Development of the HELIUS food frequency questionnaires: ethnic-specific questionnaires to assess the diet of a multiethnic population in The Netherlands.

OBJECTIVES: Ethnic minorities are often not included in studies of diet and health because of a lack of validated instruments to assess their habitual diets. Given the increased ethnic diversity in many high-income countries, insight into the diets of ethnic minorities is needed for the development of nutritional policies and interventions. In this paper, we describe the development of ethnic-specific food frequency questionnaires (FFQs) to study the diets of Surinamese (African and South Asian), Turkish, Moroccan and ethnic Dutch residents of The Netherlands. METHODS: An existing Dutch FFQ was adapted and formed the basis for three new FFQs. Information on food intake was obtained from single 24 h recalls. Food items were selected according to their percentage contribution to and variance in absolute nutrient intake of the respective ethnic groups. A nutrient database for each FFQ was constructed, consisting of data from the Dutch Food Composition table; data on ethnic foods were based on new chemical analyses and available international data. RESULTS: We developed four ethnic-specific FFQs using a standardised approach that included ~200 food items each and that covered more than 90% of the intake of the main nutrients of interest. CONCLUSIONS: The developed FFQs will enable standardised and comparable assessment of the diet of five different ethnic groups and provide insight into the role of diet in differences in health between ethnic groups. The methodology described in this paper and the choices made during the development phase may be useful in developing similar FFQs in other settings.

Potential and requirements for a standardized pan-European food consumption survey using the EPIC-Soft software.

BACKGROUND/OBJECTIVES: To describe the strengths, limitations and requirements of using EPIC-Soft software (the software developed to conduct 24-h dietary recalls in the European Prospective Investigation into Cancer and Nutrition (EPIC) Study) in pan-European food consumption surveys, and to discuss potentials and barriers for a harmonized pan-European food consumption survey. SUBJECTS/METHODS: The paper is based on the experiences in the 'European Food Consumption and Validation' Project, which included updating six existing and preparing one new country-specific EPIC-Soft version, applying EPIC-Soft in validation and feasibility studies, and estimating the intake of nutrients and flavoring substances. The experiences were discussed in the September 2009 workshop 'Pan-European Food Consumption Surveys--for Standardized and Comparable Transnational Data Collection'. RESULTS: EPIC-Soft is suitable for detailed and standardized food consumption data collection in pan-European food consumption surveys. A thorough preparation of all aspects of the food consumption survey is important for the quality and efficiency during data collection and processing. The preparation and data-handling phase of working with EPIC-Soft is labor intensive and requires trained, motivated and qualified personnel. CONCLUSIONS: Given the suitability of EPIC-Soft as standardized dietary assessment tool in European dietary monitoring, the proposed strategy toward a pan-European food consumption survey is to prepare well, to allow flexibility in national extensions and to start with a limited number of countries that are interested.

Recommendations for a trans-European dietary assessment method in children between 4 and 14 years.

BACKGROUND/OBJECTIVES: The main objective of European Food Consumption Validation (EFCOVAL)-child Project is to define and evaluate a trans-European methodology for undertaking national representative dietary surveys among children in the age group of 4-14 years. In the process of identifying the best dietary assessment methodologies, experts were brought together at a workshop. The paper presents the discussion of the best available method and the final recommendations for a trans-European dietary assessment method among 4- to 14-year-old children. SUBJECTS/METHODS: The starting point was to investigate whether the method (two non-consecutive 24-h dietary recalls (24-HDRs)) suggested for the adults in European Food Consumption Survey Method (EFCOSUM) would be usable for children in the age group between 4 and 14 years. However, all available dietary assessment methods were included in the discussion to ensure that the final recommendation would be based on the best evidence. Six criteria were defined and used as additional guidance in the process. RESULTS: The literature does not give a clear recommendation on the dietary assessment methods that are most suitable for children in the age group of 4-14 years. Nevertheless, on the basis of the literature, the recommendations were separated for preschoolers (4-6 years) and schoolchildren (7-14 years). CONCLUSION: For preschoolers, two non-consecutive days of a structured food record are recommended, using a (for children adapted) picture booklet and household measures for portion-size estimation. For schoolchildren, repeated 24-HDRs are recommended, using a picture booklet and household measures for portion-size estimation. In addition, the child should bring a booklet to register what is eaten out of home. One parent should assist the schoolchild at the 24-HDR interview, and therefore face-to-face interviews are required.

