Section 1 - The Ageing Process / 1.2 Article: How We Age

Chronological vs. Biological Ageing

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Why is it that one seventy-year-old person appears healthy and independent, whilst another can appear frail and dependent on others? This question captures the difference between chronological and biological ageing.

A person’s chronological age is simply a count of the number of years, months or days since their birth. In contrast, their biological age, to put it simply, the age they appear.

There is a wide variation in the separation between a persons chronological and biological age across a population.

Fig 3. Functional capacity curves demonstrating the effect of biological ageing. Reproduced from Kalache, A. & Kickbusch, I. (‎1997)‎, World Health, 50 (‎4)‎, 4 - 5, WHO.

Biological ageing is difficult to predict and classify as it is the result of several factors including, chronological age, genetics, socio-demographic factors like poverty, lifestyle, nutrition and disease.

It is this difference between these descriptions of ageing that makes defining ‘an older person’ very difficult. As a result, most gerontologists simply use people’s chronological age as a ‘catch-all’.