Life After Full-time Work Blog

Fascinating initial studies that suggest that our bodies age, not uniformly over time, but in spurts around two particular ages

Recently I’ve focused a lot on aspects of longevity. A blog post on explaining the often-misused term “life expectancy,” then one on whether our lifespan is influenced more by genetics or by lifestyle, then what our biological age (as opposed to our chronological age) depends on.  And now (the final one, I promise!) one on the fact that our biological age itself doesn’t change at a uniform rate, but seems to increase in spurts at specific times in our lives.

A quick reminder: our chronological age is how old we are in terms of how long it has been since we were born, whereas our biological age relates to how much the life systems in our body have aged. And since different systems in our bodies have aged at different rates and to different extents, our so-called biological age is just a rough shorthand for the average of how old our body systems seem to be. For some our biological age is less than our chronological age, for others our biological age exceeds our chronological age.

The gap between the two doesn’t stay constant. It seems that there are particular times when our biological clock accelerates.

OK, now to one recent study and its conclusions.

The study involved 108 participants aged between 25 and 75, resident in California. They were followed for varying periods of time, the longest being almost 7 years, though most of them were followed for a bit less than 2 years. There were, in all, more than 5,000 biological samples taken (oral, blood and stool samples, for sure: I couldn’t understand what else was involved), hence more than 100,000 biological features were measured, resulting in more than 200 billion data points.

Now the conclusions.

The molecules and microbes that they studied didn’t change uniformly over time. When the researchers looked at the results more closely (a colossal amount of analysis was involved), the rates of changed showed a fair amount of clustering relative to participants’ ages. (And as you can guess, the effects of many factors, for example female menopause, had to be eliminated. Insulin-sensitivity and ethnicity were other causal characteristics eliminated.) Specifically, then, they identified two major waves of aging-related molecular changes across the human lifespan.

Explaining them, a science reporter for the New York Times says that the study found that people seemed to age more rapidly around age 44, and again around age 60. The clusters of changes in the first aging spike (around age 44) appeared to be mostly related to fat and alcohol metabolism, as well as to muscle function. The second spike (around age 60), while also involving muscle function, appeared to be mostly related to immune dysfunction. (The study’s authors note that a previous study reported crests at ages 34, 60 and 78, but their data didn’t include anyone older than 75.)

A study coauthor said that the first spike could help explain why people seem to have more trouble processing alcohol starting in their 40s, while the second spike could help explain why people become more prone to illness in their 60s. (This is consistent with a recent study on the aging of mice, which suggested that there were sudden chemical modifications to their DNA, one in early-to-mid life, the other in mid-to-late life.)

I notice that they didn’t comment on muscle function, though both spikes were specifically associated with muscle function, and at my age that’s an important feature of my health.

Fascinating! So if you ever thought that you seemed to age more rapidly in a particular year or period of your life, now you’ll know that this is not unexpected.

But I’m not going to get too excited about all of this, and I don’t think we should focus too closely at ages 44 and 60. (For example, age 44 isn’t really at all close to the age 34 that the previous study suggested.) What sort of study would indeed be valid in getting us excited?

In principle it’s simple. You’d look at a very large number of people, accommodating differences in age and sex and race and whatever other characteristics you think might be relevant; you’d come up with an estimate of the initial biological age of each person in this investigation; and you’d follow up with frequent re-evaluations of their biological ages over a very long period of time. That way, for each person you’d be able to observe the rate at which their biological age changes; and for each group of people you’d be able to see whether and when their biological ages change at something other than a smooth rate. As I said, simple, at least in principle.

But what’s simple isn’t necessarily easy to actually carry out. And in fact it has proven to be remarkably difficult to do. The results cited are based on a tiny and limited study: 108 Californians aged 25-75, so, on average, two people at each chronological age; and they were followed, on average, for two years each. Not many people, not from around the world, not for very long. Not exactly definitive; in fact, barely a start. So I think these conclusions are at best an indicator of what future much larger studies should start to look at.

Would these conclusions apply, not just to a bunch of a hundred Californians, but also to people from, let’s say, South America, Australia, Japan (where people reach the highest chronological ages), Africa, etc etc? If it is found that there are still spikes in the aging process, how much do the numbers differ across people? For example, if the first spike tends to occur somewhere between 34 and 44, what does that imply for the way we should try, as individuals, to deal with it? To what extent do lifestyle and environmental factors affect the spike ages? And so on. We know nothing about any of this.

It doesn’t matter that these conclusions from the study are now being widely cited as if they’re established fact. As you can infer from the way I’m saying all of this, I think those conclusions are fascinating, yes, but hardly facts. Experts are cited in the NY Times article as saying that the findings are “quite interesting, but I would say preliminary,” and they’re just “touching the surface” of how molecular changes relate to aging. Exactly.

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Takeaway

A fascinating, but tiny and at best preliminary, study suggests that, while we age continuously, we don’t age at a uniform rate, but with spurts at around ages 44 and 60.

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