Volunteer work may be good for your mental wellbeing, but only after age 40, according to a new study.

"There is a general consensus that volunteering is beneficial to everyone regardless of the age," said lead author Dr. Faiza Tabassum of Southampton Statistical Sciences Research Institute at the University of Southampton in the UK.

"However, our study has shown volunteering may be more strongly associated with mental well-being at some points of the life-course than others," she told Reuters Health by email.

The findings could shape government policy toward engaging the elderly population in volunteering activities, which, if it improves health, would decrease dependence on the healthcare system, she said.

The researchers used survey responses from adults in 5,000 British households, including more than 66,000 responses for 1996, 1998, 2000, 2002, 2004, 2006 and 2008. Participants answered questions on mental health status and on formal volunteering.

About 20 percent of people said they had "done unpaid voluntary work," which was more common for people over age 60 and more frequent for women.

Mental health scores were better for people who had volunteered than for people who never had, and was best for those who volunteered most often - even when marital status, educational attainment, social class, and state of health were accounted for.

But when the researchers accounted for age, the positive link between volunteering and emotional wellbeing was only apparent at age 40 and older, they reported in BMJ Open.

"For middle aged and older people, volunteering has beneficial effects because of the social roles and family connections which are more likely to promote volunteering at that stage of the life-course," Tabassum said. "An example would be that many parents of school-aged children become involved in school-related activities in various voluntary capacities."

A person involved in volunteering will have more resources, a larger social network, more power, and more prestige, and this in turn may lead to better physical and mental health, Tabassum said.

"Volunteering may also provide a sense of purpose particularly for those people who have lost their earnings because volunteering regularly helps contribute to the maintenance of social networks and this is especially in case of older people who often live in isolation," she noted.

But an observational study like this one can't prove that one thing, like volunteering, causes another thing, like improved emotional wellbeing, she said.

"As a result, we were unable to examine important selection effects, such as whether poor health might have limited whether or not individuals participate in volunteering particularly at old age," she said. "Any future study should investigate this aspect."