Studies on calcium absorption from milk using a double-label stable isotope technique

Physician and Parent Perceptions on Plant-Based Beverages as Substitutes for Cow's Milk: A Single City Survey

This study assessed physician and parent perceptions regarding plant-based beverage consumption in children. We surveyed 128 physicians and 215 parents of patients at University of Miami and Jackson Memorial Hospital. Among physicians, 52% recommended plant-based beverages, typically soy (33%), for cow's milk allergy (32%). Only 40% of physicians knew the typical protein content of plant-based beverages compared to cow's milk. Most physicians (54%) did not discuss potential health risks of plant-based beverages with patients. Among parents, 48% had children <2 years old, and 22% purchased a plant-based beverage, most commonly almond beverage (39%), due to perceived health benefits (54%). In total, 85% of parents believed that plant-based beverages are nutritionally superior or equivalent to cow's milk. Most parents (52%) depended on physicians for information on plant-based beverages. Overall, less than one third of physicians and parents believed that plant-based beverages should be called milk. There is a lack of knowledge among physicians and parents regarding plant-based beverage use as a dairy substitute in children. Despite parents relying on physicians for health information, physicians are not routinely counseling parents. Removing the label "milk" from plant-based beverages may improve consumer awareness of their nutritional differences and circumvent potential associated health risks in children.

Calcium Absorption from Food Products: Food Matrix Effects

This article reviews physicochemical aspects of calcium absorption from foods. Notable differences are observed between different food products in relation to calcium absorption, which range from <10% to >50% of calcium in the foods. These differences can be related to the interactions of calcium with other food components in the food matrix, which are affected by various factors, including fermentation, and how these are affected by the conditions encountered in the gastrointestinal tract. Calcium absorption in the intestine requires calcium to be in an ionized form. The low pH in the stomach is critical for solubilization and ionization of calcium salts present in foods, although calcium oxalate complexes remain insoluble and thus poorly absorbable. In addition, the rate of gastric transit can strongly affect fractional absorption of calcium and a phased release of calcium into the intestine, resulting in higher absorption levels. Dairy products are the main natural sources of dietary calcium in many diets worldwide, which is attributable to their ability to provide high levels of absorbable calcium in a single serving. For calcium from other food products, lower levels of absorbable calcium can limit contributions to bodily calcium requirements.

Fractional absorption of active absorbable algal calcium (AAACa) and calcium carbonate measured by a dual stable-isotope method

With the use of stable isotopes, this study aimed to compare the bioavailability of active absorbable algal calcium (AAACa), obtained from oyster shell powder heated to a high temperature, with an additional heated seaweed component (Heated Algal Ingredient, HAI), with that of calcium carbonate. In 10 postmenopausal women volunteers aged 59 to 77 years (mean ± S.D., 67 ± 5.3), the fractional calcium absorption of AAACa and CaCO₃ was measured by a dual stable isotope method. ⁴⁴Ca-enriched CaCO₃ and AAACa were administered in all subjects one month apart. After a fixed-menu breakfast and pre-test urine collection (Urine 0), ⁴²Ca-enriched CaCl₂ was intravenously injected, followed by oral administration of ⁴⁴Ca-enriched CaCO₃ without carrier 15 minutes later, and complete urine collection for the next 24 hours (Urine 24). The fractional calcium absorption was calculated as the ratio of Augmentation of ⁴⁴Ca from Urine 0 to Urine 24/ augmentation of ⁴²Ca from Urine 0 to Urine 24. Differences and changes of ⁴⁴Ca and ⁴²Ca were corrected by comparing each with ⁴³Ca. Fractional absorption of AAACa (mean ± S.D., 23.1 ± 6.4), was distinctly and significantly higher than that of CaCO₃ (14.7 ± 6.4; p = 0.0060 by paired t-test). The mean fractional absorption was approximately 1.57-times higher for AAACa than for CaCO₃. The serum 25(OH) vitamin D level was low (mean ± S.D., 14.2 ± 4.95 ng/ml), as is common in this age group in Japan. Among the parameters of the bone and mineral metabolism measured, none displayed a significant correlation with the fractional absorption of CaCO₃ and AAACa. Higher fractional absorption of AAACa compared with CaCO₃ supports previous reports on the more beneficial effect of AAACa than CaCO₃ for osteoporosis.

