No abstract

A human intervention study was conducted to determine the effect of the consumption of carotenoid-rich vegetables on the immune system. Subjects, (twenty-three men), who were nonsmokers, were not restricted in their daily diet, except that they had to abstain from fruit and vegetables high in carotenoids throughout the whole study period. The study was divided into four periods, each lasting 2 weeks: weeks 1-2: low-carotenoid period; throughout weeks 3-8: daily consumption of 330 ml tomato juice (40 mg lycopene/d, 1⋅5 mg b-carotene/d) (weeks 3-4), 330 ml carrot juice (21⋅6 mg b-carotene/d, 15⋅7 mg a-carotene/d, 0⋅5 mg lutein/d) (weeks 5-6), 10 g dried spinach powder (11⋅3 mg lutein/d, 3⋅1 mg b-carotene/d) (weeks 7-8). Blood was collected weekly from subjects after a 12 h fast. T-lymphocyte functions were assessed by measuring proliferation and secretion of immunoreactive cytokines. The consumption of a lowcarotenoid diet resulted in a significantly reduced proliferation of peripheral blood mononuclear cells (PBMC) cultured with concanavalin A. After 2 weeks of tomato juice consumption and until the end of the intervention period lymphocyte proliferation was not significantly changed compared with proliferation at the end of the depletion period. Secretion of cytokines by T-helper-1-like lymphocytes (interleukin (IL)-2) and by T-helper-2-like lymphocytes (IL-4) was influenced by the dietary intervention. IL-2 and IL-4 secretion values were significantly suppressed after the low-carotenoid diet (P Ͻ0⋅001 and P Ͻ 0⋅05 respectively compared with baseline). Tomato juice consumption significantly enhanced IL-2 (P Ͻ 0⋅001) and IL-4 secretion (P Ͻ 0⋅05) compared with the end of depletion period. After carrot juice and spinach powder consumption the cytokine secretion capacity of PBMC was not significantly different from that at the end of the depletion period. In conclusion, the results of the present study indicate that a lowcarotenoid diet reduces T-lymphocyte functions and addition of tomato juice restores these functions. This modulation could not be explained by changes in the plasma carotenoid concentrations. The active constituents in tomato juice as well as the biological significance of this immunomodulation remain to be determined.

Large scale dietary assessment instruments are usually based on the food frequency technique and have therefore to be tailored to the involved populations with respect to mode of application and inquired food items. In multicenter studies with different populations, the direct comparability of dietary data is therefore a challenge because each local dietary assessment tool might have its specific measurement error. Thus, for risk analysis the direct use of dietary measurements across centers requires a common reference. For example, in the European prospective cohort study EPIC (European Prospective Investigation into Cancer and Nutrition) a 24-hour recall was chosen to serve as such a reference instrument which was based on a highly standardized computer-assisted interview (EPIC-SOFT). The 24-hour recall was applied to a representative subset of EPIC participants in all centers. The theoretical framework of combining multicenter dietary information was previously published in several papers and is called linear regression calibration. It is based on a linear regression of the food frequency questionnaire to the reference. The regression coefficients describe the absolute and proportional scaling bias of the questionnaire with the 24-hour recall taken as reference. This article describes the statistical basis of the calibration approach and presents first empirical results of its application to fruit, cereals and meat consumption in EPIC Germany represented by the two EPIC centers, Heidelberg and Potsdam. It was found that fruit could be measured well by the questionnaire in both centers (λcirc; = 0.98 (males) and λcirc; = 0.95 (females) in Heidelberg, and λcirc; = 0.86 (males) and λcirc; = 0.7 (females) in Potsdam), cereals less (λcirc; = 0.53 (males) and λcirc; = 0.4 (females) in Heidelberg, and λcirc; = 0.53 (males) and λcirc; = 0.44 (females) in Potsdam), and that the assessment of meat (λcirc; = 0.72 (males) and λcirc; = 0.65 (females) in Heidelberg, and λcirc; = 0.49 (males) and λcirc; = 0.42 (females) in Potsdam) has a center-specific bias. The application of the calibration approach to the questionnaire data will change the ranking of the two centers following the data of the reference instrument, and not well-measured food items will exhibit considerably less variation compared to the original data. We conclude that calibration is a necessary step in multicenter studies. However, this exercise shows that the current statistical framework is not yet sufficiently developed for a broad application.

In the baseline assessment of the two EPIC-Germany cohorts Heidelberg and Potsdam, dietary information was obtained with an identical food frequency questionnaire (FFQ). The optically readable FFQ was designed to assess the usual food and nutrient intake of individuals during the past 12 months. The present analysis was based on dietary data from 25,212 participants in Heidelberg (11,776 men, 13,436 women) and 26,270 participants in Potsdam (10,249 men, 16,021 women). This paper presents the first results of a descriptive dietary analysis on a food group level based on 16 food groups and selected subgroups. Each of these food groups and subgroups was divided into quintiles, and the age-adjusted mean intake for each quintile was calculated. The comparison of dietary habits between the two cohorts, as well as the comparison between men and women within each cohort showed clear differences both in the quintiles of most food groups as well as in the range between the lowest and highest quintile. Except for the food groups non-alcoholic and alcoholic beverages, sugar and confectionery, sauces, and soups, men and women participating in Potsdam reported higher intakes of all the other food groups. The amount of food intake was generally lower in women than in men, with the exception of vegetables, fruit, dairy products, and non-alcoholic beverages. Further differences between the study centers were observed regarding the use of cooking fat for meat and vegetable preparation. In conclusion, the dietary variation, e.g. the exposure variation, was increased by recruiting two geographically distinct cohorts, instead of only one, in Germany.