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Does diet and exercise prevent cardiovascular disease?

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By Ross Walker

Recommending a good diet and regular exercise program as part of a preventative strategy for cardiovascular disease is as accepted as the importance of breastfeeding, not smoking and being good to your mother.

But, a recent article in the Medical Forum Western Australia by the distinguished cardiologist, professor Peter Thompson, points out a well-known fact within cardiology circles – most of the evidence on cardiovascular benefits for diet and exercise comes from observational trials, apart from a few very selected examples.

Observational trials observe the trends in a population and are not the gold standard randomised controlled clinical trials where, typically, an active drug is studied against an inactive placebo for a set time, usually somewhere between 3-5 years.

A recent study published in the Journal of the American Medical Association - Cardiology, set out to prove within a somewhat randomised controlled trial that exercise was beneficial. They took 1,600 sedentary Americans, aged 70-89 (some of whom were frail) but all could walk at least 400m before the trial began.

They divided the cohort in two groups. Both groups participated in a workshop where they were given standard health care advice, but half were asked to walk 150 minutes per week and the other half did not. To the surprise of the researchers, after 2 and a half  years there was no difference in cardiac events including heart attack, stroke and cardiac death between both groups, with an equal 15% event rate.

So, does this mean we should encourage our patients to eat what they like and stop exercising, purely because one very selective study did not show an exercise benefit? Of course not!

First, let me make some very important points;

1. It is my opinion that randomised control trials are really only appropriate for strong medical therapies such as pharmaceutical treatments and surgical procedures that not only may be of benefit, but can potentially cause harm. You will often see an effect, either good or bad, over a three-five year period. Therefore, these studies are legitimate for strong medical therapy.

2. Many population studies are extended well beyond five years and some as long as 30 years. Although there are many confounding factors such as personal life stressors and environmental toxins (either self-induced such as smoking, and excessive alcohol, or unavoidable such as pollution, synthetic chemical exposure and electromagnetic radiation) the well-controlled observational trials do take into account many of these factors and the results are carefully controlled for these variables.

3. This particular study was a study of older, sometimes frail people and of only exercise and not diet. Additionally, these people were followed for under three years i.e. probably too little, too late in an elderly group who had likely not done much exercise in the recent past, if at all.

4. A very recent study published in the European Journal Preventative Cardiology looked at just under 800 people who were age 50 in 1963. They performed exercise testing at the start of the trial and followed these people for 45 years. The people in the trial who were the fittest had a 21% reduction in death risk equating to an extra 2 1/2 years of life.

5. Also, recently a large meta-analysis of 16 studies that looked at over 1 million people showed that prolonged sitting increased death risk by somewhere between 30-60%. Only 25% of the people in this study did an hour of exercise on a daily basis and the study clearly showed that even with 8 hours or more prolonged sitting on a daily basis, one hour of exercise negated the death risk.

Therefore, I do not believe the exercise trial in the elderly group of people really proves too much at all, except that it probably will not make much difference in a person's life if you try to make dramatic changes too late.

Let’s use the example of diet. The Mediterranean diet has been studied in a variety of ways for many years and the most recent studies, including some randomised control trials, have shown a significant benefit in reducing risks for cardiovascular disease, cancer, type 2 diabetes, metabolic syndrome, Alzheimer's disease, Parkinson's disease and chronic kidney disease by significant amounts. In some trials, there was up to a 50% reduction for some of the conditions.

A large observational trial of exercise in around 50,000 people followed for over 10 years showed a 45% reduction in cardiovascular events and a 30% reduction in cardiovascular death with regular exercise.

In conclusion, just because one particular short-term trial in a very selected group of people did not show an exercise benefit, in my view this is completely irrelevant when considering the large body of evidence that has emerged over the past 50 years supporting the enormous benefits of following the 5 Walkerisms to good health.

For example, it is impossible to perform a randomised control trial of the best drug on the planet – happiness – because it is very difficult to have a sham or placebo happiness group. Scientific studies may be one approach, but often, common sense and the bleeding obvious are more important considerations.

Published: Thursday, August 11, 2016


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