Grandparents who care for their grandchildren live up to five years longer than those who don't, remarkable new research has found.
The research indicates caring for grandchildren increases life expectancy significantly more than being healthy, active and independent.
It also has more impact on life expectancy than being diagnosed with one or more chronic or severe illnesses late in life.
"It is quite striking," says Edith Cowan University's Doctor David Coall , one of the study's authors.
"To our surprise and interest we found that grandparents who looked after their grandchildren survived five years longer than those that did not."
The study, published late last year, is the first of its kind in the world to show such a link.
There is a growing body of research showing caregiving activity – where you do something for someone and expect nothing in return – has significant health benefits, Dr Coall said.
"Talking to a lot of grandparents, we find they speak most often about the happiness, satisfaction and pride that they feel about looking after their grandchildren.
"This might be one of the only situations in your whole life where you're doing something and you expect nothing in return."
Dr Coall's research team studied 516 elderly Germans who were participating in a long-term health study.
Of that group, 80 said they regularly cared for their grandchildren.
After controlling for other variables including age and health, Dr Coall's team found caregiving grandparents lived significantly longer than non-caregiving grandparents.
"This pattern suggests that there is a link not only between helping and beneficial health effects, but also between helping and mortality, and specifically between grandparental caregiving and mortality," the study concludes.
The researchers also looked at grandparents who did housework or fixed things for their adult children, and grandparents without children who supported others in their social network. Both groups had significantly increased lifespans.
The same impact is not seen for grandparents who, sometimes through tragic circumstances, become primary carers. This group suffers a significant decline in life expectancy, Dr Coall said.
What causes the dramatic results? There are two competing theories.
First, grandparents who are thinking about or focussed on caring for their grandchildren are much more likely to also be thinking about caring for themselves – eating well, getting plenty of exercise.
The second theory puts the results down to the power of emotion.
"There is quite a bit of research now that suggests this helping behaviour and the feelings of happiness can act as a stress buffer," Dr Coall said.
"People who are helping other people, but don't expect any return, this is the help that you get the most health benefits from."
The study was published late last year in the peer-reviewed Journal of Evolution and Human Behaviour.