Methods for the assessment of biological age - A systematic review

Biological age has long been proposed to complement chronological age because it has the potential to provide a more accurate assessment of someone's ageing process and functional status. At present, there are several methods to determine an individual's biological age through the measurement of biomarkers of ageing. This review compares methods for assessing biological age in adults, analyses biomarkers of ageing, and determines the goals for which biological age can be calculated, in order to help determine a gold standard for measuring biological age. Articles were eligible if studies included a test battery and statistical method to calculate biological age. Literature research included the databases Medline, Embase, Cochrane Library, Web of Science and ClinicalTrials.gov. In total, 56 studies were included and the risk of bias in each of them was assessed. The most commonly used methods to assess biological age are Klemera and Doubal's method, principal component analysis, multiple linear regression, PhenoAge and Hochschild's method. Klemera and Doubal's method has proved the most reliable. Apart from using different statistical methods, the difference between the biological ageing scores lies in the choice of biomarkers of ageing, especially the inclusion of chronological age as a biomarker of ageing. Most of the included studies aimed to establish a new biological ageing score or compare biological age to different measurements of functionality of the human body. In conclusion, there is still no consensus on a gold standard and more research on this topic is necessary. Study protocol PROSPERO ID: CRD42021287548.