Exercise as it relates to Disease/The relationship between physical activity and coronary heart disease in men

This wikibooks page is a critical analysis of the journal article “Physical activity and coronary heart disease in men” by Sesso et al.

What is the background to this research?
Coronary heart disease (CHD) is one of the main types of heart disease. It is characterised by the restriction of blood flow around the heart, which consequently, can cause a heart attack. Sedentary behaviour is a significant risk factor for various illnesses and diseases, including coronary heart disease. More than 60% of the adult American population does not engage in regular physical activity, and thus, coronary heart disease is the leading cause of death in the United States. Sedentary behaviour is just one risk factor.

Engaging in physical activity to promote health behaviour requires an understanding of the mechanisms of exercise (which forms of exercise to do, how to do them and for how long). There is a significant gap in existing research regarding the quantity and intensity of physical activity for the prevention of coronary heart disease and therefore this article is important in closing this gap. The aim of this research is to examine the relationship between physical activity factors (intensity and quantity) with coronary heart disease risk and prevention.

Where is the research from?
This article is a Harvard Alumni Health Study that conducted research on 12,516 Harvard Undergraduates (male). The target population is worth noting, as Harvard University is one of the most academically reputable universities in the world and currently holds the title of the world’s top university. Additionally, the American Heart Association conducted the study, which is America’s oldest and largest voluntary organisation devoted to the research and prevention of heart disease.

This article was published in “Circulation”, the official journal of the American Heart Association. The primary author, Howard D. Sesso, is the Associate Professor in the Department of Epidemiology at the Harvard School of Public Health. Both the authors and publishers of this study and the target population are of academically reputable backgrounds. This study is relevant in Australia as heart disease is the leading cause of death in Australia.

What kind of research was this?
The Harvard Alumni Study is an ongoing cohort study of undergraduate male students at Harvard University between the years 1916 and 1950. Cohort studies are clinical studies that follow one or more groups of people presenting with a condition over a set period of time. In this cohort study, the researchers followed groups of men presenting with risk factors for coronary heart disease. This research was conducted in a questionnaire format.

What did the research involve?
This study was a continuation of the previous Harvard Alumni Health Study that was initiated in 1962. This study provided new research and data on both the quantity and intensity of physical activity and coronary heart disease risk among older men. The study tracked 12,516 men aged between 39 and 88 years old (M = 57.7 years), between 1977 and 1993 .The extended duration of this study would increase the reliability of the results, however, physical activity levels fluctuate greatly over extended periods of time, especially as we age. The large sample size would provide a strong foundation for comparative gender analysis in future research. This study does not investigate the relationship between physical activity and coronary heart disease in women, which may impact the generalisability of the results, however, this would be ideal to examine in future research. Larger sample sizes produce more reliable results with greater power.

The subjects physical activity were calculated in kilojoules per week from a range of activities including recreational activities, sports participation and the number of flights climbed or blocks walked. For each activity, the frequency and duration of the activity were recorded and given a resting metabolic rate score. From this, energy expenditure was able to be estimated. The type of physical activity was further categorised into the type of activity and intensity (light, moderate or vigorous). Bias towards the null hypothesis could have occurred due to the possibility of physical activity measurements being misclassified.

Additionally, information was recorded for the following: cigarette smoking, alcohol consumption, early parental death under the age of 65, age, BMI and physician-diagnosed hypertension or diabetes mellitus. First coronary heart disease occurrences were recorded through self-reporting on questionnaires sent in 1988 and 1993. Overall, this study was successful in achieving its aim of examining the association between the quantity and intensity of physical activity with CHD risk and other CHD risk factors.

What were the basic results?
The findings of the study revealed no significant differences in baseline coronary risk factors amongst study participants and participants excluded from the study. 2135 CHD cases occurred (512 from angina pectoris, 576 from myocardial infarction, 207 from revascularizations, and 840 from CHD death). The salient finding of the study was an L-shaped association between increasing physical activity levels and CHD risk, with no decline in CHD risk for levels >8400kJ/wk.

Furthermore, there was no significant evidence indicating that coronary risk factors altered the inverse relationship between physical activity and CHD risk. Significant associations were found amongst increasing levels of total activities and vigorous activities with CHD risks.

Subjects with single CHD risk factors expended >4200 kJ/wk. Comparatively, those expending > 4200 kJ/wk exhibited lower Relative Risks (RRs) of CHD than those expending < 4200 kJ/wk. When age comparisons were made, findings highlighted that men aged 60+ had lower magnitudes of RRs of CHD for increasing coronary risk factors than younger subjects. Subjects were compared to physically active men with no CHD risk factors. This comparative analysis found that older men with single risk factors expending > 4200 kJ/wk had no increased risk of CHD.

What conclusions can we take from this research?
The results of this research are applicable to and representative of the general population due to the large scale sample size. The higher the sample size, the more likely it is that statistical outliers will be included in the data and results. The authors of the study concluded that older men should expend a minimum of 4200 J/wk in total physical activity to possibly reduce the risk of CHD by approximately 20%.

The Harvard Alumni research preceding this study investigated the associations between physical activity and coronary heart disease risk in middle-aged men. The present study elaborated on the existing research by extending the study to be inclusive of older men and incorporated physical activity intensity and quantity. Additionally, the present study utilised a more detailed approach to the coding of physical activity from the 1977 questionnaire in regards to CHD risk.

Conclusively, this research contributes to the existing body of research examining the association between physical activity and the risk of coronary heart disease.

Practical advice
Based on the findings of this research and other relevant research bodies relating to the association between physical activity and coronary heart disease risk, a registered physiotherapist or exercise physiologist would be able to prescribe a training program to individuals presenting with CHD risk. A health practitioner could prescribe an appropriate exercise plan, tailoring exercise quantity and intensity to suit the demographic and physical demands of the individual to reduce their risk of developing coronary heart disease.

Further information/resources

 * https://www.heartfoundation.org.au/your-heart/heart-conditions/what-is-coronary-heart-disease
 * https://www.heartresearch.com.au/heart-disease/risk-factors/
 * https://www.heartfoundation.org.au/about-us/what-we-do/heart-disease-in-australia