How Much Cardio For Longevity
Meta-analysesI found there meta-analyses of the effect of exercise on mortality:
|Year||# of Trials||Risk Ratio||Source|
|2016||63||0.74 (CI = 0.64 - 0.86)||Anderson|
|2011||47||0.72 (CI = 0.55 - 0.95)||Heran|
The main downside of these meta-analyses is the same as the downside of the trials: they are overwhelming performed on older people with significant medical issues (usually cardiovascular) since they are easier to recruit to exercise for years and also yield higher death sample sizes. However, there use makes it unclear whether the conclusions generalize to the general population.
Longitudinal studies offer a way to overcome the problem of extremely skewed samples, but in looking at them we give up the ability to readily infer causality.
Inferences of causality are always troublesome in longitudinal studies, but in this case the issues are even more pronounced: as people approach death they frequently are less able to exercise, which means even very good controlling for confounders is basically guaranteed too fail.
Nevertheless, here are some brief summaries of a few:
The authors Lee followed 13,485 Harvard Alumni men. After controlling for age, BMI, smoking, alcohol, and how many of their parents died before age 65, they found that exercising more than 1000 calories per week predicted 23% lower mortality relative to less than 1000 calories per week. There was essentially no gain from exercising more than that.
The authors Hyde followed 16,936 Harvard Alumni men. After adjusting for age, hypertension, smoker status, weight-gain-since-college, and whether a parent had died before age 65, they found
Death rates declined steadily as energy expended on such activity increased from less than 500 to 3500 kcal per week, beyond which rates increased slightly
The First National Health and Nutrition Examination Survey
The First National Health and Nutrition Examination Survey followed 9,790 people Fang. After controlling for age, gender, race, income, education, diabetes history, smoking, blood pressure, cholesterol, eating disorders, caloric intake, and BMI, they found mortality decreased by about 23% between the people who described themselves as "very active" and "quite inactive" (where the only other choice was "moderately active").
The Oslo study Holme followed 14,846 men between the ages of 40 and 50 for 12 years. After adjusting for age, education, smoking, diabetes, history of heart attack, and history of stroke, they found both light-intensity exercise, hard-intensity exercise, and degree of leisure all correlated with reduced mortality (see Table 2).
Both RTCs and longitudinal trials find that exercise reduces mortality by ~25%. However, the RTCs generally only find significant reductions in cardiovascular-related deaths, not all deaths.
Even among very old people, cardiovascular-related deaths accounts for only a third of all deaths, which suggests that the correlations found in the longitudinal studies overstate the causal effect of exercise on mortality several times over.