ORIGINAL COMMUNICATION Selenium intakes in y-old Irish adults

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1 (2002) 56, ß 2002 Nature Publishing Group All rights reserved /02 $ ORIGINAL COMMUNICATION Selenium intakes in y-old Irish adults J Murphy 1, EM Hannon 1, M Kiely 1, A Flynn 1 and KD Cashman 1,2 * 1 Nutritional Sciences, Department of Food Science, Food Technology and Nutrition, University College, Cork, Ireland; and 2 Department of Medicine, University College, Cork, Ireland Objective: To measure the intake of selenium (Se) and the contribution of different food groups to Se intake in adults aged y in Ireland. The adequacy of Se intake in the population is also assessed. Design: Food consumption was estimated using a 7 day food diary for a representative sample (n ¼ 1379; men ¼ 662, women ¼ 717) of y-old Irish adults selected randomly from the electoral register. Se intake was estimated using updated tables of food composition. Results: Mean daily Se intakes ( s.d.) from all sources (ie food plus supplements), and from food sources alone, for the group of Irish adults aged y were 52 ( 23) and 50 ( 21) mg, respectively. Mean daily Se intake (from all sources) was significantly higher in men of all ages than women of all ages at levels of 60 and 44 mg, respectively (P < 0.001). Meat=meat products (30%), bread and rolls (24%), fish=fish products ( 11%), and milk and yoghurt (9%) were the main contributors to mean daily Se intake. Adequacy of Se intake in population groups was estimated as the percentage of the population with mean daily Se intakes that were lower than the average requirement of 40 mg. Using this measure, 45.6% of women and 17.1% of men had inadequate Se intakes. Conclusion: A significant prevalence of inadequate Se intakes was observed in Irish adults. Therefore, it would seem prudent that the Se status of the Irish population be investigated at this time. (2002) 56, DOI: =sj=ejcn= Keywords: selenium intake; Ireland; food consumption survey; 7 day food record Introduction The trace mineral selenium (Se) is an essential nutrient of fundamental importance to human biology. It is a key component of a number of functional selenoproteins required for human health. There is evidence that Se has an antioxidant role through the selenoenzyme glutathione peroxidase (EC ; GSHPx) but also through other more recently discovered selenoenzymes (Arthur & Beckett, 1994; Institute of Medicine, 2000). Three Se-dependent iodothyronine deiodinases regulate thyroid hormone metabolism (Berry & Larsen, 1992). Three thioredoxin reductases *Correspondence: KD Cashman, Nutritional Sciences, Department of Food Science, Food Technology and Nutrition, University College, Cork, Ireland. k.cashman@ucc.ie Guarantor: Professor KD Cashman. Contributors: JM contributed to design, execution, analysis and writing of the study. EMH, MK and AF contributed to design, execution and analysis of study. KDC contributed to design, analysis and writing of the study. Received 18 April 2001; revised 8 July 2001; accepted 30 August 2001 have been identified (Sun et al, 1999). Their functions include reduction of intramolecular disulfide bonds and regeneration of ascorbic acid from its oxidized metabolites (May et al, 1998). Selenoproteins have also been associated with maintenance of fertility and possibly some anti-cancer effects (Rayman, 2000). In all, about 35 selenoproteins have been identified, although many have roles that have not yet been fully elucidated (Rayman, 2000). The activity of the selenoproteins depends on an adequate Se supply from the diet. When this is not available, health can be affected, leading, in extreme cases to serious illnesses such as Keshan disease, an endemic cardiomyopathy encountered in parts of China (Institute of Medicine, 2000). Less overt Se deficiency may increase susceptibility to cardiovascular disease (Oster et al, 1986; Salonen & Huttunen, 1986; Kok et al, 1989), certain types of cancer (Willet et al, 1983; Kok et al, 1987), and possibly other disorders such as oxidative stress or inflammatory conditions, diabetes mellitus, hepatopathies, HIV infection, etc (for reviews, see Holben & Smith, 1999; Navarro-Alarcón & López-Martínez, 2000; Rayman, 2000). In the context of these health effects, low or diminishing Se status in some parts of the world,

