It is commonly believed that stress accelerates ageing. Scientists have new evidence that this is indeed so.
A team from the University of California at San Francisco has found that the stress of caring for a sick child can add about 10 or more years to the biological age of a woman's cells. It does this by affecting key pieces of DNA called telomeres which are involved in regulating cell division, they say.
Telomeres are strips of DNA at the end of chromosomes which appear to protect and stabilise the chromosome ends. However, they shorten each time a cell divides, until there is nothing left, making the cell more defect-prone after division and increasing the risk of age-related disorders. The tendency for telomeres to shorten at cell division can be mitigated by an enzyme called telomerase, which helps to regenerate the ends.
The study examined 58 women, which included 39 healthy, pre-menopausal women who were primary caregivers for a child with a chronic illness, and 19 age-matched mothers of healthy children who served as a control group.
All the women completed questionnaires asking them to evaluate the level of stress they felt they had been under during the previous month. Blood samples were also taken so scientists could carry out DNA analysis of telomeres. Levels of telomerase in immune cells were also measured.
There was no difference in the telomere length of the two groups. However, in the 14 women with the highest stress scores, telomeres averaged 3,110 units in length; the 14 with the lowest stress had telomeres that averaged 3,660 units. The scientists translate this shortening to 9 to 17 additional years of ageing.
Within the care-giving group, the longer that a woman had been a care-giver, the shorter was the length of telomeres.
The higher-stress group was also found to have lower levels of telomerase in immune cells. The researchers, led by Dr Elissa S. Epel, said this implied the immune cells could function less well and could die sooner.
It was also found that the high-stress women also had higher oxidative stress levels -- cumulative damage caused by molecules called "free radicals" -- which has been shown to speed up the shortening of telomeres in other studies.
The researchers were not able to say exactly how stress affects telomeres, but suggested that their findings showed how cellular aging could be a way in which psychological stress was linked to the earlier onset of age-related diseases.
This study has been published in the Proceedings of the National Academy of Sciences. It represents an important step towards the recognition among health experts that psychological health plays an important part in physical health.