Physical activity has been associated with health benefits, despite inconclusive data on which activities presented those benefits. The Harvard Alumni Health Study gathered former undergraduate students from 1916-1950 and assessed their health through a physical activity assessment questionnaire. For those who were eligible, activity level was compared with mortality rate using a follow-up study. Results indicated vigorous intensity activities were associated with postponement of mortality, physical inactivity and being overweight were equal in impact on mortality, and that flights of stairs climbed and blocks walked were accurate predictors of longevity.
Today it’s accepted that physical activity is a requirement of a healthy lifestyle. The type of physical activity and the intensity of that activity has remained unclear for years. The Harvard Alumni Health Study recruited a total of 13,485 men to answer questions concerning the optimal intensity of physical activity. Several studies have claimed that only vigorous-intensity is associated with longevity while others have observed positive associations with non-vigorous activity. The discrepancy in this inconclusive data became the catalyst behind The Harvard Alumni Health Study.
The Harvard Alumni Health Study targeted undergraduate men dating from 1916-1950. Starting in 1962 or 1966, health questionnaires were periodically sent out to surviving alumni. A total of 17,835 men who returned a 1977 questionnaire became eligible. 3,706 men were excluded after reporting physician-diagnosed cardiovascular disease, cancer, or chronic obstructive pulmonary disease. Another 644 men were excluded after not providing information on physical activity and covariates. The Harvard Alumni Health Study deemed 13,485 men suitable for the study.
On the 1977 questionnaire, alumni reported the daily number of blocks walked and flights of stairs climbed. They also reported recreational activities and sports during the past year, a long with the time spent per week, and the number of weeks spent participating each year. This activity assessment allowed for researchers to estimate energy expenditure using calculations for resting metabolic rate and assigning kilojoules to physical activity. Researchers further classified subjects by specific activity components. Men were divided into fourths of distance walked and flights climbed. Sports and recreational activities were categorized as vigorous, moderate, or light-intensity. Energy expenditure was broken into five groups for each intensity level (vigorous, moderate, light). Potential cofounders were asked on the 1977 questionnaire regarding alcohol habits, cigarette habits, Quetelet’s index, early parental death, and physician diagnosed diseases.
Using all of the information gathered on the 1977 questionnaire, researchers examined the association between total energy expenditure and mortality using proportional hazard models, controlling the potential cofounders. Men were categorized by age, and analyzed for two time periods, 1977-1985 and 1986-1992. Researchers compared both energy expenditure and specific activities such as walking or stair climbing to mortality. Quetelet’s index and activity level were compared to mortality to test a hypothesis that physically active but overweight men experience lower mortality rates than those inactive but thin.
Results indicated that greater energy expenditure is associated with increased longevity. Duration of walking and climbing stairs were reliable predictors of longevity. Exercise intensity also was a reliable predictor of longevity. Light-intensity activities showed no association with affecting mortality rates. Moderate intensity activities were associated with lower mortality rates, while greater energy expenditure in vigorous activities clearly predicted lower mortality rates. Longevity was affected by being overweight and physical inactivity to the same extent.
The research design was a prospective cohort study that eliminated those with the presence of disease upon entry, and followed the subjects over a lengthy amount of time. Changes in exposure were possible when researchers only checked on dietary behavior and physical activity one time during the study, ignoring the initial or final assessment of each. The prospective cohort study design was able to infer a casual relationship between physical activity and longevity and was the appropriate choice for the study. A look at multiple health outcomes was possible at the end of the study, a long with an incidence rate related to several forms of physical activity.
Weaknesses with the study are lack of validity for lower mortality rate associated with light and moderate intensities. In the study, results are described as lack of association with light activity and a weak relationship with moderate activity. Physical activity was only assessed in 1977 and therefore changes over time were not documented. Although observational studies cannot determine cause and effect relationships, it’s well documented that exercise has benefits that are associated with postponed mortality. However, lack of prolonged physical activity documentation could deter from these conclusions that the lower mortality rate was associated with physical activity, making it confounding. Further, undefined terms such as sport and recreational activities could have been misinterpreted by subjects during the activity level portion. Dietary information wasn’t gathered in 1977, although it was in 1988. Once again, another example of lack of documentation that could prove critical. The dietary intake over the span of 11 years could be just as important as the physical activity, as the study proved when comparing being overweight to inactivity.
The criteria for causation states the study must have temporal sequence, strength of association, consistency, dose response, and biological plausibility. The temporal sequence of the study is a lack of vigorous or moderate intensity activity with mortality. The strength of the association is relatively unfounded, although the biological plausibility is there. Physical activity is associated with reduced cardiovascular disease, improved blood pressure, and glucose tolerance. Therefore, a biological plausibility for the relationship between physical activity and reduced mortality is apparent, but the level of intensity seems inconclusive. The strength of association is weakened because physical activity wasn’t followed after the initial assessment in 1977. The consistency of the findings is also undetermined. Studies of Finnish men, British civil servants, and US railroad workers indicated a clear association between vigorous physical activity and longevity. Walking studies of Dutch women and men, and Japanese-American men showed an association with greater longevity. These studies reinforced the findings of the Harvard Alumni Health Study, but they weren’t the only studies that covered this topic. Several studies claimed only vigorous activity was associated with longevity, while others associated longevity with light intensity. It’s clear that physical activity is beneficial to health, but further studies under greater scientific controls must be carried out.
In the end, I believe the study was well-designed but parts of the execution weren’t very well done. Although the information gathered is useful to reference in future studies, the conclusive data had several limitations worth noting. Researchers believed that physical activity had a high association with longevity. The more energy expended, the longer the longevity. The causation there wasn’t well explained. Did the participants lose weight, and therefore become healthier? Did the participants not lose weight, but went from inactive to active? Unfortunately, the data isn’t clear enough to mine for answers. However, I applaud the time and effort. There seems to be a direct correlation between mortality rates, activity level, and weight. We can assume that activity level alone increases longevity, since active but overweight participants had a lower mortality rate than the overweight inactive participants. We can also assume that activity level coupled with weight loss would increase longevity since leaner individuals that were active had the lowest mortality rate and highest longevity. As far as the association between light, moderate, and vigorous intensity levels, energy expenditure, type of activity, and the comparison of individuals in each category, it is still hard to conclude. The most difficult aspect is that we can’t have a participant change their activity level or BMI and measure mortality rate accurately. If we can, and we have, tie health to longevity then we can prove that activity level and leaner body mass increases health and therefore lowers mortality rate. This study pointed to that association but didn’t measure health as a variable associated with mortality. I do agree that there is an association created in this study, and I also believe that we are aware of it with or without this study being perfect.
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