Feasibility of 2 × 24-h dietary recalls combined with a food-recording booklet, using EPIC-Soft, among schoolchildren.

BACKGROUND/OBJECTIVES: The aim of this study was to evaluate the feasibility of the suggested trans-European methodology for undertaking representative dietary surveys among schoolchildren: 2 × 24-h dietary recalls (24-HDRs) combined with a food-recording booklet, using EPIC-Soft (the software developed to conduct 24-HDRs in the European Prospective Investigation into Cancer and Nutrition (EPIC) Study) pc-program. SUBJECTS/METHODS: A total of 75 children aged 7-8 years and 70 children aged 12-13 years old were recruited through the Civil Registration System in Denmark, and 57 children aged 7-8 years and 47 children aged 12-13 years were recruited through schools in Spain. Each child with one parent completed two face-to-face 24-HDRs, combined with optional use of a food-recording booklet (FRB) to be filled in by the child, a parent or other proxy persons for preparing the recalls. Feasibility was evaluated by questionnaires completed by parents, children and interviewers, and by selected data from the 24-HDRs. RESULTS: The face-to-face interviews with the child and a parent together are confirmed as feasible. The children participated actively in the interviews, the oldest children being most active. The children, parents and interviewers agreed that children needed help from the parents, and that parents were of help to the child. In both countries, other proxy persons, such as teachers or the school cafeteria staff, were involved before the interview, and the majority of the parents and children reported that the FRB had been a help for the child during the interview. Further results point at specific needed improvements of the tools. CONCLUSIONS: The evaluated method is shown feasible in two culturally diverse European populations. However, the feasibility study also points to specific improvements of tools and data collection protocol that are strongly recommended before implementation of the method in each country of a pan-European dietary survey.

Evaluation of 2 × 24-h dietary recalls combined with a food-recording booklet, against a 7-day food-record method among schoolchildren.

BACKGROUND/OBJECTIVES: The aim of this study was to evaluate the estimated energy, nutrient and food intake from the suggested trans-European methodology for undertaking representative dietary surveys among schoolchildren: 2 × 24-h dietary recalls (24-HDRs) combined with a food-recording booklet (FRB), using EPIC-Soft pc-program (the software developed to conduct 24-HDRs in the European Prospective Investigation into Cancer and Nutrition (EPIC) Study), against a 7-day food-record (7-dFR) method among Danish schoolchildren. SUBJECTS/METHODS: A total of 74 children aged 7-8 years and 70 children aged 12-13 years were recruited through the Civil Registration System in Denmark. Each child and one of their parents completed two face-to-face 24-HDRs, combined with optional use of a FRB, followed by a 7-day-estimated FR. RESULTS: Energy intake was significantly higher with the 24-HDR method than with the 7-dFR method for both age groups. Mean energy intake was 6% higher for the youngest (P = 0.02) and 11% for the oldest children (P = 0.01); underreporting of energy occurs among the oldest children, being less present with the 24-HDR method. The intakes of carbohydrate and dietary fiber (absolute and related to energy) were significantly higher with the 24-HDR than with the 7-dFR for both age groups (P < 0.001). No significant differences between the two methods were observed for absolute intake of fat and added sugar between both age groups, and for intake of protein among the 7- to 8-year olds. The percentage of energy intake from fat from the 24-HDR, however, was significantly lower for both age groups and for energy intake from added sugar for the 12- to 13-year olds. CONCLUSIONS: The 2 × 24-HDR method compared with the 7-dFR yields relatively good values on the group level for many macronutrients and foods. However, some differences in estimated intakes of macronutrients suggest the need to carefully adapt the tools to be age and country specific. There is a tendency for parents and schoolchildren to report a healthier diet with the 24-HDR than with the FRs; this results in some concern about the method and has to be studied further.

