Longevity: Exercise helps you to live longer, but how important is intensity?

Regular exercise extends life, and the effect is so powerful that even people who wait until they are middle-aged to begin exercising gain extra days on earth. Overall, starting exercise in one's middle years lowers the risk of death by 23 per cent over the next two decades or so.

Excellent - or even good - athletic ability is not necessary to get the extra time. In fact, research tells us that college nerds who take up exercise in mid-life live longer than topflight collegiate athletes who later become sofa spuds. When it comes to exercise and longevity, persistence wins out over innate ability.

How much extra time can exercise buy? In the well-known Harvard Alumni Study, which examined mortality rates over a 22- to 26-year period in more than 17,000 men who had attended Harvard University, life expectancy was about two years longer for those who expended 2,000 calories per week during exercise, compared to individuals who were sedentary. Since 2,000 weekly calories can be consumed during just 15 miles of jogging, it's clear that a fairly modest investment in exercise can bring a large return.

Within limits, exercise's protective effects tend to expand as you increase your quantity of exercise. Jogging just 10 miles per week improves your chances of living longer rather dramatically, compared to completing no exercise at all. Covering 25 to 30 miles each week lowers your risk of dying even more. Beyond 30 miles, though, there's little evidence that more miles limit the grim reaper's activities any further.

Ralph Paffenbarger, M.D., one of principal investigators in the Harvard Alumni Study, summarises the benefits of exercise with a neat formula: For each hour that a person exercises, he/she gets roughly two extra hours of life! Paffenbarger's proposition is true only for reasonable amounts of exercise, though (probably for up to 30 weekly miles of running). Otherwise, immortality could be 'purchased' simply by exercising for slightly more than 12 hours each day, which would 'buy back' the lost 24-hour period.

How it works
Why does exercise help us live longer? Blood levels of high-density lipoprotein cholesterol (HDL-C) are inversely related to the risk of developing coronary heart disease (the higher the HDL-C, the lower the risk), and exercise raises HDL-C. Running just nine miles per week hikes HDL-C by 8 per cent. Running 17 weekly miles shoots HDL-C up by 12 per cent. Ambling 31 miles per week heightens HDL-C by 19 per cent. Individuals who jog just 11 to 14 miles per week can lower their risk of heart attack by 30 per cent or so.

Exercise also tends to lower blood pressure, decreasing the risk of heart attack and stroke, and trims the chances of becoming obese or developing non-insulin-dependent diabetes mellitus. Regular physical activity has also been linked with lower rates of certain kinds of cancer. In general, exercise extends longevity by diminishing the risk of a variety of different ailments.

Pick the right exercise
The type of exercise you choose matters when it comes to longevity. Recent research from Finland indicates that individuals who engage in endurance activities (running, cycling, swimming, cross country skiing, walking) live about six years longer than couch potatoes. In contrast, those who prefer team sports like basketball, ice hockey, or soccer live just four years more. And sports-active people who prefer 'power-type' activities, including weight lifting, field events, and sprinting, last for only two additional years.

However, most of the increase in lifespan enjoyed by the Finnish team-sport and power athletes is due to social status, not athletic activity (team and power athletes tend to enjoy greater social status than sedentary people, which gives them better living conditions, higher-quality food, and superior health care). When the influence of social status is removed from the analysis, only athletic-minded individuals who routinely engage in endurance-type activities enjoy greater longevity than the Finnish non-exercisers. The key difference is that participation in endurance exercise makes it highly unlikely that someone will keel over between the ages of 50 and 69. Such deaths, which occur more frequently in the team-sport, power-sport, and sedentary groups, are shifted into the seventh decade of life in those who huff and puff while running, skiing, cycling, or walking several times each week.

Do those who exercise hardest last longest?

