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Biomedical subjects

G R Howe

Publications and source records attributed to G R Howe.

At least 91 records · Page 5Linked to original sources
PubMed1991

An investigation of recall bias in the reporting of past food intake among breast cancer cases and controls.

A nested case-control study was conducted within the Canadian National Breast Screening Study to examine whether there was evidence for biased reporting of past food intake. A total of 325 case patients with breast cancer and 628 matched control subjects completed a self-administered food frequency questionnaire in 1988, recalling their diets originally reported on enrollment into the National Breast Screening Study between 1982 and 1985. Recall of food items was very similar for case patients and control subjects. The magnitude of the odds ratios for the association between these food groups and breast cancer from the prospectively and retrospectively collected data was not systematically different. There was little evidence for recall bias in the reporting of past food intake from these data.

Adult↗
PubMed1991

The effect of recall bias on the association of calorie-providing nutrients and breast cancer.

This nested case-control study conducted within a large dietary cohort study examined whether recall bias could explain the inconsistent results obtained in case-control and cohort studies of the association between dietary fat and breast cancer. Cases were defined as women diagnosed with breast cancer between 1982 and 1987 who had completed a self-administered food frequency questionnaire on enrollment in the cohort study between 1982 and 1985. They were matched to two controls each, and the study subjects were asked in 1988 to complete a second diet questionnaire addressing their diets at the time of enrollment. The mean nutrient intakes for 325 cases who completed the first diet questionnaire six months or more before breast cancer diagnosis and their 628 matched controls were very similar for the prospectively and retrospectively collected diet questionnaires. There was little difference in the magnitude of the odds ratios estimated from the two questionnaires for the association between breast cancer risk and these nutrients. These data do not provide evidence for recall bias in retrospectively collected nutrient data from breast cancer cases compared with their matched controls.

Adult↗
PubMed1991

Radon exposure, cigarette smoking, and other mining experience in the beaverlodge uranium miners cohort.

A nested case-control study within the Beaverlodge Uranium Miners Cohort was undertaken to assess any possible contribution of confounding by smoking and other mining experience to the risk estimate derived from the original cohort study. Next of kin have been interviewed for 46 lung cancer cases and 95 controls enrolled in the Beaverlodge Uranium Miners Cohort Study who died between 1950 and 1980. Confounding by cigarette smoking and other mining experience appears unlikely to have contributed to the relative risk coefficient for exposure to Rn decay products derived in the parent study. Data for smoking and exposure to Rn decay products are consistent with a multiplicative model, although considerable caution must be applied to this interpretation.

Case-Control Studies↗
PubMed1990

A case-control study of dietary and nondietary risk factors for breast cancer in Shanghai.

A case-control study of breast cancer (186 cases, 186 population, and 186 hospital controls) was conducted in Shanghai, China, between 1982 and 1984. This population has a high daily caloric intake (population control mean, 2394 kcal) and low percentage of calories from fat (22.7%) compared to Western populations. Cases have a significantly greater daily caloric intake than controls, primarily because of increased consumption of monounsaturated fat for which the relative risk is 1.89 for the highest compared to the lowest quintile (P = 0.02). This finding requires cautious interpretation but seems worthy of further study in populations with similar dietary practices.

Breast Neoplasms↗
PubMed1990

Dietary factors and risk of pancreatic cancer: results of a Canadian population-based case-control study.

Dietary information from a case-control study of pancreatic cancer conducted in Metropolitan Toronto between 1983 and 1986 is reported. A total of 249 cases and 505 population-based controls completed quantitative diet histories from which total caloric intake and the intake of a number of nutrients were estimated. A positive association with total caloric intake was observed with a relative risk of 2.39, 95% confidence interval 1.18-4.83 (highest versus lowest quartile), due primarily to the intake of carbohydrates. Inverse associations were seen with fibre from fruit, vegetable and cereal sources, with a relative of risk of 0.42, 0.22-0.78 (highest versus lowest quartile), for total fibre intake.

Age Factors↗
PubMed1990

Dietary factors and risk of breast cancer: combined analysis of 12 case-control studies.

We conducted a combined analysis of the original data to evaluate the consistency of 12 case-control studies of diet and breast cancer. Our analysis shows a consistent, statistically significant, positive association between breast cancer risk and saturated fat intake in postmenopausal women (relative risk for highest vs. lowest quintile, 1.46; P less than .0001). A consistent protective effect for a number of markers of fruit and vegetable intake was demonstrated; vitamin C intake had the most consistent and statistically significant inverse association with breast cancer risk (relative risk for highest vs. lowest quintile, 0.69; P less than .0001). If these dietary associations represent causality, the attributable risk (i.e., the percentage of breast cancers that might be prevented by dietary modification) in the North American population is estimated to be 24% for postmenopausal women and 16% for premenopausal women.

