Adults who have good relationships with their grandparents have fewer symptoms of depression, a new study indicates.

And such relationships also benefit the psychological wellbeing of the grandparents.

US researchers analysed data on 376 grandparents and 340 grandchildren who had been taking part in a long-term study between 1985 and 2004. Midway through this period, the average age of the grandparents was 77, while the average age of the grandchildren was 31.

The study found that a close relationship between grandparents and their adult grandchildren appeared to benefit both psychologically.

"We found that an emotionally close grandparent adult-grandchild relationship was associated with fewer symptoms of depression for both generations. The greater emotional support grandparents and adult grandchildren received from one another, the better their psychological health," the researchers from Boston College said.

The study also found that grandparents who were not able to offer support to their grandchildren had poorer psychological health.

"Grandparents who experienced the sharpest increases in depressive symptoms over time received tangible support, but did not give it. There's a saying, 'it's better to give than to receive.' Our results support that folk wisdom - if a grandparent gets help, but can't give it, he or she feels badly.

"Grandparents expect to be able to help their grandchildren, even when their grandchildren are grown, and it's frustrating and depressing for them to instead be dependent on their grandchildren," the researchers explained.

Tangible support includes things such as bringing people to the shops, assisting them with household chores and offering advice.

The researchers said that attempts to strengthen families should not just focus on the immediate family or families with only small children.

"Extended family members, such as grandparents and grandchildren, serve important functions in one another's daily lives throughout adulthood," they said.

Details of these findings were presented at the annual meeting of the American Sociological Association in New York.