A world authority on exercise, Professor Steven Blair from the University of South Carolina, recently visited Australia and he talks about the importance of being fit and how being fit is more likely to save your life than being less fat.

Norman Swan: Hello and welcome to the Health Report with me Norman Swan.

Today in a first for the Health Report we’re going to meditate, so get yourself comfortable and don’t worry, there’ll be no chanting.

And new evidence on the benefits of exercise, how it extends lives and how being fit overwhelms being fat. Professor Steve Blair is one of the world’s leading exercise researchers and I caught him a few days ago while he was visiting Australia.

Steve Blair: Recently we published a report on a subset of men that had had multiple examinations over many years. So 14,000 of these men and 1,000 or 1,200 of them died during follow-up, but what we were able to do was to model changes in fitness over time at these repeat examinations and also changes in bodyweight and percent fat. And then we were able to look at the trends in changes in fat, changes in weight, changes in fitness and risk of dying during the follow up period.

And interestingly enough these guys who were about 45 years of age at their first exam changes in weight, changes in fat just made no difference for their mortality risk, it was absolutely flat. But those who improved their fitness had a substantial reduction in mortality risk again during the follow up period. The fitness/fatness issue – fitness is just far more important as a determinant of health and longevity than is fatness.

Norman Swan: And when you removed fitness from the equation was there any effect at all of waist circumference and overweight and obesity?

Steve Blair: No, not changes in those variables.

Norman Swan: So if you were fat to begin with that wasn’t good, but if you became fatter as time went on it was that change that didn’t make any difference?

Steve Blair: Yeah, the change made no difference whether you gained weight or lost weight and that is consistent with – there was a fair bit of research 15 or 20 years ago and we published a couple of papers on this topic. The buzz word then was yo-yo dieting, if your weight goes up and down, up and down, is that good or bad and again almost all of those studies showed that weight stability is good in terms of mortality risk. That’s whether your weight is stable at a relatively high level or at a relatively low level or in-between.

Norman Swan: So what’s going on here, because there is such a prevalent belief that increased waist circumference, and there was quite good evidence from Swedish studies and others, that waist circumference is directly related to your chances of dying, particularly of coronary heart disease.

Steve Blair: That is true in those studies if they totally ignore physical activity and fitness, which they do. We do not, we have waist and percent fat measured in the laboratory, we have fitness measured in the laboratory and in those analyses we consider both, weight and fat and fitness. And when you adjust for fitness, fatness just has no association with all-cause mortality, cardiovascular disease mortality, incident heart attacks. So yeah, there’s a lot of literature out there that says high waist circumference is harmful, but if you look at those studies, if they mention physical activity at all, and many of them you can’t even find the words in the paper, so that’s pure junk science when that happens. If they mention it at all they say ‘we measured physical activity by self-report, using a validated instrument’ and then they give a reference. So you go to that reference and see that the correlation between their self-report and some gold standard like fitness or even doubly labelled water, the correlation tends to be .3 or .4.

Norman Swan: So there’s not much correlation between what they say they’re doing in terms of fitness and their actual fitness.

Steve Blair: No, their self-report counts for 10% or 15% of the true variants in the measure.

Norman Swan: What liars we are Steve.

Steve Blair: That’s part of it but it’s also some people just can’t remember, it’s just a bad measure.

Norman Swan: And what kind of fitness was it? There’s more and more interest these days in weight training and muscle strengthening and research here in Australia has shown that if you weight train you can in fact prevent diabetes for example and people who are at risk of diabetes. So what kind of fitness did you measure?

Steve Blair: Well, both. Now most of our research has been on cardio-respiratory fitness, aerobic fitness which you get from doing aerobic activities and one reason is that in this group of 80,000 men and women we’ve been following we have aerobic fitness on everybody. But we have muscular fitness, measured muscular strength in the laboratory, one repetition maximum bench press, one repetition, maximum leg press, but we only have those data I think it’s on 14,000 or 15,000 people, so we don’t have enough data to do as much investigation as we are able to do for aerobic fitness. But we have turned to this in the last 5 years or so and it’s really just in the last few years that we’ve learned that muscular strength, which again you get from resistance training, from weight lifting and the like, is an independent predictor of morbidity and mortality. And of course in our data base we can look at strength and adjust for cardio-respiratory fitness, we can look at cardio-respiratory fitness and adjust for strength and the bottom line is both are important, they overlap a little bit but they are both important.

Norman Swan: And you’ve just done a study of men with high blood pressure.

Steve Blair: Yes but let me go on for just a moment about strength and diabetes, you mentioned that. We’ve done some work my colleague Tim Church published a paper a year or two ago in the Journal of the American Medical Association in which we took patients with Type 2 diabetes, it was a randomised trial, aerobic exercise only, strength training only or the combo group, aerobic and strength training and he kept the number of minutes of training the same. The combo group did much better and the primary outcome was a blood measure, haemoglobin A1c, and the combo group did better. So again that’s randomised trial evidence that both strength training and aerobic training are important.

Norman Swan: And HbA1c is the measure of your blood sugar control over the last 3 months. So tell me about this study of men with high blood pressure.