While there's no doubt that endurance-type exercise helps us live longer, it hasn't been clear whether intensity has any special role to play. Theoretically, higher intensities should be helpful in promoting longer life. For example, if two previously sedentary, physiologically similar individuals decide to run 25 miles per week, but one runs with an average heart rate of 80 per cent of maximal while the other eases along at 65 per cent, the 80-per cent runner will clearly become fitter and might reasonably expect a longer lifespan. The 80-per cent runner also spends a few more calories each week (average calorie burning per mile tends to rise slightly as running velocity increases), which should be good for longevity.

Science hasn't been exactly clear about the relationship between intensity and longevity, but there is some evidence to support the idea that fairly intense exercise is better than low-intensity stuff. In the Harvard study, for example, expending more than about 400 calories per week in vigorous activity (jogging, fast walking, swimming laps, playing tennis, shovelling snow) was linked with reduced mortality, while spending more than 400 calories per week on non-vigorous efforts (slow walking, moderate yard work, gardening, working on the car, doing light repair around the house, etc.) was not.

Increasing the quantity of vigorous exertion also tended to steadily extend lifespan, while augmenting the amount of non-vigorous exercise did not. For vigorous exertion, shifting from less than 500 weekly calories expended to about 1500 weekly calories cut death-risk by about 25 per cent, and jumping from less than 500 to 3000 calories or so reduced the risk by 38 per cent. For non-vigorous exercise, there was no such trend. Interestingly, even individuals who engaged in relatively large amounts of non-vigorous work (over 1500 calories per week) gained no significant increase in life expectancy, compared to individuals who basically did nothing.

What is 'vigorous' activity?
However, vigorous activity was defined fairly loosely, at least by the standards which would be set by most of PP's readers. For the Harvard researchers, vigorous exercise was anything which was greater in intensity than about six 'METS' (e.g., greater than six times resting metabolic rate). Most PP subscribers could exceed six METS simply by jogging at faster than 11-minute per mile pace. This means that the Harvard study tells us only that really slow exertions don't seem to lower mortality risk by much (if at all). We still don't know whether seven-minute per mile running is better than 10-minute pace, or - to put it another way - whether higher exercise heart rates are superior to more moderate ones.

In a separate study which began in England in 1976, the exercise patterns of 9,376 male civil servants, aged 45 to 64, were observed over a nine-year period, during which 474 individuals had a heart attack (272 of which were fatal). The civil servants' exercise was classified as vigorous or non-vigorous, with swimming, jogging, badminton, tennis, football, hockey, hill climbing, and rowing considered vigorous sports, and dancing, golf, and table tennis non-vigorous activities.

In this study, the protective role played by intensity depended on the age of the subjects. Specifically, among those aged 45 to 54, individuals had to engage in intense, vigorous exercise at least twice a week to enjoy a lower risk of heart attack. Infarction rates were reduced by about 67 per cent in these men, compared to individuals who worked out intensely just once a week or not at all. Mortality rates were even lower - down by 80 to 90 per cent for those who worked strenuously at least twice a week, compared to civil servants who trained once a week or less. Working out intensely twice a week seemed to represent a threshold frequency, below which there no reductions in risk.

Small is beautiful
In contrast, small amounts of intense exercise seemed to help older British men (aged 55 to 64). Compared to no vigorous exercise at all, training one to three times per month lowered heart-attack risk by about 25 per cent, while doing something vigorous once a week cut risk by almost 50 per cent, and a two-a-week schedule trimmed chances of heart troubles by 65 per cent. Mortality patterns were similar. The lesson seemed to be that for older men (over 55) doing a little vigorous exertion is helpful, and doing more is even more helpful, while for younger men (below 55) it seems to be necessary to get the heart pounding at high rates at least twice a week to gain protection.

Strikingly, light or moderate exercise was not protective at all in this study. Even men who did large amounts of modest-intensity exertion (low-speed walking, playing golf, playing table tennis, replacing worn parts on the car, mowing the lawn, painting, raking, pruning, and even engaging in apparently heavy activities such as digging in the garden or working with concrete) gained no protection from heart attack or death. A history of past exercise was also not protective; men had to continue to carry on some degree of vigorous activity to remain resistant to heart maladies.

