American Journal of Epidemiology Advance Access originally published online on October 17, 2007
American Journal of Epidemiology 2007 166(11):1355-1356; doi:10.1093/aje/kwm290
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LETTERS TO THE EDITOR |
RE: "INFLUENCE OF EXERCISE, WALKING, CYCLING, AND OVERALL NONEXERCISE PHYSICAL ACTIVITY ON MORTALITY IN CHINESE WOMEN"
Division of Population Health and Information, Alberta Cancer Board, 1331-29 Street NW, Calgary, Alberta, Canada T2N 4N2
(e-mail: ilona.csizmadi{at}cancerboard.ab.ca)
The reduced risk of mortality reported by Matthews et al. (1) for women with active lifestyles, achieved by participating in either exercise or nonexercise activities, is an intriguing finding. One limitation of the study, acknowledged by the authors, was the use of retrospective self-reports to estimate energy expenditure from exercise and nonexercise activities.
While the use of objective measures of energy expenditure, applied prospectively, would have overcome this limitation, it is important to note that the study by Matthews et al. (1) (n = 67,143) simply would not have been feasible using currently available technology. Indeed, it is unlikely that today's objective approaches, such as doubly labeled water or accelerometers combined with heart rate monitors, could realistically be applied in studies with several thousand participants. Hence, we agree with Sesso (2) and with Matthews et al. (3) that self-reported methods are, and will continue to be, the primary approach to quantifying activity in large epidemiologic studies.
Unfortunately, however, the properties of the measurement error incurred when using self-report instruments to assess overall activity among large numbers of free-living people have not been adequately explored. An analogy to nutritional epidemiology made by both Sesso (2) in an accompanying commentary and the corresponding response by Matthews et al. (3) is relevant, especially in view of the comprehensive and sophisticated approaches that have been used to quantify the measurement error associated with dietary intake instruments (4, 5).
We recently conducted a review of physical activity questionnaires that have been "validated" against doubly labeled water (6), the "gold standard" for estimating energy expenditure. Limitations in study design and in analyses, and insufficient details in the reporting of results, meant that firm conclusions could not be drawn about the validity of physical activity questionnaires for estimating overall activity energy expenditure. In addition, fewer than half of the 23 validated questionnaires in our review inquired about activities undertaken at relatively low intensities. Such activities, if undertaken for long periods of time, can contribute substantially to overall activity.
Failure to ask about all activities may result in misleading estimates of energy expenditure, as illustrated in a recent study by Manini et al. (7). In that study, energy expenditure determined by both doubly labeled water and self-reported activity led to a large discrepancy in energy expenditure estimates between the two methods. While an accompanying editorial (8) strongly implicated misreporting as the most likely explanation for the discrepancy, it is important to note that Manini et al. (7) collected complete information on only a limited number of activities. Hence, in our opinion, the results should not be used to discredit the use of self-reporting methods but rather to reiterate the need for a more comprehensive self-report tool that would allow for assessment of exercise and nonexercise activities, combined.
If the "more subtle components of nonexercise or lifestyle physical activity" are to be measured and understood in relation to disease prevention and health outcomes, as Sesso advocates (2, p. 1353), then a paradigm shift must occur in the conceptual view of physical activity. We must abandon the narrow view of physical activity as merely that which consists of purposeful, structured, recreational activity. Instead, we need to recognize that ascertainment of all movement, planned or otherwise, is of value in the estimation of overall activity energy expenditure.
Thus, we believe that it is imperative that epidemiologists develop and continually evaluate new self-report tools that could be used to estimate overall activity energy expenditure in large epidemiologic studies. Without this effort, it will not be possible to make an informed evaluation of the impact of overall energy expenditure on health outcomes in large epidemiologic studies such as the one conducted by Matthews et al. (1).
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ACKNOWLEDGMENTS |
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Conflict of interest: none declared.
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NOTES |
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Editor's note: In accordance with Journal policy, Sesso and Matthews et al. were asked whether they wanted to respond to this letter, but they chose not to do so.
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References |
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 TOP References |
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- Matthews CE, Jurj AL, Shu XO, et al. Influence of exercise, walking, cycling, and overall nonexercise physical activity on mortality in Chinese women. Am J Epidemiol (2007) 165:1343–50.
[Abstract/Free Full Text] - Sesso HD. Invited commentary: a challenge for physical activity epidemiology. Am J Epidemiol (2007) 165:1351–3.
[Abstract/Free Full Text] - Matthews CE, Jurj AL, Shu XO, et al. Matthews et al. respond to "A challenge for physical activity epidemiology." Am J Epidemiol (2007) 165:1354–5.
[Free Full Text] - Kipnis V, Subar AF, Midthune D, et al. Structure of dietary measurement error: results of the OPEN biomarker study. Am J Epidemiol (2003) 158:14–21.
[Abstract/Free Full Text] - Subar AF, Kipnis V, Troiano RP, et al. Using intake biomarkers to evaluate the extent of dietary misreporting in a large sample of adults: the OPEN study. Am J Epidemiol (2003) 158:1–13.
[Abstract/Free Full Text] - Neilson HK, Robson PJ, Friedenreich CM, et al. Estimating activity energy expenditure: how valid are physical activity questionnaires? Am J Clin Nutr. (in press).
- Manini TM, Everhart JE, Patel KV, et al. Daily activity energy expenditure and mortality among older adults. JAMA (2006) 296:171–9.
[Abstract/Free Full Text] - Blair SN, Haskell WL. Objectively measured physical activity and mortality in older adults. JAMA (2006) 296:216–18.
[Free Full Text]
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