Physical Activity and AllCause Mortality: What is the DoseResponse Relation

1
Physical Activity and All-Cause Mortality What
is the Dose-Response Relation?

• Lee, I, and Skerrett, P. Medicine and Science in
  Sport and Exercise 33(6 suppl) S459-S471, 2001.

2
INTRODUCTION

• China 2500 BC evidence of physical activity
  promoted for health benefits
• Morris and Heady (1953) British workers
• Workers with higher occupational physical
  activity levels lived longer

3
INTRODUCTION

• Previous recommendations
• Vigorous-intensity exercise
• 20 minutes continuously
• Three times a week
• Current recommendations
• Moderate-intensity physical activity
• At least 30 minutes
• Most days of the week

4
INTRODUCTION

• Comparison of recommendations
• Similar volume of exercise (1000 kcals/week)
• Different intensity levels Moderate versus
  vigorous intensity
• Different duration recommendations Continuous
  versus Intermittent or Continuous

5
PURPOSE

• To describe the shape of the dose-response curve
  between physical activity or fitness and
  all-cause mortality.
• What is the minimum dose or volume required to
  decrease mortality?
• What is the minimum intensity required to
  decrease mortality?
• What is the minimum duration (if volume is help
  constant) required to decrease mortality?
• What is the minimum frequency (if volume is help
  constant) required to decrease mortality?

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METHODS

• Forty-four studies published between 1966 and
  July 2000.

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RESULTS

• A linear inverse dose-response relationship in 34
  of the 44 studies.
• Remaining 10 studies, 5 showed a threshold effect
  and 5 showed no effect.
• 24 of the 44 studies included women.
• Findings for women paralleled that of men
• Blair et al. (1995)

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Physical fitness and all-cause mortality. A
prospective study of healthy men and women.Blair
SN, Kohl HW 3rd, Paffenbarger RS Jr, Clark DG,
Cooper KH, Gibbons LW. JAMA. 1989 Nov3
262(17)2395-40

• We studied physical fitness and risk of all-cause
  and cause-specific mortality in 10,224 men and
  3120 women who were given a preventive medical
  examination.
• Physical fitness was measured by a maximal
  treadmill exercise test.
• Average follow-up was slightly more than 8 years,
  for a total of 110,482 person-years of
  observation.
• There were 240 deaths in men and 43 deaths in
  women. Age-adjusted all-cause mortality rates
  declined across physical fitness quintiles from
  64.0 per 10,000 person-years in the least-fit men
  to 18.6 per 10,000 person-years in the most-fit
  men (slope, -4.5).
• Corresponding values for women were 39.5 per
  10,000 person-years to 8.5 per 10,000
  person-years (slope, -5.5).
• These trends remained after statistical
  adjustment for age, smoking habit, cholesterol
  level, systolic blood pressure, fasting blood
  glucose level, parental history of coronary heart
  disease, and follow-up interval.
• Lower mortality rates in higher fitness
  categories also were seen for cardiovascular
  disease and cancer of combined sites.
• Attributable risk estimates for all-cause
  mortality indicated that low physical fitness was
  an important risk factor in both men and women.
• Higher levels of physical fitness appear to delay
  all-cause mortality primarily due to lowered
  rates of cardiovascular disease and cancer.

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Changes in physical fitness and all-cause
mortality. A prospective study of healthy and
unhealthy men.Blair SN, Kohl HW 3rd, Barlow CE,
Paffenbarger RS Jr, Gibbons LW, Macera CA.JAMA.
1995 Apr 12273(14)1093-8.

