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Discovering Importance of Zinc in Diets

18 December 2014

Zinc is an important mineral necessary in human diets and it has a wide array of vital physiological functions.

It has a catalytic role in each of the six classes of enzymes.

The human transcriptome has 2 500 zinc finger proteins, which have a broad intracellular distribution and the activities of which include binding of RNA molecules and involvement in protein–protein interactions.

Thus, their biological roles include transcriptional and translational control/modulation and signal transduction.

Meat, legumes, eggs, fish, and grains and grain-based products are rich dietary zinc sources.

On the basis of data from 12 dietary surveys in nine European Union (EU) countries, zinc intake was assessed using food consumption data from the EFSA Comprehensive Food Consumption Database and zinc composition data from the EFSA nutrient composition database.

Average zinc intake ranged from 4.6 to 6.2 mg/day in children aged one to less than three years, from 5.5 to 9.3 mg/day in children aged 3 to < 10 years, from 6.8 to 14.5 mg/day in adolescents (10 to < 18 years) and from 8.0 and 14.0 mg/day in adults.

The main food groups contributing to zinc intake were meat and meat products, grains and grain-based products, and milk and dairy products.

The majority of dietary zinc is absorbed in the upper small intestine. The luminal contents of the duodenum and jejunum, notably phytate, can have a major impact on the percentage of zinc that is available for absorption.

Absorption of zinc by the enterocyte is regulated in response to the quantity of bioavailable zinc ingested.

Albumin is the major transporter of zinc in both portal and systemic circulation.

Virtually no zinc circulates in a free ionised form, and the majority of total body zinc is in muscle and bone; zinc does not have an identified major storage site.

The quantity of zinc secreted into and excreted from the intestinal tract depends on body zinc concentrations, and the quantities of endogenous zinc in the faeces and exogenous zinc absorbed in normal adults are related.

The kidneys and integument are minor routes of loss of endogenous zinc.

Zinc requirements have been estimated by the factorial approach involving two stages.

The first is the estimation of physiological requirements, defined as the minimum quantity of absorbed zinc needed to match losses of endogenous zinc and to meet any additional requirements for absorbed zinc that may be necessary for growth in healthy well-nourished infants and children, and in pregnancy and lactation.

The second stage is the determination of the quantity of dietary zinc available for absorption that is needed to meet these physiological requirements.

From the published literature, 15 studies were identified that included data on endogenous faecal zinc and total absorbed zinc that enabled an estimation to be made of the physiological zinc requirements of adults

The final numbers of subjects contributing data to the estimate of physiological zinc requirements were 31 males and 54 females, from a total of 10 studies. Dietary phytate intakes were available for some of the included studies, either as mean study values or as individual’s data.

The range of dietary phytate intakes in the available data was 0–2 080 mg/day. Multiple regression analysis was used to evaluate the possible relationships between physiological requirements and sex, zinc balance (difference between absorbed zinc and total losses of endogenous zinc) and body size.

The coefficient of determination (R2) values for the models with body weight, height, body mass index and body surface area variables were 0.46, 0.42, 0.37 and 0.47, respectively.

It was decided to use the equation relating physiological requirement to body weight in further analyses, for reasons of convenience and accuracy of measurement.

The first stage of estimating physiological requirements used studies that had physiologically plausible data, specifically related to faecal excretion of endogenous zinc.

Adult physiological requirements are closely related to body size, and sex differences are not detectable after adjustment for body weight.

Average Requirements (ARs) for dietary zinc necessary to meet physiological requirements were estimated using saturation response modelling, taking into account the inhibitory effect of dietary phytate on zinc absorption.

Estimated Average Requirements and Population Reference Intakes (PRIs) were provided for phytate intake levels of 300, 600, 900 and 1 200 mg/day, which cover the range of mean/median intakes observed in European populations.

Average Requirements range from 6.2 to 10.2 mg/day for women with a reference weight of 58.5 kg and from 7.5 to 12.7 mg/day for men with a reference weight of 68.1 kg.

PRIs were derived from the zinc requirement of individuals with a body weight at the 97.5th percentile for reference weights for men and women and range from 7.5 to 12.7 mg/day for women and from 9.4 to 16.3 mg/day for men.

Average Requirements for infants from seven months of age and for children were estimated factorially, based on extrapolation from estimates of adult losses plus zinc needs for growth, and range from 2.4 to 11.8 mg/day.

PRIs for infants and children were derived by assuming a coefficient of variation of 10 per cent, and range from 2.9 to 14.2 mg/day. For pregnancy and lactation, additional zinc requirements related to foetal and maternal tissues and transfer of zinc into breast milk, respectively, were considered and additional PRIs of 1.6 and 2.9 mg/day, respectively, were estimated.

 

October 2014

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