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Age-based risk calculators that work out your 鈥渞eal biological age鈥� are increasingly popular. We hear about body age on health shows like听; gyms听听reductions in metabolic age and fitness age; games and apps听; and researchers have developed specific organ measures like听,听听补苍诲听.

It seems most people have a 鈥渂iological age鈥� that is older than it should be. Four out of five people, for instance, have an听听than their current age. But what does this really mean?

All these age calculators compare your measurements for a range of health risk factors to an average or an ideal number to come up with your score. Having an older biological age on these calculators simply means you have at least one risk factor that is higher than the number set as 鈥渘ormal鈥�.

But unless we know which specific risk factors are above normal, and how normal is defined, it鈥檚 hard to know whether you should really be worried, or what you should do about it.

In the latest season of听, researchers assess volunteers鈥� performance on 23 different tests and combine this into an overall body age. Individual test results are explained to each person, but the volunteers have little reaction to these numbers until they are converted into a body age.

Richard, an obese and inactive 49-year-old man, is reduced to tears when he sees his score: a body age of 92, more than 40 years older than his actual age. By the end of the program, he has听, to 79. Each episode has a similar example.

While a compelling story, it鈥檚 not entirely clear how these ages were calculated. Is it really plausible to reverse 13 years of ageing in just a few months?

What actually happened is Richard reduced specific risk factors to be closer to the level set as 鈥渘ormal鈥� by the calculator. By standing up at work and starting cycling, he improved at least three risk factors: he increased physical activity and muscle strength, and lost 11kg to reduce his body mass index. This is not the same as reversing the ageing process at a biological level, known as 鈥溾��.

Another example is heart age calculators, which are common online and have been听听around the world. The principle is the same: if any risk factors are higher than what has been set for 鈥渘ormal鈥�, then you will get an older heart age than your current age.

The problem is, the same person can get听听but a younger heart age on another calculator. This is because they all use听听with different risk factors and different rules. Some include blood pressure and cholesterol, while others use body mass index to听. Some听听a number for younger heart age, and set a maximum for older heart age.

You will also get a different heart age based on different definitions of 鈥渘ormal鈥� for the same risk factor 鈥� is normal the average, or the ideal?

To add to the confusion, there is no universal agreement on what is ideal, as controversy over recent听听诲别尘辞苍蝉迟谤补迟别蝉.

If the ideal systolic blood pressure is set as 120mmHg, then what happens if you have 121mmHg? On a heart age calculator, this difference is听. Clinically, this is probably not an important difference given the听.

Since one-quarter of online heart disease risk calculators don鈥檛 explain how the calculations are done, it can be very hard to know what the result means, or听.

So is there any point to age-based risk calculators? There is听听to suggest 鈥渂iological age鈥� formats like heart age have more emotional impact and may act as a wake-up call to motivate people like Richard to听听and reduce their risk factors 鈥� which is a good thing.

But they can also听听that their risk of disease is higher than it actually is. As such, they shouldn鈥檛 be used to听, such as whether to take drugs to lower cholesterol levels or blood pressure.

If you get an older 鈥渂iological age鈥� on any of these calculators, don鈥檛 get too worried about the exact number 鈥� it鈥檚 not a direct measure of ageing or life expectancy. But it might mean you have a risk factor for chronic disease that could be reduced.

Ask your doctor:

1. Which specific risk factors are too high?
2. How is 鈥渘ormal鈥� defined for those risk factors?
3. What is my absolute risk of disease (that is, my chance of having a heart attack or stroke in the next five years)?
4. How much can lifestyle and medication options reduce my risk of disease?
5. What are the risks and side effects of these options?

听

This article was first published on听听and written by听听from the School of Public Health.