It is the unfortunate reality that most of us spend much of our waking lives sitting down. From working to leisure time, many of our daily activities involve sitting. Individuals in the United States spend 55% of their waking time (or 7.7 hours a day) engaging in sedentary behaviors, such as sitting, which in modern societies is difficult for many to avoid. In turn, many potentially harmful health outcomes, easy at first to overlook, can result. But what happens to your body when you sit all day?

While scientists are still unraveling the mechanisms that might underlie the negative impact of prolonged sitting, reports link this behavior with several negative health impacts, including heightened risk of cardiovascular and metabolic diseases. In this article, we detail the associations between prolonged sitting and health, how we might mitigate these effects, and how other negative lifestyle choices might augment the impact of prolonged sitting. 

The negative impact of prolonged sitting

Prolonged sitting is an aspect of sedentary behaviors that also include being reclined, lying down, or expending low levels of energy. While the physiological mechanisms remain unknown, prolonged sitting has been linked with a number of negative health impacts — including metabolic disorders, cardiovascular function, and cognitive impairment:

• A meta-analysis consisting of nine studies and 448,285 participants found that higher total daily sitting time was significantly associated with increased risk of cardiovascular disease and diabetes. Adjusting statistical models to account for physical activity had no impact on the risk for diabetes and slightly attenuated the risk for cardiovascular disease, which remained significantly elevated. Others have found that increased sedentary time is associated with increased all-cause mortality, cardiovascular disease incidence and mortality, cancer incidence and mortality, and type 2 diabetes incidence.
• In another meta-analysis examining prolonged sitting and vascular function, researchers revealed that lower-limb vascular function is impaired as a function of sitting time. Their data demonstrated that lower limb flow-mediated dilation (a measure of vascular health) is significantly decreased at 120 and 180 minutes of sitting time. 
• One group of researchers examined the effects of prolonged sitting in overweight/obese individuals on two acute cardiovascular responses: blood pressure (BP) and pulse wave velocity (PWV) during a simulated, 7.5 hour seated workday. PWV is a particularly interesting measure as it provides more accurate reflections of harmful changes in vascular function. Since vascular function changes depending on posture, these researchers measured BP and PWV in either the seated or supine position. Their data revealed that a 7.5 hour seated workday resulted in elevated BP and PWV with posture having minimal effects. Together, the data provides evidence for the harmful impact of sitting on cardiovascular health, especially in those who regularly engage in deskwork. 
• One study demonstrated that increased TV viewing time is associated with increased risk of type 2 diabetes, cardiovascular disease, and all-cause mortality. While the association is linear, these researchers found that the risk of all-cause mortality appeared to increase when individuals watched more than three hours of TV per day. 
• In addition to cardiovascular and metabolic impacts, another alarming negative health outcome of prolonged sitting relates to brain health. In one study, researchers found that the thickness of the medial temporal lobe (an area of the brain that controls cognition and memory), is inversely related with hours of sitting per day. In other words, the longer an individual sits, the thinner the medial temporal lobe. Others have shown that increased sedentary behaviors are associated with lower cognitive function. ‍
• To add to the list, one study demonstrated that high levels of sedentary behavior are associated with increased risk for ovarian cancer. More specifically, there is a 29% increase in ovarian cancer risk when comparing low vs. high levels of sedentary behavior. 

There are myriad links between prolonged sitting and negative health impacts. However, it is important to note that many existing studies are correlational and the physiological mechanisms and causal factors are still unclear. 

The benefits of taking a break from prolonged sitting

While research has demonstrated a strong association between prolonged sitting and negative health outcomes, there are simple ways to robustly mitigate these effects. Indeed, there are several reports demonstrating that taking even a brief break from prolonged sitting can reverse some of the deleterious effects:  

