 a.m. and 11 a.m. to control for variations in circadian clock gene activity that occur throughout the day.
As a group, the participants with a history of depression had a significantly higher level of Clock mRNA expression than did participants who had never been depressed. The researchers didn't find statistically significant results for the other three genes.
Gouin said that to further define the relationship between this genetic profile and depression, researchers ideally would monitor research participants over time to measure the changes in mRNA expression in circadian genes through a 24-hour cycle.
The research has been published in the Journal of Affective Disorders.