This British study was definitely pro-intensity, although the definition of 'intense' exercise might again be considered 'moderate' or 'light' by most of PP's readers. In the British research, vigorous activity was anything carried out with an energy expenditure of 7.5 calories per minute or greater, or roughly 6 METS or more, which is also about 65% VO2max (75% of max heart rate) or higher. Again, for many people this could be attained simply by jogging at 10- or 11-minute per mile pace.

The Swiss increase the intensity
In an important Swiss study, exercise intensity was jacked up a bit. For six months, 28 previously sedentary Swiss men jogged about 90 minutes per week (three 30-minute sessions) at a nifty effort level of 75% VO2max (85% of max heart rate), while over the same time period 28 other men walked for 120 minutes per week (four 30-minute sessions) at a miserly intensity of 50% VO2max (just 65% of maximal heart rate).

After six months, both groups enjoyed a small, 7-per cent increase in VO2max. However, only in the high-intensity group was there a relationship between amount of running (some individuals ended up doing more running than others) and blood-HDL levels. Basically, the more running individuals completed, the higher the HDL concentrations advanced. Increased amounts of walking didn't have the same effect. No one died or had a heart attack during this six-month investigation, so the precise protective effect of exercise wasn't measured, but better HDL would have lowered the risk of heart maladies and death in the long run, suggesting an advantage for higher-intensity (85%-of-max-heart-rate) exercise. Experts say that each 1-per cent hike in HDL lowers the risk of coronary disease by 3 per cent.

Yes, but what about the women?
Notice that not one of these key studies has included a single woman, a sad commentary on the state of exercise-longevity research. Fortunately, women haven't been totally neglected. In their fine study, 'Women Walking for Health and Fitness,' John Duncan, Neil Gordon, and Chris Scott put 59 previously sedentary women, 20 to 40 years of age, into four different groups: 16 women walked 4.8 kilometres per day, five days per week, at a speed of 8 kilometres per hour (about 12-minute per mile pace); 12 other women walked for the same distance and frequency but at 6.4 km/hour velocity (about 15-minute miles); 18 strolled at 4.8 km/hour (20-minute pace), and 13 women served as sedentary controls.

After 24 weeks, the fastest walkers benefited from the biggest gain in VO2max (16 per cent), although the medium and slow walkers also improved (by 9 and 4 per cent, respectively). However, all three groups had comparable drops in body fat and upswings in HDL-cholesterol. The authors sensibly concluded that vigorous exercise was necessary to achieve maximum fitness gain - but not to elevate HDL and thereby lower the risk of heart disease. However, it would have been nice if the authors had included a running or racewalking group to determine whether higher intensities might have done a better job of magnifying HDL. The bottom line is that we still don't know much about the link between intensity of exercise and longevity in women.

Trying for 100
What about exercise and maximal lifespan? Does regular exercise just increase average lifespan by a couple of years, or does it also 'push the life-expectancy curve to the right' - increasing one's chances of living beyond the age of 100 or so?
'Primitive' societies in which individuals work very hard for most of their lives seem to have unusually large numbers who live past the age of 100, suggesting that perhaps exertion can raise one's chances of surpassing the century mark. However, careful studies have indicated that some of these 'centenarians' may be lying about their age, exaggerating their maturity because - in contrast to what happens in the UK or America - in their society, the older a person is, the more respect he or she gets.

If 'primitive' people actually do have longer maximal lifespans, it's also possible that something other than exercise might be increasing longevity. For example, people living in far-flung areas tend to eat far fewer calories than Americans and Europeans, and laboratory studies have shown that rats who eat below-normal numbers of calories actually live longer than rats who are well-fed. This observation has stimulated some scientists to accept the idea that ingesting a surfeit of calories speeds up ageing, while living in near-starvation conditions slows overall metabolism, as well as the ageing process.

Little real research has looked at the link between exercise and maximal lifespan, but it's reasonable to think that exercise helps. As to its relative significance, compared to genetics, other lifestyle factors, and nutrition, one can't be sure.

Owen Anderson

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