PUBHLTH6001_problemSet6

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PUBHLTH 6001 Problem Set 6 Resources: Gordis – Chapter 14-15 Questions After visiting your parents, your mother notes that you have been drinking a lot of black tea. She tells you that you should cut back to no more than one cup a day since caffeine is “bad for your health”. To prove her wrong (and justify your love of hot beverages), you do a literature review of the epidemiology and find evidence that tea drinkers have lower risk of type 2 diabetes. Before you go back to your mother with your findings, you decide to think carefully about the various lines of evidence to see if the data really seem causal. 1. You first identify a published ecological study that compared prevalent diabetes and black tea consumption in 50 countries. (Beresniak et al 2012. BMJ Open: e000648.) Their Figure 3 (shown below) illustrates their key finding, which suggests that there is lower type 2 diabetes prevalence with greater tea consumption. Comment on how strong of an argument this study makes for causality. Be sure to explain your reasoning and note what causality “criteria” may support your claim. Although this study is able to tell us there is a strong correlation that there is a lower type 2 diabetes prevalence with greater black tea consumption, the correlation doesn’t necessarily imply causality. Correlation can only indicate that there is potential for indirect or direct cause. Although we do have a plausible or reasonable pathway to link outcome to exposure, we need to do further research to prove it. We also know about ecologic fallacy, which means we can’t assume the associations we find at the group level apply at the individual level. But the information found in this study could help in future studies.

2. Next, you find a study of type 2 diabetes and tea consumption conducted using information from the Women’s Health Study, a large prospective randomized controlled trial evaluating the impacts of low-dose aspirin and vitamin E on cardiovascular disease (Song et al. 2005. J Am Coll Nutr.24(5):376-384). Self-reported tea consumption was reported at baseline, and type 2 diabetes was self-reported over the follow-up period. Personal information was also collected about other individual risk factors for type 2 diabetes. List three characteristics of this study that make it a stronger design to assess causality than the previous study. A characteristic that makes this study a stronger design to assess causality is the temporal relationship. For an exposure to be the cause of disease, the exposure must precede the disease in time. In the study, participants self-reported their tea consumption at the baseline and reported any type 2 diabetes during the follow-up. Next, Consideration of Alternative Explanations, sometimes alternative explanations for the association should be considered. The association is not causal but is due to confounding. In this study, they collected personal information about individual risk factors for type 2 diabetes, this could be accounting for possible confounding factors that may increase or decrease an individual’s risk for developing type 2 diabetes outside of tea consumption. Lastly, Biological Plausibility shows association does not conflict with current knowledge of the natural history and biology of disease. Many epidemiologic studies have identified cause-effect relationships before biological mechanisms were identified. Since there has been a large association between black tea and lowering diabetes, cause- effects may have been recognized before it was biologically proven. 3. The authors also examined associations between flavonoids (an antioxidant contained in tea and other fruits/vegetables) and plasma insulin as well as HbA1c levels (two subclinical markers of diabetes) but found no relationship. How does this information help or hurt your assessment into the causal relationship between tea and type 2 diabetes ? I believe this information could hurt the assessment because if we are looking to replicate findings, we should have been able to find a relationship between flavonoids which are antioxidants contained in tea and other fruits/vegetables, and plasma insulin as well as HbA1c levels, two subclinical markers of diabetes. A causal association is likely to be observed repeatedly in different persons, places, times, and circumstances, which means we should have been able to relate these things. But sometimes, there are good reasons why study results differ. An example could be one study that may have looked at low-level exposures while another. looked at high-level exposures. 4. Observing the data from these different papers that you reviewed, comment on if you believe the relationship between tea consumption and type 2 diabetes to be causal. After reviewing the different papers, there is still not enough concrete evidence to prove that the relationship is causal. By taking the information we have; we should be able to come up with a good hypothesis and complete more in-depth studies to truly see if the relationship is causal. 5. What study might you propose to do next to attempt to answer this question more concretely? I would use a Randomized controlled trial to measure the effectiveness of black tea on diabetes to help prove causality. Using randomization reduces bias and provides a thorough way to examine cause-effect relationships between an intervention (black tea) and outcome (lowering diabetes). This can help balance participant characteristics that we observe

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