LETTER
Trends in Physical Inactivity To the Editor: A recent article by Ladabaum et al1 raised an important question regarding the leading drivers for the obesity epidemic in US adults. We appreciate that the authors called attention to physical inactivity as an important public health problem and attempted to relate the rise in obesity to trends in leisure-time physical activity and energy intake. We agree that the prevalence of adult obesity has increased during this period. This is consistent with previous studies using the National Health and Nutrition Examination Survey (NHANES), which defined obesity according to waist circumference2 or body mass index.3,4 The authors suggest that the increase in obesity prevalence in US adults between 1988 and 2010 was due to a decrease in leisure-time physical activity, as opposed to an increase in caloric intake. They base their conclusions on data from NHANES. However, we question the conclusion because different questionnaires were used across the survey cycles analyzed, including NHANES III (1998-1994), NHANES (1999-2006), and the NHANES Global Physical Activity Questionnaire (2007-2008, 2009-2010). Unfortunately, these 3 versions of the NHANES physical activity questions are not directly comparable.5 The authors’ conclusion that the prevalence of “no leisure-time physical activity” rose from 19.1% to 51.7% in women and from 11.4% to 43.5% in men, between 1988 and 2010, is astonishingly extreme, and likely artifactual. We believe the differences to be largely, if not completely, due to the different physical activity questions used in the NHANES versions over time, the different time frames enquired about (past 30 days in NHANES III and NHANES 1999-2006 vs past 7 days in NHANES 2007-2008 and 2009-2010), and the requirement for physical activity to “count” only when carried out in bouts of at least 10 minutes (imposed for more recent NHANES surveys but not NHANES III). To more reliably examine trends in “no leisure-time physical activity,” results from identical surveys over time are needed. The Behavioral Risk Factor Surveillance System includes a single question that has remained constant since 1988. Participants were asked, “During the past month, did you participate in any physical activities or exercises such Funding: None. Conflicts of Interest: None. Authorship: Both authors had a role in writing the manuscript. 0002-9343/$ -see front matter Ó 2015 Elsevier Inc. All rights reserved.
as running, calisthenics, golf, gardening, or walking for exercise?” From 2002 to 2010, the wording was changed slightly to include the phrase “Other than your regular job.”.6 This more valid assessment of “no leisure-time physical activity” indicates little change in physical inactivity, and even a slight decline, between 1988 and 2010.6 Thus, when “no leisure-time physical activity” is assessed by a consistent survey over 2 decades, there has been little change in its prevalence. This does not mean that there has been no change in energy expenditure over this period, and some evidence exists that energy expenditure from combined leisure-time, occupational, housework, and transport-based physical activities has declined.7 However, the NHANES data used by Ladabaum et al were incorrectly interpreted as providing evidence of an increase in physical inactivity rates. David R. Bassett, PhDa I-Min Lee, MBBS, MPH, ScDb b
a The University of Tennessee, Knoxville Brigham and Women’s Hospital and Harvard Medical School Cambridge, Mass
http://dx.doi.org/10.1016/j.amjmed.2014.12.019
ACKNOWLEDGMENT The authors thank Richard Troiano (Risk Factor Assessment Branch, National Cancer Institute) for providing valuable comments.
References 1. Ladabaum U, Mannalithara A, Myer PA, Singh G. Obesity, abdominal obesity, physical activity, and caloric intake in US adults: 1988-2010. Am J Med. 2014;127:717-727.e12. 2. Li C, Ford ES, McGuire LC, Mokdad AH. Increasing trends in waist circumference and abdominal obesity among US adults. Obesity (Silver Spring). 2007;15(1):216-224. 3. Flegal KM, Carroll MD, Kit BK, Ogden CL. Prevalence of obesity and trends in the distribution of body mass index among US adults, 1999-2010. JAMA. 2012;307(5):491-497. 4. Flegal KM, Carroll MD, Ogden CL, Curtin LR. Prevalence and trends in obesity among US adults, 1999-2008. JAMA. 2010;303(3):235-241. 5. Carlson SA, Densmore D, Fulton JE, Yore MM, Kohl HW 3rd. Differences in physical activity prevalence and trends from 3 U.S. surveillance systems: NHIS, NHANES, and BRFSS. J Phys Act Health. 2009;6(suppl 1):S18-S27. 6. Moore LV, Harris CD, Carlson SA, Kruger J, Fulton JE. Trends in no leisure-time physical activity—United States, 1988-2010. Res Q Exerc Sport. 2012;83(4):587-591. 7. Ng SW, Popkin BM. Time use and physical activity: a shift away from movement across the globe. Obes Rev. 2012;13(8):659-680.
