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unit 3. assessing exposure to the environment chapter 11. Dietary intake and nutritional status Jiyoung Ahn, Christian C. Abnet, Amanda J. Cross, and Rashmi Sinha 1 t 3 1 i r n U te p Summary a Ch damage and tissue concentrations metabolism, as food is a complex Though dietary factors are implicated in chronic disease risk, are also discussed. mixture; thus, the absorption and assessment of dietary intake has metabolism of any single nutrient is limitations, including problems affected by the presence of another. Biomarkers of nutritional with recall of complex food intake exposure and nutritional For example, iron taken with vitamin patterns over a long period of status: An overview C is absorbed more efficiently than time. Diet and nutrient biomarkers by itself, but phytate can bind iron may provide objective measures and make it unavailable. Cooking Food frequency questionnaires of dietary intake and nutritional (FFQ), multiple food records, and 24- is another important factor that can status, as well as an integrated hour recalls are the most common change concentrations of nutrients measure of intake, absorption and methods to assess dietary intake or can form compounds not normally metabolism. Thus, the search for in nutritional epidemiologic studies present in foods. Obtaining this level an unbiased biomarker of dietary (1). The strengths and limitations of of detail using dietary assessment intake and nutritional status is an dietary assessment methods, as well instruments is generally not feasible. important aspect of nutritional as nutritional status biomarkers, are Furthermore, food composition epidemiology. This chapter reviews summarized in Table 11.1. Generally, tables are not available for all types of biomarkers related to the accuracy of the information nutrients, limiting the assessment dietary intake and nutritional status, collected depends on the ability to of many of them. Finally, there such as exposure biomarkers of diet integrate complex eating patterns are numerous nutrients, such as and nutritional status, intermediate concisely and the subject’s memory. selenium and vitamin D, that cannot endpoints, and susceptibility. Novel be measured adequately in the food Current dietary assessment biomarkers, such as biomarkers source. methods may not completely of physical fitness, oxidative DNA capture nutrient interactions and Unit 3 • Chapter 11. Dietary intake and nutritional status 189 Table 11.1. Strengths and limitations of intake assessment methods and nutritional status biomarkers Assess by Limitations Strengths Estimate of dietary intake Questionnaire - Prone to different types of bias - Easier to administer in FFQ - Dependent on memory population-based Food records - May not capture variability in studies 24-hour recall eating pattern - Long-term intake Diet history - does not account for absorption estimate Food composition table or bioavailability when foods are cooked or eaten as complex mixtures - Not comprehensive especially for diaries and recalls - Focused on specific nutrient - Many newer dietary compounds of interest not covered Nutritional status Biomarker of: - Collection - Objective measure - absolute intake - Storage - Error structure - correlated intake - Sensitivity different than - Specificity questionnaire-based - Laboratory variability information - Single measure may not be - Integrated measure representative of usual Diet and nutrient exposure biomarker (> 0.8) (2). The two well- the methods used to measure the biomarkers may be independent studied recovery biomarkers are recovered products are technically of the subject’s memory or urinary nitrogen and doubly-labelled challenging (4). the capacity to describe foods water. Urinary nitrogen is an example Urinary nitrogen and doubly- consumed. Biomarkers may provide of a recovery biomarker of protein labelled water are the only validated an integrated measure of intake, intake. A 24-hour urine collection is recovery biomarkers, but it must absorption and metabolism, which required, and subjects should take still be assumed that the testing may improve the accuracy of para-aminobenzoic acid (PABA) period is representative of the the estimation of the association tablets with the three main meals of subjects’ usual habits. The relative between the nutrient and disease, the day to validate the completeness complexity and high cost of these but limit the direct interpretation of of the collection (3). The amount of methods prevents these biomarkers the connection between intake and nitrogen recovered in a 24-hour from being applied to large cohort disease. However, since biomarkers urine collection can be converted studies. Thus, these biomarkers may be affected by biospecimen to protein intake using estimates of are often used as gold standards the percent of nitrogen excreted in for validating dietary questionnaires collection methods, storage conditions and laboratory variations, urine (~81%). Doubly-labelled water or developing correction factors to these factors must be carefully is another example of a recovery estimate measurement attenuation. considered in the study design. biomarker for