Age is a curious, ill-defined thing even among those who study the subject for a living. In its most pragmatic form, it is ‘chronological’ – a useful tautology, as if age could be marked truly by anything other than the passage of time.
My grandfather, frustratingly to a 4 year old, would reply when asked his age “as old as my eyes and a little older than my teeth”; though typically of his generation in later years he became quite a lot older than his teeth.
The real problem arises when people start talking about ‘biological’ age, as if that were something real and definable, which they then try to define, through telomere length, or frailty indices, collagen cross-linkage and any number of other measures.
Particularly problematic in defining ‘biological age’ is the circular confusion of age-related and age-specific – or if you prefer, age-consequent – disease; that is, the confusion of disease that is more likely to be present because of the cumulative experience of insults and disease which arises because of some theoretical, intrinsic process of ageing. Do you become ill because you are old or old because you are ill? The truth clearly lies somewhere between the two, but the manifest variability of the latter element tempts us into an assumption that it operates exclusively. Particularly in America.
Public Health England are re-promoting their ‘Heart Age’ test, which purports to tell you how old your heart is, relative to your chronological age. It has good intentions. It remains to be seen whether those good intentions have any effect. But I find it profoundly flawed theoretically.
To make real sense, it would be necessary that a heart has a basic trajectory of wearing out. I am not sure how one would measure this, but let’s suppose that it might be by an increasing liklihood of arrhythmia, or of muscle diminution and weakness, or of diminishing patency of the blood vessels. The trouble is that there is no great evidence for this. Instead the increasing probability of a dysfunctional heart in our society is largely a consequence of disease – which itself may be entirely avoidable.
This is not to say that there are not also underlying age-specific processes. Increasing stiffness of blood vessels, for example, could be determined by physico-chemical changes in non-renewable parts of their structure, similar to the racemisation and cross-linkage of proteins in the lens of the eye, which varies to a degree with UV exposure and so on, but explains why we all need reading glasses by about the same age. Importantly, the latter is not a disease. You can’t avoid it. It is a consequence of living for a sufficient period of time with a body of this particular design.
Hearts are different. Most of the heart ‘age’ risk in PHE’s calculations is Coronary Heart Disease (CHD) – which is, to coin a phrase, what it says on the tin: a disease. It isn’t ageing. It may be ubiquitous but it is not universal. There is no ‘natural’ level of CHD for an 80 year old, merely that which is typical of an 80 year old in our society at this particular time. And therein lies the problem with PHE’s concept of ‘Heart Age’. To say I have a Heart Age of 57 implies only that I am typical of men aged 57 with my behaviour and physical characteristics right now – or, more accurately, a little while ago – in the mortality figures. My heart by this measure is only averagely crap.
For fun (admittedly not very much) I changed some things around to try and make my Heart Age younger. This turns out to be pretty difficult to achieve, and even varying it downward by 3 years only increased my predicted event-free survival by a year.
On the other hand, cardiovascular risk is falling at a spectacular rate. If it carried on falling in the next two decades as it has the past two, the actual level of risk would be a fraction of that predicted here. As far as I can see, this isn’t taken into account in the calculator, which is based upon QRISK, which, in turn, is adjusted at intervals for the changing population profile of risk. Indeed, QRISK became necessary because the Framingham equations proved to be not only non-exportable to other populations but to become less accurate with time and inappropriate to other cultures.
All of this renders the whole concept a bit of a gimmick. A different way to tell people to quit smoking, lose some weight and take more exercise. These are excellent messages that we need to continue communicating and facilitating.
But if I told someone of 55 they had a Heart Age of 65, I would feel that I was making up a story to manipulate them, and I don’t think we should do that. That’s why we have science.