February 28 — 29, 2008 Advisory Committee Meeting Minutes

Subcommittee Report: Cardio-Respiratory Health

William Kraus, M.D., presented the subcommittee report on cardio-respiratory health. Dr. Kraus opened with the thought that this area is challenged by the fact that an exposure is a continuum; however, the outcomes in this area are continuous. The subcommittee reviewed eight major findings.

There are favorable dose-response relationships between increases of habitual physical activity and:

1. CHD morbidity and mortality

2. CVD morbidity and mortality

3. Cerebrovascular disease and stroke

4. Blood pressure control

5. Atherogenic dyslipidemia

6. Vascular health: brachial artery flow media dilation (BAFMD)

7. Cardio-respiratory fitness

In analyzing the characteristics of the dose-response relationships in observational and case-controlled studies increased intensity bouts appears to be associated with more favorable outcomes; however, volume in these studies are poorly controlled and it may be an important factor. In experimental studies increased intensity does not always hold (i.e., HDL, TG). Frequency and duration of activity in these studies are poorly studied.

Most, if not all CRH outcomes, are associated with favorable and reproducible responses with weekly volume of 800 MET-minutes per week (equivalent to 12 miles per week). This can be achieved and individualized with combinations of intensities, durations and frequencies. In inactive individuals, any goal should be built gradually.

The subcommittee reviewed the following 4 research questions and summarized conclusions for each question:

1. What is the relation between physical activity and the prevention of cardiovascular disease morbidity and mortality?
   

   Conclusions
   Data from prospective cohort studies and case-control studies, between 1995-2007, support a strong and consistent inverse association between level of physical activity and CHD or CVB morbidity and mortality.

   Men and women who report moderate levels of physical activity experience a 20% - 25% lower risk that their least activity counterparts, while those reporting high levels of activity experience a 30% - 35% lower risk than the least active. This is based on 68 study groups in prospective cohort studies and case-control studies with approximately 872,000 subjects.

   The inverse relation is evident in men and women at all ages and based on very limited data there does not appear to be any differences in the relationship based on race or ethnicity.

   The inverse relation between activity and CVD morbidity and mortality appears to occur in normal weight, overweight and obese men and women.

2. What are the dose response relations between physical activity and cardiovascular morbidity and mortality?
   

   Conclusions
   Much of the data since 1995 is on occupational work and commuting measuring amount of activity performed per day or week with limited data on activity intensity. The different measures make it difficult to draw conclusions across all studies. Of 33 studies reporting analysis for significant dose-response, 21 were significant.

   The data are consistent in showing significant benefit with 2 hours of moderate-intensity activity or greater per week. Lower amounts of activity show some benefit. Greater benefit is associated with higher levels of activity.

3. What is the relation between physical activity and the prevention of cerebrovascular disease morbidity and mortality?
   

   Conclusions
   Based on 24 study groups in prospective cohort and case controlled studies there is a reasonably strong and consistent inverse association for both men and women between amount of habitual physical activity performed and morbidity and mortality resulting from strokes.

   Compared to the least active, persons reporting moderate or high levels of physical activity have approximately a 25% lower risk of all and ischemic stroke. The results shown are greater between study variability than data for CHD and CVD.

4. What are the dose-response relations between physical activity and cerebrovascular disease?
   

   Conclusions
   From 24 sex specific reports on physical activity and stroke, 12 reported an analysis of dose-response.

   Lower rates of stroke are consistently reported when 2 hours, or more, of moderate-intensity activity per week is performed. Lower levels of activity are inconsistently inversely related to strokes

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