Feasibility of repeated 24-h dietary recalls combined with a food-recording booklet, using EPIC-Soft, among preschoolers.

BACKGROUND/OBJECTIVES: This study evaluates the feasibility among preschoolers of the 2 × 24-h dietary recalls (24-HDRs) method combined with a food-recording booklet (FRB), using EPIC-Soft pc-program for the 24-HDR (the software developed to conduct 24-HDRs in the European Prospective Investigation into Cancer and Nutrition (EPIC) Study). SUBJECTS/METHODS: A total of 20 and 25 (4- to 5-year-old) children were recruited, as a convenience sample, through worksites or day or healthcare in Denmark and Spain, respectively. One parent (or both parents together) completed two face-to-face 24-HDR, combined with an optional use of a FRB. Feasibility was evaluated by evaluation questionnaires completed by parents and interviewers. RESULTS: The face-to-face interviews were primarily conducted with the mothers. The FRB was used by 90% of the participants, and proxy persons, other than the parent, were also involved; involvement of proxy persons seems necessary in a majority of the recalls in both the countries. CONCLUSIONS: The results suggest that 2 × 24-HDR with one parent combined with a FRB is feasible for registering preschoolers' diet. An FRB and/or information from proxy persons, other than the parent, is needed for a majority of the parents. In future studies, it may be beneficial to develop the FRB more like a structured food record (FR), which might, in principle, change the method to a one-day FR method from more than a 24-HDR method. It is recommended then to further investigate the use of EPIC-Soft as a data-entry tool.

Operationalization of food consumption surveys in Europe: recommendations from the European Food Consumption Survey Methods (EFCOSUM) Project.

BACKGROUND: The EFCOSUM (European Food Consumption Survey Methods) Project aims at harmonizing food consumption surveys in European countries within the perspective of an overall Public Health Monitoring Programme. Harmonization implies the need for a common framework of procedures and tools, that are applicable and feasible in all potentially interested countries. A major element in such a framework is the protocol for the operationalization of a food consumption survey, referring to all practical, logistical and material conditions that need to be fulfilled in order to guarantee a successful implementation of such a survey. OBJECTIVE: The objective of this paper was to review a number of aspects of operationalization of food consumption surveys in detail. On the basis of the currently available knowledge and experience in Europe, consensus recommendations have been elaborated for an operationalization protocol that would be feasible for all European countries. METHODS: The EFCOSUM recommendations with respect to operationalization of food consumption surveys in Europe are mainly based on three sources of information, which have been discussed at several ad hoc expert meetings: experience from previous collaborative epidemiological studies, literature searches and results of two questionnaires, distributed among representatives from 23 European countries-all experts affiliated with experienced organizations in the fields of nutrition research and related fields. RESULTS: Consensus recommendations have been set up for the following topics: sampling, recruitment, fieldwork, biomarkers, interviewer qualifications and training and quality control. These recommendations have to be considered the best achievable common denominator within Europe at this time. In a number of cases, recommendations are presented in a hierarchical way, with a gradation from first choice options towards acceptable alternatives. CONCLUSIONS: It can be concluded that a high degree of standardization of fieldwork can be achieved within Europe. A number of specific problems and constraints will have to be solved in connection with the conduction of a real survey. These problems include, amongst others, country-specific decisions on, for example, target population, detailed sampling and recruiting procedures, interview setting and support. However, on the whole, these problems can be overcome and the main recommendations presented in this paper are considered feasible for every country in Europe. Application of the EFCOSUM operationalization protocol in European countries will contribute significantly to the quality and comparability of food consumption data across Europe. It is anticipated that the policy supporting and orienting potential of this type of databases-both at the national and at the EU supranational level-will be increased accordingly.

Nutrition and health among migrants in The Netherlands.

