A 2009 study followed about 9000 men for 10-20 years. It found that strength (how much you can bench and leg press) measured at the start of the study was associated with likelihood of dying of cancer during the study. Men in the upper two-thirds of the study population in strength had 40% less cancer mortality. This might be the most surprising result:
Further adjustment for BMI, percent body fat, waist circumference, or cardiorespiratory fitness had little effect on the association. The associations of BMI, percent body fat, or waist circumference with cancer mortality did not persist after further adjusting for muscular strength.
In other words, muscle strength was a better predictor than several similar measures (BMI, etc.) and these other measures stopped predicting when corrected for muscle strength. Muscle strength is closely connected to something important.
Men who are stronger by and large exercise more, no doubt. Yet muscle strength is determined by resistance training, not aerobic exercise — and it is aerobic exercise (and to some extent walking) that have been promoted by countless experts since the 1960s and the invention of the concept aerobic. Jogging reduces how much time you have for resistance training.
These findings interest me because I do a lot of resistance training — stand on one leg to exhaustion several times per day — purely to sleep better. By improving something easy to measure (sleep), these data suggest I have also been improving something hard to measure (chance of dying from cancer). Not surprising, but reassuring.
My data also suggest two different possible reasons for the strength-cancer association. One is that men who exercise more sleep better as a result; better sleep, better immune function, less cancer. Another possibility is that strength is a marker for good sleep. Among men who do equal amounts of exercise, those who sleep better will be stronger.
From The Breviary.