面包内补充叶酸不影响年轻妇女的锌吸收

有研究显示，谷物中添加叶酸可减少神经管缺陷的发病率。但也有研究显示叶酸可干扰锌的吸收，这引起了对婴儿、怀孕妇女、老年人等高危人群体内锌状态的关注。探究了添加叶酸对含高和低浓度锌的精粉中锌吸收的影响。研究结果表明，锌的吸收在食用锌含量低的面包和低浓度锌的精粉中锌吸收的影响。研究结果表明，锌的吸收在食用锌含量低的面包时依据叶酸含量的不同没有明显的差异性，食用锌含量高的面包时亦如此。锌的吸收和叶酸的含量间无显著相关性。结论为无论精粉面包中锌含量是高或低，加入常量的叶酸并不影响锌的吸收。     

有机锌在肉仔鸡小肠不同部位中的吸收特点

目的研究肉仔鸡小肠各段对无机锌和有机锌吸收特点的差异。方法采用原位结扎灌注肠段法,包括2个试验:试验1:以硫酸锌为锌源,根据锌的吸收率与肠段灌注时间(5个时间点)的曲线关系确定最佳灌注时间,试验2:在此灌注时间下比较不同形态锌(8种锌源)在肉仔鸡小肠中的吸收差异。结果(1)锌的吸收率在30min时即可达最大吸收的85%～90%;(2)不同锌源锌在回肠中的吸收均显著高于十二指肠和空肠;(3)十二指肠和空肠中锌的吸收率受到添加锌源的显著影响,其中,弱、中和强络合强度有机锌组及蛋氨酸锌组、赖氨酸锌组锌的吸收率明显高于硫酸锌、硫酸锌和蛋氨酸混合物组、硫酸锌和甘氨酸锌混合物组。结论30min为肠段的最适灌注时间;回肠是肉仔鸡小肠吸收锌的主要部位;有机锌吸收要好于无机锌。     

锌与健康

本文就微量元素锌与健康的关系作一论述。１锌的体内过程及生物学功能锌的吸收受肠粘膜细胞的含锌量所控制，即当肠粘膜细胞中锌含量逐渐增高直至达到饱和时，则从肠内容物中吸收锌的量相应地逐渐减少最后停止吸收。当身体需锌较多时，则吸收的锌也增加。吸收的锌进入血液...     

人体微量元素研究的进展(一) 锌

本文综述与人体有关的三种重要的微量元素锌、锰和铜研究的进展,特别着重体内代谢及失调方面的生理、生化和病理变化。一、锌1.吸收:一个70公斤的人体含1.4～2.3克锌。成人大约每天摄入10～15毫克锌,由小肠吸收5毫克左右。锌在小肠的吸收不是简单的扩散,而是受某种机理调节的。胃肠外给小鼠过量的~(65)Zn,可使大便中~(65)Zn排泄加速,而口服不行。在身体锌负荷增加时~(65)Zn的吸收减少。Evans等指出,锌吸收的变化与肠粘膜锌含量有关,后者又受血浆锌含量的调节。     

112 镉和锌在体内的相互作用

已知镉的许多毒性作用均源于其与一些必需微量元素(包括锌)的相互作用，这些相互作用可以发生在镉、锌这两种元素的吸收、分布和排泄等不同阶段，也可以发生在锌发挥生物学功能的阶段。一方面，镉可以干扰锌的功能发挥；另一方面，膳食锌摄人量对镉的吸收、蓄积和毒性等都有重要作用。体内锌的营养状况与镉的毒性密切相关。大量资料表明，增加锌摄人量可以降低镉的吸收和沉积，防止或减轻镉的毒性作用；反之，锌缺乏可以加强镉的沉积和毒性。本文以当前人群对镉的普遍暴露和对锌的普遍性营养缺乏为背景，对近期关于锌-镉相互作用的研究进行编译。     

锌的生物学作用及机体缺锌的表现

锌能使细胞和活体内某些生物学过程加速,在生命活动中起极重要的作用。在各种脱氢酶、醛缩酶、肽酶、磷酸酶、异构酶、转磷酸酶、碳酸酐酶和天冬氨酸转氨甲酰酶中均含有锌。这些酶参与脂肪、蛋白质和碳水化合物的代谢,并参与核酸的分解和合成。锌影响细胞膜的通透性,与钾离子有竞争作用。锌对许多内分泌腺的活动有影响。锌维持机体的正常代谢和发育过程。锌增强肝脏的合成能力和细胞对病毒的敏感性,并参与解毒,从而改善机体的防御能力。对锌在机体中的平衡调节机制研究较少。正常情况下锌的吸收系数平均约为33%。锌的需要量与吸收量之间存在明显相关。锌在小肠的吸收明显受组织锌浓度、膳食锌摄入量和胃肠道中促进和抑制锌吸收的其他食物成分的影响。已证明,人体中锌的吸收和维持随着蛋白     

