Zinc absorption and achlorhydria

Zinc absorption from 40 mumol of zinc in a water solution and from a test meal containing 22 mumol of zinc was studied in 8 patients with achlorhydria (no basal acid secretion and no secretion after pentagastrin stimulation). The test dose and the meal was labelled with 0.1 MBq of 65Zn and absorption was determined from measurement of the whole-body retention of the isotope. Zinc absorption was 68 +/- 16 per cent (mean +/- s.d.) from the water solution and 33 +/- 10 per cent from the test meal. The results did not differ from absorption in control subjects and indicate that achlorhydria per se does not affect zinc absorption.     

Zinc absorption in humans from meals based on rye, barley, oatmeal, triticale and whole wheat

The absorption of zinc from meals based on 60 g of rye, barley, oatmeal, triticale or whole wheat was studied by use of extrinsic labelling with 65Zn and measurement of the whole-body retention of the radionuclide. The cereals were prepared in the form of bread or porridge and were served with 200 mL of milk. The oatmeal flakes were also served without further preparation. The absorption of zinc was negatively correlated to the phytic acid content of the meal with the highest absorption, 26.8 +/- 7.4%, from the rye bread meal containing 100 mumol of phytic acid and the lowest, 8.4 +/- 1.0%, from oatmeal porridge with a phytic acid content of 600 mumol. It is concluded that food preparation that decreases the phytic acid content improves zinc absorption.     

Retention of zinc and calcium from the human colon

Colonic retention of zinc and calcium was studied after installation during colonoscopy of 30 mumol of zinc and 6.4 mmol of calcium labeled with 65Zn and 47Ca, and measurement of the whole-body retention of the radionuclides. After cecal installation in nine patients, retention (day 13) of zinc was 3.5 +/- 2.1% (mean +/- SD) and of calcium 3.5 +/- 2.7%. The calculated mean absorption was 4.1% for zinc and 14.1% for calcium. Application at the hepatic flexure in four patients resulted in a mean retention (day 13) of 1.2% for zinc and 0.6% for calcium. Under prevailing conditions, colonic absorption of zinc is relatively small, compared to the uptake after oral administration. Colonic absorption of calcium could, however, account for a substantial part of the total calcium uptake.     

Effect of ascorbic acid on the absorption of zinc and calcium in man

The effect of ascorbic acid on the absorption of zinc and calcium, was studied in healthy subjects by a radionuclide technique with 65Zn and 47Ca and whole body retention measurements. Addition of 100 mg of ascorbic acid to a water solution of 40 or 200 mumol zinc and 1 g of ascorbic acid to a high phytate meal with wholemeal bread had no effect on zinc absorption. Neither did 1 g of ascorbic acid added to 6.4 mmol of calcium influence the retention and calculated absorption of calcium. The results suggest that ascorbic acid does not affect the absorption of normal dietary levels of zinc and calcium.     

Phytic acid added to white-wheat bread inhibits fractional apparent magnesium absorption in humans

BACKGROUND: Phytic acid has been reported to impair the absorption of minerals and trace elements such as calcium, zinc, and iron in humans. However, limited information is available on the effect of phytic acid on magnesium absorption. OBJECTIVE: The objective was to evaluate the effect of phytic acid on fractional apparent magnesium absorption in humans. DESIGN: Two stable-isotope studies were performed with 8-9 healthy adults per study. Test meals were based on 200 g phytic acid-free wheat bread; test meals with and without added phytic acid were served on days 1 and 3 according to a crossover design. Phytic acid was added in amounts similar to those naturally present in whole-meal (1.49 mmol) and in brown bread (0.75 mmol). Each test meal was labeled with 0.7 mmol (25)Mg or 1.1 mmol (26)Mg. The total magnesium content was standardized to 3.6 mmol in all test meals. Apparent magnesium absorption was based on fecal monitoring. RESULTS: The addition of phytic acid lowered fractional apparent magnesium absorption from 32.5 +/- 6.9% (no added phytic acid) to 13.0 +/- 6.9% (1.49 mmol added phytic acid; P < 0.0005) and from 32.2 +/- 12.0% (no added phytic acid) to 24.0 +/- 12.9% (0.75 mmol added phytic acid; P < 0.01). The inhibiting effect of phytic acid was dose dependent (P < 0.005). CONCLUSION: The results show that fractional magnesium absorption from white-wheat bread is significantly impaired by the addition of phytic acid, in a dose-dependent manner, at amounts similar to those naturally present in whole-meal and brown bread.     

