Prevention: Is sport indeed murder?

3. August 2012

Physical activity has until now been the last word in relation to cardiovascular prevention. And yet for more than one in ten people individual cardiovascular risk factors worsen with the uptake of regular physical activity. Why?

In times when the majority of working people spend much of their lifetime in office chairs, it is not surprising that physical exercise is actually seen by many as a panacea. And from a medical point of view this is not so wrong. Positive effects of regular sport, or at least regular exercise, have been proven multiple times. For instance against diabetes: in trials such as the Finnish Diabetes Prevention Study and the American Diabetes Prevention Program the diabetes incidence with regular physical activity was lower by more than half. In the Framingham cohort, life expectancy is correlated to a large extent with the level of physical activity. With several types of tumors, the beneficial effects of sport as an accompaniment to the anti-tumour therapy have been described. The list goes on.

Are there non-responders to exercise?

Accordingly, the recommendation “for physical activity” has long since been incorporated into various guidelines. The German Diabetes Association designates physical activity in their Guideline for Physical Activity and Diabetes Mellitus as “causal therapy” for patients with metabolic syndrome, impaired glucose tolerance and type 2 diabetes. There is sufficient evidence that exercise delays or inhibits the development of diabetes and lowers cardiovascular mortality. In the Hypertension Guideline for hypertension carriers things sounds similar: “Patients with high blood pressure [should] be encouraged to engage in regular physical activity. (…) These activities should be performed three to four times per week for 30 to 45 minutes. “

In effect- a great deal of agreement from the clinical side. With respect to the mechanisms used in exercise in order to get the benefits, in these contexts this has however rarely been dealt with. The consensus considers that exercise has a beneficial effect on a whole raft of cardiovascular risk factors. It lowers the blood pressure, increases HDL cholesterol, lowers fasting blood sugar, lowers triglycerides and more. This leads then to the fully relevant topic of patient education on physical activity, whereby due to these broad-ranging effects it ultimately can be recommended exclusively to all . But is this really the case? Or are there with respect to physical movement also responders and nonresponders, perhaps even patients with paradoxical reaction?

Caution side effects!

A work published a few days ago by Dr. Claude Bouchard and colleagues at the Pennington Biomedical Research Center in Baton Rouge, California, in the journal PLoS One (2012, 7 (5): e37887) campaigns for there being at least a little more nuanced approach to the issue of sport and prevention. The researchers evaluated the results of six studies that examined physical activity in which a total of 1687 subjects were examined in explicit and well-controlled design experiments. They were able to show that for 8 to 13 percent of the subjects at least individual cardiovascular risk factors were modified as a result of physical activity in each case in an unfavorable direction. In 7 percent of the subjects two or more risk factors worsened.

To make it clear and maintain the analogy to drug therapy, the researchers talk about the possible “side effects” of physical activity that occur with some subjects. Specifically, HDL-C values decreased in 13.3 percent of the cases, triglycerides increased in 10.4 percent of the cases, the systolic blood pressure rose in 12.2 percent of cases and insulin levels changed for 8.4 percent of subjects in an unfavourable direction. Bouchard and his colleagues are careful not to draw any conclusions: “The clinical relevance of these findings is open”, they write explicitly. They do indicate however that patients (and their doctors) should not expect that all beneficial effects of physical activity described in the literature in individual cases also actually reaches them.

Prevention a la carte rather than prevention à la PROCAM?

What this work ultimately suggests is individualised prevention, tailored to individual patients in its recommendations on medicines, diet but also on physical activity, and not solely adjusted to classic risk factors in their profile. For this reason those factors should be identified which predict adverse reactions, for example, to certain types of physical activity. The “usual suspects” here are certain genetic and epigenetic constellations, which however first of all have to be characterised in more detail.

Initial data for this does exist. Thus Finnish scientists have as part of the Finnish Diabetes Prevention Study described polymorphisms in the TNF and interleukin 6 gene that have an impact on the anti-inflammatory effects of physical activity and thus on their preventive potential. The makers of the currently recruiting Prediabetes-Intervention Study at the German Center for Research on Diabetes are also thinking in that direction and want to develop individualised prevention strategies in connection to exercise that (also) take into account genetic factors.

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