The strength of someone's grip may reveal how fast they're aging, their education level - and even their future health, researchers say.
The International Institute for Applied Systems Analysis researchers reviewed more than 50 published studies from around the world for their article in the journal PLOS ONE.
They found that people with more education at age 69 tended to grip just as strongly as less educated people at age 65, suggesting the latter were aging about four years faster.
"According to hand grip strength, people with high education... feel several years younger compared to people with lower education," study author Sergei Scherbov said.
Another study the authors reviewed was done on more than a million Swedish adolescent males, whose handgrip strength was measured as part of an exam for military service.
Those with lower handgrip strength were significantly more likely to die earlier, have heart disease, be at higher risk of suicide and experience psychological problems.
Differences in health that correlated with handgrip strength could be seen across many of the studies, the researchers said.
"Low handgrip strength has been shown definitively to predict poor outcomes in a wide variety of mortality, morbidity, and other health outcomes," said the PLOS ONE study.
However, any educational and racial differences that could be parsed by handgrip tended to disappear as people reached their 90s.
The study was funded by the European Research Council as part of a grant to define new measures of aging based on people's characteristics, such as their longevity, health, disability status and other demographic factors.