Search PubMed⌕ Search

Biomedical subjects

R Kaaks

Publications and source records attributed to R Kaaks.

At least 91 records · Page 5Linked to original sources
PubMed1996

Evaluation of the dietary history method used in the SENECA Study.

OBJECTIVE: To evaluate a modified dietary history method applied in elderly people aged 74-79 y. SETTING AND SUBJECTS: A total of 387 men and 420 women from seven European towns participated in an observational study. METHODS: Dietary intake was assessed with a modified dietary history and compared with a 3-day estimated record. RESULTS: The modified dietary history provided consistently higher intakes of energy and nutrients than the estimated record. For most nutrients this difference was between 10% and 20%. However, in some towns differences were much larger. Physical activity ratios calculated as reported energy intake divided by estimated basal metabolic rate (BMR) showed values less than 1.5 for data obtained with the estimated record, suggesting underreporting of energy intake. Pearson correlation coefficients between estimates by the two methods of the intakes of energy and almost all nutrients ranged from approximately 0.5 to 0.75. CONCLUSION: The size of the overall correlation coefficients indicates an acceptable agreement between the dietary history and record method in ranking individuals according to their intakes. For two towns, this agreement was not that good. Results indicate that the estimated record might not be a good reference method for older adults.

Aged↗
PubMed1996

Identifiability of food components for cancer chemoprevention.

Epidemiological studies have consistently reported a reduction in risk for several cancer sites in relation to high consumption of vegetables and fruit. These findings stimulated further research aimed at identifying which compounds in fruit and vegetables are responsible for the reduction in cancer risk. Epidemiological and laboratory studies suggested that some micronutrients, particularly vitamin C, vitamin E, beta-carotene, selenium, magnesium and zinc, could reduce the risk of cancers of the oral cavity, lung, oesophagus and stomach, while dietary fibre was more specifically related to a reduced risk of colorectal cancer. However, the results of large randomized trials on various combinations of vitamins and minerals at supranutritional doses have so far failed to confirm this hypothesis or have found very weak effects. These results should stimulate profound re-thinking of the methods that led to the selection of specific molecules with potential chemopreventive action. From a methodological point of view, little attention has so far been given to four main limitations of nutritional epidemiology, which have direct bearing on the extrapolation of results from foods to food components. Measurements of micronutrient intakes through simple dietary questionnaires and current food composition tables lack precision and specificity. Micronutrient intakes are often highly correlated in nature because micronutrients tend to share the same food sources. Attribution of cancer risk to a single food constituent can be misleading if multicollinearity of dietary variables is not recognized. The etiological meaning of nutritional biomarkers is not straightforward because circulating levels of nutrients reflect not only dietary intake but also complex metabolic regulations. Studies have not considered the physical characteristics of foods, which are important determinants of physiological responses. Understanding the multidimensional nature of diet and of its relationship with different cancers is a major scientific challenge. Epidemiological studies combining detailed dietary questionnaires, appropriate food composition tables, multiple biomarkers, and appropriate statistical methods may provide better measurements of the relationships between cancer risk and specific dietary patterns and therefore contribute to the identification of food components with hitherto unforeseen potential interest for cancer prevention.

Anticarcinogenic Agents↗
PubMed1996

The epidemiology of diet and colorectal cancer: review and perspectives for future research using biological markers.

Case-control studies, and several prospective cohort studies, indicate that the risk of developing colorectal cancer is decreased in individuals who consume high levels of vegetables and fruits, and is possibly increased at high intake levels of meat and (saturated) fat. A new generation of prospective studies, following a multi-cohort design, is currently being set up in populations with diverse dietary intake patterns, and these may provide more detailed and more conclusive evidence on relations between nutritional factors and cancer risk. By including measurements of biomarkers in blood or tissue specimens, prospective epidemiological studies may also increase understanding of etiological pathways relating lifestyle factors to cancer development, and may thus help to identify nutritional factors that would need to be modified to prevent the disease.

Bile Acids and Salts↗
PubMed1995

Calibration of dietary intake measurements in prospective cohort studies.

To evaluate the accuracy of dietary intake measurements in prospective cohort studies on diet, it is generally proposed that substudies be conducted to 1) correct relative risk estimates for biases due to measurement error, and 2) account for statistical power losses when estimating the sample size requirements of the cohort. Usually the substudy takes the form of a "validity" study, based on a small group of volunteers and using repeated daily food consumption records as reference measurements. In this methodological review, the authors conclude that when relative risks are estimated for scaled, absolute intake differences rather than for quantile categories, a "calibration" study based on only a single day's food intake record (but generally on a larger number of subjects) can provide sufficient reference information to meet objectives 1 and 2. A major advantage of calibration studies based on this single-day-per-subject design is that they can be conducted on a representative sample of cohort participants more easily than validity studies in which reference measurements are repeated.

