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Epi Reading notes.docx

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McMaster University
Krista Howarth

Epi Reading REVIEW- Health Benefits of Physical Activity- the evidence Abstract- to provide further insight into the role physical activity plays in the development of chronic disease and premature death; PA is effective in disease prevention as evidence shows; current health guidelines are sufficient to elicit health benefits especially in previously sedentary people • PA is modifiable risk factor for CV disease among other diseases as well (DM, Cancer, obesity, bone and joint diseases) • Of all modifiable riskfactors, physical inactivity is highest among Canadians (51%) • Meta- analysis All-cause and cardiovascular related death Primary prevention • Several long term prospective follow up studies (Morris and colleagues 1950s, Paffenbarger and colleagues 1970s) assessed the RR of death from any cause and from specific diseases associated with physical activity • Reduce RR of death by 20-35% by increasing PA levels (in both men and women)\ • Ex. Healthy middle aged women and men- followed up for 8 years- fitness measured on a treadmill; lowest quintile of fitness was associated with increased risk of death as compared to the top quintile for fitness o RR Men0 3.4, 95% CI 2.0-5.8 o RR women 4.7, 95% CI 2.2-9.8 • Being fit/active was associated with a >50% reduction in risk of death from any cause or CV disease • Increase in energy expenditure of PA of 1000 kcal/week or 1 MET = mortality benefit of about 20%; physically inactive middle-age women 52% ^ in all-cause mortality, a doubling of CV mortality and 29% increase in cancer related mortality as compared to physically active women • These relative risks are similar to those for hypertension, hypercholesterolemia and obesity • Ppl who are fit yet have other risk factors for CV disease may be at lower risk of premature death than those who are sedentary with no risk for CV disease • Small improvements in physical fitness are associated with a significant reduction in risk • Participants with highest levels of physical fitness at baseline and who maintained or improved their physical fitness had lowest risk of premature death • People who went from unfit to fit over a 5 yr period had a 44% reduction in RR of death compared to people who remained unfit • Literature regarding primary prevention in women revealed there was a graded inverse relation between PA(as little as 1 hr walking/week) and risk of CV disease related death- most active women had a RR of 0.67 95% CI 0.52-0.85 compared to the least active women • Dose response relation appears to exist Secondary Prevention of CV Disease • Benefits of PA extend to patients with CV disease however for a long time rest and physical inactivity had been recommended • Randomized control trials (RCT) are used to study secondary prevention • Meta analysis of 48 clinical trials showed that cardiac rehab reduced incidence of premature death from any cause and CV in particular • Expenditure of about 1600kcal per week has be found to halt progression of CAD • Expenditure of about 2200 kcal per week has been show to help reduce plaque in patients with heart disease • Minimum training intensity recommended for patients with heart disease is 45% of heart rate reserve Diabetes Mellitus Primary Prevention • Prospective study- each increase in 500 kcal in energy expenditure/week = decreased incidence of type II DM; highly evident among ppl at high risk for DM • Moderate levels of PA (at least 40 mins/week) of CV fitness has been shown to protect against development of type II DM in middle aged men • RCTs showed that weight loss thru diet and exercise reduced incidence of disease among high risk ppl by 40-60% over 3-4 yrs • 150 mins of moderate physical activity/week was found to be more effective than metformin; only 7 people would need to be “treated” with the lifestyle intervention compared to 14 ppl given metformin Secondary Prevention • Prospective cohort study showed that walking at least 2 hrs/week helped reduce incidence of premature death of 39-54% from any cause and 34-53% from CV disease among patients with DM • Another prospective cohort study shows men with type II DM had a 1.7 fold increased riskof premature death compared with physically active men with type II diabetes • Aerobic and resistance training are beneficial for the control of diabetes; resistance training better for glycemic control than aerobic training • Meta analysis of 14 control trials showed exercise interventions resulted in a small but significant reduction in glycosylated hemoglobin compared with no exercise intervention • 42% reduction in diabetes related mortality observed in studies using glucose-lowering therapy compared to conventional treatments Cancer Primary Prevention • Any PA is associated with the reduction in risk of cancer and in particular colon and breast cancer • PA greater than 4.5 METS had a better protective effect than lower intensities • Men and women experienced a 30-40% reduction in RR of colon cancer; women 20-30% reduction in RR of breast cancer compared to those who were inactive Secondary Prevention • A 5.5 year follow up study with women with breast cancer revealed little association between recreational PA and risk of death from breast cancer • Recent follow up studies involving those with breast and colon cancer showed that increased self-reported physical activity was associated with decreased recurrence of cancer and risk of death from cancer • Studies going on