Does everyone age at the same rate, or do people truly age at different speeds?

At the molecular level, the rate of ageing is surprisingly uniform. In stem cells of the small intestine, large intestine and liver, roughly 40 new DNA mutations accumulate each year, and that rate barely differs between people¹. What does differ is the pattern across tissues: liver stem cells show a different profile from intestinal stem cells, which can influence the risk of tissue-specific diseases such as cancer.

Once you look at health and life expectancy, the differences become enormous. Globally, the burden of biological ageing varies by more than thirty years². An average 65-year-old in Japan carries the same disease burden as a 76-year-old world citizen. Someone in Papua New Guinea already reaches a comparable burden at age 45. Where you are born and where you live therefore makes a dramatic difference.

Income explains a large part of that gap. In the United States, the wealthiest men live on average 14.6 years longer than the poorest men; for women that difference is 10.1 years³. Between 2001 and 2014 this gap widened further: life expectancy among higher earners rose by more than two years, while that of lower earners barely increased. Among people with lower incomes, regional differences were more strongly associated with smoking than with access to healthcare.

Genetics also plays a role in how quickly certain organs age. Rare variants in genes that regulate DNA repair can substantially accelerate or slow the rate at which the ovaries age⁴. A damaging variant in such a gene leads, on average, to a menopause that arrives 5.6 years earlier. Such a genetic advantage can sometimes have a downside: a variant that extends the fertile window simultaneously raises the risk of cancer.

Cognitive ageing follows a similar pattern. In people aged 45 to 64, a lower income is associated with faster cognitive decline, partly through the neighbourhood in which a person lives⁵. Notably, it is not only chronically high blood pressure but specifically large fluctuations in blood pressure over the years that turn out to be an independent risk factor⁶. Every ten percent increase in those fluctuations is accompanied by a measurably faster decline in cognitive scores.