HEALTH STANDARDS FOR YOUNG AND OLD DIFFER LESS THAN IT SEEMS

Abstract: There is a recent trend toward relaxing the health standards for people over ~70 for weight, blood pressure and LDL. Recent studies find no increase in mortality when weight rises from BMI 22 to 27, BP rises from 140 to 150, and LDL rises to >100. I hold that these conclusions are fallacious because the studies make no distinction between robust and frail cohorts of the old.

 

In recent months I’ve come across medical advice for the old that seems sensible, but isn’t. In several areas, experimental data are presented that seem contrary to common sense although the data are not wrong. What’s wrong is the uncritical way in which the results are accepted at face value.

At this writing, I know of three areas in which I object to the interpretation of the data: optimum weight, hypertension, and the safe level of serum LDL (low-density lipoprotein).

Overweight has been recognized as a problem for decades, causing increased mortality from hypertension, diabetes, cancer and cardiovascular disease. Until recently, the ideal BMI (body mass index) for maximum longevity has seemed to be about 22, but recent publications have raised the ideal, first to 24, and recently to 27 in large cohorts of elderly people. Comparing mortality rates with body weight looks simple and foolproof, doesn’t it? But it isn’t.

Over the years, the target SBP (systolic blood pressure) for hypertension has been gradually focussed on 140 mm or less. Not that this is the ideal – all agree that lower is better (above ~90 mm) – but it’s an achievable maximum level for most people. However, recently there has been a movement to increase the suggested maximum to 150 mm for older people, on the ground that cohorts older than ~75 do not seem to benefit in longevity at 140 vis-à-vis 150 mm. Recently, a committee of cardiologists came out for 150, although a subset of these doctors emphatically disagreed, holding out for 140.

Similarly, the optimum upper recommendation for serum LDL to reduce atherosclerosis to a tolerable level has been reduced every decade. Presently it’s 100, an arbitrary number to be sure, since mortality goes down with LDL even to zero. However, we cannot achieve zero LDL, while most people can get to 100 easily with diet and, if necessary, drugs. Once again, mortality in older cohorts seems less sensitive to LDL in a range somewhat over 100.

It doesn’t make sense that a level of SBP, or BMI, or LDL that is harmful to young people is harmless to older ones. There’s no obvious reason that the old should be more resistant to noxious influences than the young. I hold that there’s no reason at all, and that it’s not true.

The fault in these studies is not that the data are incorrect, but that simple data collection is not sophisticated enough to provide meaningful insight into human health.

In any group of old persons selected solely for their age there is a major difference between two cohorts, the robust and the frail. The robust take care of themselves by keeping fit, eating nutritional diets, avoiding overweight and having good genes. The frail are also slim, but for unhealthful reasons: lack of exercise, cardiovascular disease, poor eating habits, wasting disease such as cancer, poor genes and the like. The robust have a long life expectancy, but the frail have a short one, so that the robust push up the viability of low BMI while the frail push it down. Likewise, the robust push up the viability of low SBP and low LDL and the frail do the opposite.

Therefore, the sensible thing is to report on these two cohorts separately. The inevitable result will be that the most healthy BMI, SBP and LDL will be well below the observed “normal” BMI calculated by averaging everyone at a given age.

There’s another, more subtle reason not to believe that older people are no longer subject to the dangers of high BMI, SBP or LDL. When you plot a graph of some physical measurement vs. age (or anything else), there is always a little “noise” or uncertainty in the relationship, owing to inevitable imperfections in the data, and also to subjects who are outliers (who vary from the average person and therefore don’t fit on the smooth curve). This noise shows up as data points that are above or below the “average” line, and the degree of uncertainty can be calculated according to known laws of probability.

This uncertainty obviously grows with the age of the cohort because they are closer to life’s end, so with age a point is reached for each different characteristic where the noise is comparable in magnitude to the data themselves. Beyond this age we can no longer distinguish the effect of this characteristic on mortality within the precision of the databut it is a fallacy to say that the effect on mortality has therefore vanished. It’s still there.

Conclusion: When we read that the old are no longer bound by the strictures of younger people, take it with a grain of salt.

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