Bias↗
PubMed1995

Sample size requirements for calibration studies of dietary intake measurements in prospective cohort investigations.

Pooling data from multiple cohort studies on diet and cancer has the advantage that it allows detailed cross-validation of relative risk estimates between different study populations. If there is reasonable agreement between cohort-specific relative risk estimates, a more powerful pooled summary estimate can be obtained. A complication, however, is that in different cohorts, relative risk estimates may be biased to a different degree as a result of errors in the baseline assessments of habitual dietary intake levels. Such divergent biases can be adjusted for by means of "calibration" studies, using standardized reference measurements obtained in a subgroup of each cohort. These adjustments entail a cost, however, in terms of an increase in the confidence interval of relative risk estimates within each cohort separately. In this paper, the authors evaluate the possible magnitude of such intracohort losses in precision and discuss the approximate sample size required to have a sufficient level of accuracy in dietary calibration studies to adjust for bias.

Calibration↗
PubMed1994

Estimating the accuracy of dietary questionnaire assessments: validation in terms of structural equation models.

The validity and precision of questionnaire assessments of the habitual intake of individuals are usually evaluated by comparison with reference measurements that are supposed to provide a best possible substitute for the individuals' true intake values. In the present paper, a measurement error model is presented, defining different types of error--random or systematic, and within or between individuals--that may occur in dietary intake measurements. It is then discussed how simple latent variable models (structural equation models) can be used to estimate the average magnitude of these various types of error. So far, approaches described for the analysis of dietary validity studies have all been based on the assumption that the random errors of repeat reference measurements, taken by the same method on different occasions, are uncorrelated, so that the average of a sufficiently large number of repeat reference measurements will provide an accurate ranking of individuals by true intake level. In the present paper it is described how, by additional comparison with a third type of measurement such as a biochemical marker, the validity of dietary questionnaire measurements can be evaluated even in situations where the random errors of repeat reference measurements can no longer be assumed to be independent.

Ascorbic Acid↗
PubMed1994

Adjustment for bias due to errors in exposure assessments in multicenter cohort studies on diet and cancer: a calibration approach.

An advantage of multicenter cohort studies on diet and cancer is that these may include populations over a wide range of dietary exposure. With some simplifying assumptions, the information from such multicenter studies may be divided into 1) estimated relationships within each of the separate cohorts, between individual-level measurements of dietary exposure and disease outcome, and 2) an estimated between-cohort relationship, between the mean intake measurements and mean incidence rates. Errors in the dietary exposure measurements may lead to different amounts of bias in each of these estimated relationships, in particular when dietary questionnaire methods cannot easily be standardized. A calibration approach can be used to adjust for such differences in bias. This will improve the relative weighting of within- and between-cohort components of evidence for a diet-disease association.

Cohort Studies↗
PubMed1994

Calibration in multi-centre cohort studies.

BACKGROUND: This paper is concerned with overcoming problems caused by measurement error in multi-centre studies of diet and disease. Measurement error causes differential bias, so the information on the diet-disease relationship from different cohorts is not directly comparable. Hence this information needs to be calibrated before the data are combined in an eventual meta-analysis. We consider the design of calibration substudies. We distinguish two forms of information from a multi-centre cohort study. The first is subject-level information, which comes from the variation of disease rate within cohorts. The second is cohort-level information, which comes from the variation of disease rate between cohorts. The requirements of the calibration study are different for these two forms of information. METHODS: Calibration is carried out by remeasuring diet in a subsample of each cohort using a standardized reference method. This reference measurement should yield unbiased estimates of habitual intake. RESULTS: Using a criterion of efficiency, relative to a perfectly calibrated study, we show that the sample size should be a multiple of the expected number of cases in each cohort. To control for confounding, each cohort should be stratified and the ratio of sample size to number of cases should be constant within strata. CONCLUSIONS: Since the required sample size is related not to the size of the cohort, but to the eventual number of cases of disease, calibration samples need not be prohibitively large. They should, however, be concentrated on those parts of the cohort, such as older age groups, which will yield most cases.

Bias↗
PubMed1994

Efficient use of biological banks for biochemical epidemiology: exploratory hypothesis testing by means of a sequential t-test.

