How much exercise will maximize longevity?

In an earlier article we debunked the claim that exercise will help you lose weight. What about whether exercise will help you live longer? Now, don’t get me wrong, I am certainly not anti-exercise. There are lots of studies showing that exercise has many and varied health benefits, from improving muscle strength and balance, to decreasing the risk of fractures and delaying the onset of dementia. But will it help you live longer? And if it does, how much exercise should you be getting to maximize longevity? Are the famous ”10,000 steps a day” and ”half an hour a day” recommendations enough or should you be doing more than that?

An umbrella systematic review (a systematic review of systematic reviews) that was published in 2019 in Medicine & Science in Sports and Exercise sought to answer these questions. The umbrella review was funded by the US Department of Health and Human Services. No conflicts of interest were reported.

A few things to note before we get in to the data. The studies were all observational in nature. Participants were not randomized to either one treatment or another, and there was no control group. The reason for this is that these types of big long term studies aren’t feasible to do as randomized controlled trials – partly because people aren’t willing to be randomized to exercise or no exercise, and partly because big randomized trials are hugely expensive.

This means that there is a lot of scope for confounding effects. For example, people who are seriously sick from chronic obstructive pulmonary disease or cancer often don’t have the energy to engage in any exercise, and they have a very short life expectancy. But it isn’t the lack of exercise that is killing them. As another example, people who are in to exercise are often also in to healthy eating. But is it their exercise pattern or their diet that is making them live longer? Or a combination of both? Or is it the fact that they are also less likely to smoke? In observational studies it’s impossible to know. These types of effects will generally make exercise seem better than it really is at making people live longer, which is something to bear in mind as we move forward through the data.

Another thing we need to clarify before we get in to the result is the concept of a MET (Metabolic Equivalent Task). One MET is defined as the amount of calories a person expends in one hour when at rest. Walking at a slow pace expends two METs. Walking at normal walking speed (3 miles or 5 km per hour) expends three METs. Bicycling at average speed (11 miles or 17 km per hour) expends six METs. Running at a speed of 6 miles per hour (10 km per hour) expends 10 METs. Generally, activity that expends 3 to 6 METs is considered moderate intensity, while activity that expends 6 METs or higher is considered vigorous intensity.

The official guidelines in the US recommend 150 to 300 minutes of moderate physical activity or 75 to 150 minutes of vigorous physical activity per week. The data in the umbrella review were analyzed in light of these recommendations, to determine if they are sensible.

Ok, let’s get in to the data.

One of the systematic reviews, published in JAMA in 2017, compared people who engaged in no physical activity, some physical activity (less than 150 minutes of moderate or less than 75 minutes of vigorous activity per week), and recommended physical activity (more than 150 minutes of moderate or 75 minutes of vigorous activity). They also divided people based on whether they were doing all their exercise in one or two sessions (so called “weekend warriors”) or whether they were spreading the exercise out over three or more sessions. 63,000 participants were included in the review and were followed for almost ten years on average.

Overall, when compared to the group that engaged in no physical activity, the people who engaged in physical activity were about 30% less likely to die over the ten year period. Whether they only did some or a lot of exercise didn’t seem to make a difference to longevity, and whether they did all their exercise in one session or spread it out over the week didn’t seem to make a difference either. Basically, as long as you were moving around at least a bit, your odds of not dying seemed to be improved. But how much you were moving around didn’t seem to matter.

Next we have a review that was published in 2014 in the International Journal of Behavioral Nutrition and Physical Activity. It included 280,000 people who engaged in walking and 187,000 people who engaged in cycling, with a follow-up of roughly ten years. It found that people who walked or cycled 11 METs per week (roughly four hours of walking or two hours of cycling) had a 10% lower risk of dying over the course of the ten year period. This study only included people who were healthy at baseline, which might explain why the benefit seen was so much smaller than in the preceding review.

Next up we have an analysis that was published in the British Journal of Sports Medicine in 2008. It was looking specifically at whether walking could prolong life. 459,000 participants were included in the analysis and followed for an average of 11 years. The people that expended the most energy on walking were 30% less likely to be dead at the end of 11 years than those who expended the least energy on walking. Unlike in the first review, there was a dose-response relationship, so the more walking you did, and the faster you walked, the more likely you were to still be alive at the end of the study.

Next we have a review that was published in PLoS Medicine in 2012. It included 655,000 participants who were followed for around ten years. Again, there was a clear dose-response relationship, but with a curve that quickly flattened with increasing amounts of exercise. Basically, going from zero exercise to 10 METs per week resulted in a 30-35% reduction in mortality. Going from 10 METs to 20 METs resulted in a further 5-10% reduction. And going from 20 to 30 METs resulted in an additional 1-3% reduction. So the benefits to longevity of doing three hours of moderate intensity walking per week are big. The benefits of doing an additional three hours per week on top of that are much smaller, and the benefits of doing an additional three hours on top of that are smaller still.

Finally, we have a review that was published in JAMA Internal Medicine in 2015. What is interesting about this review is that it wanted to see if there is a point where benefit turns to harm. In other words, is there such a thing as too much exercise? It included 661,000 participants who were followed for an average of 14 years. It also found a dose-response relationship, but the curve was U-shaped. In other words, very high levels of exercise were correlated with increased mortality.

At what point did exercise start to become bad for you? At around 75 METs, equivalent to about 7,5 hours of running per week. And at what point did the survival curve level off completely? At around 35 METs. In other words, from 35 METs to 75 METs per week there is no additional benefit on longevity, and if you do more than 75 METs per week you are doing more harm than good.

So what conclusions can we draw?

First of all, I want to reiterate again that all these studies were observational, so most likely, the longevity benefit from exercise is smaller than was found in these studies. As mentioned above, the people who don’t move at all are to a large extent people who are really sick to begin with, and it’s often their underlying illness that is killing them, not their lack of exercise. As a doctor, pretty much the only people I see who are completely bed-bound are people with severe diseases who are in the last few months or years of their lives regardless of what they do. And healthy habits travel together, so people who engage in exercise generally also drink less alcohol, smoke less, and eat more healthily.

At the same time, I think it is reasonable to assume that there is some significant benefit to exercise, considering all the studies that show it improves cognition, balance, bone density and so on – things that should reasonably be expected to promote longevity.

Secondly, yes, the 30 minutes per day of and 10,000 steps per day recommendations do seem pretty reasonable in light of these studies. If you do 30 minutes of moderate intensity exercise (of which walking to and from the bus station or tube definitely counts) then you are reaping at least 90% of the longevity inducing benefits of exercise.

If you do 10,000 steps a day then you are doing plenty. 10,000 steps is roughly equivalent to 5 miles (8 kilometers), which is about an hour and a half of walking at normal speed, or two hours at slow speed. In fact, you could walk half that and you would still be getting more than 90% of the longevity inducing benefits of exercise. So, even if you’re only getting 5,000 steps a day, don’t worry. You’re still getting 90% of the longevity benefits of exercise.

If you want to squeeze every last drop of longevity possible out of exercise, then you should be aiming for 35 METs per week, equivalent to 12-13 hours of walking at a moderate pace, or 6 hours of cycling, or 3-4 hours of running.

You might also be interested in my article about whether exercise is an effective way to lose weight, or my article about whether you should take fever lowering drugs when you’re sick.

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