Consequences of a plant-based diet with low dairy consumption on intake of bone-relevant nutrients

OBJECTIVE

This study examines the extent to which a plant-based dietary intervention that discourages consumption of dairy products and meat influences bone-relevant nutrients.

METHODS

A randomized controlled study design was used to evaluate the Coronary Health Improvement Project. The Project is a heart disease prevention intervention administered in an intensive 40-hour educational course delivered over a 4-week period. Participants were evaluated at baseline, 6 weeks, and 6 months.

RESULTS

After 6 weeks, participants in the intervention group compared with the control group experienced significant increases in magnesium and daily intake of fruit, vegetables, and grains but significant decreases in dairy servings per day and calcium and vitamin D from food. After 6 months, those in the intervention group showed significant increases in daily intake of fruit, vegetables, and grains and significant decreases in dairy servings per day, daily meat consumption, and protein, phosphorous, calcium, total calcium, and vitamin D from food. Serum calcium levels are the primary determinant of parathyroid hormone (PTH) release, and within 6 weeks, the intervention group's PTH levels were elevated from baseline and significantly different from the control group's PTH levels. At 6 months, urinary type I collagen N-telopeptide (NTx) levels were significantly greater in the intervention group compared with the control group.

CONCLUSIONS

The Coronary Health Improvement Project increases the intake of important food items but decreases calcium and vitamin D consumption. There is also some evidence of an increase in NTx biomarkers, consistent with increased bone resorption.

Absorption of calcium from milks enriched with fructo-oligosaccharides, caseinophosphopeptides, tricalcium phosphate, and milk solids

BACKGROUND

Adequate intakes of calcium are required for optimal bone health and protection against chronic disease. Dairy products are an excellent source of calcium.

OBJECTIVE

The absorption of calcium from a range of fortified milks was measured in humans with the use of stable isotopes.

DESIGN

Fifteen volunteers participated in a randomized, controlled, double-blind crossover study. Five types of semi-skimmed (1.9% fat) milk drinks were administered with a light breakfast: standard milk (control milk); milk enriched with calcium from milk solids and tricalcium phosphate [(TCP) MSS milk]; milk enriched with calcium from concentrated milk (CON milk); milk with added fructo-oligosaccharides [(FOSs) FOS milk]; and milk with added caseinophosphopeptides [(CPPs) CPP milk]. All the milks were labeled with 42Ca as CaCl2. The MSS milk was also labeled with 44Ca as TCP. The quantity of calcium in each drink was kept the same by varying the volume given.

RESULTS

Calcium absorption did not differ significantly between the control milk and the calcium-fortified milks (MSS and CON milk) or the FOS and CPP milks. However, calcium absorption from the TCP added to the MSS milk was significantly higher than that from the control milk (27.5 +/- 7.6% and 24.5 +/- 7.3%, respectively; P = 0.003).

CONCLUSIONS

Calcium-enriched milks are a valuable source of well-absorbed calcium. Absorption of added calcium as TCP was higher than that of calcium from the control milk, but the addition of FOSs or CPPs did not significantly increase calcium absorption. Further research is needed to ascertain the cost-effectiveness and public health benefits of consuming fortified milks.

Calcium bioavailability from a calcium-rich mineral water, with some observations on method

GOALS

The study was designed to determine whether high-calcium mineral water is an efficient additional source of dietary calcium, optimizing a method for calcium determination never used for mineral waters.

BACKGROUND

It is generally agreed that an adequate calcium intake is necessary for the acquisition of an ideal peak bone mass and for the maintenance of the bone mineral density in adults, in postmenopausal women, and in the elderly. Mineral waters are calorie free, and some, with high calcium levels, might be significant sources of calcium.

