Older adults who volunteer are getting more out of it than just an altruistic feeling -- they are receiving a health boost, according to a recent study.

Researchers from the Rotman Research Institute at Baycrest Health Sciences found that health benefits appear to peak at 100 volunteer hours annually, or 2 to 3 hours per week, for older adults.

"We discovered a number of trends ... that paint a compelling picture of volunteering as an important lifestyle component for maintaining health and wellbeing in later years," Nicole Anderson, lead investigator of the study, said in a statement.

For the study, researcher examined 73 studies published over the last 45 years involving adults aged 50-plus who were in formal volunteering roles.

They found that Volunteering is associated with reductions in symptoms of depression, better overall health, fewer functional limitations, and greater longevity. They also found that more vulnerable seniors (i.e. those with chronic health conditions) may benefit the most from volunteering.

"Taken together, these results suggest that volunteering is associated with health improvements and increased physical activity - changes that one would expect to offer protection against a variety of health conditions," Anderson said.

One troubling finding for the research team was that "very few studies" have examined the benefits of volunteering on cognitive functioning in older adults. The report noted that "not a single study" has examined the association between volunteering and risk of dementia, or the association between volunteering and a host of other health conditions that put seniors at higher risk for dementia, such as diabetes and stroke.

With dementia prevalence projected to double over 20 years, from over 30 million people worldwide today to more than 65 million people in 2030 (Alzheimer's Disease International and World Health Organization, 2012), Dr. Anderson called it a "startling omission" that the field of neuroscience research has yet to investigate the capacity of volunteering to mitigate dementia risk or delay onset.

"We encourage investigators to include more objective measures of cognitive functioning in future studies. Particularly interesting would be the inclusion of a more comprehensive battery of neuropsychological tests, so that the association of volunteering with the risks of various forms of dementia and its precursor, mild cognitive impairment, could be ascertained," the report concluded.

The findings were recently published in the journal Psychological Bulletin.