Trends in Physical Inactivity To the Editor: A recent article by Ladabaum et al1 raised an important question regarding the leading drivers for the obesity epidemic in US adults. We appreciate that the authors called attention to physical inactivity as an important public health problem and attempted to relate the rise in obesity to trends in leisure-time physical activity and energy intake. We agree that the prevalence of adult obesity has increased during this period. This is consistent with previous studies using the National Health and Nutrition Examination Survey (NHANES), which defined obesity according to waist circumference2 or body mass index.3,4 The authors suggest that the increase in obesity prevalence in US adults between 1988 and 2010 was due to a decrease in leisure-time physical activity, as opposed to an increase in caloric intake. They base their conclusions on data from NHANES. However, we question the conclusion because different questionnaires were used across the survey cycles analyzed, including NHANES III (1998-1994), NHANES (1999-2006), and the NHANES Global Physical Activity Questionnaire (2007-2008, 2009-2010). Unfortunately, these 3 versions of the NHANES physical activity questions are not directly comparable.5 The authors’ conclusion that the prevalence of “no leisure-time physical activity” rose from 19.1% to 51.7% in women and from 11.4% to 43.5% in men, between 1988 and 2010, is astonishingly extreme, and likely artifactual. We believe the differences to be largely, if not completely, due to the different physical activity questions used in the NHANES versions over time, the different time frames enquired about (past 30 days in NHANES III and NHANES 1999-2006 vs past 7 days in NHANES 2007-2008 and 2009-2010), and the requirement for physical activity to “count” only when carried out in bouts of at least 10 minutes (imposed for more recent NHANES surveys but not NHANES III). To more reliably examine trends in “no leisure-time physical activity,” results from identical surveys over time are needed. The Behavioral Risk Factor Surveillance System includes a single question that has remained constant since 1988. Participants were asked, “During the past month, did you participate in any physical activities or exercises such Funding: None. Conflicts of Interest: None. Authorship: Both authors had a role in writing the manuscript. 0002-9343/$ -see front matter Ó 2015 Elsevier Inc. All rights reserved.
as running, calisthenics, golf, gardening, or walking for exercise?” From 2002 to 2010, the wording was changed slightly to include the phrase “Other than your regular job.”.6 This more valid assessment of “no leisure-time physical activity” indicates little change in physical inactivity, and even a slight decline, between 1988 and 2010.6 Thus, when “no leisure-time physical activity” is assessed by a consistent survey over 2 decades, there has been little change in its prevalence. This does not mean that there has been no change in energy expenditure over this period, and some evidence exists that energy expenditure from combined leisure-time, occupational, housework, and transport-based physical activities has declined.7 However, the NHANES data used by Ladabaum et al were incorrectly interpreted as providing evidence of an increase in physical inactivity rates. David R. Bassett, PhDa I-Min Lee, MBBS, MPH, ScDb b
a The University of Tennessee, Knoxville Brigham and Women’s Hospital and Harvard Medical School Cambridge, Mass
http://dx.doi.org/10.1016/j.amjmed.2014.12.019
ACKNOWLEDGMENT The authors thank Richard Troiano (Risk Factor Assessment Branch, National Cancer Institute) for providing valuable comments.
References 1. Ladabaum U, Mannalithara A, Myer PA, Singh G. Obesity, abdominal obesity, physical activity, and caloric intake in US adults: 1988-2010. Am J Med. 2014;127:717-727.e12. 2. Li C, Ford ES, McGuire LC, Mokdad AH. Increasing trends in waist circumference and abdominal obesity among US adults. Obesity (Silver Spring). 2007;15(1):216-224. 3. Flegal KM, Carroll MD, Kit BK, Ogden CL. Prevalence of obesity and trends in the distribution of body mass index among US adults, 1999-2010. JAMA. 2012;307(5):491-497. 4. Flegal KM, Carroll MD, Ogden CL, Curtin LR. Prevalence and trends in obesity among US adults, 1999-2008. JAMA. 2010;303(3):235-241. 5. Carlson SA, Densmore D, Fulton JE, Yore MM, Kohl HW 3rd. Differences in physical activity prevalence and trends from 3 U.S. surveillance systems: NHIS, NHANES, and BRFSS. J Phys Act Health. 2009;6(suppl 1):S18-S27. 6. Moore LV, Harris CD, Carlson SA, Kruger J, Fulton JE. Trends in no leisure-time physical activity—United States, 1988-2010. Res Q Exerc Sport. 2012;83(4):587-591. 7. Ng SW, Popkin BM. Time use and physical activity: a shift away from movement across the globe. Obes Rev. 2012;13(8):659-680.
