Zinc in diet

Zinc Rat Lead absorption Low zinc in diets increases lead absorption Cerklewski and Forbes 1976... 

The direct determination of zinc in diet, tissue and in body fluids can be accomplished by a variety of methods. A common limitation is the chance of sample contamination prior to analysis. Some early studies using less sensitive methods may not have recognised this problem and reported erroneously high results. Older colorimetric methods required that the biological sample be efficiently digested or otherwise deproteinised, prior to formation of a coloured zinc complex. These techniques have largely been superseded by atomic absorption spectrometry which is more sensitive yet less prone to interferences. For fluids such as plasma or urine, simple dilution is all that is required prior to analysis. Tissue or diet samples only require to be dissolved in mineral acid. These simpier sample preparation procedures limit the chances of contamination. 

Barbera R, Fame R, Mesado D. 1991. Determination of cadmium, cobalt, copper, iron, lead, manganese, nickel and zinc in diets Development of a method. Nahrung 35(7) 683-687. 

Zinc is also an essential food element in the human diet. Too Httle zinc in the diet can lead to poor health, reproductive problems and a lowered abHity to resist disease. Taking too much zinc into the body through food, water or dietary supplements can also affect health. The levels of zinc that produce adverse effects are higher than the Recommended DaHy AHowances, which are 15 mg/day for men, 12 mg/day for women, 10 mg/day for children and 5 mg/day for infants. 

Organic chemicals Most organic liquids, other than the stronger acids, only attack zinc slowly. Zinc is, therefore, suitable for storage tanks for liquid hydrocarbons such as motor fuels, for phenols and for trichlorethy-lene degreasers. Zinc or zinc-coated vessels are not recommended for use in contact with acid foodstuffs, but are regularly used for dry foods. Zinc in small quantities is beneficial in the human diet. 

Sublethal effects in birds are similar to those in other species and include growth retardation, anemia, renal effects, and testicular damage (Hammons et al. 1978 Di Giulio et al. 1984 Blus et al. 1993). However, harmful damage effects were observed at higher concentrations when compared to aquatic biota. For example, Japanese quail (Coturnix japonica) fed 75 mg Cd/kg diet developed bone marrow hypoplasia, anemia, and hypertrophy of both heart ventricles at 6 weeks (Richardson et al. 1974). In zinc-deficient diets, effects were especially pronounced and included all of the signs mentioned plus testicular hypoplasia. A similar pattern was evident in cadmium-stressed quail on an iron-deficient diet. In all tests, 1% ascorbic acid in the diet prevented cadmium-induced effects in Japanese quail (Richardson et al. 1974). In studies with Japanese quail at environmentally relevant concentrations of 10 pg Cd/kg B W daily (for 4 days, administered per os), absorbed cadmium was transported in blood in a form that enhanced deposition in the kidney less than 0.7% of the total administered dose was recovered from liver plus kidneys plus duodenum (Scheuhammer 1988). 

Structural chromosome aberrations, particularly chromatid gaps and increased frequency of fragment exchange, were observed in rat bone marrow cells after 14 days of exposure to 240 mg Zn/L drinking water (Kowalska-Wochna et al. 1988). Chromosomal aberrations were observed in bone marrow cells of mice fed diets equivalent to 650 mg Zn/kg BW daily, in mice exposed to zinc oxide by inhalation, and in mice maintained on a low-calcium diet (USPHS 1989). Aberrations in bone marrow of mice given 5000 mg Zn/kg diet may be associated with calcium deficiency (Leonard and Gerber 1989). Calcium is displaced by zinc in calcium-depleted conditions, leading to chromosomal breaks and interference in the repair process (USPHS 1989). 

Concentrations of zinc in tissues of aquatic organisms are usually far in excess of that required for normal metabolism. Much of the excess zinc is bound to macromolecules or present as insoluble metal inclusions in tissues (Eisler 1981, 1984, 1993 USEPA 1987). Diet is the most signihcant source of zinc for aquatic organisms and is substantially more important than uptake from seawater (Eisler 1981, 1984). In general, zinc concentrations in sediments and tissues of aquatic organisms are elevated in the vicinity of smelters and other point sources of zinc, and decrease with increasing distance (Ward et al. 1986 Table 9.4). 

Cows fed a low (25 mg/kg ration) but adequate zinc diet had liver zinc concentrations below the expected 125 mg Zn/kg DW increasing the total zinc dietary loading to 45 or 50 mg/kg DW is recommended for counteracting reduced zinc absorption in diets with soybean products (Binnerts... 

