Epidemiological study

Early studies of the relation between intake of TFAs and the occurrence of CHD also produced conflicting results. However, the large, well-conducted prospective studies showed positive associations between TFA intake and risk of CHD. The Nurses Health Study and the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study produced statistically significant positive associations, whereas in the Health Professionals Followup Study the positive association did not attain statistical significance (Ascherio et al., 1999). There was also a significant positive association between TFA intake and CHD risk in the smaller Zutphen Elderly Study (Oomen et al., 2001). 

Differential Effect of Ruminant TFAs and TFAs from Hydrogenated Vegetable Oils 

A case-control study (Ascherio et al., 1994), a cross-sectional study (Bolton-Smith et al., 1996) and three prospective studies the Nurses Health Study (Willett et al., 1993), the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study (Pietinen et al., 1997), and the Zutphen Elderly Study (Oomen et al., 2001), separately assessed the effect of TFAs from hydrogenated vegetable oil and animal fat on the risk of CHD. With the exception of the small Zutpen Elderly Study (Oomen et al., 2001), the studies found that the positive association with the risk of CHD was explained entirely by the intake of TFAs from hydrogenated vegetable oil. 

Epidemiology may be defined as the study of the distribution and determinants of health-related states or events (including disease) in human populations, and the application of this study to the control of diseases and other health problems (WHO 2002). The word epidemiology consists of the Greek words epi which is among, demos which is people, and logos which is doctrine. 

Epidemiological studies are nonexperimental trials and involve an investigation of various individuals or groups of subjects as they happen to have been exposed. Endpoints generally measured include mortality, morbidity, medical visits or hospital admissions, and/or clinical signs and symptoms. 

Advantages of epidemiological studies include that often a heterogenous population is studied, and the exposure scenarios generally are realistic. 

Limitations include difficulties in performing a correct exposure assessment, in some cases even a lack of information on exposure, insufficient sample size (i.e., small number of subjects in the study), selected group of subjects (e.g., the workforce), short length of follow-up, exposure to more than one substance, and potential errors (bias, confounding). 

Different methods are used in epidemiology. Epidemiological studies are often divided into descriptive studies and analytic studies. 

Indeed, in its most reeent pubhcation die U.S. EPA, 10/14/98, further supports fliat approach and the panel members who evaluated the data felt that for the leukemogenic effects of benzene the linear model is consistent with the spirit of the proposed eaneer risk assessment guidelines. 

Based on the case reports, case studies, and epidemiologieal studies, the sub-elassifi-cation to cell types is indicated from a medieal point of view to treat various hematopoietie diseases and cancers with die various appropriate treatments per each type of cell injured, however the data from the experimental data and elinieal analysis of benzene cases clearly show that benzene causes damage to the stem eell and therefore it is a pluripotent toxin, causing a wide range of lymphohematopoietic malignancies. 

Linet et al. studied hematopoietic malignancies and related disorders among benzene exposed workers in China and showed a wide range of hematopoietic malignancies. Yin et al. examined a large cohort of benzene workers and concluded that benzene exposed workers have a statistically significant excess death due to leukemia, risk ratio of 2.3 with 95% confidence interval malignant lymphoma, risk ratio of 4.5 with 95% confidence interval and non-neoplastic diseases of the blood. 

Recently, a matched case-control study in a cohort of 3754 newborns in Oslo, Norway, showed an increased risk for bronchial obstraction in children living in apartments with high occurrence of plasticized polyvinylchloride, PVC, floorings. Many other factors such as ventilation, tobacco smoking and crowdedness (square meters per occupant) were included in the study. As the study showed a correlation between the risk of developing asthma and exposure to PVC floors, the authors suggested that the plasticizers, which mairdy consisted of di-(2-ethylhexyl) phthalate, DEHP, had adjuvant effect.  

Some medical researchers believe, to a reasonable medical and scientific certainty, that the effects of lead on the brain are permanent and irreversible, and they seem to worsen with time. This is reflected not only in lower intelligence quotient scores, but in a decreased ability to function in every day life. There is growing evidence that children exposed to lead have attention deficit disorder and are hyperactive. Although only about 3% of children generally suffer attention deficit disorder, 55% of children poisoned by lead paint display signs of this disorder. Such children are at high risk for aggressive and antisocial behavior in later life. 

The consequences of exposure to lead are more serious the younger the child is at the time of exposure. Evidence indicates that young children are more sensitive to injury firom lead because their nervous systems are still developing and thus more subject to permanent damage. 

