You're only as old as you feel, right?

Researchers are developing tests to calculate your true biological age. They claim that such tests can measure how well your body is coping with the rigours of life. But how accurate are these tests and could they somehow be used to predict your future health?

Ageing has long been considered an inevitable consequence of life. However, recent scientific advances have revealed that the physical decline associated with growing old is caused by an underlying biological process, influenced by both genetic and environmental factors. And if ageing is governed by biology then it is amenable to manipulation.

Being older is a major risk factor for several diseases. As the global population gets steadily older, this poses serious social, medical and economic costs to society. A better understanding of the mechanisms that cause ageing could lead to interventions to improve age-related health. For these interventions to be successful, clear read-outs of how well our bodies are ageing are first required.

Ageing rates between individuals that share the same birth year can vary significantly. As such, the number of years you have been alive – your chronological age – is not necessarily a good predictor of how well you are ageing. Instead, some measurement of biological age that identifies an age-related change in body function or composition could more accurately predict your chances of developing age-related disease. Such biomarkers of ageing could be used to identify people at risk of disease, prompting preventative measures in lifestyle or early treatment. They could also be used to check how effective new anti-ageing therapies are.

But reliable biomarkers for ageing have so far proved elusive. Physical differences clearly exist between old and young, but measuring these differences with any kind of confidence is difficult as they can vary hugely from one person to the next.

Behavioural vs biomedical tests

Tests that claim to measure biological age usually take one of two forms. The first, including the Vitality Age test, are based on an assessment of your overall health and behaviour. The online vitality test uses an algorithm that takes into account details such as your weight, your eating habits, the amount of exercise you take, your cholesterol levels and your weekly alcohol consumption. Your answers to such questions are then compared to the average score calculated from a large cohort of relatively healthy people of the same chronological age. Your biological age is calculated as a measure of risk and perhaps not surprisingly, engaging in more risky behaviours such as smoking or eating an unhealthy diet can all dramatically increase your biological age.

Other tests for biological age take a more biomedical approach. They measure some biological parameter that is more prevalent in older individuals or is subject to change as we age. A study led by a team from Kings College London claimed to have determined a genetic signature of ageing present in individuals that are ageing well. They measured the expression of 54,000 genes in healthy 25 to 65-year-olds, of which around 150 genes could reliably distinguish between young and old participants in the study.

Importantly, this genetic signature of ageing was different in people with dementia suggesting that it could prove useful in predicting those at risk of developing disease. However, while particular patterns of gene expression were linked to long-term health, they varied widely between individuals.

The GlycanAge Test claims to be the most accurate method yet to determine your biological age. The test focuses on the structure of Immunoglobulin G (IgG), a protein found in blood serum that is involved in the immune response. The IgG protein is modified by the addition of glycans – sugar molecules that decorate the surface of proteins, influencing the way in which they function. GlycanAge have analysed the structures of IgG glycans in blood samples from over 40,000 people worldwide and claim that the patterns of glycan structures on IgG proteins change with age and reflect the effects of lifestyle choices that impact on ageing such as smoking. By comparing your IgG glycan structures to those studied, GlycanAge says the test can determine how well your body is ageing.

Yet no single measurement is likely to be enough to capture the full biological complexity of ageing. Especially because not all age-related biological changes will affect health to the same extent. The MARK-AGE Consortium, an EU funded project comprised of 26 European research partners, proposes a battery of biological tests covering multiple aspects of ageing. It is this kind of an approach that will probably prove more useful in determining overall biological age and predicting age-related health.