Epidemiology studies colon cancer

Bjetke, E. Epidemiologic studies of cancer of the stomach, colon, and rectum, with special emphasis on the role of diet. Scand. J. Gastroenterol.. 9 (Suppl. 31) 1-235.1974. 

Besides age, the development of colorectal cancer appears to be caused by variety of dietary or environmental factors, comor-bid disease states, and genetic susceptibility to the disease. Table 88-1 lists well-known risk factors for developing colon cancer. Epidemiologic studies of worldwide incidence of colorectal... 

In conclusion, phytic acid forms soluble complexes with Ca2+ at intestinal pH under a variety of conditions and fails to inhibit Ca2 bioavailability to mice in our experimental system. Despite the hazard in direct extrapolation of results obtained with animals kept on a well-defined dietary regimen to humans consuming a complex diet, many elements of which affect Ca2+ bioavailability, our data demonstrate the need for a reevaluation of the putative antinutritional properties of dietary phytate. Our further contention that adequate levels of dietary phytate may actually be beneficial due to its food preserving properties and its protection against colonic cancer will warrant a prospective epidemiological human study designed to assess the longterm effects of dietary phytate on mineral bioavailability and inflammatory bowel diseases. 

Cancer. No studies were available regarding eaneer in humans or animals after inhalation exposure to chloroform. Epidemiology studies suggest an association between chronic exposure to chlorinated drinking-water sources and increased incidences of colon cancer (Young et al. 1981), pancreatic cancer (Ijsselmuiden et al. 1982) and bladder cancer (Cantor et al. 1978 McGeehin et al. 1993 Zierler et al. 

There is no clear epidemiological evidence for the carcinogenicity of chlorodibromomethane in humans. However, a number of studies suggest an association between chronic ingestion of trihalomethanes in chlorinated drinking water and increased risk of bladder or colon cancer. These smdies cannot provide information on whether any observed effects are due to chlorodibromomethane or to one or more of the hundreds of other by-products that also are present in chlorinated drinking water. 

An epidemiological study of workers potentially exposed to MDA (and numerous other agents) in the helicopter parts manufacturing industry showed limited evidence of an association between MDA and bladder cancer, colon cancer, lymphosarcoma, and reticulosar-coma." A follow-up of 10 workers who had significant exposure to MDA between 1967 and 1976 revealed one case of a pathologically... 

Several NSAIDs (including aspirin) appear to reduce the incidence of colon cancer when taken chronically. Several large epidemiologic studies have shown a 50% reduction in relative risk when the drugs are taken for 5 years or longer. The mechanism for this protective effect is... 

Epidemiologic studies suggest that long-term use of aspirin at low dosage is associated with a lower incidence of colon cancer, possibly related to its COX-inhibiting effects. 

Aloe, senna, and cascara occur naturally in plants. These laxatives are poorly absorbed and after hydrolysis in the colon, produce a bowel movement in 6-12 hours when given orally and within 2 hours when given rectally. Chronic use leads to a characteristic brown pigmentation of the colon known as melanosis coli. There has been some concern that these agents may be carcinogenic, but epidemiologic studies do not suggest a relation to colorectal cancer. 

Epidemiologic studies indicate that diets high in total fat and saturated fat and low in certain fibers are associated with an increased risk for colon cancer. In addition, certain dietary fibers and cruciferous vegetables have been associated with a reduced risk in several populations consuming the diets high in total fat. 

Wynder and Shigematsu (15) were the first to suggest that nutritional factors in general and specifically differences in fat intake may be responsible for the international variation in colon cancer incidence. Subsequent descriptive epidemiologic studies have found a strong positive association between colon cancer mortality or incidence in different countries and per capita availability in national diets of total fat (4,16) and of animal fat, estimated from food balance sheets. Such international correlations may be supportive of a hypothesis, but they should be interpreted with caution because the dietary data were based not on actual intake information but on food disappearance data. 

The epidemiologic data, relative to dietary fiber, has been supported by animal studies but experiments with dietary fat have been conflicting and generally do not indicate a fat effect. Other dietary factors which associate with colon cancer in animal studies are deficits of lipotropes and of vitamin A. 

One hypothesis linking dietary fat to colon cancer is that cholesterol is converted to bile acids which act as promoters of carcinogenesis (58). Epidemiological studies have shown however, (38) that when beef consumption in the United States doubled (between 1940-1970) the incidence of colon cancer mortality was virtually unchanged. In addition, the incidence of colon cancer is the same in Seventh Day Adventists, who eat meat sparingly (59) and Mormons, who consume a conventional diet (60). 

While there are no epidemiologic data available on lipotropic factors and colon cancer in human populations, results of animal studies suggest a possible role for this class of nutrients (choline, methionine, vitamin and folate) in colon carcinogenesis (69). Table XVI lists results typical of those observed when rats are fed a diet high in fat, low in lipotropes and exposed to a colon carcinogen. 

Epidemiological studies show that dietary fat and protein are most frequently correlated with colon cancer incidence in man (10-14). A number of studies in laboratory animals suggest that dietary fat enhances colon tumor incidence (15) although others have failed to show such enhancement (16). Summarized in this communication are animal experiments conducted by our laboratory to examine the effects of dietary protein on DMH induced carcinogenesis, mutagenesis, and toxicity. 

Overall, epidemiological evidence from within-population studies does not support an independent role for dietary fat or fat subclasses in the risk of colon cancer. However, the evidence does not preclude the possibility that certain fatty acids, such as co-6s and co-3s, may exert opposing influences. 

---