Influence of dietary calcium, phosphorus, zinc and sodium phytate level on cataract incidence, growth and histopathology in juvenile chinook salmon (Oncorhynchus tshawytscha)

To determine the influence of wide variations in dietary levels of calcium, zinc and phytic acid (as sodium phytate) on growth and cataract incidence, juvenile chinook salmon held at 10-11 degrees C were fed daily to satiation for 105 d one of nine purified diets containing one of three levels (grams/kilogram) of calcium (averaged 4.8, 17.7, 50.2), zinc (averaged 0.05, 0.15, 0.39) and phytic acid (1.62, 6.46, 25.8). Diets were formulated to have a calcium-phosphorus ratio of close to unity when considering phosphorus sources other than sodium phytate. High dietary phytic acid concentration (25.8 g/kg) depressed chinook salmon growth, food and protein conversion [protein efficiency ratio (PER)] and thyroid function, increased mortality, promoted cataract formation (zinc at 0.05 g/kg) and induced anomalies in pyloric cecal structure. Calcium at 51 g/kg (or phosphorus) exacerbated the effects of high dietary phytate and low dietary zinc on cataract incidence. Moreover, high dietary levels of calcium (48-51 g/kg) coupled with phosphorus significantly impaired the growth and appetite of low phytic acid (1.62 g/kg) groups and led to nephrocalcinosis in low and high phytic acid groups. Plasma zinc levels were directly related to dietary zinc concentration and inversely related to dietary phytic acid level. Calcium (51 g/kg) and/or phosphorus reduced zinc bioavailability when the diet concurrently contained 0.05 g zinc and 25.8 g of phytic acid per kilogram. It is concluded that zinc is essential for normal eye development in juvenile chinook salmon. Further, zinc deficiency could not be induced in chinook salmon fed diets with high ratios of calcium (or phosphorus) to zinc alone. This required the simultaneous presence of a strong mineral (zinc)-binding agent.     

Effect of reduced phytate wheat bran on zinc absorption

The rise in plasma zinc after the ingestion of 765 mumol (50 mg) elemental zinc was measured over 6 h in three groups of healthy subjects who, in a second test, also consumed a standard wheat bran, a reduced phytate, high fibre processed bran or rice-based, low phytate, low fibre breakfast cereal (Rice Krispies). Standard bran, reduced phytate bran and Rice Krispies all significantly decreased the area under the plasma zinc time curve (AUC) compared to the zinc alone test. The AUC obtained with standard bran was significantly lower than that after reduced phytate bran (mean +/- s.e.: -5.9 +/- 2.7 vs 18.5 +/- 4.2 mumol.h/l, P less than 0.001). The percentage reductions in AUC produced by the test meals were: standard bran 106.4 +/- 2.4, reduced phytate bran 75.9 +/- 4.8, Rice Krispies 46.3 +/- 10.4 per cent, P less than 0.01). Histidine, taken with standard bran in a small subgroup of subjects, tended to improve zinc absorption but the difference was not statistically significant.     

Dephytinization of a complementary food based on wheat and soy increases zinc, but not copper, apparent absorption in adults

Complementary foods based on cereals may contain high amounts of phytic acid, which binds strongly to minerals and trace elements. The objective of the study was to evaluate the effect of dephytinization of a cereal-based complementary food on zinc and copper apparent absorption in adults. A dephytinized complementary food (<0.03 mg phytic acid/g) and one containing the native phytic acid concentration (4 mg/g) were labeled extrinsically with stable isotopes ((70)Zn and (65)Cu). Apparent zinc and copper absorption was based on fecal excretion of nonabsorbed labels in 9 adults, using a crossover design. Stable isotopes were quantified by thermal ionization MS. Apparent fractional zinc absorption was significantly higher (P = 0.005; Student's paired t test) from the dephytinized complementary food (34.6 +/- 8.0%; mean +/- SD) than from the complementary food with native phytic acid concentration (22.8 +/- 8.8%). Apparent fractional copper absorption did not differ (P = 0.167; 19.7 +/- 5.1% dephytinized vs. 23.7 +/- 8.1% native phytic acid). These results clearly demonstrate the beneficial effect of dephytinization of a complementary food on fractional absorption of zinc but not of copper in adults. The long-term nutritional benefits of dephytinization of complementary foods should be evaluated in young children.     

