By Seema Gupta, MD, MSPH

Clinical Assistant Professor, Department of Family and Community Health, Joan C. Edwards School of Medicine, Marshall University, Huntington, WV

Dr. Gupta reports no financial relationships relevant to this field of study.

SYNOPSIS: Higher levels of total physical activity are strongly associated with lower risk of five common chronic diseases: breast and bowel cancer, diabetes, heart disease, and stroke.

SOURCE: Kyu HH, Bachman VF, Alexander LT, et al. 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. BMJ 2016 Aug 9;354:i3857.

Physical activity may provide a protective effect against several chronic conditions as well as all-cause mortality. The amount of time Americans spend engaging in sedentary activities, such as watching television or playing video games, is steadily rising. Such habits have been independently associated with increased risks of several chronic conditions and mortality.1

The World Health Organization (WHO) recommends at least 600 metabolic equivalent (MET) minutes of total activity per week for health benefits. For example, a patient could engage in about 150 minutes per week of brisk walking or 75 minutes per week of running.2 One MET equals the resting metabolic rate of approximately 3.5 mL O2/kg/min, and represents the approximate rate of oxygen consumption of a seated adult at rest. Although the beneficial effects of exercise appear to be dose-dependent, there is a paucity of studies that have systematically quantified the dose-response relations between physical activity and chronic disease endpoints. In the existing literature, often the focus is on studying a single activity domain, such as leisure time activity, and its effect on the chronic disease in question.3,4 Rarely is that true for a patient who engages in multiple daily physical activities. However, no study to date has been able to quantify the total physical activity required to have an effect on chronic diseases in a dose-response manner.

Kyu et al quantified the dose-response associations between total physical activity and the risk of breast cancer, colon cancer, diabetes, ischemic heart disease, and ischemic stroke events. They analyzed the results of 174 studies published between 1980 and 2016, examining the associations between total physical activity and at least one of these five chronic diseases.

The researchers found that a higher level of total weekly physical activity was associated with a lower risk of all five conditions. Most health gains occurred at a total activity level of 3,000-4,000 MET minutes per week, with diminishing returns at higher activity levels. They found that an increase from the currently recommended level of 600 MET minutes per week to 3,600 MET minutes per week reduced the risk by an additional 19%. Furthermore, the researchers found that compared with less active individuals (total activity < 600 MET minutes per week), the risk reduction for those in the highly active category ( 8,000 MET minutes per week) was 14% (relative risk [RR], 0.863; 95% confidence interval [CI], 0.829-0.900) for breast cancer; 21% (RR, 0.789; 95% CI, 0.735-0.850) for colon cancer; 28% (RR, 0.722; 95% CI, 0.678-0.768) for diabetes; 25% (RR, 0.754; 95% CI, 0.704-0.809) for ischemic heart disease; and 26% (RR, 0.736; 95% CI, 0.659-0.811) for ischemic stroke. The authors concluded that individuals who can achieve total physical activity levels several times higher than the currently recommended minimum level experience a significant reduction in the risk of the five diseases under study.

COMMENTARY

We know that physical activity is good for health, but clinicians are uncertain about how much physicial activity produces positive outcomes and to what degree. In the past, while some studies have evaluated the physical activity as a whole, others have concentrated on specific types of activity. The study by Kyu et al represents a significant advance in our understanding of the significance of total physical activity as well as its dose-response effect on a set of chronic illnesses.

As the results suggest, the total physical activity perhaps should be several times higher than the current recommended minimum level of 600 MET minutes a week to potentially achieve much larger risk reductions of these diseases. With the total physical activity concept, it may not be very difficult to achieve such a task. For example, a patient can achieve 3,000 MET minutes a week by incorporating different types of physical activity into his or her daily routine, such as climbing stairs for 10 minutes, vacuuming for 15 minutes, gardening for 20 minutes, running for 20 minutes, and walking or cycling for 25 minutes.

Although this meta-analysis was based on observational studies, and therefore may not prove a relationship between the amount and/or type of physical activity and a lowering of the risk of chronic disease, it makes sense for clinicians to prescribe prevention in the form of total physical activity. With an aging population, that does not have to be just exercise but a host of activities for patients that are easy to perform and that can become part of their lifestyle.

REFERENCES

  1. Ekelund U, Steene-Johannessen J, Brown WJ, et al. Does physical activity attenuate, or even eliminate, the detrimental association of sitting time with mortality? A harmonised meta-analysis of data from more than 1 million men and women. Lancet 2016 Jul 27. pii: S0140-6736(16)30370-30371.
  2. U.S. Department of Health and Human Services, Office of Disease Prevention and Health Promotion. Physical activity guidelines for Americans. Available at: http://bit.ly/2bXF6yT. Accessed Sept. 7, 2016.
  3. Aune D, Norat T, Leitzmann M, et al. Physical activity and the risk of type 2 diabetes: A systematic review and dose-response meta-analysis. Eur J Epidemiol 2015;30:529-542.
  4. Sattelmair J, Pertman J, Ding EL, et al. Dose response between physical activity and risk of coronary heart disease: A meta-analysis. Circulation 2011;124:789-795.