OBJECTIVE: this paper aims to give a broad overview of published data on nutrition and health among migrants in the Netherlands, as well as data on determinants of health. RESULTS AND CONCLUSIONS: Depending on the definition, 9 to 17% of the population belongs to the group 'migrants' and this proportion is expected to grow in the coming years. Roughly 2/3 of migrants are of the first generation and on average, they are younger than the Dutch population. Relatively few data concerning the health status of migrants are available. The diet of migrants showed both positive (macronutrients) and negative (micronutrients) differences with the general Dutch diet. The risk of overweight was high among both children and adult women, and the data suggest a higher risk for Turkish and Moroccan groups than for Dutch groups. The importance of health determinants, such as smoking, alcohol use and physical and social environment, was different for migrants than for the Dutch population; however, there were also differences between ethnic groups. The limited data on morbidity for migrants suggest higher risks than for the indigenous population. The same holds for mortality data, especially for the younger age groups. In general, the data that are available suggest that the health status of migrants was less favourable than that of the indigenous population. However, there were also differences between the various groups of migrants. The lower socio-economic position of migrant groups partly explained the differences in health status. Nevertheless, a study among Turkish people indicated that their health status was lower than that of Dutch people of comparable socioeconomic status.

Plant sterol intakes and colorectal cancer risk in the Netherlands Cohort Study on Diet and Cancer.

BACKGROUND: Plant sterols in vegetable foods might prevent colorectal cancer. OBJECTIVE: The objective was to study plant sterol intakes in relation to colorectal cancer risk in an epidemiologic study. DESIGN: The study was performed within the framework of the Netherlands Cohort Study on Diet and Cancer in 120852 subjects who completed a baseline questionnaire in 1986. After 6.3 y of follow-up, 620 colon and 344 rectal cancer cases were detected. A case-cohort approach was used to calculate confounder-adjusted rate ratios (RRs) and their 95% CIs for quintiles of plant sterol intake. RESULTS: The total mean (+/-SD) intake of campesterol, stigmasterol, beta-sitosterol, campestanol, and beta-sitostanol was 285 +/- 97 mg/d. Major contributors to plant sterol intake were bread (38%), vegetable fats (26%), and fruit and vegetables (21%). For men, there was no clear association between intake of any of the plant sterols and colon cancer risk when age, smoking, alcohol use, family history of colorectal cancer, education level, and cholecystectomy were controlled for. Adjustment for energy did not alter the result. For rectal cancer, adjustment for energy resulted in positive associations between risk and campesterol and stigmasterol intakes. For women, there was no clear association between intake of any of the plant sterols and colorectal cancer risk. CONCLUSION: A high dietary intake of plant sterols was not associated with a lower risk of colon and rectal cancers in the Netherlands Cohort Study on Diet and Cancer.

A prospective cohort study on antioxidant and folate intake and male lung cancer risk.

Many studies have reported inverse associations between vegetable and fruit consumption and lung cancer risk. The aim of the present study was to elucidate the role of several antioxidants and folate in this relationship. In the Netherlands Cohort Study on Diet and Cancer, 58,279 men of ages 55-69 years at baseline in 1986 returned a questionnaire including a 150-item food frequency questionnaire. After 6.3 years of follow-up, 939 male lung cancer cases were registered. A new Dutch carotenoid database was used to estimate intake of alpha-carotene, beta-carotene, lutein + zeaxanthin, beta-cryptoxanthin, and lycopene, completed with the antioxidant vitamins C and E and folate. Using case-cohort analysis, rate ratios were calculated, adjusted for age, smoking, educational level, and family history of lung cancer. Protective effects on lung cancer incidence were found for lutein + zeaxanthin, beta-cryptoxanthin, folate, and vitamin C. Other carotenoids (alpha-carotene, beta-carotene, and lycopene) and vitamin E did not show significant associations. After adjustment for vitamin C, only folate remained inversely associated, and after adjustment for folate, only beta-cryptoxanthin and vitamin C remained significantly associated. Inverse associations were strongest among current smokers and weaker for former smokers at baseline. Inverse associations with carotenes, lutein + zeaxanthin, and beta-cryptoxanthin seemed to be limited to small cell and squamous cell carcinomas. Only folate and vitamin C intake appeared to be inversely related to small cell and squamous cell carcinomas and adenocarcinomas. Folate, vitamin C, and beta-cryptoxanthin might be better protective agents against lung cancer in smokers than alpha-carotene, beta-carotene, lutein + zeaxanthin, and lycopene.

