Exercise as it relates to Disease/Which is more effective in reducing type 2 diabetes in women; walking or vigorous-intensity activity?

This is a critique of the journal article "Walking compared with vigorous-intensity Physical Activity and Risk of Type 2 Diabetes in Women" by Frank B. Hu, MD, PhD; Ronald J. Sigal, MD; Janet W. Rich-Edwards, ScD; et al. Published in 1999 in the JAMA Medical Journal.

What is the background to this research?
Type 2 diabetes makes up over 85% of all diabetes cases and is the fastest growing chronic condition in Australia, for this reason, it is an important disease to prevent. Type 2 diabetes is a progressive condition due to a genetic disposition where the body becomes resistant to the normal effects of insulin and/or gradually loses the capacity to produce enough insulin in the pancreas. Physical activity in the absence of weight loss improves blood glucose control and can prevent or delay type 2 diabetes, along with positively affecting the quality of life. The prevalence of diabetes is increasing year on year and in 2014 the World Health Organisation (WHO) recorded an increase from 108 million in 1980 to 422 million.

Strong evidence has emerged which identifies the association between physical activity and reduced risk of diabetes. Moderate-intensity physical activity such as walking is the most prevalent physical activity among older adults and is feasible, accessible, and readily adopted method for reducing type 2 diabetes. Observational studies have focused on the association of vigorous exercise and its effect on reducing the risk of type 2 diabetes. However, there is little research showing the comparison between the difference in the level of intensity of exercise has on reducing type 2 diabetes.

Where is the research from?
The research was published in JAMA which is an international peer-reviewed general medical journal that has been widely circulated around the world since 1883. The subjects for the research were registered female nurses from the Nurses’ Health Study Cohort. The Nurses’ Health Study is one of the largest prospective investigations into women’s health and factors leading to chronic diseases. Established in 1976 when 121 700 US female registered nurses aged 30–55 responded to a mailed questionnaire. The questionnaire investigated their medical history, health practices, dietary intakes and the results from the studies play an instrumental role in shaping public health recommendations.

Dr Frank B. Hu is the main author of the article and a professor of Medicine at the Harvard Medical School. His research focuses on diet, lifestyle, metabolic, and genetic determinants of obesity, type 2 diabetes, and cardiovascular disease (CVD). Dr Ron Sigal is an Associate Professor of Medicine, Kinesiology, Cardiac Sciences and Community Health Sciences at the University of Calgary. His current research focuses on physical activity, obesity, diabetes and CVD. All authors have a history with the topics being researched and therefore the knowledge presented is highly respected.

What kind of research was this?
The research was a prospective cohort study with data around the physical activity of 70,102 women as part of Nurses’ Health Study. Participants were observed at baseline (1986) and then followed up in 1988 and 1992 through a mailed questionnaire, inquiring about whether they had been diagnosed with diabetes.

Prospective studies are the gold standard in epidemiological studies. It involves assessing a cohort of participants with similar conditions from baseline to a future date whilst identifying and outcomes of interest (type 2 diabetes). The chosen research design requires a long-term follow-up, this study identified a 98% follow-up rate which provides high-quality data and validity of results.

A prospective cohort study seemed more appropriate than a retrospective cohort study, due to the benefit of being able to target for a specific outcome. The alternate method of observational studies would not have been suitable for the desired method as it involves the direct observation of individuals without forced intervention.

What did the research involve?
Over an 8-year period from 1986 70,102 female nurses who were free from diabetes were identified through a mailed questionnaire to participate in the study. The participants completed a physical activity questionnaire involving questions such as average time spent doing physical activity and the intensity of the activity. The data was analysed, and their baseline physical activity levels and weekly energy expenditure was calculated. Their energy expenditure was measured in metabolic equivalent task-hours (MET-hours) in relation to the different intensities of physical activity or walking. The above-mentioned questionnaire was first obtained in 1986 and then repeated two years later and in 1992. To control for confounding variables, the study also collected information on personal characteristics and lifestyle habits (e.g. smoking).