STUDY

The availability of the calcium contained in a high-calcium mineral water was measured in 27 healthy subjects. In 8 subjects the calcium availability of the water was compared with the calcium availability ingested with milk at the same calcium load. Milk and water were labeled extrinsically with 30 mg Ca. Fractional absorption from the oral dose was determined from plasma samples using ICP-MS technique.

RESULTS

At an ingested calcium load of 3.18 mmol, percentage of absorption for water averaged 22.53 +/- 2.53 (mean +/- SD) for men, 22.57 +/- 2.10 (mean +/- SD) for premenopausal women and 21.62 +/- 3.12 (mean +/- SD) for postmenopausal women. Percentage absorption from milk was 23.15 +/- 4.06 (mean +/- SD).

DISCUSSION

The calcium from the mineral water is thus highly bioavailable, at least as bioavailable as milk calcium, and ICP-MS appears to represent a reliable and reproducible method for calcium absorption from alimentary sources.

The effect of casein phosphopeptides on calcium absorption from calcium-fortified milk in growing rats

The effect of casein phosphopeptides (CPP) prepared from bovine casein by enzymatic hydrolysis (extrinsic CPP) on Ca absorption from Ca-fortified milk was studied in young male rats, in comparison with that produced from casein in the small intestine (intrinsic CPP). The gastrointestinal Ca disappearance (Ca ingested - (gastric Ca + intestinal Ca )) was calculated as an indirect measurement of Ca absorption. After being fasted overnight, the animals were given 2.0 ml Ca-fortified milk (30 g fat, 35 g protein, 2.7 g Ca/kg) without or with 1.0 mg extrinsic CPP/ml, by gastric intubation. The intestinal soluble Ca level after 15 min and the gastrointestinal Ca disappearance after 15 and 30 min in the rats given Ca-fortified milk with 1.0 mg extrinsic CPP/ml were significantly higher than these figures in the rats given Ca-fortified milk without CPP (P < 0.05). When the rats were given unfortified milk (1.35 g Ca/kg) in another reference experiment, no significant effect on intestinal soluble Ca and gastrointestinal Ca disappearance was apparent from the addition of CPP to milk. Ca availability was estimated by measuring 45Ca-deposits in the bones of rats 48 h after being given 2.0 ml Ca-fortified milk labelled with 45Ca (180 kBq/2 ml) with or without 0.25 mg CPP/ml. The levels of 45Ca radioactivity of the femur and tibia from the rats given Ca-fortified milk with extrinsic CPP were significantly higher than those from the control group (P < 0.05). These results suggest that the addition of CPP to Ca-fortified milk could increase Ca absorption by growing rats mainly from CaCO3 added to the milk. The mechanism of CPP related to the interaction of CPP and Ca in the gastrointestinal tract is discussed.

The bioavailability of dietary calcium

This update focuses on the bioavailability of dietary calcium for humans. Fundamentals of calcium metabolism, intestinal absorption, urinary excretion and balance are recalled. Dietary factors, especially lactose and other milk components, influencing calcium bioavailability at intestinal and renal levels are reviewed. A critical examination of all the methods used for evaluating calcium bioavailability is made. This includes in vitro assays, classical and isotopic balances, urinary excretion, isotope labeling in the urine, plasma and bones, long term evaluation of bone mineralization and the use of biological bone markers. Importance and advantages of animal models are discussed. The state of the art in the comparative bioavailability of calcium in foods is detailed including a comparison of sources of calcium (dairy products and calcium salts) in human studies and in some animal studies, casein phosphopeptides, proteins, lactose and lactase and their relation with calcium bioavailability (in humans and rats). An update on the consumption of dairy products and bone mass is presented. Emphasis on peculiarities and advantages of calcium in milk and dairy products is given.

