Photo: DCStudio/Freepik
Published on 09/11/2023
By Luciana Constantino | Agência FAPESP – Sedentary behavior is now ubiquitous in many walks of life and a risk factor for so many health problems that scientists are increasingly studying its effects. They now have an “encyclopedia” in the form of a 100-page review of the literature that researchers in Brazil and elsewhere took three years to produce, compiling information about the effects of long periods of sitting on the organism and human health, as well as concepts, definitions and recommendations.
The article reinforces the message “Sit less, move more” while pointing to gaps in clinical trials and experimental studies that need to be filled in order to elucidate more fully the physiological effects of combining exercise with interruptions in being seated. The authors say the research conducted to date is not sufficient for them to recommend the amount by which sedentarism should be reduced if its adverse effects on health are to be avoided. The article is published in the journal Physiological Reviews.
Even people who exercise moderately for some time but sit or lie for the rest of their waking hours run a greater risk of developing heart and vascular problems, for example. Energy expenditure is very low under these conditions.
The study showed that excessive and prolonged sedentary behavior can lead to insulin resistance, vascular dysfunction, reduced cardiorespiratory fitness, loss of muscle mass and strength, and increased total body and visceral fat, among other problems. In addition, the negative physiological effects of spending too much time sitting or lying are similar to the effects of physical inactivity.
According to the researchers, long-term interventions aimed at reducing or interrupting sedentary behavior with light to moderate physical activity tend to lead to negligible benefits in terms of body weight, waist circumference, percent body fat, fasting glucose, insulin levels, and vascular function in adults and the elderly. However, these practices can serve as a springboard to increase physical activity for people with difficulties in achieving exercise targets, such as the overweight and obese.
“An important point in the effort to combat sedentary behavior by undertaking very light exercise, such as standing or walking for a few minutes, is that this can be a stepping stone to becoming a more active individual in future. This idea is very attractive from a public health standpoint but requires scientific input from studies showing that it does indeed happen,” said Bruno Gualano, a professor at the University of São Paulo’s Medical School (FM-USP) and a co-author of the article.
The other researchers who took part in the study are first author Ana Jéssica Pinto (FM-USP), Audrey Bergouignan (Universities of Colorado, United States, and Strasbourg, France), Paddy Dempsey (University of Cambridge, United Kingdom), Hamilton Roschel (FM-USP), and last authors Neville Owen and David Dunstan (Baker Heart and Diabetes Institute, Australia).
“We succeeded in summarizing the physiology of sedentary behavior. In our field [physical activity science], researchers study exercise and sports a great deal, but there isn’t sufficient investigation of sedentary behavior or absence of movement, as when we remain seated for a long time,” Gualano added.
Movement
For adults in general, the World Health Organization (WHO) recommends at least 150-300 minutes of moderate aerobic physical activity or at least 75-150 minutes of vigorous exercise per week for substantial mental and physical health benefits.
Some studies show that the ideal could be at least 8,000 steps per day to reduce the risk of premature death from avoidable disease, although recent findings suggest about 7,000 steps already produce a considerable reduction in the probability of premature death. The intensity of physical activity may vary from light (such as walking while shopping) to moderate (leading to a rise in heart and breathing rates) to vigorous (leading to exhaustion).
About 1 billion people will be living with obesity by 2030, according to the World Obesity Atlas, produced by the World Obesity Federation, which in its own words has over 65 national and regional member organizations and the mission to lead and drive global efforts to reduce, prevent and treat obesity. Around 30% of adult Brazilians are believed to be obese.
Data for 2021 analyzed by the Ministry of Health’s Vigitel survey (Vigilância de Fatores de Risco e Proteção para Doenças Crônicas por Inquérito Telefônico, “Surveillance of Risk Factors and Protection for Chronic Diseases by Telephone Interview”) show that 22% of adult Brazilians are obese based on body mass index (BMI).
BMI is calculated by dividing weight by height squared, with 25-30 being considered overweight (57% of adult Brazilians) and over 30 as obese.
Obesity heightens the risk of other disorders, such as heart disease, diabetes, high blood pressure, liver disease, several types of cancer (especially colorectal and breast cancer), kidney problems, asthma, and severe COVID-19.
In recent years, sedentary behavior has also been increasingly seen as a cause of avoidable death, and even people who do some exercise but spend a long time sitting are considered at risk for health problems.
“This is the most comprehensive review of sedentary behavior we know of. We hope it will attract the interest of more researchers to the topic and inspire future research to improve the quality of the evidence, fill gaps in the literature, and avoid the current limitations in the field of sedentary behavior and health,” said Ana Jéssica Pinto, a postdoctoral fellow at the University of Colorado in the United States.
When she was studying for her PhD at the School of Physical Education and Sports (EEFE-USP) in Brazil, she won a Student/Trainee Award from Canada’s Sedentary Behavior Research Network (SBRN) in 2020, in recognition of “exemplary dedication, commitment and contributions to the field of sedentary behavior.”
She was supported by a scholarship from FAPESP during her PhD research – supervised by Gualano and FM-USP’s Applied Physiology and Nutrition Research Group – and during a research internship abroad.
Limited models
Another gap in the literature evidenced by the study, according to the authors of the review article, related to the limitations of the experimental models used by researchers in the field, hindering comprehension of the physiology of sedentary behavior. These models include bed rest, immobilization, reduced step count, and reducing or interrupting prolonged sedentary behavior.
“These are the most widely used models, and they have serious limitations. When you study the physiology of a healthy person who is bedridden or has to wear an immobilizing cast for a month, for example, you must bear in mind that this isn’t what happens in ordinary everyday life, where people normally alternate between sedentary periods and a certain amount of physical activity, which may well be very light,” Gualano said.
This point is important because most of the studies analyzed in the review involved healthy people who did not display altered risk factors. More significant effects of sedentary behavior interruption might have been observed in subjects who were not healthy. Moreover, the evidence on the adverse effects of sedentary behavior applies mainly to young adults and older people, as few studies involving children and adolescents are available.
The article compiles all the relevant physiological evidence, from body weight, energy balance and intermediate metabolism to cardiovascular, respiratory, skeletomuscular, and nervous systems, as well as the immune system and inflammatory response. It concludes that energy expenditure, heart rate, skeletomuscular blood flow and contractile activity are all higher when a person is sitting than reclining but lower than when standing or during physical activity of any intensity.
Thematic Project
The study was also supported by FAPESP via the Thematic Project “Reducing sedentary time in clinical populations: the Take a Stand for Health study”, for which Gualano is principal investigator and which aims to test sedentary behavior reduction interventions.
The project will investigate the clinical, physiological, metabolic and molecular effects of reducing sedentary behavior in clinical populations comprising rheumatoid arthritis, bariatric and mild cognitive impairment patients, including those with long COVID.
“However much we personalize prescriptions to reduce sedentary behavior and understand people’s routine so that they fit physical activity in, adherence has been difficult. We did this with patients with obesity and rheumatic disorders, and the results fell short of our expectations in terms of reducing sedentary behavior. Behavior is deep-rooted and automatic to a large extent. Adherence to programs designed to change it is hard to achieve,” Gualano said.
The article “The physiology of sedentary behavior” is at: journals.physiology.org/doi/abs/10.1152/physrev.00022.2022.
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Source: https://agencia.fapesp.br/44814