2 notably in some European countries, is giving cause for concern. For example, about 20 y ago dietary Se intakes in the UK were 60 mg=day on average, whereas a 1994 survey commissioned by UK s Ministry for Agriculture, Fisheries and Foods found that Se intake had dropped to 34 mg=day (Barclay et al, 1995; Rayman, 1997), considerably less than the UK dietary reference values of 75 mg Se=day for men and 60 mgse=day for women (Department of Health, 1991). There are similar findings elsewhere in Europe (Rayman, 1997). The falling intakes are reflected in lowered Se concentrations in whole blood and serum. In seven European Union countries, average serum Se levels fell between 1983 and 1993 to 79 mg=l (Alfthan & Néve, 1996; Rayman, 1997), which is less than the value of 100 mg=l believed to be required for optimal activity of cytosolic GSHPx, an indicator of Se repletion (Thomson et al, 1993). The substantial fall in Se intake in the UK can be largely explained by the drop in imports of Se-rich, high protein wheat for bread-making flour from North America and Canada (Barclay et al, 1995). Similar trends have been noted in other European countries (Rayman, 1997). A similar decline in Se intake in Ireland is probable, due to the increased use of Irish wheat and low-selenium, lower-protein European wheat varieties (Murphy & Cashman, 2001). However, there are currently no data on Se intakes or status of the Irish population. Therefore, the present study used the most recent Irish food consumption data (The North=South Ireland Food Consumption Survey, Hannon et al, 2001; Harrington et al, 2001; Kiely et al, 2001) together with recent food composition data (including data on the Se content of Irish foods; Murphy & Cashman, 2001) to estimate the daily intake of Se and the contribution made by major food groups to the mean daily intake of Se in adults aged y in Ireland. The adequacy of Se intake in the different age=sex categories is also assessed. Methods Sample selection and dietary survey A detailed account of the methodology of the North=South Ireland Food Consumption Survey and sampling procedure is provided elsewhere (Harrington et al, 2001; Kiely et al, 2001). In brief, from 1997 to 1999, the survey collected food intake data in a representative sample of y-old adults (n ¼ 1379, 662 men, 717 women) in the Republic of Ireland and Northern Ireland. Pregnant and lactating women were excluded from the survey sample. A 7 day food diary was used to measure food intake. Duffield and Thomson (1999) investigated the usefulness of a food record in the assessment of Se intakes and reported similar mean Se intakes obtained from 3 day duplicate diets and 3 day weighed dietary records. There was a strong correlation between the results obtained from the two methods; however, for individuals in the group, some results obtained using the 3 day diary were significantly different from those obtained using the duplicate diet analysis. In the current study, food records were analysed and Se intake was estimated using a modified version of WISP # (Tinuviel Software, Warrington, UK). Ordinarily, WISP # uses McCance and Widdowson s Composition of Foods, 5th edn (Holland et al, 1995; and supplemental volumes Holland et al, 1988, 1989, 1991, 1992, 1993, 1996; Chan et al, 1994, 1995, 1996) food nutrient database, along with additional data (manufacturers data on generic Irish foods, nutritional supplements, and on new products that were commonly consumed) to determine nutrient intakes. Modifications were made to the food compositional database to take account of recently reported Se levels in Irish and UK foods, especially bread and cereals, meat and fish, and milk and dairy produce (Murphy & Cashman, 2001), which are the food groups that provide most of the total Se in the diets of northern Europeans (see review by Van Dokkum, 1995). For food groups other than these, Se values were updated using data recently reported for UK foods by Barclay et al (1995). An independent nutritionist checked that the dietary codes used were appropriate and that the coding system was consistently applied. Assessment of adequacy of Se intakes The problem of assessing the adequacy of nutrient intakes at a population level has been a long-standing one (Carriquiry, 1999). The reference nutrient intake (RNI; or population reference interval (PRI) or recommended dietary allowance (RDA)) for a nutrient is the intake value that is calculated to satisfy the requirements of 97.5% of the population. Assessing the adequacy of the micronutrient intake of a population subgroup by estimating the percentage of that group with intakes below the RNI overestimates the percentage with inadequate intakes. The average requirement (AR) is the daily intake value that is estimated to meet the requirement, as defined by a specified indicator of adequacy, in 50% of a life-stage or gender group (Institute of Medicine, 2000). The use of the AR as a cut-off point to determine the proportion of a population subgroup with inadequate micronutrient intakes has been described by Carriquiry (1999) and has been shown to be effective in obtaining a