to find out effect of physical activity on chemotherapy • PA improves quality of life for those with cancer Osteoporosis Primary Prevention • Resistance training helps to increase bone mineral density • Athletes who engage in high impact sports have increased bone mineral density compared to those who participate in low impact sports • Longitudinal studies have examined the effects of exercise training on bone health in those of all ages which show that weight bearing and impact exercise prevents bone loss associated with aging • Meta analysis of RCTs showed that exercise training programs prevented almost 1% of bone loss per year in the lumbar spine and femoral neck in both pre and postmenopausal women; exercise reduces risk of falls • 3262 healthy men followed for 21 yrs, intense PA baseline was associated with a reduced incidence of hip fracture Secondary Prevention • Exercise training is effective in improving bone density in older women with low bone mineral density • Agility training resulted in a significant increase in cortical bone density by 0.5% at the tibial shaft; resistance training resulted in 1.4% increase in cortical bone density at the radial shaft; stretching group experience loss in cortical bone density • Study on postmenopausal-osteopenic women showed that a 2 yr intensive training program was effective in attenuating the rate of bone loss Physical activity or physical fitness? • Physical fitness refers to a state of well being that allows one to meet the demands of daily living or provides basis for sport performance or both; both are strong predictors of risk of death • Physical activity and fitness are often used interchangeably w/ fitness being more accurate measure of PA than self report • Fitness is more strongly predictive of health outcomes than PA; analyses show a reduction of at least 50% in mortality among highly fit ppl compared with low fit ppl • Blair and colleagues have argued that it is preferable to encourage ppl to become more physically active than fit b/c sedentary ppl with likely achieve the latter if they do the former Musculoskeletal fitness: a paradigm shift • Regular PA in elders can lead to reduction in risk for chronic diseases and disability w/ out markedly changing traditional physiologic performance markers • Enhanced musculoskeletal fitness is associated with an improvement in overall health status and reduction in risk of chronic disease and disability • Musculoskeletal fitness important for elderly ppl to maintain functional independence (performing daily activities) • Reduced musculoskeletal fitness leads to increased dependence; improvements in musculoskeletal fitness will delay the onset of disability, disease or dependence • musculoskeletal fitness is negatively associated with risk of falls, illness and premature death How much PA is enough? • Intense PA is inversely and linearly associated with mortality • Paffenbarger & associates revealed that regular PA was associated with an avg. increase in life expectancy of 1-2 years by the age of 80 • Avg. energy expenditure of about 1000kcal/week is associated with a 20-30% reduction in all cause mortality • Most health and fitness organization advocate a minimum volume of exercise that expends 1000kcal/week; however even lower levels of weekly expenditure may still be associated with health benefits • Dose response relationship between PA and health status usually relates to CV disease and premature death from any cause • >5.5 METS for at least 40 mins of exercise is effective in preventing type II DM; walking more than 2 hours/week has also been shown to reduce risk of premature death • Moderate PA for 30-60 minutes per day had a greater protective effect against colon and breast cancer than those of low intensity • Greatest benefit for reducing incidence of breast cancer was shown in women who engaged in 7 or more hrs or mod-vigorous activity/week • Running distances of up to 15-20 miles per week has been associated with accrual or maintenance of bone mineral density but longer distances may be associated with reduced bone mineral density How does PA and fitness lead to improved health outcomes? • Improves body composition, enhance lipoprotein profiles, improve glucose homeostasis and insulin sensitivity, reduce BP, improve autonomic tone, reduce systemic inflammation, decrease blood coagulation, improve coronary blood flow, augment cardiac function, and enhance endothelial function • RCTs have shown exercise training reduces levels of C-reactive protein (associated with many chronic diseases) • Reduces stress, anxiety, depression which is important for prevention of CV disease as well as other chronic diseases • Shear-stress-mediated improvement in endothelial function which leads to a number of health benefits (endothelial dysfunction is observed with aging, smoking, & multiple chronic diseases) • PA also results in specific adaptations that affect individual disease states ex. Increased glycogen sythase and hexokinase activity in type II DM • 46% reduction in cancer rates with regular PA including reductions in fat stores, increased energy expenditures to offset a high fat diet, changes in sex hormone levels, immune function, free radical generation • Thompson and colleagues revealed that acute dynamic exercise may result in transient changes in the form of reductions TG levels,inceases in HDL cholesterol level, decrease in BP etc. Too Much Sitting: The Population Health Science of Sedentary Behaviour • Sedentary behaviours have emerged as a new focus for r
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