镉和锌在体内的相互作用

已知镉的许多毒性作用均源于其与一些必需微量元素（包括锌）的相互作用，这些相互作用可以发生在镉，锌这两种元素的吸收，分布和排泄等不同阶段，也可以发生在锌发挥生物学功能的阶段。一方面，镉可以干扰锌的功能发挥；另一方面，膳食锌摄入量对镉的吸收，蓄积和毒性等都有重要作用。体内锌的营养状况与镉的毒性密切相关，大量资料表明，增加锌摄入量可以降低镉的吸收和沉积，防止或减轻镉的毒性作用，反之，锌缺乏可以加强镉的沉积和毒性，本文以当前人群对镉的普遍 暴露和地锌的普遍性营养缺乏为背景，对近期关于锌－镉相互作用的研究进展编译。     

赖氨酸、苯丙氨酸、酪氨酸和缬氨酸对大鼠回肠锌吸收动力学作用的研究

用原位灌流的大鼠回肠研究了赖氨酸、苯丙氨酸、酪氨酸和缬氨酸对锌吸收动力学的作用。赖氨酸对大鼠回肠锌吸收动力学常数以及快速相和慢速相半衰期、回肠锌吸收率均无影响。苯丙氨酸、酪氨酸和缬氨酸能增加回肠锌吸收率。其中苯丙氨酸组K_921)、K_(12)、K_(02)的值均高于对照组。缬氨酸组K_(21)和K_(12)值高于对照,并且快速相T_(1/2)缩短。酪氨酸组K_(21)值较对照组高,而K_(12)、K_(02)值以及快速相、慢速相半衰期无改变。本研究的结果提示:苯丙氨酸、酪氨酸、缬氨酸能促进锌在大鼠回肠的吸收。氨基酸对锌吸收的促进作用与其对锌的配合物稳定常数有关。     

锌和游离叶酸吸收的相互影响

目的：研究锌和游离叶酸吸收的相互影响。方法：７２只Ｗｉｓｔａｒ雄性离乳大鼠随机分成九组，分别饲以不同锌和游离叶酸配比的饲料，喂养２４天，观察各组大鼠血清锌浓度，股骨锌含量及大鼠粪锌排出率变化。结果：上述指标不受饲料中叶酸含量的影响。低锌低叶酸组大鼠血清叶酸水平显著低于锌正常低叶酸组，而中高叶酸组血清叶酸水平不受饲料中锌含量的影响。相关分析也显示大鼠血清叶酸水平和血清锌水平无相关关系。结论：本实验剂量（４～４０ｍｇ／ｋｇ饲料）游离叶酸的补充不影响锌的吸收。缺锌不利于游离叶酸的吸收     

四种锌化合物的生物利用率的比较

目的：以边缘性锌缺乏的大鼠和幼鼠为模型，观察硫酸锌、葡萄糖酸锌、乳酸锌和甘氨酸锌四种锌化合物在０～７２０分钟消化吸收的动态变化；四种锌化合物在不同剂量（７．６、１５、３０、６０ｍｇ／ｋｇＨ２Ｏ）时组织中的储存。结果：以相同浓度的锌灌胃（６．０ｍｇ／ｋｇｂｗ），甘氨酸锌入血快于其它三个锌化合物，在１５分钟时达到最高峰（１００μｍｏｌ／Ｌ），乳酸锌和葡萄糖酸锌３０ｍｇ／ｋｇ时吸收峰值最大（６６．０μｍｏｌ／Ｌ，７９．５μｍｏｌ／Ｌ）；硫酸锌则在６０分钟到达高峰（７８．９μｍｏｌ／Ｌ）。用不同剂量锌（１５、３０、６０ｍｇ／ｋｇＨ２Ｏ）喂养幼鼠，甘氨酸锌在１５ｍｇ／ｋｇ、乳酸锌和葡萄糖酸锌３０ｍｇ／ｋｇ时血和组织中吸收峰值最大，且成直线关系；而３０、６０ｍｇ／ｋｇ时血和组织中浓度则基本保持恒定。而硫酸锌的吸收与剂量浓度关系成正比。以硫酸锌的吸收为１００％，用药物代谢动力学软件３Ｐ８７计算葡萄糖酸锌、乳酸锌和甘氨酸锌相对生物利用率分别为：１３２％、７３％和１２４％。     

