The long-term effect of physical activity on incidence of coronary heart disease

Sundquist, K. Qvist, J. Johansson, S. Sundquist, J. “The long-term effect of physical activity on incidence of coronary heart disease: a 12-year follow-up study”

(a) What study design does this study employ, what is the exposure and what is the outcomes? [2 mark]
This study shows that the analysis of the long-term effect of leisure-time physical activity on incident cases of coronary heart disease (CHD) among women and men. A national, random sample of 2,551 women and 2,645 men, aged 35–74, was interviewed in 1988 and 1989 and followed until December 31, 2000, with respect to CHD incident cases. Women and men hospitalized for CHD 2 years before the start of the study and those who rated their general health as poor were not included in the sample. Leisure-time physical activity was divided into four levels according to the frequency of physical activity. When leisure-time physical activity increased, the risk of CHD decreased. The positive long-term effect of leisure-time physical activity on CHD risk among women and men remains even after accounting for income and other important CHD risk factors.

In the current study, we used Adult Treatment Panel III (ATP III) recommendations to define risk factors of CHD as follows: Hypertension, systolic blood pressure ≥140 mmHg or diastolic blood pressure ≥90 mmHg or taking hypertension medication; hypercholesterolemia, serum cholesterol ≥6.2 mmol/l (240 mg/dl) or taking cholesterol-lowering medication; diabetes, fasting plasma glucose ≥7.0 mmol/l (126 mg/dl) or 2 hours post-load glucose ≥11.1 mmol/l (200 mg/dl) or taking any medication for diabetes; low HDL cholesterol, HDL cholesterol <1.03 mmol/l (40 mg/dl); tobacco consumption, any tobacco product (cigarette, pipe, water pipe) in the past or currently on a regular or occasional basis; family history of CVD, history of myocardial infarction or stroke or sudden cardiac death in a male first-degree relative <55 years or female first-degree relative <65 and the high-risk age group, ages 45 and 55 years or higher in men and women respectively.

The survey was done annually by telephone calls, by which a trained nurse asked each participant about any medical event leading to hospitalization during the past year, and if positive, complementary data were collected by a trained physician using hospital records or if needed a home visit. In addition, in the case of mortality, data were collected from the death certificate, the forensic medicine report and if needed verbal autopsy. To confirm the diagnosis, an outcome committee reviewed all the collected data. The committee consisted of an internist, a cardiologist, an endocrinologist, an epidemiologist, the physician who collected the data, and other experts invited as needed. In this study, CHD events as outcomes included cases of definite myocardial infarction (MI) diagnosed by electrocardiogram (ECG) and biomarkers, probable MI (positive ECG findings plus cardiac symptoms or signs but biomarkers showing negative or equivocal results), unstable angina pectoris (new cardiac symptoms or changing symptom patterns and positive ECG findings with normal biomarkers), angiography has proven CHD and CHD death (any death due to CHD based on above criteria in the hospital or sudden cardiac death from cardiac disease occurring less than or equal to 1 hr after the onset of symptoms based on verbal autopsy documents outside of the hospital). These are comparable with ICD10 rubric I20–I25.

(b) What justifications do the authors give for conducting this study? [4 marks]
Coronary heart disease (CHD) is the most common cause of death worldwide. Mortality from CHD increases with advancing age. Coronary risk factors include socioeconomic factors, classic risk factors such as hypertension or diabetes, lifestyle factors, and family history. A variety of factors such as emotional stress or physical exertion can trigger coronary events. This risk has been increased during morning hours and winter months.

CHD narrows coronary arteries, leading to an imbalance between the functional requirements of the heart and the capacity of the coronary arteries to supply blood and oxygen. As a result, the heart muscle is damaged, which will eventually become clinically apparent with cardiac symptoms. CHD is associated with disability, impaired health-related quality of life, and premature death. In addition, disease-related costs as induced by medical resource utilization and loss of productivity are considerable. This is the justification that the authors give for conducting this study.