Steve Blair: As I said we had a subset of participants that have provided measures of muscular strength. So we looked at a group of men who had physician-diagnosed hypertension and also had the strength measured and then followed them after the exam to see who lived and who died. And the stronger guys were less likely to die than those who were weaker. And again that held after adjusting for aerobic fitness. So I’m afraid there still are probably a lot of cardiologist and internists who will tell their patients who have hypertension, ‘oh you have hypertension, don’t strain and don’t lift’ etc. And I’m not sure that’s good advice. Obviously they need to be aware of signs and symptoms when they are doing the weight training and they shouldn’t hold their breath, they should exhale when they are pumping that bar up there, but again we have evidence that muscular strength is good for those with hypertension. So I think strength training exercise should be recommended for them as well.

Norman Swan: Why are they living longer lives, so are they getting fewer heart attacks, less cancer, what are they not dying of?

Steve Blair: In that particular study I think the only outcome was all-cause mortality.

Norman Swan: And do we know any more about the route from exercise to lower cancer and heart disease rates?

Steve Blair: Well we learn more all the time. If you would have asked me many years ago, maybe you did ask me years ago when I was here, you know what is the route, what are the biological pathways, I would have carried on about blood pressure and HDL cholesterol perhaps and I think those are pathways that have some relevance but they don’t begin to explain the benefits of regular physical activity. So one of the more recent things that people have investigated is that those who exercise regularly have a greater ability to dissolve blood clots, so if you’re getting a clot developing in a coronary artery and if you are a regular exerciser you have a better chance of dissolving it before it causes the heart attack.

We’ve also learned that the coronary arteries of active and fit people are more reactive, that is they can open more and so again you’d be a little less likely to have a clot that would cause a heart attack or a fatal heart attack. Another thing, very recently, in the last two or three years we published on this, is heart rate variability, and you’ll have to help me explain this, but it’s kind of a balance between sympathetic and parasympathetic nerve action and people who have very regular heartbeats are more likely to develop heart disease than those who have a bit more irregularity. And a little bit of exercise training in very sedentary people improves their heart rate variability just very quickly within a few weeks. So there are a lot of potential mechanisms and I’m sure there are many that no one has yet thought of.

Norman Swan: And what about women, because you’ve spent most of your time studying men?

Steve Blair: Well in our population about 25% of these 80,000 individuals are women. We’ve published many papers on women as well.

Norman Swan: And the same applies?

Steve Blair: The same applies, for example just last year we published a paper on cardio-respiratory fitness and breast cancer in women and we saw the same pattern, get out of the low-fit group and your risk of breast cancer drops substantially. It certainly applies for all-cause mortality for cardiovascular disease mortality.

Norman Swan: And finally Steve Blair, where do you stand on the exercise having to be progressive? It looks as though for dementia and brain protection, it needs to be progressive for diabetes, it seems to be progressive – in other words you’ve got to keep working at it and building it up over time. Are your data telling us anything about the extent to which exercise needs to be progressive?

Steve Blair: Well to be sure I understand you - do you mean that people need to do more, and more, and more over time?

Norman Swan: Yes.

Steve Blair: I don’t think the evidence is really compelling on that point. Now we do know that, and I’ve talked about moderate fitness reducing the risk of dying in the next decade by 50%. Then if we go on out and look at our high-fit group, so those are the people doing more exercise, we see maybe another 10% or 15% reduction in risk. So more is better, at least up to a point, but you can get huge benefits for many different health outcomes just doing the standard physical activity guideline which a good target is 150 minutes a week of moderate intensity activity such as walking, or 75 minutes of vigorous activity, so you get the same dose but just in half the time. But then we also go on to say you get more benefit if you can get 300 minutes about 150 minutes of vigorous and it does appear that some outcomes, for example breast cancer you may need to get higher levels of activity to really get substantial benefits. But for most health outcomes if you’re doing that 150 minutes a week you are going to get a lot of benefit. If you can do more, if you can build in more, you’re probably going to get more benefits.

We start our guidelines by saying doing something is better than doing nothing and we’ve done a large randomised trial, 464 post-menopausal women tightly controlled exercise, all exercise in the lab measuring every heart beat, every step, we know exactly what these women were doing and we had one group, it was the control and it was keep the same habits you had, one group that did the guideline recommendation 150 minutes a week of moderate intensity, one group did half of that, so about 75 minutes of moderate and then one group did 225 minutes of moderate and we see a linear trend across those categories. So 150 minutes of moderate that’s a good target to aim for, but if you only get 75 you’re still going to get benefit and if you get 225 or 300 you will get more benefit. But I don’t think we should tell people that it was progressive in the sense that you just have to keep more and more and more to get any benefit. Hit that target, 150 minutes a week, keep doing that the rest of your life and you’ll have a lot of health benefit from that.

Norman Swan: Steve Blair, thank you.

Steve Blair: My pleasure.

Norman Swan: Steve Blair is Professor of Public Health at the University of South Carolina.

References:

Church TS et al. Effects of Aerobic and Resistance Training on Hemoglobin A1c Levels in Patients With Type 2 Diabetes: A Randomized Controlled Trial. JAMA 2010;304(20):2253-2262

Lin GM et al. Aerobic and Resistance Training for Patients With Type 2 Diabetes JAMA 2011 (Letters);305(9):891-892

Church TS et al. Effects of Different Doses of Physical Activity on Cardiorespiratory Fitness Among Sedentary, Overweight or Obese Postmenopausal Women With Elevated Blood Pressure: A Randomized Controlled Trial. JAMA 2007;297(19):2081-2091

Sui X et al. Cardiorespiratory Fitness and Adiposity as Mortality Predictors in Older Adults. JAMA 2007;298(21):2507-2516