London (CNN) Rich people live healthy, disability-free lives an average of nine years longer than less wealthy people, according to a major study that lays bare the troubling economic inequalities behind lifespans in the US and UK.

Researchers analyzed data on more than 25,000 adults over 50, looking for factors that could predict how long they lived before they started suffering from age-related disabilities, like being unable to get out of bed or cook for themselves.

The biggest socioeconomic factor in predicting when those problems began was wealth, the team discovered, with richer people enjoying almost an extra decade before experiencing difficulties.

From the age of 50, the wealthiest men analyzed could expect another 31 healthy years of life -- compared with the least well-off, who could only expect another 22 to 23 healthy years.

For women, the wealthiest were projected to enjoy 33 more years of good health, compared with 24 for the poorest.