Lifespan vs. Healthspan

There’s an interesting new review paper by University of Birmingham, US, doctoral researcher Michael McLeod and his colleagues in the journal Biogerontology, called “Live strong and prosper: the importance of skeletal muscle strength for healthy ageing.”

Now, I’m not exactly a muscle guy (as anyone who’s met me in person knows!). But I’m increasingly aware that muscle isn’t just an optional esthetic add-on, especially as you get older.

The paper lays out some grim facts about sarcopenia, the term for age-related muscle loss: by the age of 80, most people lose about 30 per cent of their muscle mass. If you don’t have much to spare in the first place, that can have a lot of serious consequences, not just for mobility but for metabolic and overall health.

There are a couple of interesting points that I took from the paper. First, on protein requirements: There’s lots of ongoing debate about how much protein you really need for optimal muscle health, with consensus beginning to point toward “More than current minimum recommendations, but less than that guy at the gym thinks.”

What I hadn’t realised, though, is that there’s some evidence that older people need considerably more protein than younger people to stimulate the same level of muscle protein synthesis. One analysis found that taking in a postworkout protein dose of 0.24 g/kg of body weight was enough to stimulate maximum protein synthesis in younger men (~22 years old), while older men (~71 years old) didn’t plateau until the dose reached 0.40 g/kg.

Another interesting discussion weighed the pros and cons of two different streams of health advice. On one hand, there’s a bunch of evidence suggesting that calorie restriction extends life in organisms ranging from fruit flies to mice. Drugs that mimic the effects of calorie restriction slow the rate of protein synthesis and also seem to extend life in lab organisms.

Exercise, on the other hand, accelerates protein synthesis (for example, to build bigger muscles). So does this mean exercising a lot and getting fit is speeding us toward an earlier grave? I’ve often wondered how to reconcile calorie restriction research with the seeming benefits of exercise.

You can read the full discussion in the paper, but a key point they make is that extending the life of mice who are coddled in a “thermo-neutral, pathogen-free environment, in conditions where food and water are abundant”—i.e. a laboratory cage—isn’t quite the same as the real world. You can get very weak and frail but still cling on to life.

Is the same true for humans? Maybe, maybe not—but perhaps the more important question is whether that’s what you’d want: “Are we looking to increase lifespan at a compromise of health-span,” the researchers ask, “or would we rather live a healthy active life that encompasses maintenance of muscle mass, strength and function?”

You can guess my answer.

Last point from the paper is an interesting visual, showing cross-sectional MRIs supplied by Leigh Breen, one of the paper’s coauthors, from three men. Of particular interest are the two 66-year-olds, the only major difference between them being the habitual level of physical activity (the guy in the middle walks 3,141 steps a day, the guy on the right walks 12,445):

MRIs of leg muscles.










It’s interesting to see that the two men actually weigh roughly the same amount in total, but one has almost triple the amount of muscle as the other. Good motivation to keep moving.

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