(c) What was the proportion of those who (i) do not do any physical activity (ii) engaged in twice a week vigorous physical activity? (You are not required to report 95% confidence intervals) [4 marks]

In 2012/2013, the crude prevalence of CHD was 9.4% with the first definition (593 000 people). Between 2000/2001 and 2012/2013, the age-standardized prevalence increased by 14%, although it has been decreasing slightly since 2009/2010. Age-standardized incidence and mortality rates decreased by 46% and 26% respectively and represented a crude rate of 6.9 per 1000 and 5.2% in 2012/2013. The proportion identified only by CHD mortality, our SCD proxy, was only significant for the incident cases (0.38 per 1000 in 2009/2010) and declined over the study period.

(d) What is the crude incidence rate of CHD in this sample what is the incidence rate in inactive men and inactive women? [4 marks]
The crude incidence rate in men was about twice that in women (11.9 vs. 6.5 per 1000 person-years). The aPAF of hypertension, diabetes, high total cholesterol, and low-HDL cholesterol was 9.4%, 6.7%, 7.3% and 6.1% in men and 17%, 16.6%, 12% and 4.6% in women respectively. This index was 7.0% for smoking in men. High-risk age contributed to 42% and 22% of the risk in men and women respectively.

(e) Calculate the relative risk of being non-active versus being “highly active” (i.e., vigorous physical activity at least twice a week) in men and in women and how would you interpret the relative risk in men and in women [4 marks]
Relative risk of non-active and highly active= 80/ (80+59) /42/ (42+59)
= 0.57/0.41
= 1.39

(f) Looking at the sex and age adjusted HR in Table 3 (the HR stands for Hazard Ratio which is similar to rate-rato) (i) how would you describe the association between physical activity and CHD [4 marks]
An increase in whole grain consumption lowers the vulnerability of CHD.
Increased exercises by women also decrease chances of CHD. Working both with a
good diet and exercise lowers the risk of CHD as compared to one method only.

(g) The authors removed from the analysis any person who self-rated their health as “bad” or “anywhere between good and bad” why? (no more than 60 words) [4 marks]
According to the plans that the author had in carrying out interview and avoid bias, since they were only after participants who had good health, anything that was between good and bad was not considered good at all to minimise bias and other factors that could make the research difficult to analyse.

(h) What possible bias could have changed the estimate for the association between physical activity and CHD – at least one, and explain why. [4 marks]
The study is a retrospective cohort study and this is associated with the selection bias and can be cause by loss of records of the survey if medical and employment were associated with the outcome or exposure. The problem with this is that the results do not come handy to the other age groups as the factors leading to the disease in the study group will often differ from that of the other groups.

(i) Do you think there is a risk of confounding bias in this research? Any answer yes or no must be justified [4 marks]
Yes, Although the randomized controlled trial (RCT) is the gold standard to measure causality in its unique advantage of random assignment, we must consider alternative research designs that permit relatively strong causal inferences. Therefore, in conducting this research observational studies researchers need to ensure that the internal validity of the study is not compromised by bias and that the results found are close to the “truth”. Biases common to all observational studies include selection bias and information bias.

Question 2: (20 points)

Tasmanian researchers conducted a case –control study to investigate the effect of dietary fat intake on skin cancer. They hypothesised that people whose dietary fat intake is low will be more susceptible to skin cancer. The study compared 500 cases of melanoma with 500 controls who were randomly selected from the state’s electoral roll. The researchers categorised the dietary fat intake into three categories High, Moderate and Low. They found that among skin cancer patients 150 were classified at the low and 80 at the high dietary fat intake whereas among control 130 were at the low and 100 were at the high.

a) Build a table to summarise the data above which will help you estimate the association between dietary fat intake and Skin cancer, pay attention to headings of columns and rows [4 points]

