Super-Geriatrics and Mitochondria

How to live to 100

It has always been a puzzle that some people age more slowly than others. Mortality data for humankind consistently shows that as first-world people start to die off in their (nowadays) late sixties a sub-population emerges in the over seventies that are destined to go on into their nineties and well beyond. Recent medical advances have blurred the distinction somewhat as it can prolong the lives of many who only twenty years ago would have died by three score and ten years; nevertheless the sub-population dubbed ‘super-geriatrics’ is still evident.

Unfortunately, having emerged from the pack as it were, super-geriatrics are too old to breed and thus are prevented from passing on their genes with the benefit of  late-life hindsight. However, I am increasingly of the opinion that super-geriatrics may be ‘made’ as much as  ‘born’ and this blog is an attempt to say why.

It is (as usual for me) all about the role of mitochondria in ageing. It is text-book conventional today to regard mitochondria as ‘ex-organisms’, organelles, a stance which whilst acknowledging their once free living existence sees mitochondria now as fully a component of the cell. I see them differently, fully as organisms that exist in an ecology provided the by cell. They reproduce, proliferate and are destroyed by their ‘environment’ which means they, like any other organism are subject to selective pressures. Like many symbionts and parasites mitochondria have outsourced functions that are either redundant or that can be taken care of by their host-environment but this does not mean that the rules of environmental selective pressures do not apply.

There is evidence to support my eco-mito view. The selection of some mitochondria over others within the population resident in a cell is well documented and is recounted in a previous blog ( Mitophagy). In fact the very existence of a reproducing population which includes sub-populations with different characteristics is the stuff of natural selection.

So this brings me to the central theme of this post. How do you live longer than the norm? A seminal paper in 1936 on post-weaned rats started the ball rolling for the longevity effects of calorie restriction in youth ( btw it just makes you thin if you try it when older!) which was supported by data obtained for humans in post war europe. It works for nematodes too. As yet no explanation for this effect has gained any real traction, but low calorie intake includes reducing free-radical damage is a standard if unconvincing old chestnut.

My thoughts now are that super-geriatrics, apart from being basically well made, have had a selection pressure applied to their mitochondria in adolescence which results in them acquiring for life a set of the best mitochondria. This is not so fanciful if one knows that this kind of thing happens to bat mitochondria once the cub takes up the very demanding flying lifestyle rather than the mouse like existence. Small bats live for ten years or more compared to the two years of mice...they have better mitochondria.

It’s not so fanciful either knowing that selective mitophagy caused by urolithins  increases the life span of nematode worms by 20%.  Finally,  in human adolescents it has been recently shown that they consume fewer calories at rest at one point in their development which puts them in today’s food rich world in danger of getting fat. Surely this means that their mitochondria are throttled back and consuming less oxygen and shunting off excess food into fat.  

All of the above is indicative of a population of ‘organisms’ that adapts to selective pressures. Therefore the question posed as to what make a super-geriatric reduces to ‘what happened to the super-geriatrics when they were young?’

One proposition would be that at a certain point they were subject to calorie restriction, not in the sense of being starved (which would induce torpor) or malnourished but  occurring maybe at a point of very high physical activity. The skinny over active youth.

The trouble with this approach is that this scenario would be commonplace ( or rather before screen time and childhood obesity was commonplace) and if it were the whole story we would be overrun with centenarians. A second proposition is that they were also subject to some hormetic challenge analogous to the effect of urolithins on nematodes referred to above and in previous blog...but what?

Could it be fever? , injury? poisoning? radiation? anoxia through altitude? Japan has the most centenarians, please don’t let it be as a result of radiation exposure in their thirties. In any case I am stuck even for a wild speculation. Any article with ‘tips’ for an old age are hopelessly unenlightening, but at least I know when and where to look for clues.