Zinc bioavailability from zinc-fortified foods

Zinc fortification is considered a potentially useful strategy for the control of zinc deficiency, but the success of such intervention programs depends on the population's access to and consumption of zinc-fortified foods and adequate absorption of zinc from these foods. The latter issue has been assessed by a variety of studies that applied zinc isotopic tracers to assess zinc uptake from zinc-fortified foods. These studies show that the additional zinc provided by zinc fortification decreases fractional absorption of zinc, but increases total zinc absorption from these foods. Available studies show no significant difference in zinc absorption from foods fortified with either zinc oxide or zinc sulfate, which are the two cheapest chemical forms of zinc that are generally recognized as safe for human consumption. It appears that high-phytate meals depress zinc absorption from zinc-fortified foods, although total zinc absorption from such foods is still likely to be greater than if the foods were not fortified with zinc. With the possible exception of Na2EDTA, putative enhancers of zinc absorption do not seem to confer major benefits for zinc absorption from zinc-fortified foods. There is little information on the effect of fortification with other micronutrients on zinc absorption from co-fortified foods, and zinc fortification does not seem to suppress iron absorption from iron-fortified foods in most studies.     

Does zinc absorption reflect zinc status?

Unlike iron, zinc absorption is influenced by dietary zinc intake, not zinc status. As dietary zinc increases, the total amount of absorbed zinc increases while the percent absorbed declines. The gastrointestinal tract maintains whole-body zinc homeostasis by adjusting endogenous zinc losses to the amount absorbed. At intakes below about 9 mg/day, zinc absorption occurs primarily by a saturable (carrier) process involving ZIP4, ZnT1, and other transporters. There is no evidence that past zinc intakes, or status, influences zinc absorption. Instead, current zinc intake is the chief determinant of zinc absorption. Supplemental zinc taken with water in the post-absorptive state initially is absorbed more efficiently than food zinc, but absorption efficiency declines within 24 hours presumably due to down-regulation of the zinc transporters. More research is needed to understand the effect of physiological state on zinc absorption.     

Evidence for the usefulness of in vitro dialyzability, Caco-2 cell models, animal models, and algorithms to predict zinc bioavailability in humans

Low bioavailability of zinc in certain diet types may contribute to zinc deficiency and its consequences in populations. As a result, several experimental models including animal models, in vitro dialyzability models, and Caco-2 cells, have been used to study these factors and estimate their impact on human zinc absorption. For the most part, consistency has been observed between the latter models and human absorption studies to identify factors that enhance or inhibit zinc bioavailability. However, dialyzability methods are limited to modeling luminal interactions among the factors as they affect zinc availability while Caco-2 cells can model luminal effects and uptake by intestinal cells. Neither animal nor in vitro methods can predict the magnitude of zinc absorption at the level of the human organism. Caco-2 cells will be useful models for understanding the mechanisms of intestinal zinc absorption. The in vitro methods are also limited to modeling absorption and the interactions that occur. Algorithms to estimate zinc absorption, based on dietary content of zinc absorption modifiers, have been derived from human studies. An algorithm derived from studies of zinc retention from radioactive zinc-labeled test meals underestimates zinc absorption compared to that derived from measurement of true zinc absorption from total diets using isotopic tracer methods. Based on the latter, phytate appears to be the only major inhibitor of zinc absorption from typical diets. Ultimately, population-based studies are needed to determine the impact of dietary factors that modulate zinc absorption on the adequacy of zinc status.     

