Heather Bryant

BACKGROUND AND OBJECTIVE: Despite assumed similarities in Canadian and US dietary habits, some differences in food availability and nutrient fortification exist. Food-frequency questionnaires designed for the USA may therefore not provide the most accurate estimates of dietary intake in Canadian populations. Hence, we undertook to evaluate and modify the National Cancer Institute's Diet History Questionnaire (DHQ) and nutrient database. METHODS: Of the foods queried on the DHQ, those most likely to differ in nutrient composition were identified. Where possible these foods were matched to comparable foods in the Canadian Nutrient File. Nutrient values were examined and modified to reflect the Canadian content of minerals (calcium, iron, zinc) and vitamins (A, C, D, thiamin, riboflavin, niacin, B6, folate and B12). DHQs completed by 13 181 Alberta Cohort Study participants aged 35-69 years were analysed to estimate nutrient intakes using the original US and modified versions of the DHQ databases. Misclassification of intake for meeting the Dietary Reference Intake (DRI) was determined following analysis with the US nutrient database. RESULTS: Twenty-five per cent of 2411 foods deemed most likely to differ in nutrient profile were subsequently modified for folate, 11% for vitamin D, 10% for calcium and riboflavin, and between 7 and 10% for the remaining nutrients of interest. Misclassification with respect to meeting the DRI varied but was highest for folate (7%) and vitamin A (7%) among men, and for vitamin D (7%) among women over 50 years of age. CONCLUSION: Errors in nutrient intake estimates owing to differences in food fortification between the USA and Canada can be reduced in Canadian populations by using nutrient databases that reflect Canadian fortification practices.

BACKGROUND: In 1992, Berkel and colleagues reported in the Journal the results of their study of the potential association of breast augmentation and breast cancer. The study reported that women who had breast augmentation had a significantly lower subsequent risk of breast cancer (P < 0.01) than the general population, with a standardized incidence ratio of 0.48 overall. Assuming a 10-year induction period (that is, assuming that cancers found within 10 years of the augmentation might have been the result of a process begun before surgery and therefore should not be considered), the reported standardized incidence ratio was 0.16. Problems were later identified involving some of the study methods. This paper reports a second analysis of these data. METHODS: We used a data set from Alberta Health Care to identify eligible women with bilateral breast augmentation. Using a combination of deterministic and probabilistic methods, we linked this data set to the Alberta Cancer Registry to identify subsequent breast cancers that developed during the study period. Multiple estimates of standardized incidence ratios were calculated on the basis of differing study-eligibility dates, induction periods, and types of breast-cancer (invasive only or invasive plus in situ). RESULTS: The reanalysis found substantial differences in the numbers of person-years at risk, resulting in higher standardized incidence ratios than in the original analysis. The final ratios for all breast cancers, with October 1, 1973, used as the starting date of the study, were 0.76 (95 percent confidence interval, 0.55 to 1.02), 0.85 (95 percent confidence interval, 0.58 to 1.19), and 0.68 (95 percent confidence interval, 0.32 to 1.25) for induction periods of 0, 5, and 10 years, respectively. None of these standardized incidence ratios were significantly different from 1. CONCLUSIONS: On the basis of this reanalysis, the incidence of breast cancer among the women who had breast augmentation could not be said to be either significantly higher or lower than that among the general population over the period during which this cohort was followed.