Effect of casein phosphopeptides on zinc and calcium absorption from bread meals

Animal studies suggest that casein phosphopeptides (CPP), formed by proteolytic digestion of casein, have a positive effect on Ca availability. The aim of this study was to investigate the ability of CPP to improve Zn and Ca absorption from phytate-containing bread meals. Secondly, it was tested whether the Ca content of the meal influenced the effect of CPP on Zn absorption from a high-phytate meal. Zn and Ca absorption from single model meals was determined by extrinsic labeling with 65Zn and 47Ca and measurement of whole-body retention. Thirty-one healthy adults (19-30 y) divided into three groups received one of three meal types based on white-wheat rolls with different phytate and Ca content: A: low-phytate/high-Ca (n = 10), B: high-phytate/high-Ca (n = 10) and C: high-phytate/low-Ca (n = 11). Each individual received the same meal type at three different occasions with 0, 250 and 1000 mg CPP added. CPP had no effect on Zn absorption: A: 14.3 +/- 4.4% (mean +/- SD) (0 mg CPP), 16.7 +/- 6.6% (250 mg CPP) and 16.0 +/- 8.8% (1000 mg CPP); B: 7.0 +/- 1.6%, 7.7 +/- 3.0% and 8.0 +/- 2.6%; C: 7.7 +/- 2.5%, 7.0 +/- 2.3% and 6.5 +/- 1.6%, respectively. Addition of 1000 mg CPP reduced fractional Ca absorption from meal A: 33.8 +/- 7.1%, 30.5 +/- 6.3% and 25.9 +/- 8.7% (p < 0.05), whereas CPP had no effect in meal B: 29.3 +/- 8.3%, 27.0 +/- 7.4% and 27.6 +/- 11.0%. However, the absolute quantity of Ca absorbed was unaffected. In conclusion, Zn and Ca absorption from these meals were not significantly influenced by the addition of CPP, Ca addition could not explain the failure of CPP to improve Zn absorption.

Insufficient calcium and iron intakes among general female population in Japan, with special reference to inter-regional differences

Dietary intakes of calcium (Ca) and iron (Fe) were investigated in 227 women (mostly housewives) in 12 regions in Japan in 1991-1993 by the 24-hour food duplicate method. Nine regions out of 12 had been previously studied in 1977-1982. Utilizing Standard Food Composition database, mean Ca and Fe-intakes in 1991-1993 were estimated to be 602 and 10.4 mg/day, respectively; the former was barely sufficient and the latter was below sufficiency when compared with the Recommended Daily Allowance in Japan for pre-menopausal women. Ca- and Fe-intake did not increase in the 10-year period. Further analysis after classification of the women into three groups of farmers in Okinawa, farmers in Mainland Japan and urban residents showed that Ca and Fe insufficiency was most evident among Okinawa farmers. The leading Ca sources were milk, pulse, vegetables and fish-shellfish, but consumption of milk was generally low, especially among Okinawa farmers. Pulse, vegetables and fish-shellfish were 3 major Fe sources; Okinawa farmers depended more on vegetables and less on fish-shellfish.

Effect of dietary calcium intake and meal calcium content on calcium absorption in the rat

Fifty-four male and forty-five female 7-week-old rats, Wistar strain, average weights 190 g and 140 g respectively, were randomized by weight into three groups of eighteen rats each (males) and three groups of fifteen rats each (females) and fed on a semi-purified diet containing (per kg) 2 (low), 5 (normal) or 20 g (high) Ca as CaCO3 for 2 weeks. Each group was then further randomized into three groups of six rats each (males) and five rats each (females) and given a meal (10 g of the same diet) containing either 2, 5 or 20 g Ca as 47CaCO3. 47Ca was determined in quantitative daily collections of faeces over 7 d and fractional absorption of 47Ca estimated by extrapolating the linear portion (days 3-7) of the plot of log 47Ca retention v. time back to the time of isotope administration. Absorption of meal Ca was higher in males than in females and was affected similarly in males and females by previous dietary Ca intake and meal Ca content. Fractional absorption of meal Ca decreased with increasing previous dietary Ca intake and with increasing meal Ca content, and the combined effect of these two variables caused fractional Ca absorption to vary from 11-89%. Absolute absorption of meal Ca decreased with increasing previous dietary Ca intake and increased with increasing meal Ca content. The influence on Ca absorption of variations in meal Ca content (load effect) was greater than that of variations in previous dietary Ca intake (adaptive effect). These results show that previous dietary Ca intake and meal Ca content are both major determinants of Ca absorption from meals in intact rats fed in the normal way and that the rat responds to these factors in a manner similar to that reported for humans. This study provides further evidence of similarities between rats and humans in dietary Ca absorption.