Influence of vegetable protein sources on trace element and mineral bioavailability

Vegetable protein sources are often mixed with cereals for complementary feeding. Both contain high levels of phytic acid, which can inhibit trace element and mineral absorption. In adults, phytic acid has been reported to inhibit the absorption of iron, zinc, calcium and manganese but not copper. There are far fewer studies in infants. Phytic acid is a strong inhibitor of iron absorption in both infants and adults, but its influence on zinc absorption in infants seems to be modest and perhaps most important in children recovering from infection. The influence of phytic acid on calcium and magnesium absorption would seem of minor importance. Because iron and zinc deficiencies are widespread in infants and young children in developing countries, the bioavailability of iron and zinc from complementary food is a major concern. Iron absorption may be as low as 2-3% from porridge based on whole-grain cereals and legumes (phytic acid approximately 1 g/100 g) even in iron-deficient subjects. Decreasing phytic acid by 90% ( approximately 100 mg/100 g dried product) would be expected to increase absorption about twofold and complete degradation perhaps fivefold or more. More modest reductions in phytic acid content may not usefully improve iron absorption. Complete enzymatic degradation of phytic acid is recommended. If this is not possible, it is recommended that the molar ratio of phytic acid to iron in an iron-fortified food be <1, preferably <0.5. At these low levels of phytic acid (20-30 mg/100 g dried product), zinc absorption should be satisfactory.     

Influence of usual zinc intake and zinc in a meal on 65Zn retention and turnover in the rat

The influences of zinc in a meal and usual zinc intake on zinc retention and turnover were investigated in 7-wk-old male rats fed diets containing 12-151 mg Zn/kg for 3 wk before and after consuming a 65Zn-labeled meal containing ZnCl2. Retention corrected to zero time and turnover rate were determined by whole-body counting. Percent zinc retention was inversely proportional to the natural logarithm of the meal zinc, between 0.09 and 26 mumol. In comparison to lower doses, higher doses resulted in lower percent retention but greater amounts of zinc retained. Although the latter relationship was slightly curvilinear, there was no indication of a limited capacity for zinc retention with high doses. However, doses above 4 mumol resulted in higher turnover rates in rats accustomed to lower zinc intakes. Percent retention and the reciprocal of the turnover rate were proportional to the reciprocal of the dietary zinc concentration. The greatest differences in retention and turnover occurred between 12 and 26 mg Zn/kg diet. The zinc dose in a meal and the usual dietary zinc separately influenced percent zinc retention. These factors also interacted, such that greater dose effects were observed at lower zinc intakes and greater dietary zinc effects were observed at lower doses.     

Dietary calcium, phytate, and zinc intakes and the calcium, phytate, and zinc molar ratios of the diets of a selected group of East African children

Dietary zinc, calcium, and phytate intakes of 66 rural Malawian children aged 4-6 y were determined during three seasons on the basis of weighed food records and analyzed food composition data. Height and weight measurements were also recorded and hair samples were collected for zinc analysis. Seasonal daily zinc, calcium, and phytate intakes of females ranged from 6.2 +/- 1.7 to 6.8 +/- 2.1 mg (mean +/- SD), from 335 +/- 170 to 401 +/- 257 mg, and from 1621 +/- 660 to 1729 +/- 592 mg, respectively and, for males, 7.0 +/- 1.7 to 8.0 +/- 2.3 mg, 342 +/- 164 to 473 +/- 310 mg, and 1857 +/- 530 to 2161 +/- 684 mg, respectively. Cereals provided greater than 42% of dietary zinc. Seasonal mean molar ratios of phytate to Zn and Ca x phytate to Zn [per 1000 kcal (4.2 MJ)] and the median Ca to phytate molar ratio ranged from 24 to 27, 151 to 188 mmol/1000 kcal (4.2 MJ), and 3.1 to 3.4, respectively. Over 78% of the children consumed diets with phytate-to-Zn and Ca x phytate.Zn-1 . 1000 kcal-1 molar ratios above values suggested to jeopardize zinc status. Correlations between hair zinc, phytate-to-Zn, and Ca x phytate.Zn-1 . 1000 kcal-1 molar ratios suggest that high phytic acid intakes may compromise zinc status in these children.     

