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R Kaaks

Publications and source records attributed to R Kaaks.

At least 73 records · Page 4Linked to original sources
PubMed2000

Validation of a food-frequency questionnaire using multiple-day records and biochemical markers: application of the triads method.

BACKGROUND: A food-frequency questionnaire (FFQ) used to assess usual food intake in Southern France has been validated by the classical means of multiple-day food records. To minimise over-estimation of the correlation between the dietary assessments by the FFQ and the reference method, which occurs if the random errors of questionnaire and reference measurement are positively correlated, a triangular comparison, the method of triads, was used. METHODS: We applied the triads model by comparing the FFQ with two multiple-day food records and three biomarkers. Only 87 subjects were included and completed the protocol. One biomarker (beta-carotene) was used for the 87 subjects and two biomarkers (urinary nitrogen and potassium) were measured in only 40 subjects. RESULTS: For beta-carotene intake assessment, the triad model, including the weighed multiple records (PETRA), was the best with estimates of validity coefficient of 0.39 [confidence interval (CI) 0.18-0.60] for the FFQ, 0.52 (CI 0.24-0.86), for PETRA and 0.85 (CI 0.43-1) for plasma levels of the nutrient. For protein and potassium intake assessment, the triad model including the estimated multiple records was the best only for the estimates of FFQ validity coefficient (0.61; CI 0.28-0.96 and 0.31; CI 0.09-0.66 respectively). CONCLUSION: Accuracy of the dietary assessment methods permitted a satisfactory estimation of the validity coefficient for beta-carotene intake by the FFQ, despite a small sample. However, the validity coefficients for protein and potassium showed wide CI values, indicating that a sample size < 50 subjects appears unsatisfactory for validation.

Adult↗
PubMed2000

Variance and confidence limits in validation studies based on comparison between three different types of measurements.

BACKGROUND: The methods used in epidemiological studies to assess exposure are often affected by a conspicuous amount of measurement error. Exposure-measurement error is recognised to cause attenuation in the association between exposure and disease. Among different possible approaches, the validity coefficient of a measurement can be estimated by a comparison of three types of measurements, using either structural equation models or factor analysis (the triads method). These approaches assume that the measurements are linearly related to true intake and have independent random errors. METHODS: In this paper we present an estimator of the variance of the estimated validity coefficient to compute the associated confidence intervals. Standard error for the validity coefficient allows the efficiency of validation studies to be evaluated. Our work was motivated by the fact that existing software does not provide correct standard errors for the estimated validity coefficient. The approach is illustrated using selected examples from dietary validation studies. RESULTS: The accuracy of our formula is evaluated by comparison with the results of a simulation study, which shows that our variance estimator provides good results for sample sizes of at least n = 100 and when the expected value of the validity coefficient is not too close to 1.0, independent of the sample size. Our estimator formula performs better than either a naïve approach, that computes the standard error for a validity coefficient as if it is a straightforward correlation coefficient, or the SAS-CALIS procedure, which uses a maximum likelihood method. CONCLUSIONS: In evaluating the validity of the type of measurement chosen to assess exposure in an epidemiological study, it is important to provide an estimate of the precision of the validity coefficient of the measurement. Our variance estimator may help calculate sample size requirements for validation studies.

Analysis of Variance↗
PubMed1999

Fatty-acid composition in serum phospholipids and risk of breast cancer: an incident case-control study in Sweden.

The study of the relationship between dietary intake of fatty acids and the risk of breast cancer has not yielded definite conclusions with respect to causality, possibly because of methodological issues inherent to nutritional epidemiology. To evaluate the hypothesis of possible protection of n-3 polyunsaturated fatty acids (PUFA) against breast cancer in women, we examined the fatty-acid composition of phospholipids in pre-diagnostic sera of 196 women who developed breast cancer, and of 388 controls matched for age at recruitment and duration of follow-up, in a prospective cohort study in Umeâ, northern Sweden. Individual fatty acids were measured as a percentage of total fatty acids, using capillary gas chromatography. Conditional logistic-regression models showed no significant association between n-3 PUFA and breast-cancer risk. In contrast, women in the highest quartile of stearic acid had a relative risk of 0.49 (95% confidence interval, 0.22-1.08) compared with women in the lowest quartile (trend p = 0.047), suggesting a protective role of stearic acid in breast-cancer risk. Besides stearic acid, women in the highest quartile of the 18:0/18:1 n-9c ratio had a relative risk of 0.50 (95% confidence interval, 0.23-1.10) compared with women in the lowest quartile (trend p = 0.064), suggesting a decrease in breast-cancer risk in women with low activity of the enzyme delta 9-desaturase (stearoyl CoA desaturase), which may reflect an underlying metabolic profile characterized by insulin resistance and chronic hyper-insulinemia.

