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Review of NDNS of young people aged 4 to 18 years to examine intakes, status and other determinants of vitamin A, iron, zinc and copper

Project Code: N08014

30/06/2001

MRC Human Nutrition Research, Elsie Widdowson Laboratory, Cambridge
Thane, C ; Bates, C

Objectives

To further examine intakes and status of vitamin A, iron (Fe), zinc (Zn) and copper (Cu) in a representative sample of young people aged 4 to 18 years living in Great Britain, and to identify socio-demographic, lifestyle and dietary risk factors associated with poor intakes and status.

Methods

The National Diet and Nutrition Survey of young people aged 4 to 18 years (Gregory et al., 2000) was conducted in 1997. Statistical analyses of 7-d weighed dietary records were limited to 1520 participants who reported being well with eating unaffected during the recording period. Average daily dietary (and total) intakes of vitamin A (retinol equivalents), Fe, Zn and Cu were compared with the current UK recommendations (RNI and LRNI) in order to assess adequacy of intake. Blood samples were also provided, which enabled the biochemical status of the four micronutrients to be compared with standard cut-off points, below which status was considered to be poor. In addition to relating low intakes and poor status of vitamin A, Fe, Zn and Cu to several socio-demographic and lifestyle factors (e.g. age, sex, region, season, social class, household income, ethnicity, vegetarianism), associations were also examined between intakes and status.

Results

Overall dietary vitamin A intake in 4-to-18-year-old children was generally adequate (82%, 95% CI 80-84%, of RNI), although adequacy of intake decreased significantly with age in both sexes, before and after exclusion of likely under-reporters. Dietary vitamin A intakes were adequate in those aged 4-6 y, but less adequate in those aged 11-18 y. Overall, 11% had low dietary vitamin A intakes (<LRNI), with higher proportions with age in both sexes. Supplements contributed 6% to total vitamin A intake but made no significant difference to proportions with low intakes. Adequacy of intake improved with increasing variety of food in the diet and tended to improve on moving from north to south. In addition, smaller percentages of children, of different ages, had low intakes with higher consumption of milk and milk products. Plasma retinol concentration (index of vitamin A status) did not differ between boys and girls, although it increased with age. Although almost no children had poor vitamin A status (plasma retinol concentration <0.70 μmol/l), one-fifth showed marginal status (plasma retinol concentration 0.70-1.05 μmol/l) although proportions decreased with age. As for intake, socio-demographic and lifestyle factors were not consistently associated with vitamin A status.

Overall average dietary Fe intake was also generally adequate (91%, 95% CI 89-93%, of RNI), although significantly lower in girls than boys for each group (4-6, 7-10, 11-14 & 15- 18 y) and lowest in girls aged 11-18 y, even after excluding likely under-reporters. High proportions of adolescent girls had low intakes (40%, 11-14 y; 48%, 15-18 y), compared with only 2% of similarly-aged boys. Conversely, intakes were generally adequate in those aged 4- 6 y. Adequacy of dietary Fe intake or tendency to have low intakes were less consistently associated with factors than with age and sex. However, smaller percentages of 11-to-18-year olds had low dietary Fe intakes when they consumed higher amounts of breakfast cereals.

Of the Fe status indices, low haemoglobin (Hb) concentration was most prevalent in girls aged 4-6 y and 15-18 y (10 & 9% respectively). A significantly higher proportion of older girls had low Hb compared with their male counterparts. These girls also had significantly lower values for serum ferritin (SF) concentration and percentage transferrin saturation (%TS) (each P<0.001). Low Hb was significantly more prevalent among non-Caucasian girls aged 11-18 y than in their Caucasian counterparts (P<0.05). Non-Caucasian girls aged 11-14 y, but not 15-18 y, were also more likely to have low SF and %TS. Vegetarian girls aged 11-18 y were also more likely to have lower SF than their meat-eating counterparts. Consumption of main food groups, as well as that of tea and/or coffee, was not consistently related to poor Fe status, although girls aged 11-18 y who consumed fruit juice were less likely to have low Hb (P<0.05).

Overall average dietary Zn intake was also adequate (80%, 95% CI 79-81%, of RNI). However, intakes were least adequate in 11-to-14-year-olds, with more girls than boys in this age group, and in those aged 4-6 y, having low intakes (32 v. 12% & 22 v. 10%; each P<0.01). Low intakes were consistently more prevalent in children with a poor self-reported variety of foods in the diet and appetite rating. Associations with other socio-demographic and lifestyle factors were inconsistent. Higher consumption of milk, meat and eggs was generally associated with smaller percentages of children, of different ages, having low dietary Zn intakes. In addition, low intakes were less prevalent in girls aged 11-18 y who consumed higher amounts of breakfast cereals. Plasma Zn concentrations (index of Zn status) were overwhelmingly normal and not consistently related to any socio-demographic, lifestyle or dietary factor, after adjusting for age and gender.

In contrast to the other micronutrients, average dietary Cu intake was adequate (102%, 95% CI 101-104%, of RNI), but not consistently associated any socio-demographic or lifestyle factor. Higher consumption of fruit and nuts, and, to a lesser extent, cereals were associated with smaller percentages of children having intakes below the RNI. Erythrocyte superoxide dismutase (E-SOD) activity (putative index of Cu status) was generally higher in non- Caucasians than Caucasians. E-SOD activity was not consistently associated with sociodemographic or lifestyle factors, or with variable consumption of main food groups.

Overall, 28% of 4-to-18-year-old children had dietary intakes of all four micronutrients below the RNI. For each age group, percentages were higher in girls than in boys, even after additional exclusion of likely under-reporters. Examination of the relationships between total daily intakes of vitamin A, Fe, Zn and Cu and corresponding biochemical status indices showed plasma Zn and retinol concentrations to be directly associated with Zn and vitamin A intakes respectively (P<0.001), and SF with haem Fe but not total Fe intake, after adjusting for age, sex and acute-phase status (indicator of current or recent infection).

Conclusions

Dietary intakes and status of vitamin A, Fe, Zn and Cu were generally adequate in the majority of 4-to-18-year-old British young people. However, almost one-half of adolescent girls (aged 11-18 y) had low Fe intakes (<LRNI), coupled with a high proportion with low Fe status indices. Poor Fe status was significantly more prevalent in adolescent girls of non- Caucasian origin and, independently, in non-meat eaters, but was not consistently associated with other socio-demographic or lifestyle factors. Further studies focusing on larger numbers of non-Caucasian and/or vegetarian adolescent girls should investigate the reasons and functional consequences of apparently poor Fe status, in order to optimise Fe nutrition in this vulnerable population group.

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