It might not seem like the most obvious danger from sitting too much – particularly compared to the well-known threat of cardiovascular disease – but a sedentary lifestyle is increasingly recognised as a major risk factor for more than a dozen types of cancer. In part, this is because too much sitting is directly correlated with weight gain and obesity. However, extended sitting also raises the risk of cancer in lean people.
It’s not hyperbole to say that cancer is a disease of modern civilisation. While there are many long-standing natural causes of cancer, and cancer rates have increased in accordance with increases in the average human lifespan, the fact remains that industrialisation and associated lifestyle changes have had a massive impact on the rates of almost all types of cancer.
Societies that maintain a more traditional way of life, involving foraging for food and only occasionally eating animals, have populations that are in many regards healthier than more ‘advanced’ societies where convenience foods, motorised transport, and sedentary pastimes are the norm. As colonialism spread across the globe, researchers working on the frontiers often noted the relative lack of cancer in native populations compared to rates seen in European societies and, later, in increasingly urbanised populations in America. Colonial science certainly had (and, arguably, has) its problems, but a wealth of evidence from recent research supports the idea that as western civilisation spread around the world, so did cancer.
Modern city living typically means gross reductions in physical activity, as well as changes in diet, and increased exposure to pollution and external stressors. Such lifestyle factors are now well recognised for their role in obesity and diabetes, but few people realise just how much of an impact our urbanised, sedentary lifestyles have on our risk of developing cancer. This list is by no means complete, and new research continues to emerge, but it should illustrate that the danger is very real and backed by solid science.
- Endometrial cancer – two to seven times more likely to develop in overweight or obese women (Setiawan et al., 2013; Dougan et al., 2015)
- Esophageal adenocarcinoma – twice to four times more likely in people who are overweight or obese (Hoyo et al., 2012)
- Gastric cardia cancer – nearly twice as likely in people who are obese (Chen et al., 2013)
- Liver cancer – up to twice as likely in people who are overweight or obese (Chen et al., 2012; Campbell et al., 2016)
- Kidney cancer – nearly twice as likely in those who are overweight (Wang et al., 2014), independent of high blood pressure, which is itself a risk factor for renal cancer (Sanfilippo et al., 2014)
- Multiple myeloma – 10-20% increased risk in people who are overweight or obese (Wallin & Larsson, 2011)
- Meningioma – 20-50% increased risk in people who are overweight or obese (Niedermaier et al., 2015)
- Pancreatic cancer – 150% increased risk in people who are overweight (Genkinger et al., 2011)
- Colorectal cancer – around 30% more likely in those who are obese (Ma et al., 2013)
- Gallbladder cancer – 20-60% increased risk in people who are overweight or obese (World Cancer Research Fund International/American Institute for Cancer Research, 2015; Li et al., 2016)
- Breast cancer – 12% increased risk with every 5-point increase in BMI (Renehan et al., 2008); among postmenopausal women who are obese, the risk is increased by 20-40% (Munsell et al., 2014); obesity also increases the risk for breast cancer in men (Brinton et al., 2014)
- Ovarian cancer – 10% increased risk with every 5-point increase in BMI among women who have never used menopausal hormone therapy (Collaborative Group on Epidemiological Studies of Ovarian Cancer, 2012)
- Thyroid cancer – 16% increased risk for women and a 21% increased risk for men with every 5-point increase in BMI; regardless of sex, being overweight raised the risk of thyroid cancer by 20%, while being obese raised the risk by 53% (Kitahara et al., 2011)
At this point you might be wondering, what about lean people? Are they off the hook? Science would suggest otherwise.
Even if a person maintains a normal body weight, sedentary behaviour is undeniably associated with underlying biochemical changes that stimulate the development of various cancers.
A sedentary lifestyle reduces the body’s ability to respond to insulin, the hormone that helps transport energy in the form of glucose into cells from the blood. In response, the pancreas begins to produce greater amounts of insulin, which is a growth factor for cells, including those which are cancerous (Gallagher et al., 2015).
Researchers have investigated this link by looking specifically at how chronic hyperinsulinemia influences endometrial cancer (Gunter et al, 2008). Hyperinsulinemia, or excess levels of insulin in the blood, appears to directly stimulate the proliferation (growth) of cells that line the uterus (the endometrium). It also contributes indirectly to cancerous growth by increasing levels of insulin-like growth factor-1 (IGF-1) in the endometrium while at the same time decreasing levels of insulin-like growth factor-binding proteins (IGFBP) (Kaaks et al, 2002).
It is also theorised that hyperinsulinemia can increase levels of bioavailable estrogens by decreasing levels of the estrogen-binding protein, sex hormone binding globulin (SHBG) (Kaaks et al, 2002). This is a particular problem for many of the cancers in the aforementioned list, which are hormone-dependent, including endometrial, breast, and ovarian cancer. However, physical activity may help decrease the risk of endometrial cancer, for example, because it reduces blood levels of the hormone estradiol and increases levels of SHBG, the binding protein for estradiol (McTiernan, 2008).
Too much sitting can also trigger a state of constant inflammation, which raises the risk of cancerous modifications (Gregor & Hotamisligil, 2011) and decreases the production of important antioxidant enzymes, such as superoxide dismutase, which leaves the body’s cells more vulnerable to damage by free radicals that can cause cancerous mutations (Azizbeigi et al., 2014).
In one meta-analysis, researchers studied almost 70,000 cases of cancer and found that people who were more sedentary had a significantly higher risk of colon, endometrial, and lung cancer. Statistically, for every two hours spent sitting each day, the risk for lung cancer is increased by 6%, colon cancer by 8%, and endometrial cancer by 10%, respectively (Schmid & Leitzmann, 2014). In another study, this time looking at more than 45,000 men, researchers found that, compared with men who mostly sat during work hours, those who sat for half the time had a 20% lower risk of prostate cancer. In fact, every 30 minutes of walking or bicycling lowered the overall risk of prostate cancer by an impressive 12% (Orsini et al., 2009).
The benefits of walking extend far beyond cancer prevention. Research suggests that cancer survivors should avoid prolonged sitting, as this can hamper recovery and make it harder to overcome the deconditioning common amongst those with cancer. Specifically, regular physical activity has been shown to help prevent – or even reverse – the negative effects of cancer and cancer treatment on the heart, muscles, blood vessels, and blood cells (Howden et al., 2018). Walking is an excellent option for those in recovery as it places little physical strain on the body, is easily accessible, low or no monetary cost, and can reduce associated emotional stress.
While we’re still just beginning to understand the interconnection between sedentary behaviour and cancer, it seems clear that walking not only helps with weight management, breathing, blood sugar control, and spinal health, but can also dramatically reduce cancer risk, by making our bodies more resilient and better able to recover from disease.
About the Author
Eric Soehngen, M.D., Ph.D. is a German physician and specialist in Internal Medicine. With his company Walkolution, he battles the negative health effects that sitting has on the human body. Walkolution develops ergonomically optimized treadmill desks, which help to bring more movement into the daily work routine in the office or home office.
Photo credit: National Cancer Institute