Prospective cohort studies

Prospective Cohort Study Prospective cohort studies are no different in principle from historical cohort studies in terms of scientific logic, the major differences being timing and methodology. The study starts with a group of apparently healthy individuals whose health and exposure are studied over a period of time. As it is possible to define in advance the information that is to be collected, prospective studies are theoretically more reliable than retrospective studies. However, long periods of observation may be required to obtain results. 

Observational studies Prospective cohort study Prospective case-control study Retrospective cohort study Retrospective case control study... 

The benefit of a prospective cohort study is the possibility for accurate exposure assessment. However, these are not common, because many occupational diseases (including cancers which are being intensely investigated currently) require long exposure times to develop. It is not practical or ethical to wait for decades before one obtains the result. 

Prospective Study—A type of cohort study in which the pertinent observations are made on events occurring after the start of the study. A group is followed over time. 

GOLDBOHM R A, HERTOG M G L, BRANTS HAM, VAN POPPEL G and VAN DEN BRANDT P A (1996) Consumption of black tea and cancer risk a prospective cohort study , JNatl Cancer Inst, 88, 93-100. 

Data concerning gastric cancer are scarce. The prospective Netherlands Cohort Study found no correlation between lutein dietary intake and gastric cancer risk, whereas findings from the Physicians Health Study and the ATBC study reported no effect of P-carotene on gastric cancer incidence. Two case-control studies and three intervention trials (ATBC, CARET, and the Physicians Health Study ) showed no association of P-carotene, lycopene, lutein, zeaxanthin, and P-cryptoxanthin. 

Other dietary factors implicated in prostate cancer include retinol, carotenoids, lycopene, and vitamin D consumption.5,6 Retinol, or vitamin A, intake, especially in men older than age 70, is correlated with an increased risk of prostate cancer, whereas intake of its precursor, [3-carotene, has a protective or neutral effect. Lycopene, obtained primarily from tomatoes, decreases the risk of prostate cancer in small cohort studies. The antioxidant vitamin E also may decrease the risk of prostate cancer. Men who developed prostate cancer in one cohort study had lower levels of l,25(OH)2-vitamin D than matched controls, although a prospective study did not support this.2 Clearly, dietary risk factors require further evaluation, but because fat and vitamins are modifiable risk factors, dietary intervention may be promising in prostate cancer prevention. 

Zheng, W., Tea consumption and cancer incidence in a prospective cohort study of postmenopausal women, Am J Epidemiol, 144, 175, 1996. 

Botterweck AA, van den Brandt PA and Goldbohm RA. 1998. A prospective cohort study on vegetable and fruit consumption and stomach cancer risk in The Netherlands. Am J Epidemiol 148(9) 842-853. 

Voorips LE, Goldbohm RA, van Poppel G, Shumans F, Hermus RJ and van den Brandt PA. 2000. Vegetable and fruit consumption and risk of colon and rectal cancer in a prospective cohort study. Am J Epidemiol 152 1081-1092. 

Merget, R. et al., Exposure-effect relationship of platinum salt allergy in a catalyst production plant conclusions from a 5-year prospective cohort study, J. Allergy Clin Immunol., 105, 364, 2000. 

The Hawaii-Los Angeles Multiethnic Cohort study, a prospective study of 212,000 men and women from four racial-ethnic groups in Hawaii and Los Angeles. 

The Shanghai Cohort study, a prospective biomarker-based study of 18,000 middle-aged men in Shanghai. 

The Singapore Cohort study, a prospective study of60,000 male and female Chinese adults in Singapore. 

Korevaar JC, van Munster BC, de Rooij SE (2005) Risk factors for delirium in acutely admitted elderly patients a prospective cohort study. BMC Geriatr 5 6 Kudoh A, Takase H, Takahira Y et al. (2004) Postoperative confusion increases in elderly longterm benzodiazepine users. Anesth Analg 99 (6) 1674-1678 McCusker J, Cole M, Dendukuri N et al. (2001) Delirium in older medical inpatients and subsequent cognitive and functional status a prospective study. Cmaj 165 (5) 575-583 McCusker J, Cole M, Dendukuri N et al. (2003) The course of delirium in older medical inpatients a prospective study. J Gen Intern Med 18 (9) 696-704 McShane R, Areosa Sastre A, Minakaran N (2006) Memantine for dementia. Cochrane Database Syst Rev 19 (2) CD003154... 

Van Loon AJM, Botterweck AAM, Goldbohm RA, Brants HAM, van Klaveren JD, van den Brandt PA (1998) Intake of nitrate and nitrite and the risk of gastric cancer A prospective cohort study. Br J Cancer 7 129-135... 

Phase IV clinical trials and prospective observational cohort studies have been criticised as no more than promotional devices used by aggressive pharmaceutical companies. The fact that misuse has sometimes happened should not be allowed to obscure the greatly more important needs of safety evaluation and the further development of new and improved therapies. A set of guidelines has been published in the United Kingdom which are specifically intended to provide the high standards of study design and methodology necessary for observational cohort studies. It is to be hoped that similar procedures will be adopted internationally. 

Choi, H. K. and Curhan, G. T. (2008). Soft drinks, fructose consumption, and the risk of gout in men Prospective cohort study. BMJ 336,309-312. 

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. 

Almgren T, Persson B, Wilhelmsen L, Rosengren A, An-dersson OK. Stroke and coronary heart disease in treated hypertension - a prospective cohort study over three decades. I Intern Med 2005 257(6) 496-502. 

Bearden, C.E., Rosso, I.M., Hollister, J.M., Sanchez, L.E., Hadley, T, and Cannon, TD. (2000) A prospective cohort study of childhood behavioral deviance and language abnormalities as predictors of adult schizophrenia. Schizophr Bull 26 395 10. 

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