Bioavailability of calcium of fresh cheeses, enteral food and mineral water. A study with stable calcium isotopes in young adult women

True fractional Ca absorption from six foods was measured in twelve normal healthy women, aged 20-29 years. The tested foods were commercially available fresh cheese, fresh cheese prepared by new technology and rich in Ca, similar cheese with added Fe, enteral food, mineral water alone and combined with a spaghetti meal. The aim of the study was to investigate: (1) Ca absorption from a new Ca-rich fresh cheese and to compare it with that from the traditional commercial type of fresh cheese; (2) the effect of Fe enrichment of the new cheese on Ca absorption; (3) Ca absorption from the mineral water and the enteral product and to compare it with that from the dairy products; (4) the effect of a meal combined with the mineral water on Ca absorption. All test foods were consumed by all subjects according to a design with two Latin squares. Each treatment of 2 d was followed by a wash-out period of 2 weeks. Ca absorption was measured using a double stable-isotope (44Ca and 48Ca) extrinsic labelling technique. Mean fractional Ca absorption from the new fresh cheese was not significantly different from that from the traditional type (37.7 (SD 10.2)% v. 42.2 (SD 11.6)%). The addition of Fe to the new cheese did not significantly influence Ca absorption. Ca-absorption values from the mineral water (37.0 (SD 9.8)%) and from the enteral product (42.6 (SD 11.4)%) were not significantly different from those from the dairy products (37.7-42.2%, SD 10.2-11.6%). The co-ingestion of a spaghetti meal with the mineral water significantly enhanced Ca absorption from 37 (SD 9.8)% to 46.1 (SD 11.7)%. It is concluded that a new process leading to a fresh cheese with a higher Ca concentration does not alter Ca bioavailability compared with the standard technology and for a constant Ca supply. Thus this new fresh cheese would probably provide more Ca than the standard one. The fractional Ca-absorption values for mineral water and the enteral product indicate that these products can make an interesting contribution to Ca supply for populations with a low Ca intake and patients with specific diseases respectively.

Use of the true absorption coefficient as a measure of bioavailability of radiocaesium in ruminants

Limitations of existing methods to describe the bioavailability of dietary radionuclides to ruminants (the transfer coefficient and apparent absorption coefficient) have led to the alternative suggestion of using the true absorption coefficient (A(t)). Various approaches to estimating A(t) for radiocaesium, involving the intravenous administration of a second isotope, are presented and discussed with reference to results from studies in which a range of radiocaesium sources were examined in sheep. Although estimates of A(t) differed between the sources, they were reasonably consistent between measurement techniques. Those methods which involved the estimation of endogenous faecal excretion of radiocaesium could be used with previously contaminated animals and did not require continuous administrations of radiocaesium isotopes, but gave unreliable results for sources of low bioavailability. Methods based on estimating the turnover rate of dietary radiocaesium through blood plasma were sufficiently sensitive to measure A(t) for the range of sources studied. However, they require previously uncontaminated animals and continuous administration of both isotopes for approximately 7 days. Bioavailability is more effectively measured as A(t) than as the transfer or apparent absorption coefficients since A(t) does not incorporate factors relating to the metabolism of radiocaesium in the tissues of the animal. The results of these studies show that differences in transfer coefficients between sheep and cattle and between sheep of differing ages are not due to variation in absorption across the gut. The potential for applying these approaches to other radioactive elements is discussed.