In view of recent advances in molecular and biochemical epidemiology, there is growing interest in the creation of biological banks of blood, urine, tissue, or other biological specimens collected from participants in prospective cohort studies. The existence of biological banks may make it possible to study a multitude of etiologic hypotheses, by comparing biochemical parameters measured in the biological specimens of subjects who will eventually develop the disease of interest ("cases") and of control subjects, using a nested case-control or a case-cohort design. In practice, however, the amount of biological material available per subject (in particular, that of cases) will limit the number of hypotheses that can be tested. The present paper discusses the use of a sequential t-test which, compared with an analogous fixed sample procedure, will on average require fewer biological specimens before a given study hypothesis can be accepted or rejected. The sequential test should thus facilitate an early decision on whether a new hypothesis is worth further investigation, while avoiding wasting too much biological material on testing hypotheses that may eventually prove unfruitful. If the test reveals an exposure difference of interest, the study may be extended so that relevant epidemiologic effect measures can be estimated more accurately.

Biological Specimen Banks↗
PubMed1993

Application of a sequential t-test in a cohort nested case-control study with multiple controls per case.

Application of sequential analysis may avoid unnecessary experimentation and achieve economical use of available biomaterial stored in biological banks. When, as often happens in cohort case-controls studies, cases are scarce, it may be possible to use multiple control observations per case to increase the power of a test for detecting differences between cases and controls. Samples from a biological data bank were analysed. We compared results of a non-sequential analysis with results of sequential t-tests for 1 to 5 controls matched per case in a cohort nested case-control study. Simulations are performed to get an idea of the unreliability and the power of the sequential test. In general the sequential t-tests are too conservative with respect to the achieved power. Average sample numbers are lower for the sequential tests and decrease with multiple controls. More than 3 or 4 controls per case does not give a meaningful increase in efficiency.

Adult↗
PubMed1992

Dietary intake of fiber and decreased risk of cancers of the colon and rectum: evidence from the combined analysis of 13 case-control studies.

BACKGROUND: Colorectal cancer is a major public health problem in both North America and western Europe, and incidence and mortality rates are rapidly increasing in many previously low-risk countries. It has been hypothesized that increased intakes of fiber, vitamin C, and beta carotene could decrease the risk of colorectal cancer. PURPOSE: The objective of this study was to examine the effects of fiber, vitamin C, and beta-carotene intakes on 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. The study was designed to estimate risks in the pooled data, to test the consistency of the associations across the studies, and to examine interactions of the effects of the nutrients with cancer site, sex, and age. METHODS: Original data records for 5287 case subjects with colorectal cancer and 10,470 control subjects without disease were combined. Logistic regression analysis was used to estimate relative risks and confidence intervals for intakes of fiber, vitamin C, and beta carotene, with the effects of study, sex, and age group being adjusted by stratification. RESULTS: Risk decreased as fiber intake increased; relative risks were 0.79, 0.69, 0.63, and 0.53 for the four highest quintiles of intake compared with the lowest quintile (trend, P < .0001). The inverse association with fiber is seen in 12 of the 13 studies and is similar in magnitude for left- and right-sided colon and rectal cancers, for men and for women, and for different age groups. In contrast, after adjustment for fiber intake, only weak inverse associations are seen for the intakes of vitamin C and beta carotene. CONCLUSION: This analysis provides substantive evidence that intake of fiber-rich foods is inversely related to risk of cancers of both the colon and rectum. IMPLICATIONS: If causality is assumed, we estimate that risk of colorectal cancer in the U.S. population could be reduced about 31% (50,000 cases annually) by an average increase in fiber intake from food sources of about 13 g/d, corresponding to an average increase of about 70%.

Adolescent↗
PubMed1992

Diet and gastric cancer. A case-control study in Belgium.

A case-control study was carried out in 2 Belgian provinces with contrasting gastric-cancer mortality. The results were analyzed for the total study group and also separately in each of the 4 sub-groups: men and women in each province. Only risks which appeared consistently in at least 3 of these 4 sub-groups were retained in the discussion. Consumption of most vegetables, either cooked or raw, and of fresh fruit was found to be protective. There was an increased risk associated with meal and flour products, including white bread. Added sugar also increased the risk of gastric cancer. Consumption of lean meat was associated with a decreased risk. There was no clear effect for most sources of fat, but for oils with a high P/S ratio there was a decreased risk. Together with our earlier finding on salt, these results are to a large extent similar to those of other recent studies on gastric cancer.