Fat intake Skin cancer Controls
High 80 100
Moderate 270 270
Low 150 130

b) Calculate the appropriate measure of relative risk (RR) of having melanoma between those consuming low fat intake versus high fat intake; calculate the appropriated measure of RR of having melanoma between those consuming medium to high fat intake and explain in words the meaning of what you found [4 points].
RR (high fat intake versus low fat intake)
RR = (80/180) / (150/280) = 0.8296
RR (medium to high fat intake)
RR = (270/540) / (80/180) = 1.125
The low intake of fat was significantly related to the increased risk of
contracting the skin disease and this implies that individuals who
consume stuffs that are have low fat intake are at a high risk of getting
skin cancer.

c) Calculate the percent attributable risk due to exposure to low-dietary fat intake on Melanoma and explain in one or two sentences the meaning of your findings [4 points]

ARP = (RR – 1) /RR

RR = EER/CER = (150/500) / (130/500) = 1.1538
ARP = (1.1538 – 1)/ 1.1538 = 0.1333*100 = 13.33
The individuals who consume those products with low fat intake experience an
increase of 13.33 percent of getting skin cancer than those who are in the medium and
high level of fat intake.

d) Calculated the population attributable risk of low-fat intake on melanoma and explain in words the meaning of such finding [4 points]

PAT = (150 + 130)/1000 = 0.28 = 28 per 1000

PAT is 28 percent and this value represents the number of skin cancer that would not be present if the individuals will not take low fat stuffs.

e) What do you think about the conclusions of the PAR regarding exposure to low fat diet to reduce melanoma? (no more than 3-4 sentences) [4 points}
The population attributable risk shows that 28 percent of those participants at high
risk of getting skin cancer due to low intake of fat and that this proportion of the
population can be saved from getting the disease if they avoid consuming low fat

Question 3

A study aims to determine the incidence of type 2 diabetes. A cohort of 200 people age 65 years or older who were initially disease –free participated in the study. One hundred and fifty people were examined at the end of 3 years. Fifty other participants from the initial cohort could not be examined, including 11 people who had died. Does this loss of participants represent a source of bias? Justify your answer. [4 points]
Initially for the study 200 people of 65 years of age are selected. But 150 among them are ultimately examined as 50 out of them are initially could not examined and 11 among them are died.
The loss of participants are not a source of bias. As –

  1. Principal of human dignity and fidelity = in code of ethics there is a code of human dignity and fredility. That is there will be no leakage of data that are given by the participants, the confidentiality will always be maintained.
  2. Principal of justices = all research group must follow this principal the all clients who are participate in this study will all get a fear treatment from the research group. The clients will not get harm due to the research study. So, there is no bias.
  3. Consent = a fully informed consent must be given to the all participants at the beginning of the study. So, the clients who participated all are signed that consent. Initially the 200 people are participating in that study but 50 out of them are withdrawal themselves as some of my thought the will get hamper from the study and some of them (11 people) are died. So, there is no bias of study.
  4. Principal of withdrawal = according to code of ethics the participants can withdraw themselves at the middle of study. So, there is no bias of study. The 11 people who are died are not due to the effect of research study. The die as they were chronically ill or due to other cause. There is no bias of research study.

Question 4
A telephone survey is being administered by several interviewers in order to collect data regarding the outcome in a randomised controlled trial. Identify the key issues the researchers should have considered in order to minimise measurement error of the outcome. Discuss the impact these issues may have on the study. [4 points]

  1. Train the interviewers before conducting the survey – if the interviewers are not well trained, they can mislead the respondents easily or make errors during recording the respondent feedback
  2. Try to come up with an alternative if one technique fails – this days due to advanced technology anything can happen say for example a cyber-attack, if the interviewer does not have a place where data can be backup then he/she is going to fake data to finish the project assigned if the consequences set are tough.
  3. Create awareness to the people who will be interviewed such that they can give honest feedback – creating aware is the best preparation of collecting data, through adverts and other sources one can easily know the kind of products the organisation is producing, through this one can easily be able to answer any random question if asked.
  4. The identification of the data collection organization. – having a brand identity is one way of making a respondent build trust in his private information including voice, date of birth if applicable in the interview.

Leave a Comment

Your email address will not be published. Required fields are marked *