Strengths;

 * Large cohort and follow-up time
 * Comparable results with similar studies
 * Gold Standard Study Design

Limitations;

 * Questionnaires - leads to misclassification and over-reporting of physical activity. Self-reporting bias can appear due to different perceptions of exercise intensities, making it not as effective as electronic devices.
 * Standard classification for energy expenditure based on the activities not the individual, therefore results used are an estimate. Waviered due to the cohort size
 * All participants are Nurses with similar socioeconomic status and therefore may reduce external validity of the study and mean the results may not be generalisable to the general population.
 * ‘National Diabetes Data Group’ criteria were used to diagnose subjects and therefore exclude them. If the new criteria had been used, then some women would have become ‘excluded’ and vice versa.

What were the basic results?
The research showed that there is a positive relationship between physical activity and reduced risk of type 2 diabetes in women. Within the 8 year follow up 1419 cases of type 2 diabetes were recorded corresponding to an incidence rate of 265 per 100 000 person-years. In summary, the below points outline the key results;


 * Women who increased their activity level from 2.1-10.4 MET-hours in 1986 to >10.4 MET-hours in 1988 had a lower risk (RR = 0.71; 95% CI, 0.55-0.93) compared with those who were consistently sedentary.
 * Walking and vigorous activity was associated with comparable risk reductions when the energy expenditures were similar. Identifying substantial reductions of approximately 0.43 for individuals in the highest energy expenditure quintiles
 * The relative risk associated with a 5 MET-hours per week increase in energy expenditures were 0.95 (0.92-0.98) for vigorous activity and 0.92 (0.88-0.95) for walking.
 * Walking pace was an independent predictor for risk of type 2 diabetes. Multivariate RR for ‘normal pace’ was 0.72 compared to ‘brisk’ pace which was 0.41.

What conclusions can we take from this research?
If nothing else this study identifies that any exercise is better than none. Evidence shows that a 30-minute walk each day will reduce your risk of diabetes meaning it doesn’t have to be high intensity to see results. However, both intensities are associated with reduced risk of type 2 diabetes, therefore, it is a personal preference.

The findings show that the amount of physical activity required to reduce the relative risk is reliant on total energy expenditure rather than what type of exercise is undertaken or for how long. When the energy expenditure of moderate and vigorous was equivalent within the study the benefits were comparable. Whilst there are many other inflammatory markers that can increase risk of type 2 diabetes, regular physical activity alone is shown to reduce this risk regardless of changes in weight loss, lifestyle habits (e.g. smoking) or other metabolic factors. There are many misconceptions regarding the need to exercise vigorously to see any benefit however these results dismiss them.

The findings support the current guidelines from 'Centers for Disease Control and Prevention' and the 'National Institutes of Health' that individuals should participate in at least 30 minutes of moderate physical activity at least five days a week.

Practical Advice
Implementing some form of physical activity into your daily routine will not only decrease your risk of type 2 diabetes it will also improve your daily life and overall health.
 * Start somewhere; often getting started is the hardest part! Use the Physical Activity Guidelines as recommendations.
 * Make it enjoyable; find a form of physical activity that you enjoy (e.g. swimming, tennis, aerobics, walking) which will make it 'easier'.
 * Avoid long periods of sedentary behaviour (i.e. watching TV, sitting at your desk) by breaking it up with physical activity.
 * Choose activities that suit your lifestyle
 * If any form of physical activity causes severe pain or you have concerns, seek expert advice

Further Information
If you are interested in further information please see the links below;
 * Find out if you’re at risk of diabetes? https://www.diabetesaustralia.com.au/risk-calculator
 * Physical Activity Fact Sheet. Get Active. https://www.heartfoundation.org.au/active-living/get-active
 * Need help getting started? Find an exercise Professional nearby; https://www.essa.org.au/find-aep