Does the country you live in affect your biological age?

Yes, it makes a considerable difference. A study of nearly 162,000 people from 40 countries found that people in Europe age most favourably on average: their biological age lags least behind their calendar age. The gap was largest in Egypt and South Africa, where the body aged biologically at a significantly faster rate than the calendar would suggest. Asian and Latin American countries fell in between. There were also differences within Europe: eastern and southern Europe scored worse than the rest.

Which factors explain this? Lower income was the strongest predictor of accelerated biological ageing: people with less money aged faster, and this held true at both the individual and regional level. The association was medium to large in magnitude. Poor air quality and sociopolitical circumstances, such as high inequality, limited political freedoms and gender inequality, were also associated with faster ageing.

The consequences are concrete. People who age biologically faster had, at follow-up measurements, a greater likelihood of cognitive decline and loss of daily functioning. The functional difference was the largest: the association had a medium to large effect size.

An important caveat: the study is observational. This means that country or income have not been proven to cause ageing, but they are strongly associated with it. People who move from a poor country to a wealthy one, for example, also bring part of their biological clock with them. Nevertheless, the researchers point to a 'likely causal' interpretation, given the breadth and consistency of the findings.