At the molecular level of stem cell mutations, people age at a surprisingly uniform rate, but at every other measurable level the differences are enormous: life expectancy, cognitive decline and organ ageing are strongly determined by income, lifestyle, genetics and place of residence. The evidence comes from several large associative studies in humans, but not from randomised research. From a practical standpoint, lifestyle factors such as quitting smoking and stabilising blood pressure are the most identifiable and modifiable levers.
No, not everyone ages at the same rate. At the molecular level, in stem cells of the small intestine, large intestine and liver, roughly 40 new DNA mutations accumulate each year. That rate is surprisingly consistent from person to person. At this basic level, biological ageing is therefore a fairly universal, steady process. The types of mutations do differ by tissue, however: liver stem cells show a different pattern than intestinal stem cells, which can influence the risk of tissue-specific diseases such as cancer.
At the level of overall health and life expectancy, the differences are enormous. Globally, the biological 'ageing burden' spans more than thirty years: an average 65-year-old in Japan carries the same health burden as a 76-year-old world citizen, while someone in Papua New Guinea reaches a comparable burden as early as age 45. Where you are born and where you live therefore makes a dramatic difference to how quickly you age biologically.
Income and socioeconomic position play a major role. In the United States, the wealthiest men live on average 14.6 years longer than the poorest men; for women this gap is 10.1 years. Between 2001 and 2014 this gap actually widened: life expectancy for higher incomes rose by more than two years, while that of lower incomes barely increased. Geographic differences in life expectancy among people with low incomes were strongly associated with smoking behaviour, more so than with access to healthcare. Lifestyle is therefore an important explanation for regional inequality in ageing.
Genetics also partly determines how quickly certain organs age. Rare variants in genes such as ZNF518A and SAMHD1 can substantially accelerate or delay the rate at which the ovaries age: a damaging variant in ZNF518A leads on average to a menopause that occurs 5.6 years earlier. Genetic advantages sometimes come with disadvantages elsewhere: a variant that extends the fertile period simultaneously raises the risk of cancer.
Cognitive ageing follows a similarly unequal pattern. In middle-aged people (45 to 64 years), lower income is associated with faster cognitive decline, partly through the influence of the neighbourhood in which a person lives. It also turns out that not only chronically high blood pressure, but particularly large fluctuations in blood pressure over the years accelerate cognitive decline. Every ten percent increase in blood pressure variability is accompanied by a measurably faster decline in cognitive scores.
Based on several large associative studies: a global burden of disease study (PMID 30851869), a large American income and life expectancy study (PMID 27063997), a stem cell mutation accumulation study in humans (PMID 27698416), a genomic study on menopause variability (PMID 39261734), and two cohort studies on cognition in middle-aged and older adults (PMID 39177423, 34167328). None of the studies is a randomised trial; the associations are observational.