According to the World Health Organization, 60 to 85 percent of people in the world lead a sedentary lifestyle, making it a serious public health concern in current society, as physical inactivity is the leading cause of disease and disability.
Earlier this month, results of a study suggesting that sitting too much, and not just lack of exercise, is detrimental to cardiovascular health made headlines. However, the concept of physical inactivity being a leading cause of disease and disability isn’t really new. A dozen years ago, the World Health Organization pointed out that physical inactivity can have serious health implications, attributing approximately 2 million deaths per year to physical inactivity, and issuing a warning that sedentary lifestyles could very well be among the 10 leading causes of death and disability in the world.
The WHO noted that sedentary lifestyles increase all causes of mortality, double the risk of cardiovascular diseases, diabetes, and obesity, and increase the risks of colon cancer, high blood pressure, osteoporosis, lipid disorders, depression and anxiety, and also estimated that nearly two-thirds of children are also insufficiently active, with serious implications for their future health.
Earlier this month, a study by cardiologist researchers at UT Southwestern Medical Center in Dallas found that sedentary behaviors may lower cardiorespiratory fitness levels, the scientists noting that new evidence suggests that two hours of sedentary behavior can be just as harmful as 20 minutes of exercise is beneficial.
The UT Southwestern study, which was published in the July 7 online edition of Mayo Clinic Proceedings, examined the association between fitness levels, daily exercise, and sedentary behavior, based on data from 2,223 participants in the National Health and Nutrition Examination Survey (NHANES) , and noted that sedentary behavior involves low levels of energy expenditure activities such as sitting, driving, watching television, and reading, among others, and the findings suggest that sedentary behavior may be an important determinant of cardiorespiratory fitness, independent of exercise.
NHANES is an ongoing series of studies conducted by the National Center for Health Statistics and the Centers for Disease Control and Prevention. The database contains health and nutritional data from a diverse population, representative of the U.S. population.
“Previous studies have reported that sedentary behavior was associated with an increased risk for cardiovascular outcomes; however, the mechanisms through which this occurs are not completely understood,” says Dr. Jarett Berry, Assistant Professor of Internal Medicine and Clinical Science and senior author of the study in a UTSW release. “Our data suggest that sedentary behavior may increase risk through an impact on lower fitness levels, and that avoiding sedentary behavior throughout the day may represent an important companion strategy to improve fitness and health, outside of regular exercise activity.”
The study was funded with support from the National Heart, Lung and Blood Institute, the American Heart Association, and an unrestricted endowment provided to Dr. Berry by the Dedman Family, and entitled “Association Between Cardiorespiratory Fitness and Accelerometer-Derived Physical Activity and Sedentary Time in the General Population“ (July 07, 2014 DOI: http://dx.doi.org/10.1016/j.mayocp.2014.04.019), and published online in Mayo Clinic Proceedings, is coauthored by Jacquelyn P. Kulinski, MD, Amit Khera, MD, MS, Colby R. Ayers, MS, Sandeep R. Das, MD, MPH, James A. de Lemos, MD, Steven N. Blair, PED, and Jarett D. Berry, MD, MS.
In order to determine the association between cardiorespiratory fitness and sedentary behavior, independent of exercise activity, the research team included 2223 participants (aged 12-49 years; 1053 females [47%]) without known heart disease who had both cardiovascular fitness testing and at least 1 day of accelerometer data from the National Health and Nutrition Examination Survey 2003-2004. From accelerometer data, they quantified bouts of exercise as mean minutes per day for each participant. Sedentary time was defined as less than 100 counts per minute in mean minutes per day. Cardiorespiratory fitness was derived from a submaximal exercise treadmill test. Multivariable-adjusted linear regression analyses were performed with fitness as the dependent variable. Models were stratified by sex, adjusted for age, body mass index, and wear time, and included sedentary and exercise time.
The researchers found that an additional hour of daily exercise activity time was associated with a 0.88 (0.37-1.39; P<.001) metabolic equivalent of task (MET) higher fitness for men and a 1.37 (0.43-2.31; P=.004) MET higher fitness for women. An additional hour of sedentary time was associated with a 0.12 (0.02 to 0.22; P=.03) and a 0.24 (0.10 to 0.38; P<.001) MET difference in fitness for men and women, respectively. They conclude that after adjustment for exercise activity, sedentary behavior appears to have an inverse association with fitness, and that these findings suggest that the risk related to sedentary behavior might be mediated, in part, through lower fitness levels, and that that negative effects of six hours of sedentary time on fitness levels were similar in magnitude to the benefit of one hour of exercise.
“We also found that when sitting for prolonged periods of time, any movement is good movement, and was also associated with better fitness, commented Dr. Jacquelyn Kulinski, a recent graduate from the UT Southwestern Cardiology Fellowship Training Program and first author of the Mayo Proceedings paper. “So if you are stuck at your desk for a while, shift positions frequently, get up and stretch in the middle of a thought, pace while on a phone call, or even fidget.”
To stay active and combat sedentary behavior, UT Southwestern preventive cardiologists also recommend taking short walks during lunch and throughout the day, using a pedometer to track daily steps, taking the stairs instead of the elevator, hosting walking meetings at work, and replacing a standard desk chair with a fitness ball or even a treadmill desk, if possible.