Zinc utilization in young men fed adequate and low zinc intakes

Zinc absorption and balances were measured in six young men who were confined while participating in a 75-d metabolic study. A diet of conventional food providing either 16.5 or 5.5 mg Zn/d was fed. Apparent absorption of zinc was calculated from the zinc balance data and from the absorption of a zinc stable isotope added to the diet. The apparent zinc absorption calculated from the isotope data was about 25% when 16.5 mg zinc was fed; it increased to about 53 and 49% after 13 and 42 d, respectively, when 5.5 mg zinc was fed. Total zinc absorption fell from 4.1 mg/d to 2.7-2.9 mg/d during the low zinc period, however. This zinc absorption was sufficient to maintain crude zinc balances in five of the six subjects. Neither serum nor urinary zinc levels changed significantly during the period of feeding low levels of zinc. It appears that zinc absorption readily responds to changes in dietary zinc and that an intake of 5.5 mg Zn/d for about 8 wk does not cause serum or urinary zinc level to fall.     

Stable isotope studies of zinc absorption and retention in young and elderly men

Zinc absorption was determined with 67Zn and 70Zn, stable isotopes of zinc, in six young men and six elderly men who were confined to a metabolic unit for 12 wk. Their purified formula diets, supplemented with select food items, contained 15 mg of zinc per day. Zinc absorption was determined twice for each subject by combining zinc enriched with either 70Zn or 67Zn with the formula diet. Serum, urinary, and fecal zinc and zinc balance were determined by atomic absorption spectrometry. Zinc absorption averaged 17% in elderly men, significantly less than average zinc absorption of 31% in young men. Serum zinc was also lower in elderly men and increased in both groups during the course of the study. Zinc balance did not differ between groups, and endogenous zinc losses were less in the elderly than in the young men. The results suggest that while zinc absorption is less in elderly men than in young men, the lower absorption may reflect a lower requirement for absorbed zinc by the elderly. Alternatively, less efficient zinc absorption could result in decreased endogenous losses.     

Production of stable-isotope-labeled bovine heme and its use to measure heme-iron absorption in children

BACKGROUND: The use of stable isotopes has provided valuable insights into iron absorption in humans, but the data have been limited to nonheme iron. OBJECTIVE: Our objectives were to produce heme iron enriched in (58)Fe and to use it to study the absorption of heme iron and the effect of iron and zinc intakes on heme-iron absorption in children. DESIGN: Labeled bovine heme was produced in a bovine model. Forty-eight children were randomly assigned to consume identical meals containing 1 of 3 doses of labeled heme iron (2, 4, or 8 mg as hemoglobin) and 1 of 2 doses of inorganic zinc (1 or 9 mg); successful measurements of iron absorption, zinc absorption, or both were made in 40 of these subjects. We hypothesized that fractional heme-iron absorption would decrease as heme-iron intake increased and that higher zinc intakes would decrease heme-iron absorption. RESULTS: (58)Fe heme was produced with an enrichment (mass/mass) of 9.5%. Fractional iron absorption in children was significantly affected by the intake of heme iron (P = 0.0013) and of zinc (P = 0.0375), but, contrary to expectations, heme-iron absorption was higher at higher zinc intakes. Absolute heme-iron absorption was higher in the group with higher zinc intakes, but only for those with the lowest heme-iron intake (2 mg; P = 0.0147). Although fractional zinc absorption decreased as zinc intake increased (P = 0.031), absolute zinc absorption continued to increase across the intake range studied (P = 0.018). CONCLUSIONS: Heme iron intrinsically labeled with (58)Fe can be produced at sufficient enrichments for use in human studies. In children, heme iron and zinc absorption decrease as the dose of each mineral increases. Heme iron did not inhibit zinc absorption. At lower heme intakes, zinc intakes may increase heme-iron absorption.     

Effect of a micronutrient fortificant mixture and 2 amounts of calcium on iron and zinc absorption from a processed food supplement

BACKGROUND: Iron, zinc, and calcium can interact with each other in a way that inhibits their respective absorption. On the other hand, mineral fortification has been used to improve simultaneous iron and zinc absorption from food supplements. OBJECTIVE: We evaluated the effect of a novel fortificant mixture consisting of NaFeEDTA, zinc methionine, ascorbic acid, and citric acid on iron and zinc absorption from a dry food supplement designed for preschool children. DESIGN: The standard food supplement contained cereal and legume flour, dried milk, and a mixture of micronutrients including ferrous sulfate and zinc sulfate as sources of supplemental iron and zinc, respectively. Standard and novel food products were prepared as porridge with or without the addition of 200 mg Ca as calcium phosphate. Iron absorption and zinc absorption from the food products were evaluated simultaneously in 13 nonpregnant, adult women by extrinsically labeling the products with radioisotopes of iron and zinc and carrying out whole-body counting 7 d after the food products were consumed in random order. RESULTS: The absorption of iron from the NaFeEDTA-containing (novel) food product was 1.7 times that from the ferrous sulfate-containing (standard) product (P = 0.015). There was no significant effect of dietary calcium on iron absorption. Zinc absorption was not associated with the form of zinc consumed, but higher dietary calcium was marginally associated with lower zinc absorption (P = 0.071). CONCLUSIONS: A mixture of fortificants containing NaFeEDTA, zinc sulfate or zinc methionine, ascorbic acid, and citric acid, but without calcium, can improve iron and zinc absorption from food products. A cost-benefit analysis of the novel fortificant mixture needs to be performed.     

