We have recently had this question posed to us by our social media followers. I was surprised people had even heard of this! We have amazingly well-read followers. This may have initially filtered from the scientific media to more mainstream media after Thomas Insel, director at the national institute of mental health in the States wrote about the seminal study done on this back in October 2014. The study he commented on was one unusual bit of research elegantly addressing that very question. It recruited the 10 to 14 year-old healthy daughters (no diagnosis of any mental health problems) of mothers who had had multiple episodes of depression. By age 18, 60% of them had had an episode of depression - so far nothing terribly unexpected as it has been known for quite some time that if you have a first degree relative with depression you are more likely to suffer from it yourself.
In a stroke of inspiration the researchers decided to look into the chromosomes of the daughters of the women with depression and compare them with very similar girls whose mothers had never had depression. What was unexpected is the daughters of women with depression had shorter telomeres than the daughters of women who had never had depression.
Telomeres are the bits at the end of chromosomes that keep them from unravelling or sticking to other chromosomes. As a cell ages telomeres get shorter and telomere length is probably the best way to tell a cell's biological age.
The mystery was—how is it possible for the cells of 10-14 year olds to be showing signs of aging? These girls also had a more marked cortisol response when stressed than those with normal length telomeres. Cortisol is a hormone that we release when feeling stressed. This finding indicated that girls with shorter telomeres struggled to cope with stress as compared to those with normal length telomeres. The problem with this is that researchers did not know whether releasing more cortisol lead to the shorter telomeres or the other way round. This is the paper that reports the findings if you are interested.
We won't know what causes what for a while. Since 2004 researchers have observed shortened telomeres in individuals with life-long high perceived stress. Here's the first paper I read on the subject. As you can see the assumption was that it was the stress that shortened the telomeres—the new study casts doubt on that assumption. The girls were healthy when their telomeres were first measured, and they were already shorter. This makes it more likely that whatever causes the short telomeres (faster than normal cell aging) also causes the increased cortisol release. Alternatively it could be that the accelerated aging is what causes the increased cortisol release when stressed. So the answer to the question is: not necessarily—it may be that having shorter telomeres (biologically 'older' cells) makes us prone to stress and depression.
What can be done? The researchers will report back in a few years, by then we will probably know what causes what. This will hopefully enable us to find ways to both slow the accelerated aging process and prevent depression. In the meantime keeping ourselves healthy and doing the things that help keep depression at bay could help keep our cells younger. Read our recent post on tips to cope with depression for some pointers.