How Prolonged Sitting Affects the Body: From Cancer Risk to Physical Activity

Scientists and healthcare professionals have studied the effects of prolonged sitting for years. Although many people may overlook the issue, research shows that time spent sitting substantially affects quality of life and overall health. Excessive sitting brings serious health problems, making it essential to determine how much physical activity is needed to prevent or alleviate them.

Prolonged inactivity is known to increase the risk of cardiovascular disease, type-2 diabetes and certain cancers. Physical activity may reduce this risk. How much movement is needed to counter the health effects of a sedentary lifestyle is an important research question.

For example, you might sit at an office desk for hours, watch television for long periods or play computer games. The US Centers for Disease Control and Prevention (CDC) estimates that Americans sit for an average of 6.5-8 hours daily. Similar figures are thought to apply across Western societies.

Let us examine how prolonged sitting affects the body, how much is unhealthy and how to avoid the consequences of a sedentary lifestyle.

How Much Sitting Is Unhealthy?

Doctors describe prolonged sitting and inactivity as a "sedentary / inactive lifestyle." Research suggests this can increase the risk of type 2 diabetes, heart disease and cancers such as colon, breast and uterine cancer.

Excessive sitting and insufficient activity throughout the day can harm physical health as well as

• sleep patterns,
• mental health and
• cognitive performance.
• It may also harm bone health, since regular movement and exercise help maintain bone density and reduce osteoporosis risk.

There is no definitive amount of sitting that is unhealthy. It depends on the individual and how much exercise they get each day. 

Risk thresholds for sitting-related health problems are:

• Low risk: Sitting less than 4 hours a day.
• Moderate risk: Sitting 4–8 hours a day.
• High risk: Sitting 8–11 hours a day.
• Very high risk: Sitting more than 11 hours a day.

The CDC considers 150 minutes of moderate activity a week sufficient to reduce some health risks associated with a sedentary lifestyle.

How Does Prolonged Sitting Affect the Body?

Prolonged sitting can have several effects:

• Discomfort / Pain: A 2018 study suggested an association with musculoskeletal discomfort, affecting areas such as the neck, shoulders, lower limbs, lower back, hips, thighs, wrists and hands.
• Slower Metabolism: Metabolism is how the body breaks down and uses energy. A 2021 study suggested prolonged sitting may affect metabolism after meals. 
• Changes in Blood Flow: The same 2021 research found that prolonged sitting may reduce blood flow, particularly to the legs, potentially causing swelling.
• Hypertension: A 2017 study reported an association between prolonged sitting and hypertension (high blood pressure).
• Musculoskeletal Disorders: A 2018 paper highlighted associations between prolonged sitting and certain lower-limb musculoskeletal disorders.
• Mental Effects: The same 2018 study described negative effects on mental well-being in people who sit for long periods, potentially affecting creative problem-solving.

Which Cancer Risks Does Prolonged Sitting Increase, and by How Much?

Prolonged sitting can increase cancer risk. A sedentary lifestyle may raise the risk of several cancers, including colon, breast and uterine cancer.

• Colon Cancer: Many studies link prolonged sitting particularly to colon cancer. A meta-analysis reported a 30% increase in risk with inactivity. Colon cancer has the strongest association with inactivity.
• Breast Cancer: Research suggests a sedentary lifestyle can increase breast cancer risk. Women sitting for long periods have shown higher risk than more active women.
• Uterine (Endometrial) Cancer: Women with high levels of inactivity have been reported to face higher uterine cancer risk.

Can Sitting Too Long Be Deadly?

According to the World Health Organization (WHO), insufficient physical activity is the 4th leading risk factor for death, causing 3.2 million deaths worldwide each year.

A 2017 paper suggested that people who sit for long periods at work face nearly 1.4 times higher premature mortality risk after 12 years than those who do not . Prolonged sitting therefore has implications beyond immediate health effects: it may also reduce long-term survival.

How Can We Address the Effects of Sitting All Day?

Being active is the best way to address or prevent these effects. The CDC recommends at least 150 minutes of moderate-intensity activity weekly, which could be five 30-minute sessions.

Moderate activities include brisk walking, water-based exercise and cycling on level ground. People can start with less intense exercise and gradually build endurance.

A 2021 research paper suggested that regular activity offers more benefits than replacing prolonged sitting with prolonged standing.

Preventing the Effects of Sitting All Day

Staying active is the best approach, including at least 150 minutes of physical activity weekly or regular movement breaks.

Tips to Avoid Sitting All Day

Office workers could try:

• Requesting sit-stand desks or workstations
• Alternating between standing and sitting every 30 minutes
• Holding walking meetings
• Stretching regularly while seated or standing
• Walking to speak with a colleague instead of emailing

Sitting all day without physical activity may increase the risk of conditions including heart disease, type 2 diabetes and certain cancers. People can nevertheless reduce these risks by being more active overall and breaking up long periods of sitting with movement.