1. Describe the study research design. (2 sentences)
The health professional follow up study is a prospective cohort study. The study follow up the male cohort for four years to asses the relationship between vitamin E intake and the risk of coronary heart disease.
2. What are the strengths of the research design mentioned above?
Since the participants are observed for a period, there is no recall bias. Other strength of the study is that multiple outcomes and exposures can be observed.
3. What are the weaknesses of the research design mentioned above?
Prospective cohorts study is conducted for several years to observe an association exposure and outcome. The study is expensive because it is conducted for several years among a large cohort. The loss to follow is a weakness of the study because often cohort relocate and get exposed to other environmental factors. They discontinue responding and drop out from the study .
4. Which method of dietary assessment was used in this study?
The food frequency questionnaire method used to assess cohort’ diet.
5. Describe the method.
The study recruited 39,910 male cohort who were between 40 to 75 years old. The cohort were free of cardiovascular disease, diabetes and hypercholesterolemia . The cohort received a dietary questionnaire to assess Vitamin E, Carotene and vitamin C and followed up from 1986 to 1990. The cohort were asked to report about vitamin supplements with type and dose, brands of multivitamin, cooking oil and cold cereal intake.
6. What are the strengths and weaknesses of this method for assessing dietary intake?
The strength of Food frequency questionnaire is that it is inexpensive and individuals’ total diet can be known. FFQ asks frequency of food intake based on recall and memory. Since it is retrospective data can be erroneous, reports on food intake may not be accurate and precise.
7. Was supplement use considered in assessing vitamin E intake?
Yes, the FFQ is on 131 food items and 10 additional questions that asked the usage of vitamin supplement intake including type, dose and duration.
8. Which outcome was examined in this study? (1sentence)
A high intake of Vitamin E was associated with lower the risk of the coronary disease among men.
9. Explain what the relative risk means (in your own words) (1 sentence)
Relative risk refers to how many times higher or lower the disease risk is among a group of people who are exposed to a disease or an exposure as compared to the unexposed group.
10. Write one sentence about the relative risk associated with levels of vitamin E intake.
Those who took atleast 100 IU Vitamin E supplement daily had 0.63 times the risk of coronary heart disease compared to the men who did not take Vitamin E.
11. Which range of vitamin E intake was linked to lower risk of heart diseases in this study?
Consuming 100 IU to 249 IU of vitamin E daily for two or more years was related to the lower the risk of heart disease.
12. Which confounders were controlled?
Smoking, fiber intake, aspirin use and physical activity were controlled.
Multivitamins in the prevention of cardiovascular disease in men
1. Describe the research study design.
The Physicians’ Health Study II was double blind, placebo controlled, randomized, 2 X 2 X 2 X 2 factorial study of multivitamin to determine whether long term multivitamin supplementation lower the risk of cardiovascular disease among 14,641 men.
2. What are the strengths of the research design mentioned above?
Randomized study design reduces the risk of selection bias since everyone has an equal chance to be placed into the control or placebo group. A major strength of the study shows the causal relationship and an effectiveness of an intervention
3. What are the weaknesses of the research design mentioned above?
There are few weakness of randomized controlled trial. It is unethical to recommend an intervention to a participant unless it is good for the group. The participants cannot be blinded to certain intervention especially with diet. A participant will know what type of of diet is given if it is dietary intervention. Since the study is conducted over a long period of time, adherence to intervention is an issue also. However, if only healthy and adherent to intervention participants are observed, then it creates participant bias. Healthy user bias refers to the participant who follow any recommendation faithfully but they do not represent the population. Thus a larger population is needed to study an intervention.. Another disadvantage is that this intervention trial assesses only one outcome.
4. Describe the vitamin intervention (amount, type, and frequency of consumption).
The participants took one Centrum Silver multivitamin pill or placebo daily from June 2011 to August 2012.
5. Did the study determine compliance to the intervention?
Yes, the study determined the compliance to the intervention. Taking at least two third of the multivitamin pills was considered as an adherent to the pill.
6. Did they also consider dietary intake of vitamins?
The researchers did not consider dietary intake of vitamins. However, they observed dietary fruit and vegetable, whole grain intake and red meat intake.
7. Which outcome was examined in this study?
Daily multivitamin intake among men did not reduce the risk of myocardial infarction, stroke and cardiovascular death.
8. What were the results? Compare the difference in the risk (or hazard of the disease) among the groups.
Among 14,641 participants, 1732 men had major cardiovascular events. The cohort who took multivitamin had 1.0 times the risk of cardiovascular events, 0.93 times the risk of MI, 1.06 times the of stroke and 0.95 times the risk of cardiovascular mortality as compared with the placebo group.
9. Was the intervention associated with the outcome?
A daily multivitamin supplementation was not associated with lowering the risk of myocardial infarction, stroke and cardiovascular death as compared with placebo group.
10. Difference in the results of these two studies?
There were 667 cases of coronary disease out of 39,910 cohort in Vitamin E study but 1732 cardiovascular events occurred in 14,641 participant multivitamin study.