energy expenditure, in which the average metabolic Biomarkers of correlated intake: Types of biomarkers rate of a human is measured over Concentration biomarkers a period of time. A dose of doubly- Exposure biomarkers labelled water, in which both the Biomarkers of correlated intake are hydrogen and the oxygen have based on concentrations in the body Biomarkers of absolute intake: been partly or completely replaced (i.e. in blood, urine, saliva, hair, nails Recovery biomarkers for tracking purposes (i.e. labelled) or tissue), reflecting current intake with an uncommon isotope of these status. Concentration biomarkers Biomarkers of absolute intake, elements, is administered to the are correlated with intake, such or recovery biomarkers, reflect individual. The loss of deuterium and that higher concentrations of these a balance between intake and O-18 is then measured over time by biomarkers result from higher output over a defined period, with regular sampling of heavy isotope intake. The measured concentration relatively high correlation between concentrations in the body water is a consideration of intake, uptake, the absolute dietary intake and the (by sampling saliva, urine or blood); and metabolism. Concentration 190 biomarkers can enhance dietary For example, in the EPIC study, useful estimate of true exposure. assessment, or in some cases be high serum concentrations of In addition, because menstruation the primary method of assessment α-tocopherol were associated with can lead to very different amounts of nutrient exposure. significantly lower risks of gastric of iron loss in women, the estimation cancer, but estimated dietary intake of intake may not be biologically Nutrients of vitamin E was not (11). relevant. There are several Biomarkers as the primary biomarkers for iron, including This type of biomarker may be method of assessment. This type of serum iron and serum ferritin; both used to enhance assessment and biomarker may be used to measure are subject to homeostatic control measurement of dietary components intake for dietary components that and influenced by inflammation, that are currently captured by dietary are not currently captured by dietary respectively. questionnaires. Vitamin C is thought questionnaires. The selenium Vitamin D is a third example of to protect against oxidative stress, but content of foods is highly dependent a nutrient that is not well measured by intake estimates. Liver, fatty assessment of intake is complicated on local soil concentrations, by the varying concentration in foods which range over several orders fish, ergocalciferol in mushrooms, and fortified milk are major dietary and the widespread and episodic of magnitude. Wheat is an use of vitamin C supplements. important selenium source in many sources of vitamin D; however, for Vitamin C is water soluble and populations, but the selenium content most people, the primary source of responsive to short-term changes of wheat can vary considerably; vitamin D is produced internally upon in intake; any single measure of therefore, wheat used to produce exposure of the skin to ultraviolet B vitamin C may not accurately rank flour, bread, pasta and other noodles (UVB). This production depends subjects’ typical exposure. Because from different geographic areas can on the melanin content of the skin the serum or plasma must be stored result in variable levels of selenium. and the amount of UVB exposure. using metaphosphoric acid or other Several well-established biomarkers Estimating sun exposure is complex, preservatives, few epidemiologic of selenium have been developed, because of differences in time spent 1 t 3 1 outside, amount of exposed skin, i studies use vitamin C biomarkers including serum and toenail n r (5). selenium, which provide a valid weather conditions and sunscreen U te use. Thus, circulating 25-hydroxy p estimate of selenium status. More a Vitamin E, especially α-tocopherol, has been the focus of than 20 studies have examined the vitamin D is considered a more Ch a great deal of scrutiny because of association between serum, plasma reliable indicator of vitamin D status, its potential benefits in reducing the or nail selenium and risk of prostate capturing both dietary intake and risk of cancers and cardiovascular cancer; a meta-analysis concluded endogenous production. 25-hydroxy diseases (6,7). The correlation that serum and plasma selenium vitamin D has been used in several of estimates of vitamin E intake were consistently lower in cases prospective epidemiologic studies from questionnaires with serum compared with controls (12). Serum to assess the role of vitamin D in concentrations is highly variable, and toenail selenium are common chronic disease prevention (13). since most dietary vitamin E is validated biomarkers of selenium obtained from vegetable oils used in status (9). Non-nutritional components cooking (8) and intake of such oils is Iron is another example of a not estimated well by food frequency concentration biomarker than may An important aspect of the better reflect exposure and provide questionnaires (FFQs)(9). For connection between diet and example, the correlation between a more informative assessment of chronic