Adult↗
PubMed1992

Validation of a method for the estimation of food portion size.

In the context of the planning phase of a large cohort study on dietary habits and cancer, we have developed a food frequency questionnaire on usual food intake, which includes a set of pictures to estimate the portion size of 23 different dishes. The validity of the estimation of portion size of recently consumed foods has been questioned by other researchers. To validate the use of pictures, we organized a field trial with 103 volunteers. They were invited to a dinner where standard Italian dishes were offered (total 17 foods); all of the portions they chose were recorded and weighed. The following day, we interviewed the volunteers on what they consumed during the dinner, and we compared the weight of the food actually eaten with the weight of the food represented in the pictures. The volunteers overestimated the portion size by more than 20% for six foods and underestimated the portion size by more than 20% for four foods. In addition, we found a tendency toward overestimation of portion size by those who ate smaller portions and underestimation, by those who ate larger portions ("flat slope syndrome").

Adult↗
PubMed1991

Cancer and polyps of the colorectum and lifetime consumption of beer and other alcoholic beverages.

Two parallel case-control studies were conducted in the Marseilles metropolitan area of France from 1979 to 1985 on cancers and adenomatous polyps of the colorectum. All cases of cancer (n = 389) and polyps (n = 252) were incident and histologically confirmed. Controls (n = 641) matched for sex and age were selected among patients undergoing functional reeducation for injury or trauma in one of five hospital centers. Intake of alcoholic beverages was investigated by questions on daily or weekly intake of wine, beer, apéritifs, and distillates during different life periods. Questions on alcoholic beverages were integrated in a detailed diet history interview questionnaire. The risk of rectal cancer was elevated in male beer drinkers (relative risk = 1.73, 95% confidence interval 1.01-2.95) and in men and women combined (relative risk = 1.71), while beer consumption was not associated with colon cancer. Total ethanol intake and consumption of wine and distillates were not associated with the risk of cancer of the colon or rectum, nor with risk of polyps. Adjustment in the statistical analysis for energy intake and for other dietary variables (fiber from fruits and fiber from vegetables), which were found to be risk factors in the study, did not substantially change the results found for beer and other alcoholic beverages. Etiologic hypotheses related to nitrosamine content of beer are discussed in the light of growing epidemiologic evidence that beer consumption specifically increases the risk of rectal cancer.

Aged↗
PubMed1988

Colorectal cancer and the consumption of foods: a case-control study in Belgium.

A case-control study on 453 cases with colon cancer, 365 with rectal cancer, and 2,851 population controls was carried out in two Belgian provinces known to differ in certain dietary habits, particularly with regard to the use of butter. All raw vegetables had a clear protective effect for both colon and rectal cancer; bread was also protective for colon cancer. Starchy foods and foods rich in oligosaccharides (sugar) caused an increased risk for both colon and rectal cancer. No other foods were found to have a systematic effect in both sexes and in both provinces, either in one direction or in the other, except for maize, soybean, and sunflower oils, which were clearly protective in all cases. Among the foods contributing to the intake of fats, there was no effect either for butter, margarine, or fatty meats; the only clear-cut protective effect was that of the oils having a high polyunsaturated-to-saturated ratio. These findings are consistent with our previous findings on the role nutrients play in the relationship with colon and rectal cancers.

Adult↗
PubMed1987

Colorectal polyps and diet: a case-control study in Marseilles.

This study investigates the differences in usual past diet between 252 subjects with newly diagnosed adenomatous or villous polyps of the colon and rectum and a group of 238 hospital controls. Cases and controls were interviewed in hospital by 3 nutritionists using a dietary history questionnaire focused on the diet during the preceding year. Nutrient intake was estimated by means of ad hoc food tables adapted from French and British tables. Out of 16 food groups considered in the analyses, the cases reported lower consumption of oil and potatoes and higher consumption of sugar added to food and drink. Among nutrients, we found that cases had a lower consumption of carbohydrates (not taking into account added sugar), potassium, magnesium and vitamin B6. We found a slightly lower intake of fibre and a slightly higher intake of saturated fat among cases, though neither was statistically significant. Intake values for fibre and for carbohydrates were highly intercorrelated and, due to measurement errors, the effect of one may be masked by the other and vice versa. The hypothesis that some components of carbohydrates (starches, fibre and natural sugars but not added sugar) play a protective role in relation to the biology of tumours of the intestinal tract is considered in further multivariate analyses and in the "Discussion".

Adolescent↗