realistic estimate of inadequacy. The percentage of the population with a mean nutrient intake that is lower than the average requirement is the percentage of the population with inadequate intakes. The estimate is most accurate if intakes and requirements are independent, if the s.d. of intakes is at least twice as large as the s.d. of requirements, and if the requirements are symmetrically (but not necessarily normally) distributed. The estimate of intake should represent habitual intake and the estimate of adequacy can be impaired by the presence of under-reporting. Selenium intakes and requirements are independent. There is no information available on the distribution of the requirements for Se, but the Food and Nutrition Board of the Institute of Medicine (2000) assumed that the coefficient of variation (CV) of the estimated average requirement for Se is 403

3 404 10%, which implies that the requirement is symmetrically distributed. In the current population, the s.d. of mean Se intakes in men and women was 20, which was twice the assumed CV of the requirement. A 7 day food diary is considered a useful measure of habitual intake with respect to minerals (Bingham et al, 1994). As with any dietary survey where food intake is self-reported, there is evidence of misreporting, in particular under-reporting, in the present study (McGowan et al, 2001). In the current analysis, the proportion of the population with intakes below the AR for Se of 40 mg (Scientific Committee for Food, 1993; Food Safety Authority of Ireland, 1999) was estimated as the proportion with inadequate Se intakes. The proportion with Se intakes below the lowest threshold intake (LTI) of 20 mg (Scientific Committee for Food, 1993; Food Safety Authority of Ireland, 1999) was also determined. Statistical analysis Data manipulation and statistical analysis of the data was conducted using SPSS 1 for Windows TM version 9.0 (SPSS Inc., Chicago, USA). The Mann Whitney test (Coakes & Steed, 1999) was used to test differences in means of Se intakes and nutrient (Se) density between men and women in the three different age categories and men and women of all ages, if intakes were not normally distributed and also if the Levene test for equality of variance was not satisfied. In cases where both of these conditions were satisfied, an independent t-test (Coakes & Steed, 1999) was used. Differences between age groups within each sex were evaluated using a one-way analysis of variance (ANOVA; Coakes & Steed, 1999) for multiple comparisons. When statistically significant effects were encountered (P < 0.01), comparisons of means were made using either Tamhane, if the Levene test for equality of variance was not satisfied, or Scheffe post hoc (Coakes & Steed, 1999) multiple comparisons to ascertain which specific means differed. The contribution of major food groups to Se intake was calculated. Owing to the large sample size, even a small difference between group means was highly statistically significant. Greater emphasis was placed on descriptive rather than a formal statistical analysis of this data. Results The daily intake of Se (mg) from all sources (ie food and supplements) and from food sources alone, by sex and age, is shown in Table 1. Mean daily intake ( s.d.) of Se (from all sources) for the group of Irish adults aged y was 51.6 ( 23 mg). Mean daily intake of Se (from all sources) was significantly higher in men of all ages than women of all ages at levels of 59.7 and 44.2 mg, respectively (P < 0.001). Mean daily intake ( s.d.) of Se (from food sources only) for the group of Irish adults aged y was 50.0 ( 21 mg). Mean daily intake of Se (from food sources alone) was significantly higher in men of all ages than women of all ages at levels of 58.6 and 42.1 mg, respectively (P < 0.001). Most of the daily total Se intake (ie 97%) by this group came from food sources. In both men and women, mean daily Se intake (from all sources and food sources alone) was significantly lower in the y-old age category than in the y-old age category (P < 0.01). Table 1 Mean daily intake of Se (mg) from all sources (food and supplements) and from food sources only, by sex and age category Men Women y y y All ages y y y All ages (n ¼ 253) (n ¼ 236) (n ¼ 173) (n ¼ 662) (n ¼ 269) (n ¼ 286) (n ¼ 162) (n ¼ 717) All sources (mg) Mean 56 a 63 b 60 ab a 47 b 45 ab 44 s.d Median th th Food sources (mg) Mean 56 a 62 b 59 ab a 44 a 43 ab 42 s.d Median th th Differences in mean Se intakes (from all sources and from food sources alone) between men and women were significant (P < 0.001) for all age groupings. Significant differences (P < 0.01) between age groupings in each sex group separately are denoted by different superscript letters.

