Trace element availability from the human diet

Aluminum levels in convenience and fast foods: in vitro study of the absorbable fraction

We evaluated the levels of aluminum in a total of 120 samples of 35 different convenience and fast foods that are widely consumed in Spain. Aluminum was determined in the samples mineralized with HNO3, HClO4 and V2O5, using electrothermal atomic absorption spectrometry as the analytical technique. Reliability of the procedure was checked by statistically comparing the results with those obtained with a previous microwave oven mineralization stage and by analysis of several certified reference materials. No matrix effect was observed and aqueous standard solutions were used for calibration. The detection limit was 4.0 pg and the characteristic mass of 10.0 pg. Aluminum concentrations ranged from 0.85 to 38.10 microg/g, refereed to fresh weight of the edible portion. The presence of this metal was detected in all the samples we analyzed, but the most elevated levels were encountered in pork- and chicken- based foods (mean 8.45 and 13.94 microg/g, respectively). The more elevated Al concentrations were detected in foods with a greater content of spices and aromatic herbs, pasta, certain vegetables and additives, and foods packaged in Al vessels. The absorbable fraction of Al estimated with in vitro assays was between 0.85 and 2.15%. The growing popularity of these products in recent years requires additional data and a periodical control. In addition, the present findings are of potential use to efforts aimed at determining tolerable levels of Al intake from the diet.

Estimation of chromium bioavailability from the diet by an in vitro method

An in vitro method was used to study the dialysable fraction of chromium (Cr) from the diet which simulates human gastric and intestinal digestion. The percentage of dialysed Cr was used to assess the bioavailability. The duplicate diet approach was used to obtain ten different sets of samples each representative of the normal diet consumed in southern Spain. In each case triplicate analysis of Cr was carried out by electrothermal atomization-atomic absorption spectrometry in acid-mineralized samples. The Cr dietary intake ranged from 16 to 117 microg/day, and the dialysable Cr fraction ranged from 0.4% to 1.6%. The Cr absorption was higher for low levels of daily dietary intake of Cr (< 40 microg) than for levels of 40-80 microg; for high levels (> 80 microg) there was an increase in the dialysable fraction. The energy and nutrient intake of these diets was also evaluated.

Dietary zinc intake of a group of long-stay mentally handicapped women: some bioavailability considerations

Dietary factors affecting zinc bioavailability were evaluated according to their relative distribution in the individual daily meals making up the basic diet of 17 institutionalized, mentally handicapped adult women. Mean intake values of zinc, phytate, nonstarch polysaccharides (NSP), calcium, protein, and energy were calculated from a dietary survey of 7 consecutive days, which also served to obtain values for the two zinc bioavailability predictor formulas, phytate/Zn millimolar ratio and [Ca][phytate]/[Zn][energy] ratio. Mean daily zinc intake was 8.5 +/- 1.8 mg, with noon and evening meals accounting for the highest contribution to this value (45% and 35%, respectively), whereas breakfast meals' contribution was 16%. The mean protein intake was 55 +/- 13 g, with noon and evening meals being the major contributors to total daily intake (42% and 38%, respectively). Breakfast meals accounted for 77% of daily phytate intake, giving a respective phytate/Zn millimolar ratio of 20.4 +/- 7.6 and a [Ca][phytate]/[Zn][energy] ratio of 336 +/- 127 mmol/Mcal. Values for both ratios based on noon and evening meals were negligible in comparison. The mean daily NSP intake was 9.8 +/- 4.2 g, with 53% of total daily intake supplied from breakfast meals, whereas noon and evening meals accounted for 30% and 14%, respectively. The results, while suggesting that zinc bioavailability is unlikely to be adversely affected, indicated that dietary fiber intake levels are probably inadequate, particularly in view of the nonambulant condition and low physical activity prevalent in such individuals, who may, as a consequence, be susceptible to health disorders associated with impaired bowel function and constipation.

