Thomas K. French

Adult dietary intake and prostate cancer risk in Utah: a case-control study with special emphasis on aggressive tumors

A population-based case-control study in Utah of 358 cases diagnosed with prostate cancer between 1984 and 1985, and 679 controls categorically matched by age and county of residence, were interviewed to investigate the association between dietary intake of energy (kcal), fat, protein, vitamin A, β-carotene, vitamin C, zinc, cadmium, selenium, and prostate cancer. Dietary data were ascertained using a quantitative food-frequency questionnaire. Data were analyzed separately by age (45–67, 68–74) and by tumor aggressiveness. The most significant associations were seen for older males and aggressive tumors. Dietary fat was the strongest risk factor for these males, with an odds ratio (OR) of 2.9 (95 percent confidence interval [CI] 1.0–8.4) for total fat; OR=2.2 (CI=0.7–6.6) for saturated fat; OR=3.6 (CI=1.3−9.7) for monounsaturated fat; and OR=2.7 (CI=1.1−6.8) for polyunsaturated fat. Protein and carbohydrates had positive but nonsignificant associations. Energy intake had an OR of 2.5 (CI=1.0−6.5). In these older men, no effects were seen for dietary cholesterol, body mass, or physical activity. There was little association between prostate cancer and dietary intake of zinc, cadmium, selenium, vitamin C, and β-carotene. Total vitamin A had a slight positive association with all prostate cancer (OR=1.6, CI=0.9−2.4), but not with aggressive tumors. No associations were found in younger males, with the exception of physical activity which showed active males to be at an increased but nonsignificant risk for aggressive tumors (OR=2.0, CI=0.8−5.2) and β-carotene which showed a nonsignificant protective effect (OR=0.6, CI=0.3−1.6). The findings suggest that dietary intake, especially fats, may increase risk of aggressive prostate tumors in older males.

Tobacco, alcohol, coffee, and caffeine as risk factors for colon cancer in a low-risk population.

We used data from a population-based case-control study to examine how use of tobacco products and consumption of alcohol, coffee, and caffeine relate to colon cancer in Utah. We hypothesized that low use of these substances is one factor contributing to the low colon cancer incidence in Utah and could help explain the low risk associated for colon cancer with being a member of the Church of Jesus Christ of Latter-day Saints. In females, we observed little or no increase in risk of colon cancer from smokingcigarettes or from consumption of alcohol, caffeine, or coffee. Males who used pipes, however, experienced an increased risk for colon cancer (OR = 4.1, 95% CI = 1.3–12.3). Risk for colon cancer associated with alcohol use was greatly attenuated after adjusting for caffeine and pipe use in males; males who consumed-higher levels of caffeine during the two to three years prior to the interview were at higher risk than males who consumed low levels of caffeine (OR = 2.0, 95% CI = 1.0–4.2); similar associations were observed for coffee consumption. Nonuse of these substances could explain the low colon cancer incidence rates observed in members of the Church of Jesus Christ of Latter-day Saints and Utah males.

Dietary vitamins A, C, and E and selenium as risk factors for cervical cancer.

The relation between cervical cancer and dietary intake of vitamins A, C, and E, beta-carotene, and selenium was examined in a population-based case-control study in Utah. Cervical cancer cases (n = 266) and population-based controls (n = 408) were interviewed between 1984 and 1987. Protective effects were observed for vitamins A, C, and E and beta-carotene but were attenuated by age, level of education, and lifetime cigarette use. Associated risk (comparing highest with lowest quartiles of intake) went from 0.53 (crude) to 0.71 (adjusted) for vitamin A; from 0.55 (crude) to 0.82 (adjusted) for beta-carotene; from 0.45 (crude) to 0.55 (adjusted) for vitamin C; from 0.58 (crude) to 0.60 (adjusted) for vitamin E; and from 0.95 (crude) to 0.70 (adjusted) for selenium. Adjustment for number of sex partners and church attendance, factors significantly related to cervical cancer risk, only slightly attenuated these adjusted risk estimates.