Body Height↗
PubMed1990

Dietary factors and risk of lung cancer: results from a case-control study, Toronto, 1981-1985.

Associations between dietary factors and risk of lung cancer are reported from a study of 839 cases and 772 population-based controls interviewed in metropolitan Toronto between 1981 and 1985. Increased consumption of vegetables is associated with a decreased relative risk of 0.60 (95% confidence limits = 0.40 to 0.88) for those in the highest compared with the lowest quartile. Cholesterol intake is associated with increased risk, but this is restricted to those in the highest quartile for whom the relative risk is 1.58 (95% confidence limits = 1.05 to 2.38) compared with those in the lowest quartile. The results of this study suggest that dietary factors may affect the risk of lung cancer, but identification of the specific constituents involved will require further research.

Adult↗
PubMed1990

Role of epidemiology in health risk assessment.

Human health risk assessment has been the object of systematic study in recent years, with formal models of risk assessment and risk management having been proposed by several national and international health agencies. The particular model developed by the Environmental Health Directorate of Health and Welfare Canada was examined in some detail and used to focus on the role of epidemiology in the overall process of risk assessment. In addition to providing information fundamental to the identification of environmental carcinogens and the estimation of carcinogenic risks, epidemiology may also play a role in shaping risk perception and in improving risk communication practices. Taken collectively, epidemiologic data on health risks provide a basis for improved disease surveillance and prioritization of public health concerns. Both descriptive and analytic epidemiologic protocols may be used to gather information on disease etiology. Because of the potential for bias and confounding in observational studies of human populations, epidemiological data should be subjected to careful evaluation in accordance with established criteria before a causal relationship between exposure and disease is inferred. Toxicological studies using nonhuman test systems may be used to avoid these problems, but at the expense of obtaining indirect information on human health risks. Nonetheless, toxicological data provide an important complement to epidemiological data, providing information on potential health risks in advance of human exposure and offering a means of indirectly assessing risks in situations where human studies fail to provide informative results. The complementary roles of epidemiology and toxicology in health risk assessment were examined using four case studies. While the epidemiological evidence linking tobacco consumption to lung cancer is now unequivocal, the corresponding data on involuntary smoking, although strongly suggestive of increasing the relative risk of lung cancer, requires further confirmation before providing the same degree of evidence as now exists for active smoking. At present, the best estimates suggest that overall mortality attributable to active smoking may exceed that due to passive smoking by roughly 100-fold. Despite this large difference in health impact, passive smoking continues to be the focus of much public concern, in part because of the involuntary nature of the risk involved. Because of the abundance of good epidemiological data on tobacco, toxicology has assumed a secondary role in defining the health risks associated with smoking. In contrast, while epidemiological studies with saccharin and formaldehyde have provided unequivocal evidence of carcinogenic effects in animals exposed to high doses, thereby raising concerns over potential human carcinogenicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Canada↗
PubMed1989

Mortality from breast cancer after irradiation during fluoroscopic examinations in patients being treated for tuberculosis.

The increasing use of mammography to screen asymptomatic women makes it important to know the risk of breast cancer associated with exposure to low levels of ionizing radiation. We examined the mortality from breast cancer in a cohort of 31,710 women who had been treated for tuberculosis at Canadian sanatoriums between 1930 and 1952. A substantial proportion (26.4 percent) had received radiation doses to the breast of 10 cGy or more from repeated fluoroscopic examinations during therapeutic pneumothoraxes. Women exposed to greater than or equal to 10 cGy of radiation had a relative risk of death from breast cancer of 1.36, as compared with those exposed to less than 10 cGy (95 percent confidence interval, 1.11 to 1.67; P = 0.001). The data were most consistent with a linear dose-response relation. The risk was greatest among women who had been exposed to radiation when they were between 10 and 14 years of age; they had a relative risk of 4.5 per gray, and an additive risk of 6.1 per 10(4) person-years per gray. With increasing age at first exposure, there was substantially less excess risk, and the radiation effect appeared to peak approximately 25 to 34 years after the first exposure. Our additive model for lifetime risk predicts that exposure to 1 cGy at the age of 40 increases the number of deaths from breast cancer by 42 per million women. We conclude that the risk of breast cancer associated with radiation decreases sharply with increasing age at exposure and that even a small benefit to women of screening mammography would outweigh any possible risk of radiation-induced breast cancer.