Intestinal absorption and losses of copper measured using 65Cu in zinc-deprived men

The absorption and intestinal losses of endogenous Cu in response to a low Zn diet were studied in five young male subjects using stable 65Cu as an oral tracer. The subjects received a semi-purified formula diet providing 85 mumol (5.6 mg) Zn/d during 15-day baseline and repletion phases and 12 mumol (0.8 mg) Zn/d during an intervening period of 25 days. Thirty-eight mumol (2.4 mg) Cu/d was provided throughout the study. In four of the subjects, the mean +/- SEM luminal disappearance of 65Cu was 37 +/- 4 per cent during the baseline phase and was unaffected by Zn deprivation (32 +/- 7 per cent) or repletion (30 +/- 7 per cent) as were intestinal losses of endogenous Cu [7 +/- 4, 8 +/- 3, 8 +/- 3 mumol/d (0.4 +/- 0.1, 0.5 +/- 0.1, 0.5 +/- 0.1 mg/d) during baseline, Zn deprivation and Zn repletion phases, respectively]. In a fifth subject, who had some evidence of a resolving alcohol-induced hepatitis, the luminal disappearance of 65Cu was 31, 44 and 42 per cent and the intestinal losses of endogenous Cu 11, 2 and 6 mumol/d (0.7, 0.1 and 0.4 mg/d) during the baseline, Zn deprivation and Zn repletion phases respectively. Plasma Cu concentrations, however, fell throughout the study in all the subjects, despite consistently positive Cu balances. There may be subtle effects of a low dietary intake of Zn on Cu metabolism which were not revealed by the methods used in this study.     

Zinc absorption from a low-phytic acid maize

BACKGROUND: Phytic acid reduction in cereal grains has been accomplished with plant genetic techniques. These low-phytic acid grains provide a strategy for improving the mineral (eg, zinc) status in populations that are dependent on grains, including maize (Zea mays L.), as major dietary staples. OBJECTIVE: The objective was to compare the fractional absorption of zinc from polenta prepared from maize low in phytic acid with that prepared from a wild-type isohybrid maize (control) after short-term consumption by adults whose habitual diet is low in phytic acid. DESIGN: Healthy adults served as their own control subjects in a crossover design. All meals on 1 d consisted of polenta prepared from a low-phytic acid maize homozygous for the recessive low phytic acid 1-1 (lpa1-1). On the preceding or following day, all meals consisted of polenta prepared from a sibling isohybrid homozygous wild-type maize with a "normal" phytic acid content. The low-phytic acid maize contained approximately 60% less phytic acid than did the wild-type maize. All test meals were extrinsically labeled with zinc stable-isotope tracers. The fractional absorption of zinc was determined on the basis of fecal enrichment. RESULTS: The molar ratios of phytic acid to zinc in the polenta prepared from lpa1-1 maize and the wild-type maize were 17:1 and 36:1, respectively. The corresponding fractional absorptions of zinc were 0.30 +/- 0.13 and 0.17 +/- 0.11, respectively (P < 0.005). CONCLUSION: Substitution of a low-phytic acid grain in a maize-based diet is associated with a substantial increase in zinc absorption.     

Inorganic zinc and the intestinal absorption of ferrous iron

The effect of inorganic zinc on the absorption of inorganic iron (Fe+2) from a solution was assessed in two studies on healthy male volunteers. In the first study coadministration of 344 mumol of zinc had no effect (p less than 0.5) on the absorption of 842 mumol of radiolabeled Fe, assessed by the area under plasma Fe increment time curve during the 3 (AUC3) and 6 (AUC6) h postadministration (Fe alone AUC3 = 176.4 +/- 39.3; AUC6 = 387 +/- 101; Fe + Zn AUC3 = 180 +/- 33.1; AUC6 = 396 +/- 73.1 mumol.h-1.L-1), total plasma content of 59Fe, and whole-body retention of 59Fe. In the second study only the plasma appearance of Fe was monitored. After administration of 421 mumol of Fe alone, the AUC3 and AUC6 were 167 +/- 21.2 and 429.4 +/- 57 mumol.h-1.L-1, respectively; these were reduced to 56.4 +/- 17 and 119 +/- 34 (p less than 0.002) by 421 mumol Zn and further reduced by 1048 mumol Zn to 33 +/- 15 and 43.4 +/- 23.8 mumol.h-1.L-1 (p less than 0.001), respectively. It is concluded that Zn can impair the intestinal absorption of Fe.     