Chromium, copper, iron, manganese, selenium and zinc levels in dairy products: in vitro study of absorbable fractions

Because milk and dairy products are some of the most widespread foods in the human diet, they contribute a large fraction of mineral intake. We determined levels of chromium, copper, iron, manganese, selenium and zinc in 60 samples of 10 widely consumed dairy products. Graphite furnace atomic absorption spectrometry was used to analyze samples processed with a slurry procedure to minimize sample pretreatment. The accuracy and precision of our method were verified. In analyzed samples, mean values ranged from not detectable to 0.950 microgram/g for Cr, from 0.020 to 2.800 micrograms/g for Cu, from 0.750 to 20.0 micrograms/g for Fe, from 0.010 to 0.900 microgram/g for Mn, from not detectable to 0.140 microgram/g for Se, and from 0.250 to 4.500 micrograms/g for Zn. The highest levels of Cr, Cu, Fe, Mn and Zn were detected in children's milk. Increased concentrations of Cr, Cu, Fe and Mn were detected in products packaged in glazed ceramic containers. We also studied the absorbable fractions of these elements using in vitro techniques which simulate human gastric and intestinal digestion.

Relationship between dietary iron intake, corrected for diet reporting error, and serum ferritin in Danish women aged 35-65 years

Several studies have failed to demonstrate an association between Fe status and intake of dietary Fe. However, in the long term, it seems logical to presume that body Fe reserves are, fundamentally, dependent on the intake of bioavailable dietary Fe. This discrepancy may depend on several factors: (1) interindividual variation in biological availability of dietary Fe (differences in intestinal absorption), (2) interactions between dietary Fe and absorption enhancers and inhibitors, (3) variations in physiological (menstruation, childbirth) or unphysiological (blood donation) Fe losses, (4) the failure to adjust dietary intake data for Fe supplements, (5) uncertain food composition data (discrepancies between calculated and chemically measured Fe content in the diet), and (6) diet reporting error (reported intake of dietary Fe may deviate considerably from the true intake). The present study examined associations between dietary intake of Fe (assessed by diet history interview) and Fe status (assessed by ferritin status) among 167 Danish women aged 35-65 years, who were not blood donors, by taking into account diet reporting error (assessed from p-amino benzoic acid-validated urinary N), physiological blood losses (menstruation, childbirth, abortions), and Fe supplementation. Our results indicate that the lack of a general association between Fe status and dietary Fe intake may, in part, be caused by selective diet reporting error.

Dietary intake and micronutrient status of adolescents: effect of vitamin and trace element supplementation on indices of status and performance in tests of verbal and non-verbal intelligence

Relationships between micronutrient intake and status, and micronutrient status and performance in tests of intelligence were investigated in a group of adolescents (13-14 years old). Dietary intakes were assessed using a 7 d weighed dietary record method, coupled with the collection of duplicate diets. Vitamin and trace mineral intakes calculated using food composition tables were compared with those obtained by direct analysis of duplicate diets. Micronutrient status was judged via a range of biochemical indices measured in blood samples taken after a 12-15 h fast. Blood samples were taken both before and after a 16-week period of vitamin and trace mineral supplementation. Individual tests of verbal and nonverbal intelligence were also performed pre- and post-supplementation. The results of this study indicate that the use of food table data may lead to substantial over- or underestimation of the intake of several micronutrients. In general, the total calculated or analysed amount of a specific micronutrient consumed did not adequately predict status, as judged by a range of biochemical indices. There were significant changes in status measurements over the 16-week study period, irrespective of supplementation, and these changes were markedly influenced by the initial status of the subject. There was no effect of supplementation on performance in tests of intelligence. However, there was a significant association between plasma ascorbic acid and initial non-verbal intelligence quotient (IQ) in the boys, and between whole blood glutathione peroxidase (EC 1.11.1.9) activity and non-verbal and verbal IQ in both sexes. These findings are discussed in relation to other recent studies of the influence of micronutrient supplementation on the psychological performance of children.

