We hear from scientists and health officers that we should all get at least half an hour of exercise a day to stay healthy. And if you already do that you should try to make that half hour a whole hour. This guideline is on the low side, epidemiologists at the University of Washington report in the BMJ. According to their meta-analysis, our health only really improves if we get two to three hours of physical activity a day.
The researchers accessed 174 epidemiological studies on the relationship between physical exercise and the risk of chronic disease. They then gathered all the data and reanalysed it. The researchers confined themselves to ischaemic heart disease [heart attacks in plain language], strokes, breast cancer, bowel cancer and type-2 diabetes.
Health scientists express physical exercise in metabolic equivalent of task minutes and hours, or Met-minutes and -hours.
For most of the chronic diseases that the researchers investigated, the relationship between physical exercise and the risk of contracting the disease looks like the one shown in the figure below. The one illustrated is for heart attacks.
The more exercise people get, the lower the chance of a heart attack. The most protective effect of exercise is gained by doing between 3000 and 4000 Met minutes of physical activity. Doing more exercise than that will not have a bad effect, but is unlikely to add any health benefit.
The figure below shows the effect of physical activity on the chance of heart attack, stroke, breast cancer, bowel cancer and type-2 diabetes.
At present the World Health Organization advises at least 600 Met minutes of physical activity per week. That’s the equivalent of 150 minutes of brisk walking or 75 minutes of running.
In rich countries information officers translate that into 30 minutes of activity a day. They assume that inhabitants of those countries are so spoiled that on at least two days a week they do absolutely nothing, not even walking a small distance.
The study published recently in the BMJ suggests that positive health effects will only be gained by doing much more than 600 Met minutes of exercise â€“ somewhere between 3000 and 4000 Met minutes to be exact. So that’s seven times more than that half an hour of walking.
“A person can achieve 3000 metabolic equivalent minutes per week by incorporating different types of physical activity into the daily routine”, explained first author Hmwe Kyu in an interview with The Guardian, an English newspaper. [theguardian.com 9 August 2016]
“For example, climbing stairs for 10 minutes, vacuuming for 15 minutes, gardening for 20 minutes, running for 20 minutes, and walking or cycling for transportation for 25 minutes, on a daily basis, would together achieve about 3,000 metabolic equivalent minutes a week.”
In practice only athletes and people who do physical work are likely to attain the optimal amount of physical activity.
Physical activity and risk of breast cancer, colon cancer, diabetes, ischemic heart disease, and ischemic stroke events: systematic review and dose-response meta-analysis for the Global Burden of Disease Study 2013
Objective To quantify the dose-response associations between total physical activity and risk of breast cancer, colon cancer, diabetes, ischemic heart disease, and ischemic stroke events.
Design Systematic review and Bayesian dose-response meta-analysis.
Data sources PubMed and Embase from 1980 to 27 February 2016, and references from relevant systematic reviews. Data from the Study on Global AGEing and Adult Health conducted in China, Ghana, India, Mexico, Russia, and South Africa from 2007 to 2010 and the US National Health and Nutrition Examination Surveys from 1999 to 2011 were used to map domain specific physical activity (reported in included studies) to total activity.
Eligibility criteria for selecting studies Prospective cohort studies examining the associations between physical activity (any domain) and at least one of the five diseases studied.
Results 174 articles were identified: 35 for breast cancer, 19 for colon cancer, 55 for diabetes, 43 for ischemic heart disease, and 26 for ischemic stroke (some articles included multiple outcomes). Although higher levels of total physical activity were significantly associated with lower risk for all outcomes, major gains occurred at lower levels of activity (up to 3000-4000 metabolic equivalent (MET) minutes/week). For example, individuals with a total activity level of 600 MET minutes/week (the minimum recommended level) had a 2% lower risk of diabetes compared with those reporting no physical activity. An increase from 600 to 3600 MET minutes/week reduced the risk by an additional 19%. The same amount of increase yielded much smaller returns at higher levels of activity: an increase of total activity from 9000 to 12?000 MET minutes/week reduced the risk of diabetes by only 0.6%. Compared with insufficiently active individuals (total activity <600 MET minutes/week), the risk reduction for those in the highly active category (?8000 MET minutes/week) was 14% (relative risk 0.863, 95% uncertainty interval 0.829 to 0.900) for breast cancer; 21% (0.789, 0.735 to 0.850) for colon cancer; 28% (0.722, 0.678 to 0.768) for diabetes; 25% (0.754, 0.704 to 0.809) for ischemic heart disease; and 26% (0.736, 0.659 to 0.811) for ischemic stroke.
Conclusions People who achieve total physical activity levels several times higher than the current recommended minimum level have a significant reduction in the risk of the five diseases studied. More studies with detailed quantification of total physical activity will help to find more precise relative risk estimates for different levels of activity.