Breast Neoplasms↗
PubMed1998

Nutrient intake patterns and gastric cancer risk: a case-control study in Belgium.

A case-control study on gastric cancer risk in relation to nutrient composition of diet was conducted in the 2 Belgian provinces of Oost-Vlaanderen and Liège as part of a large epidemiological study on cancers of the digestive tract, also including colorectal cancer. The statistical analysis was carried out on a total of 301 men and women aged 35-74 years with histologically confirmed stomach tumors and 2,851 population controls. Dietary intake assessments were obtained by interview, using a dietary history questionnaire. Gastric cancer risk was increased for diets rich in mono- and disaccharides, according to statistical models based on energy-adjusted residuals [odds ratio (OR) = 1.88 for upper vs. lower quartiles of energy-adjusted intakes] or energy decomposition models, but showed no increase for high intake of polysaccharides. Intake of polyunsaturated fats, particularly linoleic acid, was inversely associated with gastric cancer risk. High intake of vitamin C, beta carotene and vitamins B1 (thiamine), B3 (nicotinic acid) or B6 (pyridoxine) was also associated with decreased risk, whereas increased risk was observed for high intake of vitamin A (retinol) or vitamin B2 (riboflavin). Many of these associations between gastric cancer risk and nutrient composition were similar to those found in the analysis of a parallel study on cancers of the colon and rectum.

Adult↗
PubMed1998

Breast-cancer incidence in relation to height, weight and body-fat distribution in the Dutch "DOM" cohort.

In a cohort of 11,663 participants in a breast-cancer screening program, height, weight, waist circumference and hip circumference were measured, and information about menstrual and reproductive history was obtained by questionnaire. After exclusion of 83 women with unclear menopausal status, the subjects were divided into 3 sub-cohorts: 5,891 women who were pre-menopausal at the time of data collection, 3,521 women who had entered the study after natural menopause, and 2068 women who had been hysterectomized and/or ovariectomized. After a median follow-up of 10.6 years, 147, 76 and 52 incident cases of breast cancer were detected in the 3 respective sub-cohorts. No statistically significant association was found in any of the sub-cohorts between breast-cancer risk and height, weight, body-mass index (BMI) or hip circumference. In the sub-cohort of women with natural menopause, however, risk of breast cancer was positively and significantly associated with the ratio of waist-to-hip circumferences (WHR) (RR = 2.63 for upper vs. lower quartile), and this association did not change after adjustment for variations in disease risk related to body height and weight. Although similar to observations in other cohort studies showing positive associations between obesity and breast-cancer risk in post-menopausal women, our results are different, in that WHR and not BMI appears to be the more specific indicator of breast-cancer risk.

Adipose Tissue↗
PubMed1998

Occurrence, trends and environment etiology of pancreatic cancer.

This review summarizes data on the occurrence, the trends, and the life-style, environmental, occupational and genetic determinants of pancreatic cancer. Epidemiologic evidence implicates tobacco smoking as one cause. The evidence regarding alcohol consumption is inconsistent. Although both positive and inconclusive findings are encountered, the bulk of the evidence on coffee consumption is negative. Fat intake is linked with obesity and diabetes mellitus, which are risk factors for pancreatic cancer. Fruit and vegetable consumption appears to be protective. No occupational or environmental agent has been confirmed to increase the risk, but epidemiologic evidence is inconsistent, Little is known about the role of genetic polymorphisms of metabolic enzymes in pancreas carcinogenesis. Pancreatic cancer shows high rates of mutations of Ki-ras and losses or mutations of tumor suppressor genes (p53, p16INK4A, and SMAD4/DPC-4). Ki-ras mutations have been associated with life-style factors in relation to pancreatic cancer, but the evidence is still scant and inconsistent.

Female↗
PubMed1997

The role of multi-centre cohort studies in studying the relation between diet and cancer.

In spite of important progress made during recent decades in nutritional epidemiology methods, many questions about the role of diet in determining cancer risk remain elusive. One example of an unresolved question is whether a high percentage of energy intake in the form of fat (especially saturated fat) is associated with an increased risk of breast cancer. Observations from international correlation and case-control studies support this hypothesis, while results from prospective cohort studies, generally considered less prone to bias, do not. In this paper, we review the advantages and limitations of these different types of epidemiological study design, and discuss how multi-centre studies may help answer some of the unresolved questions about relations between diet, nutritional status, and cancer risk. Multi-centre cohort studies may have the advantage of increased statistical power because of larger variations in individuals' dietary intake patterns and disease risk (as in international correlation studies), while at the same time offering all the possibilities of individual-level studies to model confounding and/or interaction effects.

