Prospective cohort epidemiologic studies

A prospective cohort epidemiologic study approximates to a parallel-group clinical trial in its scientific basis, and epidemiologists will be as aware as clinical trialists of the bias that can be introduced if the study groups do not contain comparable, well-bal-... 

To compare the epidemiological, clinical, and economic impacts of the HIV epidemic in Italy prior to and after the introduction of HAART, Tramarin et al. (2004) conducted a prospective and observational study with a multi-center design. They used data collected on an AIDS cohort from 1994 and updated data from a comparable cohort in 1998. Mortality and medical costs of 251 patients were measured in 1994 and in 1998, respectively. A considerable difference was observed in mortality (33.9% in 1994 vs. 3.9% in 1998). The cost per patient per year was US 15,515 in 1994 and US 10,312 in 1998. Based on the comparison of the two cohorts between both years, the authors concluded that after the introduction of HAART, hospital-based provision shifted from an inpatient-based to an outpatient-based service, with major focus on pharmaceutical care. 

Carotenoids and prostate cancer — Numerous epidemiological studies including prospective cohort and case-control studies have demonstrated the protective roles of lycopene, tomatoes, and tomato-derived products on prostate cancer risk other carotenoids showed no effects. " In two studies based on correlations between plasma levels or dietary intake of various carotenoids and prostate cancer risk, lycopene appeared inversely associated with prostate cancer but no association was reported for a-carotene, P-carotene, lutein, zeaxanthin, or p-cryptoxanthin. - Nevertheless, a protective role of all these carotenoids (provided by tomatoes, pumpkin, spinach, watermelon, and citrus fruits) against prostate cancer was recently reported by Jian et al. ... 

Epidemiological studies have different strengths and weaknesses associated with their design (Table 4) shows some of the strengths and weaknesses of the two main methods of prospective cohort studies and retrospective case-control studies. 

Nulman I, Einarson TR, Koren G. Birth defects after maternal exposure to corticosteroids prospective cohort study and meta-analysis of epidemiological studies. Teratology 2000 62(6) 385-92. 

Jedrychowski W, Bendkowska I, Flak E, Penar A, Jacek R, Kaim I, Spengler JD, Camann D, Perera FP (2004) Estimated risk for altered fetal growth resulting from exposure to fine particles during pregnancy An epidemiologic prospective cohort study in Poland. Environ Health Perspect, 112(14) 1398-1402. 

Kritchevsky and Kritchevsky (2000) provided a summary of the evidence linking dietary cholesterol to the risk of CHD in 10 cohorts from eight large, well-conducted prospective studies that were reported since 1980, which included the Nurses Health Study, the Health Professionals Followup Study and the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study. In eight of the cohorts there was no statistical association between cholesterol intake and the risk of CHD. In one of the positive studies the association was established by simple univariate analysis and was not adjusted for other dietary variables. The other study adjusted only for fat intake. There is no compelling evidence from these epidemiological studies that dietary cholesterol is associated with the risk of CHD. 

EXPOSURES RELEVANT TO HEALTH THE CONCEPTUAL FRAMEWORK 246 Considerations of Exposure Timing 246 Considerations of Exposure Route 247 Practical Context of Pesticide Exposure 248 EPIDEMIOLOGICAL STUDY DESIGNS AND EXPOSURE ASSESSMENT 248 Prospective Cohort Studies 248 Retrospective Cohort Studies 249 Case-Control Studies 250 Cross-Sectional Studies 252 EXPOSURE ASSESSMENT STRATEGIES 252 INFLUENCE OF THE ACCURACY OF EXPOSURE PROXIES ON MEASURES OF ASSOCIATION 254 Errors in Qualitative Proxies 254... 

Epidemiological evidence of the overall association between analgesic abuse and the development of renal impairment is documented in nine case-control studies [16-18, 20-21,33-34, 36-38], two prospective cohort studies [39, 40] and two observational cohort studies [41, 42] published in the last decades (Figure 1). It is inherent to epidemiological studies however, that the observed association between chronic renal failure and analgesic consumption does not establish cause and effect. Moreover, serious flaws in study design and analysis of the data have to be considered and were discussed in several reviews (Table 1) [7, 43,44,45]. 

Since the publication of these two early studies, a number of studies have adopted a more prospective cohort approach to the examination of statin use in patients who develop dementia and AD over the course of a set period (usually between 5-10yrs). While many of the subsequent studies described seemingly protective effects in cross-sectional case-control analysis [36,45-51], the majority of prospective cohort analysis failed to identify a reduced risk of dementia in incident cases of dementia or AD [36, 46,47,51[. One notable exception comes from a study that examined a population identified by common AD risk facfors and co-morbidities (e.g., first degree relatives) [52]. In a high AD risk population, statin use was associated with a lowered risk of AD [52]. A summary of the epidemiological findings for stafin use in AD are shown in Table 1. 

An epidemiological study in which a defined group of persons known to be exposed to a potential disease risk factor is followed over time and compared to a group of persons who were not known to be exposed to the potential risk factor to evaluate the differenees in rates of the outcome. Also termed a prospective study, followup study, incidence study, retrospective cohort, or historical cohort study. 

Although fruit and, more consistently, vegetable intakes are inversely associated with colorectal cancer risk, the epidemiological evidence for vitamin C as a specific protective factor is less consistent. Since 1990, two out of four prospective studies have observed a significant inverse association between vitamin C intake and the risk of colon or rectal cancer. In a prospective cohort study that followed 4277 elderly men and 7300 elderly women over 8 years, women who consumed more than 225mg/d of vitamin C had a 39% lower risk of colon cancer than women who consumed less than 155mg/d, but no association between vitamin C intake and colon cancer risk was observed for men. A similar decrease in colon cancer risk was observed in women who took vitamin C supplements. A recent study of colon cancer mortality in more than 700,000 U.S. men and women found that the use of vitamin C supplements for at least 10 years was associated with a 60% reduction in rectal cancer risk, but was not significantly associated with colon cancer risk. ... 

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