We’d all like to live longer; at least, I would. But what about enjoying the time we have while we’re here and living healthier?
Over the past century, human life expectancy has dramatically increased for a variety of reasons. Chief among these are our advances in sanitation, public health, nutrition and medicine that have reduced mortality, especially in young people. As a result, many more people are able to reach older age.
According to Statistics Canada, in 2021, Canadians had a life expectancy of 81.6 years, which is a astonishing increase of 24.5 years since 1921. By the year 2050, it is projected that the number of people aged 85 years and older will triple.
The extension of life expectancy in the 20th century and beyond is one of humanity’s greatest achievements. However, it is crucial to draw a distinction between lifespan — the amount of time between birth and death — and healthspan, which is the amount of time during which a person is healthy within their lifespan. Older people are spending more time in poor health, and this represents a major individual and public health burden.
At an advanced age, the ability to maintain an independent lifestyle largely defines a person’s quality of life. As such, it’s not enough to merely extend life without a sufficiently long healthspan to accompany it. Our goals should therefore be to bring lifespan and healthspan as close together as possible.
The idea of extending healthspan is important because it challenges the idea that age-associated diseases are inevitable and can’t be mitigated or ablated.
Why muscle is important for extending healthspan
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One major health challenge in the aging population is the decline in muscle mass, strength and function (otherwise known as sarcopenia), which can lead to functional impairment, loss of autonomy, metabolic disease and a greater risk of falls and fractures.
Alongside its role in posture and locomotion, muscle is a major contributor to resting metabolism, serving as an important reservoir of glucose (sugar) and lipids (fats). It also represents an important “buffer” of amino acids during periods of catabolic stress, such as that seen in critical illness. Markers of muscle health on admission to intensive care units are predictive of important outcomes like the number of ventilator-free days and mortality, and being older compounds this risk.
Beginning at around the fifth decade of life, muscle mass is lost at a rate of about one per cent per year, and strength at about three per cent per year. These reductions in mass and strength are typically interspersed with periods of muscle disuse (hospitalization and/or illness, for example) that accelerate losses in muscle mass and strength.
Even a relative reduction in walking activity (measured by a decline in daily step count) for as little as two or three weeks can bring about negative changes in body composition, reduced muscle strength and quality, anabolic resistance (an impaired ability to use dietary protein for muscle building), and disrupted blood glucose control in older people.
Given the fundamental role of muscle tissue in metabolic and general health, the maintenance of adequate muscle mass and quality has particular relevance for extending healthspan.
Maintaining muscle health with age
Skeletal muscle tissue is highly plastic: it remodels in accordance with the physical stresses placed upon it. It grows (termed “hypertrophy”) in response to the application of external loads and is rapidly lost (termed “atrophy”) when these loads are withdrawn — if you’ve ever had your arm or leg in a cast, you know what I mean. The good news is that we can leverage the plasticity of muscle tissue to our advantage.
In kinesiology professor Stuart Phillips’s research group at McMaster University, we study the impact of exercise and nutrition on human skeletal muscle health, with a particular interest in aging.
The lab’s work has shown that resistance exercise (strength training), even when performed sporadically and with lighter loads, can be an effective strategy to offset muscle losses during periods of reduced activity and disuse in older people. What’s more, this type of training can enhance the sensitivity of muscle tissue to dietary protein and help overcome anabolic resistance. It can also make your muscle more ready to take up glucose and reduce your risk of diseases like Type 2 diabetes.
Research now indicates that older people require more dietary protein (the source of “building blocks” for muscle) than the established guidelines suggest. Recent work from our lab has shown that higher-quality protein sources can improve muscle growth in older people. The optimal strategy appears to be consuming 1.2 – 1.6 grams per kilogram of body weight of protein daily (50 to 100 per cent greater than what is currently recommended), from a mixture of animal (e.g., meat, fish, dairy) and plant-based (e.g., legumes) sources.
No matter what age you start, you can build the metabolic equivalent of a retirement savings plan by repeatedly engaging in physical exercise and consuming adequate high-quality protein. In doing so, you can effectively close the gap between healthspan and lifespan, maintain independence and maximize quality of life in older age.
Matthew Lees is supported by a Canadian Institutes of Health Research (CIHR) Postdoctoral Fellowship award (Funding Reference Number 187773).
