Sedentary behaviour and Covid-19 risk
The study has been authored by Ekta Jain
The pandemic caused by the novel coronavirus continues to test medical and public health systems across the globe as cases of the latest variant Omicron continue to surge. The first Covid-19 wave in India in 2020 was relatively less intense as compared to most other parts of the world, where it spread unchecked. However, India’s public health systems did not anticipate the fury of the second wave, which witnessed record surges and a high prevalence of severe forms of the disease. Between April and May 2021, India witnessed an unprecedented 400,000 daily incident cases, with deaths peaking to around 5,000 for a particular day. These figures may well be underreported.
The positivity rates climbed to record highs, reaching 50% in Bengaluru in Karnataka. Breaking the chain of transmission had been the initial strategy in managing the pandemic. However, as the pandemic continued, the focus extended to reducing the severity of the disease. Public health agencies pressed for the need for timely check of symptoms so that the infection would not progress and hospitalisations could be reduced. Other changes have been observed as the pandemic has prolonged. When the World Health Organization (WHO) first declared Covid-19 as a pandemic, age (above 60 or 65 years) and underlying non-communicable diseases were identified as risk factors for developing severe forms of Covid-19.
Other risk factors have been suggested since, and one such is sedentariness. An epidemiological study by Robert Sallis and colleagues at the Kaiser Permanente Medical Center and Pomona College at the University of California, found that a sedentary lifestyle had been a factor in higher odds of hospitalisations, admissions to intensive care units, and death, in individuals who contracted Covid-19. This analysis lays down an important foundation for activity levels as a clinical predictor of the progression of the Covid-19 disease. Sedentary behaviour goes beyond being a behavioural or lifestyle risk factor in public health studies. It has clinical consequences as well. Indeed, its role in increasing the risk for cardiovascular diseases and diabetes is already well-known.
Though the term ‘sedentary behaviour’ is often used interchangeably with ‘physical inactivity’, the two are different. ‘Physical inactivity’ refers to insufficient levels of physical activity; ‘sedentariness’ or ‘sedentary behaviour’ is defined as any waking behaviour characterised by an energy expenditure that consumes more than 1 and less than 1.5 times the oxygen consumed when the body is at rest. This is commonly represented in the form of a Metabolic Equivalent Task (MET) value. Sedentary behaviour is measured in terms of duration in minutes or hours per day or per week. Any measurement of sedentary behaviour does not take into account the intensity of the activity being performed. Physical activity, on the other hand, is any activity characterised by energy expenditure of more than 1. MET, and is further classified based on intensity of the activity. Some examples include walking at a slow speed, such as in one’s office (2.0 MET), which is a light-intensity physical activity; sports such as cycling at 5.5 mph speed (3.5 MET), a moderate-intensity physical activity; and running at 5 mph (8.3 MET), a high-intensity or vigorous physical activity.
For survey-based public health research, the compendium of physical activities essentially provides a system to classify activities and lists them along with their MET values. This compendium serves as a resource that characterises activities by energy expenditure. Sedentary activities are mostly performed in a reclining, lying or seated position, such as writing, watching television, or playing a board game. Public-health studies often capture television watching and using a computer as screen-viewing activity. (Most of these studies are based on high income countries and have focused on children’s screen-viewing times.)
The Canadian Society of Exercise and Physiology (CSEP) and Australia’s national guidelines were the first available guidelines for sedentary behaviour. These guidelines, formulated after reviewing current published evidence at the time (including systematic reviews), were only incorporated with WHO’s activity guidelines for November 2020. The WHO guidelines only mention total sedentary behaviour and mandate that prolonged sitting be reduced.
There are guidelines and recommendations on levels and intensity of physical activity that an individual should undertake to gain optimal health benefits as well as to maintain current health. In comparison to the guidelines for minimising sedentary behaviour, those for promoting physical activity are more developed. This also finds basis in the types of activities classified as ‘physical activity’. For sedentary behaviour, the number of activities enlisted are a handful but can account for a larger proportion of one’s day. For example, sitting is a sedentary activity and can easily be performed for six to eight hours per day. The main takeaway from the sedentary behaviour guidelines is that individuals should reduce sedentary behaviour to derive health benefits.
(The study has been authored by Ekta Jain)