4 405 Figure 1 Percentage contribution of main food groups to mean daily intake of Se in men and women. Figure 1 presents the mean daily intakes of Se (% of total intake) from the main food groups in men and women and for the total population. Meat and meat products (30%), bread and rolls (24%), fish and fish products ( 11%), and milks and yoghurt (9%) were the main contributors to mean daily intake for men and women of all ages. The daily intake of Se (mg per 10 MJ total energy) from all sources (ie food and supplements) and from food sources alone, by sex and age is shown in Table 2. Nutrient density of Se intake (from all sources) was higher in women than for men of all ages and those in the y-old age category (P < 0.01; Table 2). There were no significant differences in nutrient density of Se intake (from food sources only) between men and women of all ages or in any of the three age categories. In both men and women separately, mean nutrient density of Se intake (from all sources and from food sources alone) was significantly lower in the y-old age category than in the other age groups (P < 0.001). Adequacy of Se intake in population groups was estimated as the percentage of the population with mean daily Se intakes that were lower than the AR of 40 mg (Scientific Committee for Food, 1993). Using this measure, 45.6% of women and 17.1% of men were found to have inadequate Se intakes. In addition, 2.6% of women and 0.8% of men had mean Se intakes that were below the LTI of 20 mg (Scientific Committee for Food, 1993), shown in Table 3. Discussion Suboptimal Se status may reduce the activity levels of selenoproteins including the intracellular antioxidant enzyme glutathione peroxidase, which may increase susceptibility to oxidative stress and promote the development of cardiovascular disease (Oster et al, 1986; Salonen & Huttunen, 1986; Kok et al, 1989), certain types of cancer (Willet et al, 1983; Kok et al, 1987), and possibly other disorders such as inflammatory conditions, diabetes mellitus, hepatopathies, HIV infection, etc (for reviews, see Holben & Smith, 1999; Navarro-Alarcón & López-Martínez, 2000; Rayman, 2000). In the context of these health effects, low or diminishing Se status in some parts of the world, notably in some European countries, is giving cause for concern. With regard to the situation in Ireland there are no data on Se intakes or status of the Irish population. Therefore, it is important to obtain an estimate of the adequacy of Se intake in the Irish population, especially in light of the fact that Ireland has one of the highest incidences of cardiovascular disease in Europe (World Health Organization, 1998), and that low Se status may contribute to this risk. A relatively high proportion of Irish women of all ages ( 46%) had inadequate Se intakes, as determined by the percentage of women with mean daily Se intakes that were lower than the AR. A smaller percentage (17%) of Irish men of all ages had inadequate Se intakes. As already mentioned,

5 406 Table 2 Mean daily intake of Se (mg per 10 MJ total energy) from all sources (food and supplements) and from food sources only, by sex and age category Men Women y y y All ages y y y All ages (n ¼ 253) (n ¼ 236) (n ¼ 173) (n ¼ 662) (n ¼ 269) (n ¼ 286) (n ¼ 162) (n ¼ 717) All sources (mg=10 MJ) Mean 49 a 59 b 60 b a 62 b 63 b 59 s.d Median th th Food sources (mg=10mj) Mean 49 a 57 b 59 b a 58 b 61 b 56 s.d Median th th Differences in mean Se intakes (from all sources) between men and women were significant (P < 0.01) for the y-old age category and all ages only. There were no significant differences in mean Se intakes (from food sources only) between men and women in age category or all ages. Significant differences (P < 0.001) between age groupings in each sex group separately are denoted by different superscript letters. Table 3 Percentage of population groups with mean daily Se intakes (mg=day from all sources) below the average requirement (AR) and lowest threshold intake (LTI) a Men Women y y y All ages y y y All ages (n ¼ 253) (n ¼ 236) (n ¼ 173) (n ¼ 662) (n ¼ 269) (n ¼ 286) (n ¼ 162) (n ¼ 717) Percentage below AR a Percentage below LTI a a AR and LTI for Se are 40 and 20 mg=day, respectively (Scientific Committee for Food, 1993). intake of Se at less than an individual s requirement may increase susceptibility to cardiovascular disease and other disorders. The LTI of a nutrient (the intake below which nearly all individuals will be unable to maintain metabolic integrity according to the criterion used