Does drinking green tea can prevent or reduce the risk of cardiovascular disease? Essay

Does drinking green tea can prevent or reduce the risk of cardiovascular disease?In the prospective study initiated by the Ohsaki National Health Insurance, the population consisted of 40530 Japanese adults aged 40 to 79 years who were without history of coronary heart diseases, stroke or even cancer, to investigate the relationships between the consumption of green tea and the occurrence of cardiovascular diseases, cancer, all causes and cause-specific mortality.  The participants were from Northeastern Japan and where consumption of green tea is known to be consumed more. 80% of the population drinks green tea and more than half of this population consumes 3 or more cups daily. In this cohort study, a self-administered questionnaire and items on dietary intake were delivered to the participants. Basically, those who did not respond and withdrew from the survey were eliminated from the final list.

Moreover, those participants who died before the collection of the history files; those who submitted insufficient data regarding their green tea intake; those who took very high daily energy intake and those participants with reported history of cancer, myocardial infarctions ands strokes were eliminated. The questionnaire included frequency of average consumption of green tea, oolong tea, black tea and coffee; 36 items about food; consumption of alcohol and tobacco; personal and family history of disease; job status; level of education; body weight; height; sports activities, exercise and amount of time spent on walking per day. To determine the level of frequency for each of the attributes, specific category is set for every exposure. The relative risk for the exposure is then calculated to quantify the relationship between the exposure and the outcome. This study made use also of the comparison between the age-and sex-adjusted model and multivariate model.Through this, estimates were known to be fair and unbiased by multicollinearity. However, there were some limitations defined in the study. First, it might not have enough statistical power in detecting small increases or decreases in the risk of cancer at their individual sites, in relation to the consumption of green tea.

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Another limitation of the study is significant percent of the population was lost during the course of the study. Third limitation is that, there might have been some misclassification of consumption status in estimating the effect of the beverage because the questionnaires were self-administered. As a result, this could underestimate the impact of green tea consumption.            The second study focused on the relationship between habitual green tea consumption and the risks of an aneurismal rupture subarachnoid hemorrhage, which was conducted in Nagoya, Japan, using a case-control study.

Subarachnoid hemorrhage is a condition “characterized by the rupture of a cerebral aneurysm resulting from focal weakness of the artery wall of the cerebral artery wall.” Incidence of SAH cases were gathered and identified and were individually matched by age and gender to hospital and community controls. This study, like the cohort, made use of structured questionnaire. It made use of logical regression models. Also, it included history of hypertension, educational levels and engaging in smoking.

Unlike the cohort with a bigger population, this case study recruited 201 SAH patients. The study dealt purely with participants with proven rupture of an intracerebral aneurysym by cerebral angiography. The study also set up community controls with no history of SAH, matching to each patient for age and gender.

These controls were randomly elected of the same area as the SAH patients. These matched controls and SAH patients were directly interviewed. The interview for the SAH patients was one month after they were admitted to the hospital; the interview for community controls was within two weeks after they were being identified. During the interview, all participants were asked of their lifestyle and food preferences five years prior to acquiring SAHH, by the use of a structured questionnaire. In cases when the patients could not supply the interviewer with the right information, proxies were then allowed. Aside from lifestyle, patients’ dietary information was also obtained through food frequency questionnaires. Like the cohort, frequency of green tea consumption was also divided into categories, and used the multiple conditional logistic regression models, in which possible confounders of SAH were monitored.

Here, odds ratio was used to calculate the relationship between the exposure and outcome.            The third study was on the effects of drinking green tea on cardiovascular and liver diseases. Here, a cross-sectional study or otherwise known as ‘prevalence survey’ was used. This study aimed to investigate the relationship between the consumption of green tea and various serum markers in the Japanese population.

This study was conducted in Yoshimi, Japan where 1371 men aged 40 years were the participants. These participants were surveyed basing on their living habits as well as their consumption of green tea. Then, their blood samples were collected and subjected to biochemical evaluation.  Like the other two studies, this also used a self- administered questionnaire which included 90 lifestyle and history of disease; present state of health and medication. Here, multivariate analysis of variance was used to control for the effects of the confounding factors.

The possible covariates considered in this analysis were age, cigarette smoking, alcohol consumption, and relative body weight. Like the studies above, levels of frequency came in several categories. Basically, the study dealt and focused on the serum lipoproteins concentrations in the body, and whether or not, these were affected by consumption of green tea.            If we examine the studies mentioned above, we can say there are a number of differences between them, with regard to their designs and approaches. Both the cohort and case control studies examine multiple outcomes for single exposure, making them more effective and applicable in examining the causes of cardiovascular diseases and the effects of an increased consumption of green tea. Cross-sectional study, on the other hand, takes a “snapshot” of what is happening in a particular population and are rather good for examining the relationship between a variable and a disease.

Cohort requires a bigger population; case-control studies require fewer case-subjects while cross-sectional studies only require a certain population. Cohort is expensive because it involves a longer span of time to arrive as well as a large supply of resources to meet its objectives; case-control and cross-sectional studies are less expensive and are quick to implement. Case-control studies are not suitable for studying rare exposures.

Moreover, because of the methods used to select controls, these may be subject to biases. Case-control studies do not allow a researcher to directly measure the incidence of disease. And also, these studies may create uncertainty about the sequential relationship between exposure and disease. On the other hand, cross-sectional studies are ideal in conducting preliminary studies rather than identifying the causes at the onset of a disease.

Here, it is not possible to determine if exposure to the risk factor happened before or after the disease developed, making this study a disadvantage as compared to the other two studies mentioned.            In my opinion, the cohort study most probably produced the most reliable results because it does not limit itself to the cause or the effect of a condition, but goes beyond that by examining multiple exposures, wherein incidence of disease for these exposures are easily calculated. In this study, a large number of population was used, including their lifestyles, food intake and physical activities, which are all contributory to an individual’s health status.  From here, the participants’ green tea consumption is then compared to the exposures mentioned above.

We are made to conclude that there were no biases during the course of the study. The occurrence of the disease has been viewed along with the other predisposing factors that might be a threat to a person. Enough time is also one best aspect of this study. Though the span of time spent in this study, the researchers were able to deal entirely with the objectives of the study.  Indeed, through the logical sequence of processes in this study, it could be assured that it was directed to an intelligent, reliable and clear understanding of the relationship between increased consumption of green tea and the occurrence of cardiovascular diseases.  Through the larger population, enough span of time spent, the resources used during the study, the consideration of other predisposing factors, the elimination of possible biases as well as identifying concrete exposures, are what make this study more reliable in the statistical information it provides and in the conclusions it has made.


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