A small amount of physical activity could reduce mortality and prolong life expectancy

By Dr. W.A. Arrindell, psychologist and consultant

The health benefits of leisure-time physical activity are well known, but whether less exercise than the 150 minutes a week (or 30 minutes a day, 5 days a week) proposed in the Global Recommendations on Physical Activity for Health by the World Health Organization in 2010 can have life expectancy benefits is unclear. A methodologically superior and unique study published online, ahead of print, in the prestigious and high-impact medical journal The Lancet (August 2011) provides an answer to this question. The study was carried out by Dr. Chi Pang Wen, Dr. Jackson Pui Man Wai and associates from the National Health Research Institutes, China Medical University Hospital, National Taiwan Sport University, Chung Shan Medical University, MJ Health Management Institution (all in Taiwan), University of Washington (Seattle, WA, USA), and the University of Texas School of Public Health and MD Anderson Cancer Center (both in Houston, Texas, USA).

Background

Dr. Weng and colleagues argued that identification of a minimum amount of exercise (or minimum dose) sufficient to reduce mortality is desirable because a small amount of exercise can be easier to achieve in order to generate health benefits; patients might be more easily motivated to exercise if their physician recommends an easily manageable amount (dose), especially if health messages are simple and related to the disease in question.

Method of study

In a prospective study conducted in Taipei, Taiwan, 416,175 healthy individuals (216,910 women and 199,265 men) ages 20 or older participated in a standard medical screening program. In the 13-year study period, participants were followed up between 1996 and 2008 (average follow-up=8.05 years). Every individual's identification number was matched with the National Death file and the National Cancer Registry file.

On the basis of the amount, duration, and intensity of weekly exercise indicated in a self-administered questionnaire, participants provided information for researchers to calculate to which of the following five categories of exercise volume they could be allocated: (1) inactive (sedentary), (2) low volume, (3) medium volume, (4) high volume, or (5) very high volume. Categories (3), (4), and (5) reflect physical activity meeting recommendation by the World Health Organization. Examples of exercise types according to intensity were "light" (e.g., walking), "moderate" (e.g., brisk walking), "medium-vigorous" (e.g., jogging), or "high-vigorous" (e.g., running).

The researchers also classified each participant by exercise intensity into one of two groups: moderate-intensity exercise or vigorous-intensity exercise.

In addition, Dr. Wen and associates collected information on 13 so-called confounders. Confounders are background variables that are (or: may be) associated with physical activity and/or health, in which case they could affect the outcome of statistical analyses and lead to erroneous conclusions. The potential confounders were age, biological sex, education, physical labour at work, smoking, drinking, pre-diabetes, pre-hypertension, total cholesterol, body mass index (obesity), diabetes, hypertension, and history of cancer.

Basic findings

Compared with individuals in the inactive group (and holding constant the influences of potential confounders), those in the low-volume activity group (who exercised 15 minutes a day for 6 days per week or 90 minutes a week) had a 14% reduced risk of all-cause mortality, a 10% reduced risk of cancer mortality, and a 20% reduced risk of mortality from cardiovascular disease. In addition, they also had a three-year longer life expectancy.

Every additional 15 minutes of daily exercise beyond the minimum amount of 15 minutes a day further reduced all-cause mortality by 4% and all-cancer mortality by 1%. This pattern held up to 100 minutes a day (or 600 minutes a week), after which additional exercise gave no additional health benefit. Thus, the association between weekly physical activity and health benefits was not a straight line (linear), but followed a curve (curvilinear as shown in the figure) which expressed a steady increase starting at 90 minutes a week up to 600 minutes a week after which the curve levelled off, that is, indicated that there were no further benefits beyond this point.

The health benefits were applicable to all age groups and both sexes, even to those with cardiovascular disease or lifestyle risks (e.g., smoking, drinking).

In addition, the advantages of vigorous-intensity exercise over moderate-intensity activities at an identical volume or the next higher volume of activity were demonstrated. This suggests that, for example, two hours a week of vigorous-intensity exercise could generate similar health benefits as would four hours a week of moderate-intensity exercise.

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Explanation (mechanism)

In a commentary in the same Journal on the findings obtained by Dr. Wen and associates, Dr. Anil Nigam and Dr. Martin Juneau (Montreal Heart Institute and Université de Montréal, Montreal, Quebec, Canada) argued that exercise can reduce cardiovascular and coronary mortality by many mechanisms, including risk-factor control and improvements in endothelial function (the endothelium is the thin layer of cells that lines the interior surface of blood vessels), in cardiovascular function (heart rhythm), and in immune function (body's defence system). Improved endothelial function leads to the prevention and stabilization of coronary atherosclerosis, thereby reducing the risk of sudden cardiac death. Cancer, like coronary heart disease, shares several common risk factors such as poor nutrition, obesity, poor immune function, and physical inactivity. Therefore, improvements in some of these risk factors with regular exercise could plausibly explain the cancer mortality benefits recorded by Dr. Wen and associates.

Policy implications

Dr. Wen and colleagues point out that if the minimum amount of exercise that they suggest is adhered to, mortality from heart disease, diabetes, and cancer could be reduced. This low-volume of physical activity, which is half of that recommended worldwide, could play a central part in the global war against non-infectious diseases, reducing medical costs and differences in the quality of health and health care across different population subgroups.

Dr. Wen and associates warn that although their proposed low-volume exercise may seem very low, such is actually not the case because for such exercise to yield health benefits, it needs to be done for most days of the week for many years.

Dr. Nigam and Dr. Juneau formulate their policies as follows. The knowledge that as little as 15 minutes per day of exercise on most days of the week can substantially reduce an individual's risk of dying, could encourage many more individuals to incorporate a small amount of physical activity into their busy lives. Governments and health professionals both have major parts to play in spreading this good news story and in convincing people of the importance of being at least minimally active.