for each nutrient; Scientific Committee for Food, 1993) is sometimes used as a cut-off value to assess the prevalence of nutrient inadequacy. However, while the LTI can be used to detect individuals with a very high probability of inadequate intakes, it is of limited value for assessing the prevalence of a nutrient inadequacy in populations. The UL (tolerable upper intake level) is defined as the maximum level of daily intake of a nutrient that is unlikely to pose risks of adverse effects to almost all individuals in a specified life-stage group (Institute of Medicine 2000; Scientific Committee for Food, 2000). The 95th percentile intake for Se for all groups ( 76 mg and 104 mg for men and women of all ages, respectively) was less than the UL for Se of 300 mg=day for Europe (Scientific Committee for Food, 2000) or 400 mg=day for the US and Canada (Institute of Medicine, 2000). Thus, there appears to be little risk of excessive intake of Se in this population. Although the mean daily intake of Se in men of all ages was significantly higher than in women of all ages, the mean daily intake of Se (from all sources) expressed per 10 MJ total energy (nutrient density of Se intakes) was higher in women of all ages than in men of all ages. The lower nutrient density for Se in y-old men and women compared to older adults (36 64-y-old) may reflect differences in consumption of particular food groups as well as possibly different patterns of supplement use. Further analysis of the database will be required to explain the age and sex differences in nutrient density of Se intakes. For men and women of all ages, meat and meat products (30%), bread and rolls (24%), fish and fish products (11%), and milks and yoghurt (9%) made significant contributions

6 to the mean daily intake of Se. Meat, poultry and fish, bread and cereals, and milk and dairy products are the food groups that provide most of the total Se in the diets of northern Europeans (see review by Van Dokkum, 1995). Over the past two decades Se intakes have fallen in the UK and elsewhere in Europe (Rayman 1997). For example, about 20 y ago dietary Se intakes in the UK were 60 mg=day on average, whereas a 1994 survey commissioned by UK s Ministry for Agriculture, Fisheries and Foods found that mean Se intake had dropped to 34 mg=day (Barclay et al, 1995; Rayman, 1997), considerably less than the reference nutrient intakes of 75 mg=day for men and 60 mg=day for women (Department of Health, 1991). Furthermore, there has been little change in UK estimates of Se intakes since For example, the current mean Se intake in the UK population is estimated to be 39 mg=day (Ysart et al, 2000). The substantial fall in Se intake over the last 20 y can be largely explained by the drop in imports of Se-rich, high protein wheat for breadmaking flour from North America and Canada (Barclay et al, 1995). Due to EU policies and changes in bread-making technology, there has been an increased use of low-se, low-protein UK and European wheat varieties (Rayman, 1997). While in 1985 bread was a major source (47%) of dietary Se in the UK, it now only supplies 20% of the dietary provision (Barclay et al, 1995), comparable to the 24% observed in the present study of the Irish population. Similar trends have been noted in other European countries (Rayman, 1997). While difficult to confirm, owing to the lack of previous data, a similar decline in Se intake in Ireland is probable, due to the increased use of Irish wheat and low selenium, lower protein European wheat varieties (Murphy & Cashman, 2001). Earlier surveys in Ireland have reported on mean daily intakes of some minerals (1990 Irish National Nutrition Survey (Lee & Cunningham, 1990), 1998 Survey of Diet, Health and Lifestyle in Northern Ireland (Barker et al, 1988)), but they did not, unfortunately, include Se. Regardless of whether a decline in Se intakes in Ireland has or has not occurred over the past two decades, current mean Se intakes in Ireland ( 52 mg=day) are about a third higher that those in the UK (39 mg=day; Ysart et al, 2000). On a European level, Irish daily Se intakes are placed about midway within the range of national Se intake levels, mg=day (Rayman, 2000; Scientific Committee for Food, 2000). Conclusion A significant prevalence of inadequate intakes of Se in Irish adults, as determined by the percentage of the group with mean daily Se intakes that were lower than the AR was observed. This was more prevalent in women (46%) than men (17%). 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