Influence of Dairy Products on Bioavailability of Zinc from Other Food Products: A Review of Complementarity at a Meal Level

In this paper, we reviewed the role of dairy products in dietary zinc absorption. Dairy products can have a reasonable contribution for dietary zinc intake in Western diets, where dairy consumption is high. However, the co-ingestion of dairy products can also improve zinc absorption from other food products. Such improvements have been observed when dairy products (e.g., milk or yoghurt) were ingested together with food such as rice, tortillas or bread products, all of which are considered to be high-phytate foods with low inherent zinc absorption. For foods low in phytate, the co-ingestion of dairy products did not improve zinc absorption. Improved zinc absorption of zinc from high-phytate foods following co-ingestion with dairy products may be related to the beneficial effects of the citrate and phosphopeptides present in dairy products. Considering that the main dietary zinc sources in areas in the world where zinc deficiency is most prevalent are typically high in phytate, the inclusion of dairy products in meals may be a viable dietary strategy to improve zinc absorption.     

The effect of individual components of soy formula and cows' milk formula on zinc bioavailability

Zinc absorption from human milk, cows' milk formulas, and soy formulas was studied in human adults by a radioisotope technique using 65Zn and whole body counting. Individual dietary components were investigated for effects on zinc absorption. Phytate was found to have a strong inhibitory effect on zinc absorption; addition of phytate to cows' milk formula (yielding a phytate concentration similar to that of soy formula) resulted in a decrease in zinc absorption from 31 to 16% similar to the absorption for soy formula (14%). Carbohydrate source, calcium, and zinc levels of the diet did not affect zinc absorption significantly. Iron supplementation of cows' milk formula decreased zinc absorption from 24 to 18% although this decrease was not found to be significant (p less than 0.1). Absorption of zinc from a whey-adjusted cows' milk formula was higher (31%) than from a nonmodified cows' milk formula (22%). Increasing the zinc supplementation level in cows' milk formula but not in soy formula increased zinc absorption to approximate that from breast milk. It is suggested that reduction of phytate content of soy formula may be a more effective avenue of modification than increased level of zinc supplementation.     

Adaptation in human zinc absorption as influenced by dietary zinc and bioavailability

BACKGROUND: An understanding of the relations among dietary zinc intake, bioavailability, and absorption is necessary for making dietary intake recommendations. OBJECTIVES: We aimed to assess adaptation in human zinc absorption to controlled differences in zinc and phytate intakes and to apply the results to predictive models. DESIGN: In 3 experiments, radiotracers were used to assess zinc absorption by healthy adults (n = 109) from controlled diets, before and after 4 or 8 wk of dietary equilibration. Subjects consumed 4-29 mg Zn/d from 1 of 10 diets, 5 with molar ratios of phytate to zinc from 2 to 7 and 5 with ratios from 15 to 23. RESULTS: Absorptive efficiency was inversely related to dietary zinc from both low- and high-phytate diets. In response to low zinc intakes (<11 mg/d) for 4-8 wk, zinc absorption was up-regulated to as high as 92%, but only if the diets were low in phytate. The results help validate and refine a published saturable transport model that predicts zinc absorption from dietary zinc and phytate. Possible biomarkers of impaired zinc status, including erythrocyte osmotic fragility, in vitro erythrocyte (65)Zn uptake, and leukocyte expression of the zinc transport proteins Zip1 and ZnT1, were unresponsive to dietary zinc content. CONCLUSIONS: Humans absorbed zinc more efficiently from low-zinc diets and adapted to further increase zinc absorption after consuming low-zinc, low-phytate diets for several weeks. Such adaptation did not occur with higher phytate diets. Zinc absorption can be predicted from dietary zinc and phytate after allowing for dietary equilibration.