Cows and calves fed low-zinc diets of 25 mg Zn/kg ration showed a decrease in plasma zinc from 1.02 mg/L at start to 0.66 mg/L at day 90 cows fed 65 mg Zn/kg diet had a significantly elevated (1.5 mg Zn/L) plasma zinc level and increased blood urea and plasma proteins (Ram-achandra and Prasad 1989). Biomarkers used to identify zinc deficiency in bovines include zinc concentrations in plasma, unsaturated zinc-binding capacity, ratio of copper to zinc in plasma, and zinc concentrations in other blood factors indirect biomarkers include enzyme activities, red cell uptake, and metallothionein content in plasma and liver (Binnerts 1989). 

Domestic goats (Capra sp.) fed a zinc-deficient diet (15 mg Zn/kg) developed skin histopathology and alopecia (hair loss) after 177 days zinc-deficient diets lacking Vitamin A hastened the process, with signs evident between 46 and 68 days (Chhabra and Arora 1989). No signs were evident in goats fed Vitamin A-adequate diets containing 80 mg Zn/kg ration (Chhabra and Arora 1989). 

Domestic sheep (Ovis aries) fed a low-zinc diet (2.2 mg Zn/kg DW diet) for 50 days, when compared to those fed a zinc-adequate diet (33 mg Zn/kg DW diet), excreted less zinc (<4 mg daily vs. 23 to 25), consumed less food (409 g daily vs. 898), and had lower plasma zinc concentrations (0.18 mg/L vs. 0.53 to 0.58) a reduction in plasma alkaline phosphatase activity and an increase in plasma zinc binding capacity were also noted (Khandaker and Telfer 1990). Sensitive indicators of zinc deficiency in lambs include significant reductions in plasma alkaline phosphatase activity and plasma zinc concentrations signs were clearly evident in lambs fed 10.8 mg Zn/kg DW diet for 50 to 180 days (Vergnes et al. 1990). A normal diet for lambs contains 124 to 130 mg Zn/kg DW ration vs. 33 for adults (Vergnes et al. 1990). One recommended treatment for zinc-deficient sheep is ruminal insertion of zinc-containing boluses every 40 days bolus zinc release is about 107 mg daily (Khandaker and Telfer 1990). 

Fed diets containing 3000 mg Zn/kg feed, and higher, for 30 days Age 7 weeks. Fed diets containing 3000, 6000,9000 or 12,000 mg Zn/kg dry weight (DW) diet for 60 days zinc in form of zinc carbonate... 

No effect on growth, survival, or feed conversion. Zinc accumulated in tissue metallothioneins, especially in liver and kidney levels normal after 5 days on zinc-deficient diet (Oh et al. 1979). 

Devineau, J. and C. Amiard Triquet 1985. Patterns of bioaccumulation of an essential trace element (zinc) and a pollutant metal (cadmium) in larvae of the prawn Palaemon serratus. Mar. Biol. 86 139-143. Dib, A., J.P Clavel, and J.P. Carreau. 1989. Effects of gamma-linolenic acid supplementation on lipid composition of liver microsomal membranes. I. Pregnant rats fed a zinc-deficient diet and those fed a balanced one. Jour. Clin. Biochem. Nutr. 6 95-102. 

All of the studies were conducted with weanling, male albino rats of the Sprague-Dawley strain (Holtzman company). The basal diet used for these studies consisted of casein, starch, vegetable oil, vitamin and mineral mixtures, and cellulose. The Wesson Modification of the Osborne-Mendel mineral mixture was used in all studies. This mineral mixture contained no zinc, but it was adequate in the other minerals required by the rat. Most of the non-zinc-supplemented diets used in the various experiments contained approximately 7 ppm zinc. The level of mineral mixture used in the basal diets was 4%, and based on the chemical composition of the mixture, the basal diets contained approximately 0.57% calcium and 0.41% phosphorus ... 

A deficienqf of zinc in humans will retard growth, both physically and mentally, and contribute to anemia. It is present in many foods, particularly proteins (meat). A balanced diet provides an adequate amount of zinc. Not more than 50 milligrams per day of dietary zinc supplement should be taken, given that high levels of zinc in the body are toxic. Human bodies contain about two grams of zinc. A deficiency of zinc can cause a lack of taste and can delay growth as well as cause retardation in children. 

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