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School of Sport & Exercise Sciences

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School of Sport & Exercise Sciences

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  1. School of Sport & Exercise Sciences Physical activity, obesity and cancer – a review of current knowledge and recommendations Adrianne E Hardman

  2. Outline • Measuring exposure to physical activity • Colorectal cancer • Breast cancer • Other cancers • Recommendations • Summary

  3. Assessment of exposure • Sources – activities of daily living, occupation, recreation • Components – intensity, duration, frequency • Time periods in life – childhood, adolescence, – lifetime, recent • Fitness – acquired through participation in high levels of vigorous activity

  4. Measures of physical activity • Intensity • Participation in activities known to incur a high rate of energy expenditure • METs – multiples of resting metabolic rate • Descriptors – ‘vigorous’, ‘hard enough cause sweating’ • ‘Volume’ = intensity x duration x frequency • Energy expenditure in MJ (kcal) per week • MET-hours

  5. Examples • 1000 kcal (4.2 MJ) per week - approximately 2.5 h of moderate intensity physical activity per week • MET-h • Brisk walking (4.5 METs) daily for one hour is (4.5 x 1 x 7) = 31.5 MET-h per week • Doubles tennis (6 METs) for 1.5 hours, three times per week is (6 x 1.5 x 3) = 27 MET-h per week

  6. Outline • Measuring exposure to physical activity • Colorectal cancer • Breast cancer • Other cancers • Recommendations • Summary

  7. Physical activity and risk of colon cancer in Harvard alumni High; >2500 kcal/wk Mod: 1000-2500 kcal/wk Lee I-M et al J Natl Cancer Inst 1991;83:1324

  8. Relative risk of colon cancer by leisure-time physical activity P trend = 0.03 Martínez et al J Natl Cancer Inst 1997;89:948

  9. Energy balance, physical activity and risk of colon cancer in men Slattery et al Cancer Res 1997;57:75

  10. Risk of colon cancer in people with high energy intake & high BMI Odds ratio 95% CI Low physical 3.35 2.09 – 5.35 activity High physical 1.28 0.81 – 2.03 activity Slattery et al Cancer Res 1997;57:75

  11. Exercise and colon cancer: ‘convincing’ evidence • Consistent 30-40% lower risk, RR 0.6-0.7 • Independent of confounding factors, including BMI • Findings replicated in different populations • Dose-response evident: 30-60 min/day of moderate to vigorous activity is optimal • No effect on risk of rectal cancer

  12. Outline • Measuring exposure to physical activity • Colorectal cancer • Breast cancer • Other cancers • Recommendations • Summary

  13. Physical activity & breast cancer risk in Norwegian women Thune et al N Engl J Med 1997;336:1269-75

  14. Physical activity and breast cancer: case-control study Friedenreich et al Am J Epidemiol 2001;154:336-47

  15. US Women’s Health Initiative Cohort Study McTiernan A et al JAMA 2003:290:1331-6

  16. Breast cancer risk by activity level and BMI McTiernan A et al JAMA 2003;290:1331-6

  17. Physical activity and breast cancer – ‘convincing’ evidence • 55 observational studies (23 cohort, 32 case-control) • Reasonably clear pattern of lower rates among active women – median RR 0.8 (20-30% lower risk) • Stronger, more consistent effect for postmenopausal women (median RR 0.7) • Linear trend in two thirds of the studies that looked at dose-response • Lowest risk in lean, physically active women

  18. Outline • Measuring exposure to physical activity • Colorectal cancer • Breast cancer • Other cancers • Recommendations • Summary

  19. Physical activity and risk ofprostate cancer • At least 36 studies • Inconsistent findings, median RR 0.9 • Harvard Alumni Study and Health Professionals’ Follow-up Study provide some support BUT……… • Overall, available epidemiological evidence does not support a role for physical activity in preventing prostate cancer

  20. Physical activity and cancer risk at other sites • Lung ‘possible’ • Endometrial ‘possible’ • Testicular ‘insufficient’ • Ovarian ‘insufficient’ • Other (kidney, ovary, testes, liver, oesophagus, pancreas, gall-bladder) all ‘insufficient’ IARC Handbooks of Cancer Prevention, Vol 6: 2002 Friedenreich (2001) Cancer Epidemiol Biomarkers Prevention 10:287-301

  21. Outline • Measuring exposure to physical activity • Colorectal cancer • Breast cancer • Other cancers • Recommendations • Summary

  22. Recommendations • 30 to 60 min moderate- to vigorous-intensity physical activity on most days • Sustain physical activity over lifetime • Avoid weight gain • Maintain BMI between 18.5 and 25.0 • Remember additional benefits from physical activity

  23. What is ‘moderate’ intensity? • For majority of middle-aged and older adults, 3 to 6 METs • What matters is intensity relative to one’s capacity • 40 to 60% of VO2max (remember that VO2max decreases with age) • Rating of perceived exertion 12-13 . .

  24. Brisk/very brisk walking (4 to 4.5 METs) typifies moderate intensity physical activity for the majority of middle-aged and older adults

  25. Modelling the effect of increased walking on colon cancer incidence Health Professionals Follow-up Study* data • adding 3 h of walking per week to all participants suggests a 17% decrease in the incidence of colon cancer • adding 3 h walking per week to the most sedentary men (24%) would reduce incidence by only 7% Colditz GA et al Cancer Causes Control 1997:8:649-67 * Giovannucci E et al Ann Internal Med 1995;122:327-34

  26. Summary I • Convincing evidence that physical activity plays a role in reducing risk of colon and breast cancer • Associations unlikely to be due to other healthy behaviours • Details of dose-response curves and optimal amount of activity unclear • Inactivity is an important, avoidable risk factor for these common cancers

  27. Summary II • One third of cancer deaths in US can be attributed to diet and activity habits† • Taken together, inactivity and excess body weight probably account for one third to one fourth of deaths from cancer of colon and breast § † Byers T et al CA Cancer J (2002) 52:92-119 §IARC Handbooks of Cancer Prevention, Vol 6: 2002

  28. Key References • Friedenreich CM, Orenstein MR (2002) Physical activity and cancer prevention: etiologic evidence and biological mechanisms. J Nutrition 132:345S-64S. • Friedenreich CM (2004) Physical activity and breast cancer risk: the effect of menopausal status. Ex Sports Sci Revs 32:180-4. • International Agency for Research on Cancer (2002). IARC Handbooks of Cancer Prevention: weight control and physical activity, Vol. 6. Lyon: IARC Press. • Lee, I-M (2003) Physical activity and cancer prevention – Data from epidemiologic studies. Med Sci Sports Exerc 35:1823-7. • McTiernan A (2003) Physical activity, exercise, and cancer: prevention to treatment – Symposium overview. Med Sci Sports Exerc 35:1821-2 (and associated papers) • Slattery ML (2004) Physical activity and colorectal cancer. Sports Medicine 34:239-52.