Case-Control Studies↗
PubMed1997

The relationship between dietary fat intake and risk of colorectal cancer: evidence from the combined analysis of 13 case-control studies.

The objective of this study was to examine the effects of the intake of dietary fat upon colorectal cancer risk in a combined analysis of data from 13 case-control studies previously conducted in populations with differing colorectal cancer rates and dietary practices. Original data records for 5,287 cases of colorectal cancer and 10,470 controls were combined. Logistic regression analysis was used to estimate odds ratios (OR) for intakes of total energy, total fat and its components, and cholesterol. Positive associations with energy intake were observed for 11 of the 13 studies. However, there was little, if any, evidence of any energy-independent effect of either total fat with ORs of 1.00, 0.95, 1.01, 1.02, and 0.92 for quintiles of residuals of total fat intake (P trend = 0.67) or for saturated fat with ORs of 1.00, 1.08, 1.06, 1.21, and 1.06 (P trend = 0.39). The analysis suggests that, among these case-control studies, there is no energy-independent association between dietary fat intake and risk of colorectal cancer. It also suggests that simple substitution of fat by other sources of calories is unlikely to reduce meaningfully the risk of colorectal cancer.

Adult↗
PubMed1997

Reproducibility of a food frequency questionnaire used in the New York University Women's Health Study: effect of self-selection by study subjects.

OBJECTIVE: The aim of the study was to investigate the reproducibility of a food frequency questionnaire (FFQ) used in a cohort of 14,290 women enrolled in the NYU Women's Health Study. DESIGN: A subset of 474 cohort subjects who completed the dietary questionnaire at baseline (FFQ-1) were approached again on the occasion of a second visit to the mammography study centre and asked to complete the questionnaire a second time (FFQ-2) two to four years after FFQ-1. Two to three months later the questionnaire was mailed to the subjects, and they were asked to complete it a third time (FFQ-3). SETTING: A breast cancer screening clinic. SUBJECTS: Of the 474 subjects selected, 100% completed the second questionnaire while only 56% completed and mailed back FFQ-3. This made it possible to compare the long-term reproducibility of dietary intake measurements and baseline dietary habits between the two groups of subjects 'respondents', who agreed to complete the questionnaire a third time, and 'non-respondents', who did not. RESULTS: Among respondents (56% of study subjects), energy-adjusted correlation coefficients for short-term reproducibility between FFQ-2 and FFQ-3 ranged from 0.50-0.64 for nutrients, and from 0.44-0.67 for foods. The long-term reproducibility was lower, ranging from 0.36-0.53 for nutrients, and from 0.31-0.48 for specific food groups. Among those who did not respond to FFQ-3, crude correlations for long-term reproducibility, unadjusted for energy intake, were generally lower than among respondents. Nevertheless, after adjustment for energy intake, correlations for long-term reproducibility (FFQ-2 to FFQ-1) were of similar magnitude in both groups. In addition, 'non-respondents' reported lower intake of fruit and vegetables and higher intake of meat. CONCLUSIONS: The results of this study suggest that subjects who volunteer to participate in substudies on the validity or reproducibility of dietary questionnaire measurements may tend to provide more accurate responses to the questionnaire. The phenomenon seems related more to accuracy of reporting of absolute intake levels than of the relative composition of diet, self-selection may be associated with differences in dietary habits.

Adult↗
PubMed1997

Validation and calibration of dietary intake measurements in the EPIC project: methodological considerations. European Prospective Investigation into Cancer and Nutrition.

The statistical power of prospective studies on diet in relation to chronic disease risk can be improved by maximizing the variation in true intake levels actually distinguished--or 'predicted'--by dietary questionnaire assessments collected at baseline. This can be achieved by 1) developing a questionnaire method that provides measurements with the smallest possible random errors, thus maximizing the correlation of measured with true habitual intake levels; and 2) increasing the between-person variation in true dietary intake levels when combining multiple cohorts in populations with diverse consumption patterns. The first approach implies that, during the development or selection of the questionnaire method, correlations between measurements and true intake levels can be monitored; the second approach requires adjustment for between-centre differences in over--or underestimation of dietary questionnaire measurements. Besides optimizing the statistical power, it is important that the magnitude of the predicted variation in true intake level is estimated accurately, so as to allow unbiased estimations of relative risks. To meet these various objectives, substudies must be conducted for the 'validation' or 'calibration' of dietary questionnaire assessments, by comparison with additional measurements that have independent sources of error. This paper reviews the methodological considerations underlying the design and implementation of such substudies in the EPIC project, a collaborative multicentre study in nine Western European countries.