disease is the assessment the FFQ-estimated vitamin E intake the association between iron and of potentially hazardous dietary and serum α-tocopherol ranged from disease than intake estimates. components. The human diet may 0.47 in Dutch men to −0.08 in Italian Dietary iron is acquired from plant contain inadvertent contaminants men in the European Prospective and animal sources, as well as that are formed during food Investigation into Cancer and fortified grain in some countries. processing or cooking. Examples of Nutrition (EPIC) (10). Many studies There are large differences in contaminants formed during cooking have found an association between the bioavailability and absorption are heterocyclic amines (HCAs) and serum α-tocopherol levels and pathways of heme and non-heme polycyclic aromatic hydrocarbons chronic disease risk, but not with iron, suggesting that estimating (PAHs). Some developing countries dietary estimates of vitamin E. total iron intake will not give a lack an integrated food delivery Unit 3 • Chapter 11. Dietary intake and nutritional status 191 system that affords the chance to Figure 11.1. Potential heterocyclic amines (HCAs) biomarkers (71) regulate some undesirable food contaminants, such as mycotoxins or by-products of processing (e.g. silica from grinding grain or nitrosamines in salted fish). Food-cooking by-products. HCAs and PAHs, both known carcinogens in animal models, are formed in the highest concentrations in meat cooked well-done using high-temperature cooking methods, such as pan-frying or grilling. The assessment of exposure to these compounds can be estimated using questionnaires, but may benefit from the use of biomarkers With a large sample size, though, Mycotoxins. Fungal carcinogens of exposure. Moreover, there is urinary HCAs could still be used to are another example of a food no national database available for validate intake of HCAs as estimated contaminant whose study may food by cooking methods. A limited by questionnaires. benefit from the use of an exposure database, CHARRED, has been HCA-DNA adducts can be biomarker. Aflatoxin (AFB1) is created that is based on the type measured in lymphocytes and HCA produced by Aspergillus flavus and of meat, cooking method and the metabolites bound to circulating other related species, and plays an degree of doneness (http://charred. blood proteins, such as haemoglobin important role in the high rates of cancer.gov/). (Hb) or serum albumin (SA). The hepatocellular carcinoma seen in HCAs are formed from the measurement of these biomarkers southern China and parts of Africa reaction at high temperatures can provide an estimate of exposure (20). Assessment of AFB1 exposure between creatine or creatinine and the biologically effective dose, by questionnaire is very limited, (found in muscle meats), amino but they do not provide a measure of as the amount of infection in grain acids, and sugars (14–17). HCAs genetic damage directly in the target and the amount of toxin produced undergo extensive metabolism by tissue. DNA and protein adducts varies by locality, crop and storage phase I and II enzymes. Various of HCAs have been detected in conditions. In communities where biomarkers of HCAs have been experimental animal models by most food is grown and stored at investigated in urine, blood and hair, 32P-postlabelling. There is a paucity home, the ability to develop general with each having advantages and of data on HCA biomarkers in exposure metrics applicable to limitations. humans, however, as their detection questionnaire data is minimal. Urine is a useful biological fluid Therefore, the development of and quantification remains a for the measurement of exposure to challenging analytical problem: the biomarkers of exposure to these various classes of carcinogens, since concentration of HCAs in the diet is dietary contaminants is critical. large quantities may be obtained at the parts-per-billion level, and the Extensive work on the non-invasively. HCAs are rapidly quantity of HCA biomarkers formed metabolism of AFB1 led to the absorbed from the gastrointestinal in humans occurs at very low levels. identification of AFB1 adducts tract and eliminated in urine as Accumulation of HCAs in human with DNA and albumin, including multiple metabolites, with several hair, which may serve as a potential AFB1-DNA adducts in urine (21), percent of the dose present as the long-term biomarker to assess as correlates of the effective dose unmetabolized parent compound chronic exposure of HCAs, has of AFB1. Using urinary AFB1-DNA within 24 hours of consuming grilled been suggested but not yet validated adducts as a biomarker, a nested meats. HCAs in urine have short (18,19). Similar, but larger, issues case–control study demonstrated a half-lives, however, and may not be exist for PAHs, as these compounds 5-fold increased risk of liver cancer ideal measures of “usual” intake in are even more ubiquitous in the food in subjects who had measurable etiologic studies, especially if there source and environment. levels of these adducts (22). In the is substantial day-to-day variability. same study, dietary aflatoxin intake 192
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