Science Friday – Turns Out Stronger People Really Are Harder to Kill

There’s a really interesting study I wanted to share entitled “Association between muscular strength and mortality in men: prospective cohort study.” This is the only study I’ve found that has tried to look at how maximal strength might be correlated to mortality for individuals over a broad range of age, health factors, body types and family history.

This study involved a baseline health and strength assessment of 8,762 men aged 20-80 and follow-up assessments over the course of 19 years. During this time 503 deaths occurred and this study’s analysis attempts to find out what health and strength factors were highly correlated with these deaths. Individual strength was measured using a 1RM test in the bench press and leg press. All participants were broken up into 3 different strength levels and Table 1 (pdf) shows the participant data.

If we start by looking at the columns in the linked table (not the one embedded on the right) labeled survivors and decedents we will see some obvious correlations. Going from the bottom of the table up we see that, on average, those that died had a higher family incidence of cardiovascular disease, high cholesterol, high blood pressure, higher incidence of diabetes and smoking, were more sedentary, weaker and heavier. None of this is too shocking but I suppose now you can say you’ve seen real data that shows these things lead to premature death.

However, what we’re interested in is what the effect of strength is on these mortality rates. For example, what if I have high blood pressure but I’m strong – does that help me at all? Also, how does the probability of mortality change if I have good cardiovascular endurance but I’m weak? Table 2 (embedded on the right) shows this data.

This table looks complicated but I’ll explain what you’re seeing. The first column breaks the data down into various causes of death. There’s all causes, cardiovascular disease and cancer. Within each one of these causes the data is broken out into the 3 different strength levels that participants were grouped into. Columns 2-3 show the absolute number of deaths and death rate in each category respectively. Finally 4-6 show how much more likely individuals are to die based on their strength level when compared to the lowest strength level.

This will require a bit more explanation so hang in there. If we look at column 4 we see that there’s a hazard ratio of 1 for the lowest strength levels. This is the baseline value that the middle and higher strength levels (reported in the next two rows) are compared to. For this, the smaller the number, the less likely you are to die. In the all cause case one can see that strength levels 2 & 3 are significantly less likely to die. Similar numbers are calculated down in column 4 for cardiovascular disease death rates as well as cancer. It’s important to note that column 4 is adjusted for age since clearly the older you are the more likely you are to die. This means that regardless of your age, getting stronger will help you live longer.

Column 5 shows the same data but it is adjusted for several other variables including age, physical activity, current smoking, alcohol intake, body mass index, baseline medical conditions, and family history of cardiovascular disease. This is significant because the data clearly shows that regardless of all those other variables, being strong still significantly reduces your likelihood of premature death.

Column 6 adjusts for cardiovascular fitness and shows that all cause and cancer mortality is still greatly reduced in those that are strong regardless of the cardiovascular fitness. I should point out that the data specifically for cardiovascular disease mortality shows that having high strength levels may not be important relative to having a good level of cardiovascular fitness. This is interpreted through the higher p-value shown but that’s beyond the scope of this discussion. As usual, better to be strong and fit.

Conclusions:

Here’s what the autors said:

Muscular strength was independently associated with risk of death from all causes and cancer in men. These findings are valid for men of normal weight, those who are overweight, and younger or older men, and are valid even after adjusting for several potential confounders, including cardiorespiratory fitness. Muscular strength seems to add to the protective effect of cardiorespiratory fitness against the risk of death in men.

More simply put the data shows that regardless of any other health marker, being stronger makes you less likely to die. What also shows up in the data is that “strong” in this case just means stronger than the bottom 3rd and increasing strength levels don’t necessarily continue to improve survival rates. So I’m not suggesting you need to become a competitive power lifter. As long as you’re stronger than 1 out of every 3 people your age then you’re on the right track.