Adolescent↗
PubMed1989

Risk of bladder cancer by source and type of tobacco exposure: a case-control study.

The association between tobacco use and risk of bladder cancer was investigated in a population-based case-control study conducted in Alberta and south-central Ontario, Canada, between 1979 and 1982. In all, 826 histologically-confirmed cancer cases and 792 randomly selected controls, individually matched to cases for age, sex, and area of residence, were recruited into the study. Compared to those who had never smoked cigarettes, males and females who had ever smoked cigarettes had a statistically highly significant 2-fold increase in risk of bladder cancer; for ex-smokers, the risk was intermediate between that for current smokers and never-smokers. There was a dose-dependent increase in risk of bladder cancer with total lifetime cigarette consumption, of similar magnitude for males and females. In males, risk increased with self-reported degree of inhalation in ex-smokers and in current smokers (statistically significant trend), while in females there was no association in current smokers, and a statistically significant inverse association in ex-smokers. Overall, risks of bladder cancer associated with lifetime consumption of plain and filter cigarettes were similar, and there was little evidence to suggest that switching from plain to filter cigarettes was beneficial. Neither passive smoking nor other forms of tobacco consumption (pipes, cigars, chewing tobacco, or snuff) were associated with altered risk of bladder cancer. The population attributable risk for cigarette smoking was about 47% in males and about 33% in females.

Adult↗
PubMed1989

An exploratory case-control study of brain tumors in children.

An exploratory case-control study of childhood brain tumors was conducted in southern Ontario between 1977 and 1983, on 74 cases and 138 age- and sex-matched population controls. A significantly elevated risk (perhaps due to early case symptoms) was seen for skull X-rays at least 5 years prior to diagnosis, and for head or neck injuries which required medical attention. However, no evidence of an increased risk appeared for exposure to sick pets or to pesticides, maternal or paternal history of smoking, and various birth characteristics or antenatal exposure of the child, though these have previously been reported to be associated with childhood brain tumors. With respect to the hypothesis that N-nitroso compounds may be involved in the etiology of childhood brain tumors, most exposures of this type were not associated with risk, though a significant positive association was seen for consumption of beer by the mother during pregnancy, and a significant negative association was seen with consumption of fruit juice by the child. Other findings in the present study include an association with developmental problems relating to height and weight and with certain socioeconomic characteristics of the mother. Further investigation of these results in future studies is warranted.

Adolescent↗
PubMed1989

Analysis of case-control data with covariate measurement error: application to diet and colon cancer.

We propose a method for estimating odds ratios from case-control data in which covariates are subject to measurement error. The measurement error may contain both a random component and a systematic difference between cases and controls (recall bias). A multivariate normal discriminant analysis model is assumed. If the distribution of measurement error is known, then a simple correction to naive (biased) estimates of odds ratios from logistic regression of disease on fallible measurements of covariates removes bias. The same correction yields confidence intervals and significance tests. We apply the proposed methods to data from a case-control study of colon cancer and diet.

Analysis of Variance↗
PubMed1989

A study of repeatability of dietary data over a seven-year period.

A repeatability study of dietary intake has been carried out using 94 control subjects from a previously reported case-control study of diet and colorectal cancer. Dietary histories readministered on average seven years after an initial interview were used to estimate intake of various macro- and microdietary components. Comparisons of current intake with intake of seven years previously yielded good reliability for macrocomponents among subjects reporting no dietary change during the time period. Reliability was poorer for microcomponents and for subjects reporting a dietary change. Comparisons were also made between diet measured seven years previously with subjects' recall of that diet. It is concluded that current diet is at least as reliable a measure of past diet as that assessed by a questionnaire addressed to the past period.

Aging↗
PubMed1989

Cigarette smoking and breast cancer: case-control studies of prevalent and incident cancer in the Canadian National Breast Screening Study.