Zinc and acute tropical ulcers in Gambian children and adolescents

28 Gambian children and adolescents with acute tropical leg ulcers entered a double blind trial of oral zinc supplements as an adjunct to standard treatment. Analysis of the area healing of the ulcers resulted in a mathematical expression which showed that for each subject re-epithelialization reduced the ulcer radius at a constant healing rate (k). k was derived from the equation At = pi X (r - k X t)2, where At = residual ulcer area at time "t", r = initial ulcer radius and t = time from start of treatment. In the zinc treated group k was 0.55 +/- 0.39 mm/day, and 0.51 +/- 0.25 mm/day in the placebo group. The initial low plasma zinc of 6.5 +/- 1.9 mumol/L in the ulcerated subjects was not significantly lower than that of 7.5 +/- 3.6 mumol/L in the nonulcerated controls. Oral zinc supplements significantly elevated plasma zinc concentrations by 5.8 +/- 4.8 mumol/L compared to the placebo group's change of 0.4 +/- 2.0 mumol/L (p less than 0.001). Plasma alkaline phosphatase activities and fatty acid profiles did not change with zinc supplementation. Thus unequivocal clinical and biochemical evidence of zinc deficiency in these ulcerated subjects was not established, despite changes in plasma zinc. This study does not indicate any role for zinc supplementation in the management of acute tropical ulcers.     

Does the oral zinc tolerance test measure zinc absorption?

Increases in plasma zinc concentration were compared with radiozinc absorption after oral test doses. Ten healthy, fasting subjects were each given 385 mumol zinc chloride (25 mg Zn) labelled with 0.5 muCi 65ZnCl2 and a non-absorbed marker, 51CrCl3, dissolved in 100 ml of water; another 10 persons were given 354 mumol zinc chloride and 125 g of minced turkey containing 31 mumol zinc also labelled with 65Zn and 51Cr. Measurements were made of plasma zinc concentration at hourly intervals for 5 hours, radiozinc absorption by stool counting of unabsorbed radioactivity 12-36 hours later, and radiozinc retention by whole body counting at 7 days. The mean percentage of radiozinc absorbed and retained in the body from the two test meals was found to be identical (42%). In contrast the increased area under the plasma zinc curve up to 5 hours after the turkey meal, 28 +/- 9 mumol/L (mean +/- SD) was significantly less than that for zinc chloride alone, 47 +/- 15 mumol/L, p less than 0.005. Despite this difference, a good correlation was found between the area under the plasma zinc curve and 65Zn absorption in individual subjects after each meal. The discrepancy between the results of zinc absorption derived from the plasma zinc curve and 65Zn absorption for the liquid and solid test meals was most likely explained by binding of zinc to food and delayed gastric emptying of the solid meal. With a test meal of turkey meat at least this dampened the plasma appearance of zinc but did not affect its overall absorption.     

Body burdens of lead in hypertensive nephropathy

Chronic lead exposure resulting in blood lead concentrations that exceed 1.93 mumol/l (40 micrograms/dl) or chelatable urinary lead excretion greater than 3.14 mumol (650 micrograms) per 72 h has been associated with renal disease. A previous study had found greater chelatable urine lead excretion in subjects with hypertension and renal failure than in controls with renal failure due to other causes, although mean blood lead concentrations averaged 0.92 mumol/l (19 micrograms/dl). To determine if chelatable urinary lead, blood lead, or the hematologic effect of lead (zinc protoporphyrin) were greater in hypertensive nephropathy (when hypertension precedes elevation of serum creatinine) than in other forms of mild renal failure, we compared 40 study subjects with hypertensive nephropathy to 24 controls having a similar degree of renal dysfunction due to causes other than hypertension. Lead burdens were similar in both the study and control groups as assessed by 72-h chelatable urinary lead excretion after intramuscular injection of calcium disodium EDTA (0.74 +/- 0.63 vs. 0.61 +/- 0.40 mumol per 72 h, respectively), and by blood lead (0.35 +/- 0.23 vs. 0.35 +/- 0.20 mumol/l). We conclude that subjects from a general population with hypertensive nephropathy do not have greater body burdens of lead than renal failure controls.     