Association of energy and fat intake with prostate carcinoma risk: results from The Netherlands Cohort Study.

BACKGROUND: The roles of energy and fat intake as risk factors for prostate carcinoma are still questionable. Therefore, these factors were evaluated in the Netherlands Cohort Study described in this article. METHODS: The cohort study consisted of 58,279 men ages 55-69 years at baseline in 1986. After 6.3 years of follow-up, 642 incident prostate carcinoma cases were available for analysis. Intake of energy, fat, and separate fatty acids were measured by means of a self-administered questionnaire; fat intake was adjusted for energy by regression analysis. The case-cohort method was used to calculate rate ratios (RRs). Analyses were conducted for all prostate carcinoma cases together as well as for case subgroups (latent vs. nonlatent and localized vs. advanced). RESULTS: No associations were found in multivariate analyses between prostate carcinoma and intake of energy, total fat, total saturated fatty acids, or total trans unsaturated fatty acids (RR highest vs. lowest quintile: 0.99, 1.10, 1.19, and 0.99, respectively). Oleic acid intake showed a nonsignificant positive association (RR = 1.38, 95% CI: 0.88-2.19). Positive associations were also observed for intake of oleic acid in subgroup analyses. Linoleic (RR = 0.78, 95% CI: 0. 56-1.09) and linolenic (RR = 0.76, 95% CI: 0.66-1.04) acid intake were associated with nonsignificantly decreased risks; only for linolenic acid did these associations persist in subgroup analyses. No associations were found for intake of arachidonic acid, eicosapentaenoic acid, or docosahexaenoic acid. CONCLUSIONS: These data suggest that certain fatty acids might be involved in prostate carcinoma occurrence, although the possibility that these were chance findings cannot be ruled out.

The contribution of various foods to intake of vitamin A and carotenoids in The Netherlands.

This study presents data on dietary intake of specific carotenoids in the Netherlands, based on a recently developed food composition database for carotenoids. Regularly eaten vegetables, the main dietary source of carotenoids, were sampled comprehensively and analysed with modern analytic methods. The database was complemented with data from recent literature and information from food manufacturers. In addition, data on intake of vitamin A are presented, which are based on the most recent update of the Dutch Food Composition Table. Intake of vitamin A was calculated for adult participants of the second Dutch National Food Consumption Survey in 1992, whereas intake of carotenoids was calculated for participants of the Dutch Cohort Study on diet and cancer, aged 55 to 69 in 1986. Mean intake of vitamin A amounted to 1.1 and 0.9 mg RE/day for men and women, respectively; the contributions of meat, fats and oils, vegetables and dairy products to total intake were 35%, 24%, 16%, and 16%, respectively. Mean intake of alpha-carotene, beta-carotene and lutein plus zeaxanthin was 0.7, 3.0, and 2.5 mg/day respectively for both men and women, while mean intake of lycopene was 1.0 mg/day for men and 1.3 mg/day for women. The most important foods contributing to intake of beta-carotene and lutein plus zeaxanthin were carrots (beta-carotene only), spinach, endive and kale.

Intake of nitrate and nitrite and the risk of gastric cancer: a prospective cohort study.

