Exercise as it relates to Disease/Fitness and fatness as reliable predictors of cardiovascular disease mortality

The article critiqued in this wikibooks page is regarding “Fitness and Fatness as Predictors of Mortality from All Causes and from Cardiovascular Disease in Men and Women in the Lipid Research Clinics Study”. The study was completed by June Stevens, Jianwen Cai, Kelly R. Evenson, Ratna Thomas, and was published in the American Journal of Epidemiology on 1st November 2002.

What is the background to this research?
Cardiovascular disease (CVD) refers to a class of diseases and conditions that are associated with the heart and/or blood vessels. Regarding mortality, CVD is a major cause of death in Australia, with nearly 44,000 deaths being attributed to CVD in 2016. The prevalence of CVD is known to increase with age. It has been established that there is strong correlation between the elderly population and increased obesity prevalence, whilst also correlating strongly with low fitness levels. The following article critique aims to assess the reliability of obesity and low fitness levels as a predictor of CVD.

Where is the research from?
The research was carried out by four American professors, three of which come from the University of North Carolina. June Stevens, PhD, was an award recipient in 2014 from ‘The Obesity Society’ for an authored article. The study was published in the American Journal of Epidemiology, which is highly regarded as a top health and medical science publication, ranking highly for citations in the last five years. Whilst the authors, co-authors and journal outlet used for this study are all highly reputable, the research itself was conducted in the USA. Although the obesity figures between the USA and Australia are similar and the study is dependent on ‘fitness and fatness’, there are sure to be some variations in the findings of the study compared to the Australian public.

What kind of research was this?
The research was of a correlational design consisting of two stages. People were aged 30-75 and were asked to fill in questionnaires about their education and physical activity levels, from which a random sample was chosen to be the final cohort for the study. This type of research has been useful in this area previously.

What did the research involve?
The research involved using data from the lipid research clinic's first prevalence studies and the mortality follow-up studies years later. The research involved two stages, starting in 1972 where, during the first stage, basic plasma lipid levels of all participants were collected. For the second stage, a random sample of 15% of the participants from stage one were chosen, however all of these participants had elevated plasma lipids. In this second stage, ‘fitness and fatness’ measures were obtained which finished in 1976. The final study sample size was 5,366 (2,506 women, 2860 men) after thousands of participants were rejected due to reasons such as mortality prior to the second stage, having pre-existing illnesses, contraindications to exercise or those already with CVD. Fatness measures were obtained using the BMI of each participant. Fitness measures were obtained using the Bruce protocol during a standardized treadmill test. Metabolic Equivalents (METs) were used to determine fitness levels. ECG measures, heart rate and blood pressure were monitored throughout the test, which concluded if participants reached 90% of their predicted max heart rate, or earlier if risk factors were established. From 1987-1998, the researchers used listed participant contacts and epidemiology research to find death rates and the causes of death in participants of the study.

What were the basic results?
The results generally stated the average BMI result was in the overweight category for both genders, although higher in women. Only 65% of women, and 38% of men were of a normal BMI range. For fitness measures, the average METs for women 8.4 and 10.3 for men. These results places both genders in the ‘heavy’ intensity exercise category for a test which is not considered vigorous. The CVD mortality research showed that males who lasted less than 6 minutes in the test (before 90% max HR was reached) had 5.1 deaths per 100,000 person-years, whereas males who lasted more than 9 minutes in the test had only 3.1 deaths per 100,000 person-years. For females, those who lasted less than 5.7 minutes had 2.8 deaths per 100,000 person-years, whereas those females who lasted longer than 9.3 minutes in the test had only 0.9 deaths per 100,000 person-years.The number of male deaths were 682, with 270 caused by CVD (40%). The number of female deaths was 484, with 179 due to CVD (37%). For mortality caused by CVD, death rates increase as the BMI classes increase. CVD mortality research showed there were 4.7 deaths per 100,000 person-years in males with a BMI over 28.7, with only 2.9 deaths per 100,000 person-years in males with a BMI less than 23.7. For females, there were 2.8 deaths per 100,000 person-years for a BMI over 27.7, with only 2.1 or less deaths per 100,000 person-years for those females with a BMI of less than 24.5.

What conclusions can we take from this research?
This research shows first and foremost that there are a large number of all deaths caused by CVD (39%). There is a genuine trend in obesity, with over 50% of men and women being in the overweight category of the BMI scale. Although, questions have always been raised about the accuracy of using BMI as a singular measure of obesity, with studies suggesting it can be highly inaccurate. This means that there may be a reduced figure of people classed as overweight through the use of other anthropometric measures. Secondly, low fitness levels and high BMI scores were both greatly associated with higher CVD mortality rates, on occasion more than twice as high as low BMI and high fitness levels. However, some evidence suggest that the equations used for the Bruce Protocol can be inaccurate, often overestimating VO2 values. This would alter the results, as the varying VO2 values would alter the METs of each participant which are used to determine their fitness levels. However, this study does support other research regarding obesity and low fitness levels being great risk factors for CVD. Ultimately, ‘fitness and fatness’ can be largely accurate predictors of CVD mortality, although measurement techniques in this study can be improved.

Practical advice
The Bruce Protocol was developed in the 1960s, which is slightly outdated when compared to today’s technology. As it has been established that there can be up to an 11% error in VO2 measures in this protocol, it would improve the accuracy and reliability of the research to use protocols shown in other studies. Also, to improve validity of the research, using anthropometric measures such as skinfolds and girth measurements are much better options to measure obesity in individuals, rather than BMI. Exercising with an accredited professional is the best method to reduce ‘fitness and fatness’ levels to reduce the risk of CVD.

Further information/resources
For more information on CVD, you can visit https://www.baker.edu.au/health-hub/fact-sheets/cardiovascular-disease or https://www.heartfoundation.org.au/about-us/what-we-do/heart-disease-in-australia or visit your local GP To find and exercise professional, you can use https://meetyourpersonaltrainer.com.au/ or https://www.beactive.com.au/personal-training/ You may also wish to see your GP before commencing an exercise program.