All-cause mortality

All cause mortality is the risk of dying from any cause over a given period. It is the outcome health research reaches for when it wants to avoid a specific kind of self deception: an intervention can reduce deaths from one disease while raising them from another, and only counting every death catches that.

That is why it carries more weight than a disease specific result. Something associated with lower all cause mortality is associated with living longer overall, rather than with dodging one illness on the way to another. Cardiorespiratory fitness, muscular strength and not smoking produce some of the largest such associations anyone has measured.

Read the wording carefully, because the phrasing does a lot of work. Associated with lower all cause mortality means people who had more of the thing tended to live longer. It does not mean the thing caused it. Fitter people differ from less fit people in dozens of ways that no statistical adjustment fully removes.

Relative and absolute framings differ enormously here too. A 50% reduction sounds transformative and can mean a fall from two deaths per thousand to one. Both describe the same finding; only one of them tells you what it is worth to you.

The strongest evidence for causation comes from stacking study designs rather than from any single one: randomised trials where they exist, natural experiments, dose response gradients, and biological plausibility. When those agree, as they do for smoking and for physical activity, the causal reading is safe.

It is also a blunt instrument on purpose. It says nothing about the quality of the years, which is why healthspan sits beside it as the other half of the question, and why a longevity claim that ignores function is only half a claim.

In practice, when you see the phrase in a headline, ask three things: how large in absolute terms, over what follow up, and compared with whom. Our lifestyle life expectancy tool works from a cohort study that reports its findings this way.

Sources

• Li Y, et al. Impact of Healthy Lifestyle Factors on Life Expectancies in the US Population. Circulation 2018;138:345-355
• Mandsager K, et al. Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing. JAMA Netw Open 2018;1(6):e183605