The association between the intake of nitrate or nitrite and gastric cancer risk was investigated in a prospective cohort study started in 1986 in the Netherlands, of 120,852 men and women aged 55-69 years. At baseline, data on dietary intake, smoking habits and other covariates were collected by means of a self-administered questionnaire. For data analysis, a case-cohort approach was used, in which the person-years at risk were estimated from a randomly selected subcohort (1688 men and 1812 women). After 6.3 years of follow-up, 282 microscopically confirmed incident cases of stomach cancer were detected: 219 men and 63 women. We did not find a higher risk of gastric cancer among people with a higher nitrate intake from food [rate ratio (RR) highest/lowest quintile = 0.80, 95% CI 0.47-1.37, trend-P = 0.18], a higher nitrate intake from drinking water (RR highest/lowest quintile = 0.88, 95% CI 0.59-1.32, trend-P = 0.39) or a higher intake of nitrite (RR highest/lowest quintile = 1.44, 95% CI 0.95-2.18, trend-P = 0.24). Rate ratios for gastric cancer were also computed for each tertile of nitrate intake from foods within tertiles of vitamin C intake and intake of beta-carotene, but no consistent pattern was found. Therefore, our study does not support a positive association between the intake of nitrate or nitrite and gastric cancer risk.

Meat consumption and preparation, and genetic susceptibility in relation to colorectal adenomas.

Epidemiological evidence suggests that a high meat consumption and/or animal fat intake may increase the risk of colorectal cancer. The objective of this study is to examine the role of dietary factors, in particular meat preparation and consumption, in relation to colorectal adenomas, the pattern of DNA-mutations (e.g. K-ras and p53), and genetic susceptibility (NAT2, HNPCC). In a case control study on diet and colorectal adenomas (sporadic and HNPCC), acetylator status (NAT2) of cases and controls as well as K-ras and p53 mutations in adenomas will be assessed. Consumption and preparation of meat, the primary interest of this study, will be assessed by a food frequency questionnaire designed especially for this purpose.

Rationale, design and methods of a study on micronutrient status among adults.

OBJECTIVE: To describe the rationale, design and methods for a nutrition surveillance study with special reference to vitamin B6 and other micronutrients. RATIONALE AND DESIGN: Several studies in the Netherlands have shown that differences in dietary intake and in nutritional status indicators are relatively small among various socio-demographic groups, so that the relevance of this traditional risk group identification in terms of public health and nutrition policy is limited. Therefore, it was decided to use the diet itself as primary selection criterion for a study on the adequacy of the vitamin B6 supply. The first Dutch national food consumption survey in 1987/88 showed, among other things, that mean vitamin B6 intake (per gram of protein) was substantially below the adequate level for all age-gender groups studied. Since the potential impact on public health of this observation may be relatively large, intake of vitamin B6 was chosen as first selection criterion. A study design that creates the largest possible distinction in vitamin B6 intake would be most efficient to study the health risks as a consequence of a low vitamin B6 intake. Several arguments, such as the need to estimate the prevalence of an inadequate status of vitamin B6 and other micronutrients, led to the decision to use a random population sample as a reference group for comparison with the group with low habitual vitamin B6 intake. Other major arguments underlying the study design and the selection of the nutritional status indicators, as well as the framework of the Dutch Nutrition Surveillance System, are discussed. Finally, the design and methods of the study are described in detail (except food consumption methods).

Food consumption methods. Development, reproducibility and validation of a food frequency questionnaire for vitamin B6.