• One report demonstrated that interrupting prolonged sitting with regular activity breaks can have a positive effect on vascular function and glucose metabolism. More specifically, by interrupting prolonged sitting sessions with two minutes of walking every 30 minutes, participants exhibit increases in blood flow and improvements in glucose regulation compared to those who don’t take breaks. Interestingly, improvements associated with movement are more significant than improvements associated with prolonged standing, suggesting that frequent movement might be more beneficial than replacing sitting with standing. (In other words, that treadmill desk might be a better option than a standing desk.) 
• Others have demonstrated that interrupting prolonged sitting with simple, three minute resistance exercises (for example, half-squats or knee raises) every 30 minutes may also improve glucose metabolism. 
• Similar results have been found in a meta-analysis examining the effects of physical activity on prolonged sitting and relevant metabolic markers associated with type 2 diabetes. Here results showed that regular physical activity breaks attenuate postprandial glucose (a marker of how well glucose is metabolized after a meal), insulin, and triacylglycerol. 
• In a systematic review of 45 studies, one report revealed that interrupting sitting with walking is particularly effective at improvements in cardiovascular function. This study incorporated a number of walking parameters including duration (1.5-30 minutes), intensities (light to vigorous) and frequencies (every 20 minutes to every 2 hours). Overall, these data revealed that walking breaks were particularly effective at improving a number of cardiovascular functions such as blood pressure and flow-mediated dilation.
• There have been mixed results on the effects of interrupting sitting on cognitive function. However, while it seems there are no apparent improvements (or detriments) on cognition, one study demonstrated that physical activity breaks from sitting can facilitate functional connectivity patterns in the prefrontal cortex (an important brain region for cognition). 

The vicious cycle: Negative lifestyle factors that compound prolonged sitting

Unfortunately many individuals suffer a vicious cycle between negative lifestyle habits (i.e., obesity, smoking, excessive alcohol consumption, etc.) and prolonged sitting. However, while one condition might exacerbate the other, those with pre-existing conditions see a greater positive impact by taking a break from prolonged sitting. In fact, studies show that although pre-existing conditions and negative lifestyle behaviors worsen the impact of prolonged sitting, individuals with pre-existing conditions also benefit more from the practice of interrupting sitting:

• One particularly alarming risk factor that perpetuates the negative impact of prolonged sitting is obesity. In one longitudinal study examining this vicious cycle, researchers demonstrated that physical inactivity in adolescence strongly predicts the risk of obesity into adulthood. Moreover, physical inactivity was not only predictive of obesity development, obesity can also predict physical activity. Overall these data suggest that adolescent sedentary behaviors can not only increase risk of obesity, but obesity itself can result in sedentary behaviors. Fortunately, other studies have shown that changing activity levels during adolescence can significantly reduce this risk. ‍
• To emphasize the point above, another study examined the effects of consuming a high-fat meal prior to bouts of prolonged sitting. Compared to a low-fat meal, a high-fat meal consumed 180 minutes prior to an uninterrupted sitting bout significantly augmented markers of cardiovascular disease risk. ‍
• A cross-over comparison of overweight/obese individuals with or without insulin resistance during prolonged sitting vs. prolonged sitting with breaks revealed a greater beneficial impact of breaks on postprandial glucose and insulin in those with greater insulin resistance. The study authors concluded that “those with higher underlying levels of insulin resistance may derive greater metabolic benefits from regularly interrupting prolonged sitting than their healthier counterparts.”
• Similarly, individuals with a higher BMI exhibit greater glycaemic attenuation when interrupting prolonged sitting with physical activity breaks.

Benefits are not limited to improvements in metabolic markers as a direct result of interrupting prolonged sitting, either. For example, obese individuals who smoke are more likely to quit smoking when they limit sedentary behaviors and engage in higher levels of physical activity.

Overall, while many negative lifestyle choices can exacerbate the harmful effects of prolonged sitting, the cycle can be broken. The data reported in these studies highly suggest that taking small steps towards increasing levels of physical activity can have a tremendous impact on improving your health.

How you can decrease your sitting time

Since prolonged sitting is strongly ingrained in many of our lifestyles, it might be difficult to avoid completely. Fortunately there are many ways to decrease your sitting time — whether you’re in the workplace or at home: 

• Take frequent, short breaks. Many of the studies described here propose 1-3 minutes of walking every 20-30 minutes. This can be a walk around the office to talk to your co-workers, or taking a call while walking. ‍
• Set a schedule. Sometimes it can be easy to be engrossed in your work while sitting at a desk. Set an alarm to remind yourself to get up and walk or signs around your computer to keep you aware of your sitting time. ‍
• Multitask. Instead of sitting on the couch and watching TV, engage in simple indoor exercises such as stretching, walking in place, or using a stability ball. 

Key takeaways

Although we don’t fully understand the mechanistic and causal underpinnings that result in the negative outcomes of prolonged sitting, many reports have established strong associations between such sedentary behavior and several cardiovascular and metabolic disorders. Nevertheless, modifying sedentary behaviors through lifestyle choices can be achieved by millions of us. Even if you work long hours sitting at the office or at home, a conscious effort to engage in a healthy lifestyle will make a world of difference. Combining a little bit of physical activity together with a healthy diet can mitigate the negative effects of prolonged sitting.