101 Facts About Ageing #43: Low Muscle Mass And (Especially) Low Muscle Strength Correlates With Mortality

As Daniel Patrick Moynihan, an American sociologist, politician, and diplomat once said: “Everyone is entitled to his own opinion, but not his own facts”. And we wholeheartedly agree. A shared set of facts is the first step to building a better world with longevity for all. In that spirit, we are creating a series that covers 101 indisputable facts about ageing, health and longevity.

Declining muscle mass and strength with age (sarcopenia) is associated with increased mortality risk. A meta-analysis of 6 studies of nursing home residents (1494 participants in total) found that those who meet diagnostic criteria for sarcopenia (which included calf circumference, appendage lean mass and mid arm muscle circumference) were 60% more likely to die within the study period compared to those who did not meet the conditions for sarcopenia.

Low muscle mass doesn’t necessarily mean low muscle strength. The two can be measured separately to clarify whether one is more important than the other. A study of 4449 individuals aged 50 years or older measured lean appendage mass as a approximation of muscle mass, and used knee extension power as a measure of muscle strength. They then studied the relationship between these metrics and all cause mortality.

The above graph shows relative risk of death depending on whether a person is defined as having low muscle mass (LMM) and/or low muscle strength (LMS). The number above each bar is the risk relative to someone who doesn’t have low muscle mass or strength. For example, a value of 2 means twice the risk of death compared to someone who has neither low muscle mass or strength.

The graph shows that for those who did not have low muscle strength, having low muscle mass didn’t have a statistically significant association with their risk of death. Those who did have low muscle strength, meanwhile, were about twice as likely to die as those who did not, even if they had adequate muscle mass. The current evidence therefore suggests that low muscle strength is more strongly associated with mortality than low muscle mass.

The above studies attempted to control for confounding variables such as the existence of other chronic diseases of ageing, but such measures are not perfect, varied from study to study in the meta-analysis, and sometimes relied on self-reported data. A causal link between low muscle strength and mortality, though probable, cannot be considered fact based on this data. The fact here is that there is a strong relationship between all-cause mortality, low muscle mass and especially low muscle strength.