OBJECTIVE: The correct classification of adults with a habitual low vitamin B6 intake by means of a food frequency questionnaire (FFQ). Assessment of reproducibility of the food frequency questionnaire and of the relative validity as compared to 3 d diet records (DR). DESIGN: A self-administered food frequency questionnaire (FFQ) to measure habitual vitamin B6 intake was developed using the data base of the first Dutch National Food Consumption Survey 1987/88 (DNFCS). The frequency and quantity of consumption of 92 (combinations of) food products, contributing to about 95% of vitamin B6 intake, were asked for. Recent food consumption was measured with 3 d diet records. Reproducibility of the FFQ was assessed after 10 months (n = 330). SUBJECTS: Randomly selected men and women aged 20-79 y, stratified for 10 y age classes and sex. RESULTS: A total number of 2867 FFQs was adequately completed (response rate 46%). A low vitamin B6 group was selected from the lowest tertile of age-gender specific vitamin B6 intake (36 men and 36 women, aged 20-49 and 36 men and 36 women, aged 50-79) and a so-called reference group (n = 300) was selected at random. The ratio of vitamin B6 intake according to FFQ and DR (FFQ/DR) varied between 0.77 and 0.99 for the various age-gender-study groups; for vitamin B6/g protein the FFQ/DR ratio varied between 1.00 and 1.10. After correction for intraindividual variance Pearson correlation coefficients between vitamin B6 intake according to FFQ and DR varied between 0.27 and 0.95 for the various age-gender-study groups, for vitamin B6/g protein the corrected Pearson correlation coefficients varied between 0.27 and 0.65. Of the subjects selected in the low B6 groups, 61-81% fell in the lowest tertile of vitamin B6 intake according to diet records and 3-6% fell in the extreme opposite tertile. The percentage subjects selected in the same/opposite quartile of vitamin B6 intake according to FFQ and DR was 50/11 for men, and 45/18 for women. Pearson correlation coefficients for vitamin B6 intake according to the first and the second FFQ were 0.64 and 0.72 for men and women, respectively; for vitamin B6/g protein these values were 0.70 and 0.51 for men and women, respectively. The proportion of subjects classified in the same/extreme opposite tertile of vitamin B6 intake was 56/6 and 62/5 for men and women, respectively. CONCLUSIONS: It is concluded that the FFQ was adequate for the selection of subjects with a habitually low vitamin B6 intake.

The study population: general characteristics and potential confounding factors.

OBJECTIVE: To test the representativity of the study population and to identify potential selection bias. DESIGN: Non-response analysis and comparison with other representative samples from the Dutch population. Description of physical and clinical biochemical variables as well as health and lifestyle characteristics among low vitamin B6 groups and reference groups. RESULTS AND CONCLUSIONS: The non-response rate for the food frequency questionnaire was 54%; subsequently, non-response for the detail study was 42%. A greater proportion of respondents to the FFQ and of participants in the reference group of the study followed a special dietary regimen or a therapeutic diet or used dietary supplements compared with non-respondents, indicating that we may have selected a somewhat more health conscious reference group. There were no differences in vitamin B6 intake (absolute or per g protein) between participants and the total group of non-respondents for the detail study. Selection of a low B6 group did not result in important bias regarding physical, biochemical or general health and lifestyle characteristics. Exceptions were a difference in the proportion of dieters (younger women) and supplement users (older women) and a difference in creatinine clearance and supplement use between reference and low B6 groups. The differences found, however, were small. Nonetheless, these factors have to be taken into account when analysing and interpreting the results.

Dietary intake among adults with special reference to vitamin B6.

OBJECTIVE: To assess the adequacy of the dietary intake in general, and that of vitamin B6 intake especially. DESIGN AND SUBJECTS: Dietary intake based on 3 d diet-records was assessed among a random sample of the adult Dutch population (the reference group, n = 300) aged 20-79 y, stratified for age and gender and among a group with a low vitamin B6 intake, selected by means of a food frequency questionnaire. RESULTS: Among the reference group, absolute vitamin B6 intake on average amply met the RDA in all age-gender categories, whereas the adequate level of 20 microg vitamin B6 per gram protein, was on average met by men only. The prevalences of a vitamin B6 intake below the minimum requirement (absolute) of 1 mg/d was 1-11% and below the average minimum requirement of 15 microg/g protein was 5-12% for the various age-sex reference groups. Average intake of folate among women of childbearing age did not meet the recommendation of 400 microg/d for those who want to become pregnant. Average intake of iron and iodine was also below recommended levels among women aged 20-49 y. Both absolute vitamin B6 intake and the vitamin B6/protein ratio calculated with the diet records was lower among the low vitamin B6 groups than among the reference groups, indicating that the preselection of groups with low vitamin B6 intakes on the basis of a food frequency questionnaire was successful. Intake of energy and macro- and micronutrients, as well as a nutrient density of the diet were lower among low vitamin B6 groups than among reference groups. CONCLUSIONS: It is concluded that a low vitamin B6 intake is the result of both the quantity (energy) and quality (nutrient density) of the food consumed. The effects of this are not restricted to vitamin B6 and therefore, the low vitamin B6 groups have a combination of relatively low intakes.