Other UT Southwestern researchers involved in the study include Dr. Amit Khera, Director of the Preventive Cardiology Program and Associate Professor of Internal Medicine; Dr. Sandeep Das, Assistant Professor of Internal Medicine; Dr. James de Lemos, Associate Program Director of the Cardiology Fellowship Program and Professor of Internal Medicine; and Colby Ayers, Faculty Associate in the Department of Clinical Science.
TV Couch Time And Cancer Risk
A Free Access study by Drs. Daniela Schmid and Michael F. Leitzmann of the Department of Epidemiology and Preventive Medicine at the University of Regensburg, Regensburg, Germany, entitled “Television Viewing and Time Spent Sedentary in Relation to Cancer Risk” (J Natl Cancer Inst (2014) 106 (7): dju098 doi: 10.1093/jnci/dju098), published in March of this year by the Journal of the National Cancer Institute, also found that background Sedentary behavior is emerging as an independent risk factor for chronic disease and mortality. However, evidence relating television (TV) viewing and other sedentary behaviors to cancer risk has not been quantitatively summarized.
Drs. Schmid and Leitzmann performed a comprehensive metanalysis of electronic literature in Cochrane, EMBASE, Medline, and SciSearch databases through February 2014 for published articles investigating sedentary behavior in relation to cancer incidence, including 43 observational studies, and representing more than 4 million individuals’ responses to questions about their sitting behavior and cancer incidences. The researchers examined nearly 70,000 cancer cases, finding sitting to be associated with a 24% greater risk of colon cancer, 32% higher risk of endometrial cancer, and a 21% increased risk of lung cancer, concluding that prolonged TV viewing and time spent in other sedentary pursuits is associated with increased risks of certain types of cancer.
However, there is encouraging news as well on this file, at least for those of us who make an effort to get some exercise and maintain reasonable levels of fitness. This week, the American Cancer Society announced that results of yet another study published in Mayo Clinic Proceedings find that the association between prolonged sedentary time and obesity and blood markers associated with cardiovascular disease is markedly less pronounced when taking fitness into account.
Another report entitled “Sedentary Behavior, Cardiorespiratory Fitness, Physical Activity, and Cardiometabolic Risk in Men: The Cooper Center Longitudinal Study” (Mayo Clinic Proceedings, 2014; DOI: 10.1016/j.mayocp.2014.04.026) is coauthored by Kerem Shuval, PhD., of the American Cancer Society; Carrie E. Finley, MS; Carolyn E. Barlow, MS, and David Leonard, PhD of the Cooper Institute at Dallas; and Drs. Kelley Pettee Gabriel PhD, and Harold W. Kohl III PhD of the University of Texas School of Public Health.
To examine the association between sedentary behavior and cardiometabolic risk, while taking into account cardiorespiratory fitness (fitness) and physical activity, the team of researchers led by Dr. Kerem Shuval examined the association of sedentary behavior, physical activity, and fitness (exposure variables) to cardiometabolic biomarkers and metabolic syndrome (outcome measures) among a historic cohort of 1304 men seen at the Cooper Clinic in Dallas, Texas, between 1981 and 2012. Founded in 1970 by “Father of Aerobics” Kenneth H. Cooper MD, MPH, the Cooper Clinic claims that the Cooper Center Longitudinal Study (CCLS is the largest and most comprehensive data set in the world on fitness and health, and that research using CCLS data has affected much of America’s public health policy.
Sedentary time was composed of self-reported television viewing time and time spent in a car self-reported on a 1982 survey. Fitness was determined by a treadmill test during the medical examination at clinic visits.
The researchers report that they estimated the association (cross-sectionally and longitudinally) of sedentary behavior along with physical activity and fitness to lipids and lipoproteins, glucose, blood pressure, and markers of adiposity, including body mass index, waist circumference, and body fat percentage, then prospectively examined the effects of baseline sedentary time on the incidence of metabolic syndrome, while adjusting for physical activity, fitness, and other covariates in multivariate models.
The study showed that more sedentary time was significantly associated with higher levels of systolic blood pressure, and total cholesterol and triglycerides, as well as lower levels of HDL, the good cholesterol. Inactivity was also associated with BMI, waist circumference, and body fat percentage. However, when researchers controlled for fitness, they found prolonged sedentary time was only significantly associated with a higher triglyceride/HDL cholesterol ratio (an indicator of insulin resistance). Sedentary time was not associated with metabolic syndrome (a clustering of risk factors). In comparison, higher fitness levels were associated with reduced adiposity and metabolic measures.
However, the authors caution that interpretation of their study’s findings should be tempered by its limitations. For example, sedentary behavior was based on self-report at one point in time, whereas fitness was assessed objectively during clinic visits.
Nevertheless, the scientists conclude that associations between prolonged sedentary time and cardiometabolic biomarkers is markedly less pronounced when fitness is a positive factor, but note that although their findings suggest a need to encourage achieving higher levels of fitness through meeting physical activity guidelines to decrease metabolic risk, further exploration of the effects of sedentary behavior on cardiometabolic risk is warranted in cohorts with available fitness data, but provisionally their findings underscore the need to encourage achieving higher fitness levels through meeting physical activity guidelines to decrease disease risk factors.
UT Southwestern Medical Center
Mayo Clinic Proceedings
Journal of the National Cancer Institute
The Cooper Clinic, Dallas
American Cancer Society
World Health Organization
UT Southwestern Medical Center