Diet↗
PubMed1997

Pilot phase studies on the accuracy of dietary intake measurements in the EPIC project: overall evaluation of results. European Prospective Investigation into Cancer and Nutrition.

BACKGROUND: As part of the European Prospective investigation into Cancer and Nutrition (EPIC), preliminary studies were conducted to evaluate the accuracy of individuals' dietary intake measurements from newly developed questionnaires. METHODS: In six countries that adhered from the very beginning to the multicentre, co-ordinated EPIC project, the validity studies were based on two repeat questionnaire measurements at the start and at the end of a 1-year period, in groups of about 100 volunteers of both sexes. In addition, during this year, up to 12 24-hour recalls per person were taken monthly, and up to four blood and urine specimens were collected for measurement of biochemical markers. In three countries that joined EPIC later, the designs of the validity studies and type of 'reference' measurement chosen were somewhat different. The results presented in this overview paper are taken partly from more detailed, country-specific publications, and partly from a central (re-)analysis of the original data, to ensure a uniform approach to the statistical analyses and presentation. RESULTS: Averaged over subgroups by country and gender, Spearman coefficients of correlation between questionnaire measurements and the individuals' average 24-hour recalls ranged from 0.37 for fish to 0.68 for dairy products and 0.79 for alcoholic beverages. For energy-adjusted nutrient intakes (or nutrient densities, in the UK), mean Pearson correlation coefficients, corrected for residual attenuation due to day-to-day variations in the 24-hour recalls in all but two countries, ranged from 0.37 for retinol and 0.48 for vitamin E to 0.60 for carbohydrates and 0.12 for total alcohol intake. Correlations between energy-adjusted nutrient intakes and biochemical markers on average were low, but varied considerably between study centres. CONCLUSIONS: On average, most estimated correlation coefficient were of similar magnitude to those observed by independent research groups. The role of the preliminary validity studies, and various benefits drawn from these studies for further planning of the EPIC project are discussed.

Diet↗
PubMed1997

The EPIC Project: rationale and study design. European Prospective Investigation into Cancer and Nutrition.

BACKGROUND: The most consistent result of epidemiological studies on diet and cancer is that a diet rich in vegetables, fruit and, more generally, in plant foods is associated with a reduced risk of cancer at several anatomical sites. Epidemiological studies have been less consistent regarding the putative increase in risk related to consumption of fat or meat. In addition it has not been possible to identify clearly the biological role of specific nutrients or non-nutrient food components in the prevention or causation of cancer. Limitations in the precision and validity of traditional dietary intake measurements and limited use of biomarkers combined with narrow ranges of variations in dietary habits within single populations, have been the main reasons for the limited success in identifying more specific diet and cancer links. METHODS: EPIC is a multi-centre prospective cohort study designed to investigate the relation between diet, nutritional and metabolic characteristics, various lifestyle factors and the risk of cancer. The study is based in 22 collaborating centres in nine European countries and includes populations characterized by large variations in dietary habits and cancer risk. Data are collected on diet, physical activity, sexual maturation and reproductive history, lifetime consumption of alcohol and tobacco, previous and current illnesses and current medication. Following a common protocol and using identical equipment, blood samples are collected, aliquoted into plasma, serum, white blood cells and erythrocytes, and stored in liquid nitrogen at -196 degrees C for future laboratory analyses on cancer cases and matched healthy controls. Anthropometric measurements are taken according to a standard protocol. It is planned to include around 400,000 middle-aged men and women. RESULTS AND CONCLUSIONS: The collection of questionnaire data, anthropometric measurements and blood samples is under way. Almost 340,000 subjects had been included in the study by mid-1996, and recruitment is expected to be almost complete by 1997. Follow-up for cancer incidence and total mortality has started and it is expected that about 23000 cancer cases will be identified during the first 10 years of follow-up.

Adult↗
PubMed1997

Biochemical markers of dietary intake.

The primary objective of nutritional epidemiology is to identify, in combination with other forms of research, which aspects of diet and nutritional factors are causally related to cancer development. However, traditional epidemiology can evaluate with only a limited degree of specificity to which individual dietary factors an increased occurrence of cancer can be attributed. The two main reasons for this are: (1) dietary intake levels of specific foods or food constituents can be strongly intercorrelated; (2) dietary intake levels of specific food constituents are generally measured with rather large errors. Biochemical markers are increasingly seen as measurements that may help to overcome some of the above-mentioned methodological problems in nutritional epidemiology.

