British scientists say poor people live shorter lives, partly because greater stresses cause their cells to age more quickly.

The study, led by Dr. Tim Spector of St. Thomas’ Hospital in London, found working class women in their late 40’s are on average seven years biologically older than women of the same age in more wealthy social groups, The London Telegraph reported.

The researchers note having a partner in a higher social class might add years to an individual’s life span.

Spector said the study shows social class can have an effect not just on when you die, but on how fast your body is aging.

The research appears in the journal Aging Cell.