Absorption and metabolism of oral zinc gluconate in humans in fasting state, during, and after a meal

The absorption and metabolism of zinc in a commercial form for oral use (Rubozinc, 15 mg zinc as gluconate) were investigated in 10 subjects by a kinetic study of the serum zinc profile after administration of 45 mg zinc under three conditions: after an overnight fast, during a standardized breakfast, and 2 h after this meal. The pharmacokinetic parameters were calculated by a method suitable to the characterization of rebound effects (recycling of the element in the gastrointestinal tract). In fasting state, the parameters were comparable to those previously collected in the same subjects with oral 45 mg zinc as sulfate, except with very significantly higher Cmax and area under curve (AUC), showing a better bioavailability for zinc in the commercial form. The light meal perturbed the absorption process as evidenced by the significant increases in the lag time (+180%), the tmax (+57%), and the lag times for the first two cycles during the meal. However, the parameters returned to normal values 2 h after the meal. The Cmax only moderately decreased during the meal (31%) as did the AUC (-28%). An important delay in the absorption of zinc in the commercial form when taken during a meal was therefore demonstrated, but the effect on zinc bioavailability was only moderate.

The effects of dietary ligands on zinc uptake at the porcine intestinal brush-border membrane

Intestinal brush-border-membrane vesicles were prepared from the porcine small bowel by magnesium precipitation and differential centrifugation, and were functionally intact. The influence of dietary ligands on 65Zn uptake was determined using a 65Zn concentration of 5 microM, an incubation time of 1 min and a reaction temperature of 27 degrees, with a rapid filtration technique. At this low Zn concentration the addition of an excess of folate, histidine or glucose had no effect on Zn uptake. Addition of picolinate, citrate and phytate to the incubation medium significantly reduced Zn uptake at all concentrations of ligand examined. Any inhibitory effects of folic acid in vivo may thus be due to a mucosal rather than lumen interaction. Those ligands inhibiting absorption may have done so through the formation of Zn-ligand complexes, which are either insoluble, or which reduce the binding of Zn to its mucosal receptor. This in vitro model of Zn absorption is useful for comparing the effects of potential Zn-binding ligands in the diet.

Zinc administration restores the impaired immune response observed in mice receiving excess copper by oral route

To study if treatment with zinc (Zn) was able to restore to normal levels the depressed immune response determined by oral administration of excess copper (Cu), groups of mice receiving 100 ppm or 200 ppm of Cu in the drinking water for 8 weeks, were injected ip once a week with Zn (1.14 mg/kg of body weight), throughout the experimental period. Administration of Zn restored to normal levels the proliferative response to mitogens and the antibody response to sheep red blood cells in the group of mice receiving 100 ppm of Cu in the drinking water. Similarly, the treatment with Zn significantly enhanced the depressed proliferative response to mitogens and the antibody response to sheep red blood cells of mice receiving 200 ppm of Cu in the drinking water. By contrast, increment in Zn supply was not able to modify the high production of auto-antibodies observed in animals receiving excess Cu. The results suggest that the impairment of the immune response observed in animals receiving excess Cu could be in part due to antagonistic interactions between this cation and Zn.

The effect of Gypsophila saponins in the diet on mineral status and plasma cholesterol concentration in the rat

1. Immature, male Wistar rats were allocated to one of six groups and caged individually. The first group was given a semi-synthetic diet containing 38 mg iron and 55 mg zinc/kg (basal group). The second and third groups were given a diet containing 10 mg Zn and 12 mg Fe/kg respectively (low-Zn and low-Fe groups). Groups four, five and six were given similar diets containing 20 g Gypsophila saponins/kg. After 21 d the Fe and Zn status of the rats was estimated and plasma cholesterol concentration determined. 2. Measurements of whole blood haemoglobin concentration, packed cell volume and liver Fe stores indicated that rats in the basal + saponin and low-Fe + saponin groups had a significantly reduced Fe status when compared with their controls. Rats in the low-Zn + saponin group also showed a trend toward reduced Fe stores. 3. Zn status, as judged by femur Zn concentration, was not adversely affected by the inclusion of Gypsophila saponins in the diet. 4. Consumption of the saponins resulted in a significant reduction in blood cholesterol concentration, with rats in both the low-Fe groups having significantly lower concentrations than their basal and low-Zn counterparts. 5. In view of suggestions that the consumption of saponins should be encouraged because of their ability to lower blood cholesterol, possible effects on Fe metabolism should be investigated further, particularly with respect to the levels and sources of saponin in the human diet.