Effect of protein level and protein source on zinc absorption in humans

The effect of increasing levels of various protein sources on zinc absorption from a legume-based meal was studied in humans with the use of a radionuclide technique. The meals were extrinsically labelled with 65Zn and absorption was determined from measurements of the whole-body retention of the isotope. The mean fractional zinc absorption for the 13 meals was 24.7 +/- 6.9% and was only influenced by the protein content of the meal to a limited extent (r = 0.45). However, the amount of zinc absorbed from the meals was strongly correlated with both the protein (r = 0.85) and zinc content (r = 0.86): 5.9 +/- 1.7 mumol of zinc was absorbed from the basal bean meal which had the lowest protein content; the addition of low zinc chicken doubled the protein content and increased zinc absorption to 10.3 +/- 2.0 mumol; the addition of zinc-rich beef also doubled the protein content, however, zinc absorption was increased to 15.9 +/- 4.7 mumol. It is concluded that the zinc content of the main protein source of the diet determines the amount of zinc absorbed to a large extent. However, relatively small amounts of animal protein can significantly improve the value of a legume-based meal as a source of zinc.     

Preventive effect of selenium against the testicular injury by cadmium]

An experimental study was performed on orchiopathy (testis disorder) by using cadmium (Cd) and on the prevention of orchiopathy by the administration of selenium (Se). By a single administration of Cd 1.4 mg/kg (12.4 mumol/kg) or a second administration of Cd 1.4 mg/kg 24 hr after the administration of Cd 1.0 mg/kg (8.9 mumol/kg), the testis of a mouse showed ex-tensive necrosis, and an extreme decrease of glutathione (GSH) concentration accompanied by an increase of thiobarbituric acid reactive substances (TBARS). When Se 1.4 mg/kg (17.7 mumol/kg) was given at the same time as Cd 1.0 mg/kg, the disorder was completely prevented and their serum Cd and Se concentrations were 1165 +/- 268 ng/ml and 534 +/- 128 ng/ml, respectively. However, when Se was given, separately from the Cd administration, either 24 hr or 72 hr before Cd administration, no effect to prevent testis disorder was found. On the other hand, when Se 1.4 mg/kg and Cd 1.0 mg/kg were given simultaneously and then Cd 1.4 mg/kg was administered 24 hr and 72 hr after the simultaneous injection, respectively, there was no sign of disorder caused by the second administration of Cd. When Cd was given after administration of Cd and Se, Cd concentration in the testis (0.88 +/- 0.078 microgram/g and 0.77 +/- 0.03 microgram/g) was about twice as much as the concentration in the case of no administration of Se (0.30 +/- 0.04 microgram/g). The testicular dysfunction could not be explained by the increased Cd concentration in the testis. The groups with high Cd concentration in the testis were accompanied by an increase in metallothionein (92.8 +/- 18.6 micrograms/g and 92.5 +/- 7.3 micrograms/g), but these did not exceed the level of the control group (94.5 +/- 8.4 micrograms/g) which had neither Cd nor Se injections. In the groups with testicular necrosis, concentrations of zinc (Zn) and magnesium (Mg) were decreased while an increase in concentrations of calcium (Ca) and iron (Fe) was observed. These results suggest that Se concentration must be maintained to prevent the testicular disorder caused by Cd.     

学前儿童膳食植酸摄入量及对锌生物利用率的影响

用改良的离子交换法测定了学龄前儿童膳食植酸的摄入量,并用植酸/锌摩尔比值及人体代谢平衡实验评价和观察植酸抑制锌吸收利用的程度。 膳食植酸平均摄入499mg/d,植酸/锌摩尔比值平均为6.66。当摄取植酸含量高的食物时,植酸/锌摩尔比值也仅达到10.6。而抑制锌吸收的临界比值范围为10～20。代谢平衡实验未观察到锌的生物利用率受到抑制。 因此,在我国目前的膳食条件下,锌缺乏与植酸关系不大。