Biomarkers, Tumor↗
PubMed1996

Comparison of one-sample two-sided sequential t-tests for application in epidemiological studies.

In epidemiological prospective cohort studies, exposure levels of cases with disease and disease-free control subjects can be measured by laboratory analysis of previously stored biological specimens. In such studies, a sequential t-test can be used for preliminary evaluations, at the expense of the smallest possible number of specimens, of whether a new aetiological hypothesis is worth further investigation or whether specimens should rather be spared to test other, more fruitful, hypotheses. For this purpose, we recently compared two sequential probability ratio tests (SPRTs), in which the log-likelihood ratio was either based on an approximation, or computed exactly, and which were adapted to account for various control-to-case matching ratios. The tests turned out relatively conservative, particularly in terms of the significance level achieved. In the present paper, we compare an SPRT for matched or paired data based on Rushton's approximation to the log-likelihood ratio with a profile log-likelihood method developed by Whitehead. The comparison is partly mathematical, and partly based on computerized simulations. Average sample size for a sequential test is already smaller than for the equivalent fixed sample test. Increasing the number of controls matched per case further reduces the average sample size necessary to come to a decision. We show that, irrespective of the number of controls per case, pre-specified levels of statistical power and significance are respected closely by Whitehead's method, but not by Rushton's SPRT. This last procedure can lead to a significant loss in power. Since, in addition, Whitehead's method has been implemented in a commercially available computer program (PEST), we conclude that this method can be preferred to the methods we described earlier. Moreover, compared with the method of Rushton, Whitehead's method has the advantage that it can also be applied to groupwise inspection of the data and that it can also be converted easily into a truncated procedure.

Breast Neoplasms↗
PubMed1996

Nutrition, hormones, and breast cancer: is insulin the missing link?

Breast cancer incidence rates are high in societies with a Western lifestyle characterized by low levels of physical activity, and by an energy-dense diet rich in total and saturated fat and refined carbohydrates. Epidemiologic studies, so far mostly on postmenopausal women, have shown that breast cancer risk is increased in hyperandrogenic women, with decreased levels of plasma sex-hormone binding globulin, and with increased levels of testosterone and of free estrogens. This paper describes the role of hyperinsulinemia as a physiologic link between nutritional lifestyle factors, obesity, and the development of a hyperandrogenic endocrine profile, and reviews evidence that may or may not support the theory that chronic hyperinsulinemia is an underlying cause of breast cancer. An hypothesis is presented, stipulating that breast cancer risk is increased not only in hyperandrogenic postmenopausal women, but also in premenopausal women with mild hyperandrogenism and normal (ovulatory) menstrual cycles. The author suggests further investigation as to whether there is a positive association between risk of breast cancer before menopause and subclinical forms of the polycystic ovary syndrome (PCOS), and to what extent diet and physical activity during childhood, by modulating the degree of insulin resistance during adolescence, may or may not be determinants of a PCO-like hyperandrogenic endocrine profile persisting into adulthood.

Adolescent↗
PubMed1996

Nutrition and laryngeal cancer.

The main etiologic factors of cancers of the larynx and hypopharynx are alcohol and tobacco, and their prevalence in different populations explains, to a large extent, the wide variations in incidence observed around the world. Besides these two main risk factors, however, diet also seems to play a role in determining the risk of these cancers. There is consistent evidence that low consumption of fruit and vegetables is associated with higher risk, after statistical adjustment for alcohol and tobacco. Consumption of vegetable oils and fish and a moderately high polyunsaturated/saturated fatty acid ratio (P/S ratio) were reported to be associated with reduced risk. Low intake of vitamin C, beta-carotene and vitamin E were reported consistently to be associated with higher laryngeal cancer risk, but there was no clear evidence that these micronutrients are better predictors of cancer risk than the principal food groups from which their intake levels were estimated, i.e., fruits, vegetables, vegetable oils, and fish. Given the overwhelming role of tobacco and alcohol in the etiology of these cancers and the extremely low incidence among nonsmokers/nondrinkers, the available studies provide no estimate of the role of diet in subjects not exposed to these factors. The evidence indicates, however, that, in the presence of tobacco and/or alcohol, low intake of fruit and vegetables may account for 25 to 50 percent of the cases among men.

Alcohol Drinking↗