• OBJECTIVE--To evaluate the relationship between
  changes in physical fitness and risk of mortality
  in men.
• DESIGN--Prospective study, with two clinical
  examinations (mean interval between examinations,
  4.9 years) to assess change or lack of change in
  physical fitness as associated with risk of
  mortality during follow-up after the subsequent
  examination (mean follow-up from subsequent
  examination, 5.1 years).
• SETTING--Preventive medicine clinic.
• STUDY PARTICIPANTS--Participants were 9777 men
  given two preventive medical examinations, each
  of which included assessment of physical fitness
  by maximal exercise tests and evaluation of
  health status.
• MAIN OUTCOME MEASURES--All cause (n 223) and
  cardiovascular disease (n 87) mortality.
• RESULTS--The highest age-adjusted all-cause death
  rate was observed in men who were unfit at both
  examinations (122.0/10,000 man-years) the lowest
  death rate was in men who were physically fit at
  both examinations (39.6/10,000 man-years). Men
  who improved from unfit to fit between the first
  and subsequent examinations had an age-adjusted
  death rate of 67.7/10,000 man-years. This is a
  reduction in mortality risk of 44 (95
  confidence interval, 25 to 59) relative to men
  who remained unfit at both examinations.
  Improvement in fitness was associated with lower
  death rates after adjusting for age, health
  status, and other risk factors of premature
  mortality. For each minute increase in maximal
  treadmill time between examinations, there was a
  corresponding 7.9 (P .001) decrease in risk of
  mortality. Similar results were seen when the
  group was stratified by health status, and for
  cardiovascular disease mortality.
• CONCLUSIONS--Men who maintained or improved
  adequate physical fitness were less likely to die
  from all causes and from cardiovascular disease
  during follow-up than persistently unfit men.
  Physicians should encourage unfit men to improve
  their fitness by starting a physical activity
  program.

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RESULTS Volume

• Statistically significant decrease in all-cause
  mortality was found
• gt1000 kcal/wk
• gt980 kcal/wk
• average of 512 kcal/wk
• gt500 kcal/wk
• walked 1-2 miles/day
• Risk reductions ranged from 20-30.
• Paffenbarger et al. (1998)

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Physical activity, all-cause mortality, and
longevity of college alumniRS Paffenbarger, RT
Hyde, AL Wing, and CC Hsieh New England Journal
of MedicineVolume 314605-613

• We examined the physical activity and other
  life-style characteristics of 16,936 Harvard
  alumni, aged 35 to 74, for relations to rates of
  mortality from all causes and for influences on
  length of life.
• A total of 1413 alumni died during 12 to 16 years
  of follow-up (1962 to 1978).
• Exercise reported as walking, stair climbing, and
  sports play related inversely to total mortality,
  primarily to death due to cardiovascular or
  respiratory causes.
• Death rates declined steadily as energy expended
  on such activity increased from less than 500 to
  3500 kcal per week, beyond which rates increased
  slightly.
• Rates were one quarter to one third lower among
  alumni expending 2000 or more kcal during
  exercise per week than among less active men.
• With or without consideration of hypertension,
  cigarette smoking, extremes or gains in body
  weight, or early parental death, alumni mortality
  rates were significantly lower among the
  physically active.
• Relative risks of death for individuals were
  highest among cigarette smokers and men with
  hypertension, and attributable risks in the
  community were highest among smokers and
  sedentary men.
• By the age of 80, the amount of additional life
  attributable to adequate exercise, as compared
  with sedentariness, was one to more than two
  years.

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RESULTS Intensity

• Four studies reported intensity levels
• gt4.5 METS or moderately vigorous (1 study)
• gt6 METS or vigorous (3 studies)

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RESULTS Duration

• None of the studies held intensity constant while
  looking at duration
• Likely that duration does not matter as long as
  total volume is great enough

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CONCLUSIONS

• There is an inverse dose-response relationship
  between volume of physical activity and all-cause
  mortality
• Minimal volume of 1000 kcal/wk reduce all-cause
  mortality by 20-30
• Increasing physical activity is also associated
  with a decrease in all-cause mortality

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CONSLUSIONS

• No randomized controlled studies have been
  conducted
• Did poor health cause people to decrease physical
  activity before the start of a study? Unlikely
• Did other health factors (smoking, diet, etc.)
  confound the results? Active people generally are
  more health conscious.

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OTHER QUESTIONS

• Is physical activity or physical fitness more
  important in defining health benefits? (Blair,
  Cheng, and Holder MSSE 2001, pp S379).
• Absolute versus relative intensity. (Shephard, R
  MSSE 2001, pp S400).
• Short versus long duration (Hardman, MSSE 2001,
  pp S421)
• Are there similar physical activity dose-response
  relationships for fitness and health? (Oja, P.
  MSSE 2001, pp S428).
• Different exercise prescriptions for health,
  fitness and competition?