抄録
Sackett DL et al systematized the method of evidence-based medicine (EBM) , which translates epidemiological methods into clinical decision making. Originally, EBM was only used for clinicians. Now it has become a basic approach for all kinds of decision making in health science such as public health and nutritional intervention. Observational and intervention studies are major types of studies in epidemiology. Typical examples of the first one are cohort studies and case-control studies. An example of the latter is randomized controlled trials (RCT). Generally, cohort studies prove causality and RCT proves effectiveness of an intervention. Usually, the results of these are coincident; however, we sometimes observe discrepancy between them. For example, high plasma homocysteine was a risk factor for atherosclerotic diseases in many observational studies. In a prospective, nested, case-control study of the Japanese, high plasma homocysteine was associated with increased risk of ischemic stroke, of which multivariate odds ratio (95 % CI) for highest versus lowest quartiles of homocysteine was 3.89 (1.60 to 9.46). Because high plasma homocysteine levels can be reduced efficiently by dietary supplements of B-complex vitamins such as folate and vitamin B12, many RCTs attempted to decrease atherosclerotic diseases by vitamin supplementation. However, almost all RCTs evaluating the effects of vitamin supplementation failed to show any decrease in atherosclerotic diseases. So the discrepancy between cohort studies and RCTs suggests reverse-causality in cohort studies. On the other hand, meta-analysis is thought to be a good way for decision-making in EBM. Recently, we performed a combined meta-analysis of observational and intervention studies that examined the association between vegetarian diets and blood pressure. Seven intervention studies and 32 observational studies already published met our inclusion criteria. In both study designs, vegetarian diets were associated with lower blood pressure. In the field of nutrition research for humans, we should always consider EBM, in which final decision making is based on systematic epidemiological methods.