Validity of cigarette smoking habits in three epidemiologic studies in Utah

Utah has lower incidence and mortality for many smoking-related forms of cancer and heart disease. It is an important epidemiologic question to assess whether the population attributable risk associated with cigarette smoking in this low-risk population is biased from under-reporting because of societal pressures not to smoke. To answer this question, we compared reported cigarette use to serum cotinine values in three different epidemiologic study designs. Included in these analyses were data from men interviewed for a cross-sectional study of dietary intake and hormones, women interviewed as a part of a case-control study of cervical cancer, and men interviewed in conjunction with a cardiovascular disease and hypertension family follow-up study. Cross-sectional study participants reported accurate cigarette usage 93.8% of the time; case-control participants accurately reported cigarette use 98.5% of the time; participants interviewed in the family cohort study correctly reported usage 82.8% of the time. Most inaccurate reporting of smoking was by exsmokers being followed for a disease known to be linked to smoking. The low attributable risk of smoking related to diseases in Utah is not from underreporting of cigarette smoking, and makes Utah an ideal population to examine other risk factors for diseases where smoking increases risk.

Coffee consumption and the risk of cancer of the exocrine pancreas: a case-control study in a low-risk population.

Data from a population-based, case-control study of 149 cases of cancer of the exocrine pancreas (excluding insulinomas) and 363 controls were used to test the hypothesis that coffee consumption increased the risk of cancer of the exocrine pancreas. Because of the high mortality from cancer of the pancreas, all information was obtained from proxy respondents for cases and controls. Increased risk was present for coffee drinkers [odds ratio (OR)=2.38], cigarette smokers (OR=2.27), and alcohol users (OR=1.60), but the effect for alcohol disappeared after adjustment for cigarette use. Risk increased with the amount of coffee drunk with an OR of 2.38 in the those having at least 50,000 lifetime cups. This gradient was present in both men and women, and in cigarette smokers and nonsmokers. Increased risk was present for users of regular and decaffeinated coffee, but the risk was higher for users of decaffeinated coffee than users of regular coffee. Cigarette smoking, after controlling for coffee consumption, was an independent risk factor for pancreatic cancer, with odds ratios in the heaviest smokers of 2.71 (95% confidence interval=1.41−5.21). (Epidemiology 1992;3:164–170)

Misclassification of exposure in a case-control study : the effects of different types of exposure and different proxy respondents in a study of pancreatic cancer

This investigation addressed three questions about misclassification in a case-control study of risk factors for pancreatic cancer in which all exposure data were obtained from proxy respondents. These questions were: (1) To what degree was misclassification dependent on the type of exposure? (2) To what degree did misclassification vary by the type of proxy? (3) What was the magnitude of the effect of proxy misclassification on odds ratios measured across several levels of exposure? To answer these questions. we interviewed 163 control (index) subjects and next-of-kin (proxy) respondent pairs. Each of the controls and their respective proxies reported the controls use of coffee, cigarettes, and alcohol and weekly exposure to beef, milk, bacon, fruits, and vegetables. Nonspouse proxies misclassified exposures more than spouse proxies with the exception of cigarettes. Cigarette use was the most accurately reported exposure, followed by alcohol, coffee, and foods. For nondifferential misclassification between cases and controls, the slope of a dose-response curve was decreased from 6.6% to 100% depending on the exposure and the type of proxy respondent. Investigators conducting studies using proxy respondents need to recognize that misclassification is a function of multiple factors, including both the type of exposures under study and the type of proxies available. (Epidemiology 1992;3:223-231)

Collinear nutrients and the risk of colon cancer

The relationship between colon cancer risk and the relative contributions of fat and caloric intake are assessed. A lack of consensus exists regarding the role of each of these dietary factors in the development of colon cancer. This lack of agreement originates from the high correlations between the nutrients, as well as the manner in which researchers treat these dietary variables in their analyses. Four proposed methods are evaluated which attempt to address the collinearity problem in nutritional epidemiology: (1) exclude one or more collinear variables, (2) use the proportion of calories consumed attributable to each dietary component, (3) use a regression-adjustment approach to purge the collinearity correlated nutrients, and (4) ridge regression. Diagnostic tests are reported which assess the degree of collinearity on data collected for a case-control study of colon cancer conducted in Utah between 1979 and 1983. Using logistic regression analyses, we apply each of these methods to case-control data. We find that the risks associated with fat and caloric consumption are extremely sensitive to a priori analytic decisions made by epidemiologist about the underlying collinearity problem.