The 1988 Agency for Toxic Substances and Disease Registry (ATSDR) Report to Congress estimates that there is still 5 million tons of lead in the 

United States in household paint. Seventy percent of the houses built before 1960 have lead-based paint on interior and exterior surfaces. The ATSDR further estimates that there are 6 million homes with leaded surfaces that have decayed or deteriorated and in which 2 million young children presently reside. Ingesting lead from chipped, peeling, or chalking paint places these children at extremely high risk of lead poisoning. 

Human bones from the Bronze Age found to contain lead. 

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Epidemiologic studies in Japan indicate an increased risk of stomach cancer owing to consumption of broiled fish and meats (116). In the United States, stomach cancer incidence has steadily declined since the 1940s, whereas consumption of broiled food has increased (108). In addition, the average human intake of PAHs is only 0.002 of that required to produce cancer in half of animals fed. Test results are often contradictory (117) and many components of food, such as vitamin A, unsaturated fatty acids, thiols, nitrites, and even saUva itself, tend to inhibit the mutagenic activity of PAHs (118—120). Therefore, the significance of PAHs in the human diet remains unknown (121,109). 

J. C. Contassot and co-workers, "Epidemiological Study of Cancer Morbidity Among Workers Exposed to Hydrazine," poster presented at the XXII International Congress on Occupational Health, in Sydney, AustraUa, Sept.—Oct., 1987. 

Epidemiological studies of nickel-producing and nickel-using workers seldom indicate excess mortaUty from nonmalignant respiratory disease. Evidence for such effects exists mainly as a few reports of isolated incidents of asthma, pulmonary fibrosis, chronic bronchitis, and emphysema in nickel workers. Nickel may or may not play a causal role in these incidents (131). 

Anxiety disorders and insomnia represent relatively common medical problems within the general population. These problems typically recur over a person s lifetime (3,4). Epidemiological studies in the United States indicate that the lifetime prevalence for significant anxiety disorders is about 15%. Anxiety disorders are serious medical problems affecting not only quaUty of life, but additionally may indirecdy result in considerable morbidity owing to association with depression, cardiovascular disease, suicidal behavior, and substance-related disorders. 

Health ha2ards linked to carbon disulfide are extensively covered (136). Also available are epidemiological studies (144—146), general reviews containing many references (147—150), and a Material Safety Data Sheet (151). 

S. Shindel and S. Ulrich, Report of Epidemiologic Study Warner Electric Brake eV Clutch Co., South Beloit, III, Jan. 1957 to July 1983, Ergotopology Investigative Mediciue for Industry, Milwaukee, Wis., Aug. 1984. 

Effects in Humans. In chlorophenol production, irritation symptoms of the nose, eyes, respiratory tract, and skin resulting ia chloroacne have been observed. The results of epidemiology studies on the long-term effects of chlorophenols are quite contradictory and have not allowed the experts to reach any firm conclusions (54). 

Hecdth effects data come from three types of studies clinical, epidemiological, and toxicological. Clinical and epidemiological studies focus on human subjects, whereas toxicological studies are conducted on animals or simpler cellular systems. Ethical considerations limit human exposure to low levels of air poUutants which do not have irreversible effects. Table 7-1 lists the advantages and disadvantages of each type of experimental informahon. 

Exposure to sulfur dioxide in the ambient air has been associated with reduced lung function, increased incidence of respiratory symptoms and diseases, irritation of the eyes, nose, and throat, and premature mortality. Children, the elderly, and those already suffering from respiratory ailments, such as asthmatics, are especially at risk. Health impacts appear to be linked especially to brief exposures to ambient concentrations above 1,000 ixg/in (acute exposures measured over 10 minutes). Some epidemiologic studies, however, have shown an association between relatively low annual mean levels and excess mortality. It is not clear whether long-... 

Hazard identification through animal experiments, epidemiological studies, or structure activity analyses... 

Exposure assessment to reveal the exposure of different groups of people, and to compare their exposure levels to the doses that cause harmful effects in humans as shown in epidemiological studies, or to doses that cause toxic effects in experimental animals... 

Malker, H. S. R. and Gemne, G. (1987). A register-epidemiology study on cancer among Swedish printing industry workers. Arch. Environ. Health 42, 73-82. 

There has been some controversy over the effect of traces of anesthehc gases in the operating room on the health of personnel working there daily Numerous animal studies usmg low levels of anestheltic gases have failed to show any effects, and several epidemiological studies show that human health is not affected by traces of anesthetic gases [20]... 

Because risk at low exposure levels is difficult to tneasure directly either by animal experiments or by epidemiologic studies, the development of a slope factor generally entails applying a model to the available data set and... 

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