Effects of double-blind controlled calcium supplementation on calcium absorption in Chinese children measured with stable isotopes (42Ca and 44Ca)

A double-blind controlled Ca supplementation trial was conducted for 6 months in thirty-four 7-year-old Chinese children from Hongkong and Jiangmen, China. The children were randomly allocated to the study group (n 17) or control group (n 17), and a CaCO3 tablet (300 mg Ca) or a placebo tablet was taken daily. True fractional Ca absorption (TFCA) was evaluated before and after the trial using stable isotopes: 8 mg 44Ca mixed in 100 g chocolate milk was given after an intravenous injection of 0.75 mg 42Ca. There was no significant difference in baseline TFCA between the study group (60.6 (SD 11.4)%) and the controls (58.2 (SD 9.0)%; P = 0.55). Serum 25-hydroxycholecalciferol levels were comparable between the two groups (P = 0.71). After 6 months, TFCA of the study group (55.6 (SD 12.7)%) was significantly lower than that of the controls (64.3 (SD 10.7)%; P = 0.015). By comparing the individual changes in TFCA after the trial between the two groups there was a non-significant reduction in TFCA (5.03 (SD 12.4)%; P = 0.11, Wilcoxon signed-rank test) in the study group (60.6-55.6%), whereas a significant increase in TFCA (6.17 (SD 7.7)%; P = 0.004, Wilcoxon signed-rank test) was observed in the controls (58.2-64.3%). The differential in TFCA between the two groups after 6 months was significantly different (P = 0.001), and remained significant after adjustment for baseline dietary intakes, weight and height by multiple-regression analysis (P = 0.003). If the mechanism of TFCA from chocolate milk in response to the treatment effects is similar to that from the total diet, then our results suggest that children with adequate vitamin D status can adapt to a change in Ca intake by adjusting the efficiency of TFCA. In corollary, children on habitually-low Ca diets have a higher TFCA than the counterparts with higher Ca diets.

True fractional calcium absorption in Chinese children measured with stable isotopes (42Ca and 44Ca)

True fractional Ca absorption (TFCA) was compared in children with different habitual Ca intakes using a double-label stable-isotope technique. Chinese children aged 7 years from Hongkong (n22) and Jiangmen (n12) participated in the study. An oral administration of 8 mg 44Ca in 100 g chocolate milk was given shortly after an intravenous injection of 0.75 mg 42Ca. Ca isotopic ratios were determined in urine samples collected 24 h later using thermal-ionization mass spectrometry. There was no significant difference in TFCA between Jiangmen and Hongkong children (P = 0.16). TFCA of a lower-Ca-intake group (Ca < or = 500 mg/d, n19) with mean Ca intake 359 mg/d was 63.1 (SD 10.7)% and that of a higher-Ca-intake group (Ca > 500 mg/d, n15) with mean Ca intake 862 mg/d was 54.8 (SD 7.3)%; the difference in TFCA was significant (P = 0.016). Serum levels of 25-hydroxycholecalciferol of the children were adequate (33.7 (SD 7.7) ng/ml). The present study indicates that growing children accustomed to a low-Ca diet appear to be able to enhance their absorptive capacity. If it is assumed that dietary Ca absorption by Chinese children resembles their TFCA from a single meal of chocolate milk, then the recommended dietary allowance (RDA) for Ca for Chinese children would be lower than the US RDA (800 mg/d), which is based on an estimated 40% Ca absorption as reported for Caucasian children. A comparative absorption study is necessary to determine whether there is any difference in TFCA between Caucasian and Chinese children.

