PHYSICAL ACTIVITY, LONGEVITY AND PHYSICAL HEALTH
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first step in behavioral epidemiology framework is to establish link between physical
activity and health – no doubt, this has been done
summary of current scientific understanding of the effects of physical activity and
inactivity on indicators of physical health
PHYSICAL ACTIVITY AND LONGEVITY
- studies of this type help answer the question of whether exercise adds years to life
- best answer; it consistently reduces risk of dying at any one point in time
- physically active individuals live longer, therefore the benefits outweigh the risks
- most common type – assess physical activity in a sample population at some endpoint, compare morbidity rates between those physically active and those that are not
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classic study by Paffenbarger, et al. 1986, showed all-cause mortality reduced by 53%
in men who played sports 3 or more hrs per week compared to those < 1 hr per week
death rates 33% lower in men who walked > 15 km per week compared with men
who walked < 5 km per week
active men lived ~ 2 years longer than inactive men
Blair et al (1989) used fitness measures (as opposed to subjective questionnaire
responses and found that highest fit men had a 71% lower death rate than fit men
also, men in lower high fit categories had lower death rates (60% all-cause mortality)
than least fit men
analogous findings were also shown for women
subsequent studies by Blair (1996) showed that independent of other risk factors –
those with higher fitness levels had lower death rates
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what about changing fitness category?
Paffenbarger et al. (1993) – evaluated the changing of physical activity levels in
10,000 men and concluded: compared with men physically inactive at two different
assessments, those who became active decreased risk by 15% (44% reduction as
reported by Blair et al. 1995), those who became inactive increased their risk by 10%
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last question: How much activity is needed for health benefits? Figure 2-1
what is the general trend and where are the greatest benefits seen?
PHYSICAL INACTIVITY’S CONTRIBUTION TO THE BURDEN OF DISEASE AND
PREMATURE DEATH
- estimate the number of deaths for which physical inactivity is responsible –
“population attributable risk” is based on RR associated with inactivity and the
prevalence of inactivity in the population
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for example, inactivity doubles risk of CHD; high prevalence > 50% <
recommendations
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population attributable risk is large – Hahn et al (1990) estimated > ¼ million deaths
in 1985 could have prevented if physical inactivity was eliminated
~ 23% of all deaths; while 33% smoking, 23% lipids, 24% obesity
PHYSICAL ACTIVITY AND CARDIOVASCULAR DISEASE
- physical activity decreases all-cause mortality by reducing risk of cardiovascular
diseases (the most common form of death in industrialized nations)
- arteriosclerosis in the arteries which eventually leads to blockage of blood flow
- heart attack – blockage in the heart; stroke – blockage in the brain
- CHD is most deadly form of CVD
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there is a dose-response relationship with the largest change occurring from sedentary
to some level of activity
~35% of deaths from CHD due to physical inactivity; HP 2000 – 30% goal
PHYSICAL ACTIVITY AND RISK FACTORS FOR CARDIOVASCULAR DISEASE
- statistically adjusting for other risk factors for CVD decreases strength of association
with physical activity
- indicative of what? – positive influence of physical activity on other risk factors
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vigorous activity reduces risk of hypertension 19-30% in men; physically active
women 30% less likely to get hypertension then sedentary (6-7 mm Hg drop in both
systolic and diastolic)
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cholesterol? – physical activity doesn’t necessarily affect total cholesterol or LDL
cholesterol; however, physical activity increases HDL: 20-30% higher in endurance
trained athletes; HDL – reverse cholesterol transport
PHYSICAL ACTIVITY AND PREVENTION OF OBESITY
Physical Activity and Body Fat
- overweight and obesity linked to several diseases: CVD, hypertension, cancer
- excess body fat is the culprit; however, difficult to measure in epidemiological
research
- BMI = wt (kg)/ht2(m)
- overweight increasing rapidly: 1970 – 25%; 1990 – 33% (adults); 10.9% of
children > 95th percentile compared to children in 1963 (more than doubled)
- highest prevalence: African-American and Mexican-American women 49 and
47%, respectively
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excess body fat believed to develop from energy imbalance – genetics also plays a
role – however, prospective studies generally support effectiveness of physical
activity in preventing excess weight gain
Fitness or Fatness?
- fit men had same risk of dying no matter status of overweight
PHYSICAL ACTIVITY AND WEIGHT LOSS
- exercise alone results ~ 3 kg weight loss
- not much, but the combination of weight loss (fat) with increases in muscle mass lead
to exponential benefit
- physical activity – very important in the maintenance of weight loss
PHYSICAL ACTIVITY AND DIABETES
- excessive levels of glucose in the blood and inability of insulin to metabolize it
(insulin resistance)
- NIDDM ~ 90% of all cases of diabetes – 3-6% prevalence with equal numbers being
undiagnosed
- higher for non-Caucasian and 40-80% higher for females
- can lead to blindness and liver disease – but, most importantly a CVD risk factor
- can be eliminated through weight loss
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positive benefits of physical activity in two ways:
o reduces blood glucose and increase insulin sensitivity
o reduces central obesity
15% reduction for women who exercised vigorously at least once per week; 25% in
men
population attributable risk – physical activity responsible for 35% of NIDDM deaths
now recognized as important as prescription medication in treatment
PHYSICAL ACTIVITY AND CANCERS
- second leading cause of death in many industrialized nations
- lung, breast, prostate and colon
- 32% of deaths due to colon cancer – physical inactivity (“PAR”)
- some evidence for prostate and breast cancer
PHYSICAL ACTIVITY AND OSTEOPOROSIS
- peak bone mass and rate of decline determine risk of osteoporosis – both of which are
directly related to physical activity
PHYSICAL ACTIVITY AND FUNCTIONING IN THE ELDERLY
- ADL
- loss of function is due to inactivity
PHYSICAL ACTIVITY AND LOW-BACK FUNCTION
- experienced by 80% of population at some point in life
- not much evidence one way or the other
PHYSICAL ACTIVITY, PSYCHONEUROIMMUNOLOGY AND HIV
- the study between psychological variables, the nervous system and the immune
system
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evidence is emerging that demonstrates positive affects of physical activity in dealing
with the stress of HIV
also, important for enhancing strength of immune system – decreases depression,
decreases strength of stress inducing hormones (cortisol and catecholamines),
increases beta endorphins and direct and positive effects on immune system
HEALTH RISKS OF PHYSICAL ACTIVITY
- benefits should outweigh the risks
- risks include musculoskeletal injuries and cardiac deaths
- risks and benefits – Table 2.1
PHYSICAL ACTIVITY AND THE HEALTH OF CHILDREN AND ADOLESCENTS
- influence morbidity but not mortality, why?
- positive affects on body weight, psychological stress, athletic performance, strengthen
immune system
- reduces risk for CVD as an adult
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aerobic fitness important now and in the future
a difficult parameter to measure and elicit statistical relationship with other, logical
parameters
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overweight and obesity – similar to fitness levels
measures of sedentary living and adiposity are very consistent and strong
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Table 2.2 – Physical Activity and Health
SUMMARY
- ~ 200,000 deaths attributable to sedentary lifestyles each year