Two case-control studies of Canadian women aged 40-59 years are reported investigating the relation of cigarette smoking with initial visit (prevalent) and subsequent visit (incident) breast cancer detection, respectively, within the Canadian National Breast Screening Study. The analysis of prevalent breast cancer (1982-1985), which involved 254 cases and 762 controls, showed no evidence of an elevated risk for women with a history of cigarette smoking, with odds ratios of 0.9 (95% confidence interval (Cl) 0.6-1.5) and 1.2 (95% Cl 0.8-1.8) in premenopausal and postmenopausal subjects, respectively. Similarly, in the incident breast cancer analysis (1981-1987) based on 317 cases and 951 controls, women with a history of cigarette smoking had odds ratios of 1.2 (95% Cl 0.8-2.0) and 1.2 (95% Cl 0.9-1.7) in the premenopausal and postmenopausal categories, respectively. No evidence of dose response or of elevated risk in ex-smokers or current smokers was found in either study. These results persisted despite adjustment for several important variables. The present data demonstrate no association between smoking and prevalent or incident breast cancer in either menopausal category, contradicting the authors' previous finding of a positive association with premenopausal prevalent disease earlier in this screening study. The relation of smoking and breast cancer remains controversial. Further study is required to determine whether an association truly does not exist or whether smoking might have both protective and harmful effects that are mediated through different pathways, thus accounting for the paradoxical findings in the literature to date.

Adult↗
PubMed1988

Methodological issues in cohort studies. II: Power calculations.

A simple model is described for estimating power in cohort studies, in which the exposure is treated as a polytomous variable, with a known distribution in the population from which the sample is drawn. The model then requires the specification of the expected number of deaths which will occur in the cohort, calculated from the population rates, the dose-response relationship, and the size of the cohort. The model also allows for misclassification of exposure, the rule rather than the exception in epidemiological studies. The model is applied to a proposed study of saturated fat intake and risk of death from colorectal cancer in a male cohort drawn from the general population. It is demonstrated that this approach leads to an optimization of the power estimates, and in particular that maximization of power can be achieved by using a relatively small number of categories, eg four. It is also demonstrated that the effect of misclassification is less extreme if a polytomous dose-response model is used for analysis as compared to the usual simple dichotomous exposure model.

Adult↗
PubMed1988

The reliability of passive smoking histories reported in a case-control study of lung cancer.

A test-retest design has been used to examine the reliability of passive smoking histories reported in personal interviews. A total of 117 control subjects initially interviewed in a lung cancer case-control study conducted in metropolitan Toronto, Canada, between 1983 and 1984 were reinterviewed on average six months later. Responses to initial screening questions used to detect a person's exposure to passive smoke were more reliable for residential than for occupational exposure. Respondents also more reliably reported residential exposure to spouse's passive smoke than to the passive smoke of others at home. Quantitative measures of exposure to passive smoke, i.e., number and duration of exposure, were even less reliably reported. Nonsmoking respondents gave the most reliable information. The low reliability of self-reported duration of exposure to passive smoke is consistent with the inability of several studies to detect a significant dose-response relation with lung cancer risk when measures of dose that depend solely on duration are used.

Data Collection↗
PubMed1988

Dietary factors and the incidence of cancer of the urinary bladder.

A case-control study of diet and bladder cancer was conducted during 1979-1982 in Edmonton, Calgary, Toronto, and Kingston, Canada. A total of 826 histologically verified cancer cases were individually matched by age, sex, and area of residence to 792 randomly selected population controls. Subjects were interviewed concerning their histories of exposure to a number of dietary factors, including table-top artificial sweeteners, low calorie foods and drinks, beverages containing caffeine or ethanol, and certain other food items. Also, subjects provided information on their past medical, occupational, and residential histories, in addition to their exposures to tobacco and other life-style factors. For the analysis, conditional logistic regression methods were used. Under adjustment for cumulative lifetime amount of cigarette smoking, the dietary factors, with little exception, were not associated with significant alteration of risk for bladder cancer. In particular, ever regular use of artificial sweeteners did not appear to be associated with increased risk, either among men (odds ratio = 0.95, p = 0.70) or among women (odds ratio = 1.15, p = 0.53). However, daily intake of cholesterol, calculated from reported frequencies of consumption of nine relevant food items, suggested a mild increase in risk; the odds ratio estimate of trend was 1.07/100 mg average daily intake (i.e., 1.07(5.5) = 1.45 for 550 mg cholesterol per day, as might be consumed in one egg; p = 0.009). A history of diabetes mellitus of onset after age 20 years also seemed to be associated with increased risk of bladder cancer (odds ratio = 1.65, p = 0.019), but this increase did not appear to be the result of use of insulin or other medications, or use of artificial sweeteners or low calorie foods. Thus, this study tends to confirm reports of a lack of association between use of artificial sweeteners and subsequent risk of bladder cancer.

Adult↗