The first study showed that just walking can reduce your risk of breast cancer. They took 73,615 women as part of the American Cancer Society Cancer Prevention Study II and followed them to see how many got cancer, and whether it was related to any of their lifestyle factors.
Their work aimed to build on the studies which suggest that being physically active will decrease your risk of breast cancer by around 25%. At the start of the study, women were asked how much of their time they spent doing various physical activities, such as walking. I did find it interesting that while they were asked about “aerobics” and “dancing”, there was no mention of any sort of strength training. However, the study started in 1992, back when the fitness world was in full lycra mode... The questionnaire also asked about the amount of leisure time spent sitting per week (ie watching TV).
9.2% of the women studied said they performed no physical activity at all, and 47% said their only physical activity was walking. The more physically active women had less body fat, were less likely to smoke but more likely to drink alcohol.
- Those who were the most active (equivalent to at least six hours of light jogging per week) had a 25% lower risk of postmenopausal breast cancer compared to those who were the least active (less than one hour jogging per week).
- Those who walked for an hour a day also had a 14% reduced risk compared to those who walked for less than half an hour per day.
- Body Mass Index (BMI) and use of hormone replacement therapy did not affect the risk of breast cancer.
- There was no risk associated with sitting for long periods of time.
The last point is interesting, because more and more evidence seems to suggest that the act of sitting down is actually killing us, increasing risk of death from all causes, particularly cardiovascular disease and cancer.
The first large study on sitting came out five years ago. 17,013 Canadian men and women took part in the Canadian Fitness Survey (CFS), where their weekly physical activity and sitting time (amongst other basic information) was recorded. Unlike most similar studies where participants are emailed a questionnaire, everyone in the CFS was visited at home, making their information more likely to be accurate. What they found was that men who sat “almost all of the time” had a 50% increased chance of death compared to those who sat very little. In women, the risk was more than doubled! There was also a dose-response between sitting and mortality. In other words, the more sitting you do, the earlier you are likely to die. This effect held true regardless of BMI, smoking status or level of physical activity.
So if you get up, drive to work, sit at a desk all day and then spend your evening relaxing at home on the sofa, you will be in the highest risk category, even if you spent an hour at the gym after work!
A more recent study of patients with colorectal cancer also showed that spending more than 6 hours of leisure time per day sitting increased the risk of death by around 30% compared with those sitting for less than 3 hours a day. Increased activity equivalent to two and a half hours of walking a week also decreased mortality by 28%. Obviously those that are able to be more active are more likely to be fit enough for more radical treatment regimens such as surgery or chemotherapy, and therefore likely to live longer. Patients might be sitting because they’re unwell rather than unwell because they’re sitting. However, when they removed the most unwell patients (those who died within 2 years of diagnosis) from the analysis, the risk was still there. The cancer studies also only examined “leisure” time sitting, but it is worth thinking about the fact that most of our sitting is likely to happen at work. Death doesn’t care whether you’re at a desk or staying up late watching Game of Thrones.
It will no doubt take some time to unpick the reasons behind exercise vs sitting and causes of death, but we know that exercise improves the balance of sex hormones (ie oestrogen, progesterone and testosterone), which is relevant to breast, endometrial and prostate cancers. It also improves blood pressure and glucose and insulin control, reducing associated risks of type 2 diabetes and heart disease. Conversely, sitting has been shown to increase the risk of diabetes and cardiovascular disease. It is thought that sitting directly causes:
- Increased inflammation.
- Reduced ability to control blood glucose.
- Lower vitamin D levels (most of our sitting happens indoors).
- Reduced activity of the enzymes that control the fat and cholesterol in the blood (lipases).
- Lower sex hormone levels.
If you take nothing else away from this, remember that more sitting equals less horny, and that can’t be a good thing.
As I have recently moved from a job where I ran around a hospital frantically to one where I sit at a laboratory bench for most of my day, I think about how I can reduce the risk associated with the change in my activity:
- Walk outdoors for at least half an hour a day.
- Supplement with vitamin D and Omega-3s (to reduce inflammation).
- Balance hormones by doing some exercise.
To reduce the risk of you getting bored, I’ll split this post up. Coming up in Part II – exercise is better than drugs.
1. Hildebrand JS, Gapstur SM, Campbell PT, Gaudet MM, Patel AV. Recreational Physical Activity and Leisure-Time Sitting in Relation to Postmenopausal Breast Cancer Risk. Cancer Epidemiol Biomarkers Prev. 2013 Oct;22(10):1906-1912.
2. Katzmarzyk PT, Church TS, Craig CL, Bouchard C. Sitting time and mortality from all causes, cardiovascular disease, and cancer. Med Sci Sports Exerc. 2009 May;41(5):998-1005.
3. Campbell PT, Patel AV, Newton CC, Jacobs EJ, Gapstur SM. Associations of recreational physical activity and leisure time spent sitting with colorectal cancer survival. J Clin Oncol. 2013 Mar 1;31(7):876-85.
4. Lynch BM. Sedentary behavior and cancer: a systematic review of the literature and proposed biological mechanisms. Cancer Epidemiol Biomarkers Prev. 2010 Nov;19(11):2691-709.