It has become one of the most natural actions we do every day: to take a seat, sit down, and feel comfortable. We don’t even realize how much time we spend sitting every day and how harmful this habit can be.
At the office, in the car, on public transportation, at home, almost everywhere we find ourselves, we sit down. We enjoy the comfort, crave it, without realizing that we are denying our biological nature. The pure scientific truth is that we were not created to sit down, a fact demonstrated in the studies of Professor Daniel Lieberman.
Sitting down is a habit integrated into the lives of most people today, which can increase the risk of serious conditions such as cardiovascular diseases and type 2 diabetes, as reported by BBC.
The harmful effects of prolonged sitting have been observed for several decades. In 1953, epidemiologist Jeremy Morris discovered that London bus drivers were twice as likely to develop heart diseases as conductors working on these buses.
In terms of age, sex, and income, the two groups of employees were similar, but they had one significant difference: conductors had to stand and climb stairs frequently on the double-decker buses in London, while drivers remained seated at the wheel all the time.
You Can Exercise but Still Sit Too Much
Morris's study laid the foundation for research on the links between physical activity and coronary diseases. Its results are more relevant than ever. The COVID-19 pandemic has led to a global shift towards working from home, which predisposes to prolonged sitting. Without the commutes to the meeting room and breaks spent with colleagues, it's easy to spend hours on end in a chair.
The office work culture has changed our lives so much that in the '80s, some researchers noted that our species should no longer be called Homo Sapiens but Homo Sedens. Sitting in a chair is now considered another form of smoking.
Prolonged sitting is defined as a form of sedentary behavior, characterized by a significant reduction in energy expenditure in a seated or reclined position. Sedentary behaviors usually include activities such as watching TV, playing games, driving, or working at a desk.
Sedentary behavior is associated with a high risk of cardiovascular diseases, type 2 diabetes, premature death, and the time spent sitting has been identified as an independent risk factor in a range of conditions. In 2020, the World Health Organization proposed several measures to reduce sedentary behavior.
Since 2010, scientists have continued to emphasize that sedentary behavior does not just mean lack of physical activity. You can get plenty of exercise every day and still sit too much. However, the risks of sedentary behavior are higher for those who do not get enough exercise.
What Happens When We Sit in a Chair
How does sedentary behavior increase the risk of heart disease? Researchers believe that the main cause of diseases caused by sedentary behavior is high vascular dysfunction, especially in the legs. The vascular system keeps blood and lymph fluid - part of the immune system - moving through the blood vessels.
"What characterizes sitting down is a reduction in muscle activity," says David Dunstan, a physiologist at the Institute for Physical Activity and Nutrition at Deakin University in Melbourne, Australia, who has extensively researched the effects of prolonged sitting and possible interventions.
The reduced muscle activity of the leg muscles reduces their metabolic demand. Metabolic demand is the primary determinant of blood flow, so it is also reduced.
Sitting biomechanics, with the legs usually bent, can lead to blood pooling in the calves - a study on 21 healthy young volunteers showed that their calves increased in circumference by almost 1 cm within two hours. This can also reduce blood flow.
Normal blood flow generates a friction force, known as arterial shear stress, against the endothelial cells lining the blood vessel walls. The endothelium responds to this force and secretes vasodilators such as adenosine, prostacyclin, and nitric oxide, which keep the vessels sufficiently dilated and maintain the vascular system's ability to self-regulate - known as homeostasis.
Reduced blood flow reduces shear stress, and the endothelium produces vasoconstrictors like endothelin-1, which cause narrowing of blood vessels. This sets up a vicious circle - vasoconstriction further reduces blood flow, and blood pressure increases to keep the blood moving. Hypertension is one of the predominant risk factors for cardiovascular diseases.
Recent studies support this theory of vascular dysfunction. A study on 16 young and healthy men found that sitting for three hours increased blood pooling in the legs, peripheral vascular resistance, diastolic blood pressure, and leg circumference.
Another study found that blood pressure increases with uninterrupted sitting time. Researchers generally agree that 120-180 minutes of uninterrupted sitting is probably the threshold at which an individual spends too much time in a seated position. Vascular dysfunction increases, however, generally with prolonged sitting time.
The skeletal and muscular systems can also be affected. Prolonged sitting contributes to reduced muscle strength, decreased bone density, and increased total and visceral fat in adipose tissue.
In addition, prolonged sitting is associated with physical discomfort, workplace stress, higher depression rates, and can even lead to ulcers.
Sedentary behavior also causes an increase in post-meal blood sugar and insulin, increasing the risk of cardiovascular diseases and diabetes, says Dunstan, who specializes in type 2 diabetes research. Moreover, sitting for an extended period after a high-fat meal is considered particularly harmful.
How to Incorporate More Movement
If there are so many adverse consequences, why do we still end up sitting so much?
"I think people become more sedentary because society encourages it," says Benjamin Gardner, a social psychologist at the University of Surrey who has researched why people sit for such long periods.
In 2018, Gardner and his colleagues found that the idea of holding standing meetings faced social obstacles. Other solutions include using adjustable standing desks, tall chairs, treadmill workstations, and fidgeting while sitting to improve blood flow.
However, the simplest and most effective measure is to get up occasionally and take a short walk or climb some stairs.
Smart devices can also be helpful. In a new promising study, wearable devices with accelerometers provided 24/7 data on individual behavior patterns, including sitting and standing time, sleep, and physical activity.
The devices suggest optimal time intervals for sitting and standing and send automated messages whenever we sit for too long. However, using technology is not without disadvantages, as some users may get frustrated or be passive to its requests.
Above all, Gardner and colleagues encourage switching between sitting and standing positions as often as possible. The idea of breaking up sitting time by simply standing up is simple and has significant health benefits, especially for individuals with low activity levels. For wheelchair users or others with mobility constraints, specific exercises can be beneficial.
For many, sedentary behavior may seem like an inevitable consequence of modern life and work. However, even small changes to the routine – whether it's stretching more often, fidgeting, or getting up for a cup of coffee – can help us combat the habit of sitting for prolonged periods.
T.D.