The use of the stable isotope 44Ca in studies of calcium incorporation into dentin

The incorporation into rat incisor dentin of two calcium isotopes, the stable 44Ca and the radioactive 45Ca, was studied using secondary ion mass spectrometry (SIMS) step-scanning and imaging, and autoradiography, respectively. The results demonstrated a time-dependent incorporation of the calcium isotopes into the mineral phase of dentin. With the SIMS step-scanning, detecting 44Ca, the ion yield was high in the odontoblasts 2 min after intravenous injection. After 10 min a marked increase in signal intensity was found at the dentin mineralization front. This result was consistent with those obtained by 45Ca autoradiography; a peak of incorporation occurred 10 min after injection of the isotope. Likewise, localization of 44Ca to the mineralization front could be demonstrated 10 min after injection by SIMS imaging. In images obtained at earlier intervals, no such increase in ion yield could be detected. The results show that the nonradioactive, stable isotope 44Ca can be used as a marker for biomineralization in a similar way to radioactive 45Ca.

Plasma kinetics of magnesium and calcium stable isotope tracers in a human subject after simultaneous oral ingestion of 25Mg and 44Ca determined by thermal ionization mass spectrometry

The plasma concentrations of stable isotope tracers of magnesium (25Mg) and calcium (44Ca) were determined during a 50 h period, after simultaneous oral tracer ingestion in an adult man. The measurements were performed by magnetic sector field mass spectrometry using surface ionization ion sources. The data were used to evaluate the potential of this method in long-term kinetic studies. It is concluded that under the experimental conditions specified, the isotopic tracers will be detectable in blood plasma with sufficient precision and accuracy for approximately 600 h after oral ingestion. The differences in the plasma concentration curves of 25Mg and 44Ca were analysed by means of the convolution integral method. These differences indicate inhomogeneities in the distribution of absorption activity relative to magnesium and calcium within the upper small intestine.

Zinc absorption in adult men from a chicken sandwich made with white or wholemeal bread, measured by a double-label stable-isotope technique

Eleven fasted adult men consumed a chicken meat sandwich made with white or wholemeal bread, extrinsically labelled with 2 mg 67Zn, on two different occasions. Immediately after eating the sandwich they were given an intravenous injection of 1.5 mg 70Zn. True Zn absorption (which was approximately 7% higher than apparent absorption) was determined by the faecal balance technique by making an allowance for endogenous excretion from measurements of faecal excretion of 70Zn. There was no significant difference in mean true Zn absorption from the white or wholemeal bread sandwich, 33.6 and 25.4% respectively. It was concluded that the substitution of wholemeal for white bread does not reduce Zn absorption from meat-based sandwiches.

Minerals and trace elements in milk

The nutritional roles, requirements, and metabolism and the quantitative relationship between dietary intakes and health for a number of the minerals and trace elements have been more clearly defined in recent years, but there are still considerable deficiencies in our understanding of these issues, e.g., the significance of calcium in the etiology and treatment of osteoporosis and hypertension. Reliable information is now available on the content, and the principal factors affecting it, of most of the minerals and trace elements in human and cow's milks. However, for some of the trace elements, there is still a wide variation in reported values in the literature, which is due, at least in part, to analytical difficulties. The contribution of cow milk and milk products to the diet in Western countries is significant for sodium, potassium, chloride, calcium, phosphorus, zinc, and iodine. Iodine is the only trace element for which there has been any suggestion of excessive amounts in cow milk. However, there is evidence of a decline in milk iodine concentrations in the United States in recent years, although the situation in other countries less clear. Breast milk usually has adequate mineral and trace element contents for feeding full-term infants, with the exceptions of fluoride, for which supplementation of infants is recommended, and of selenium in some countries, such as Finland and New Zealand, where maternal intakes are low. However, breast milk selenium contents have increased in these countries in recent years due to increased maternal selenium intakes. The concentrations of minerals and trace elements in infant formulas for full-term infants are generally higher than in human milk, and all appear to be more than adequate, with the possible exception of selenium, which may need to be increased in some formulas. Considerable changes in the mineral and trace element contents of formulas have been instituted in recent years in the light of improved knowledge of infant requirements. While the chemical forms of the macrominerals and some of the trace elements (iron, zinc, copper, and manganese) in milks are fairly well defined, the forms of many of the trace elements are unknown. Sodium, potassium, chloride, and iodine are believed to be almost totally absorbed from milks and infant formulas.(ABSTRACT TRUNCATED AT 400 WORDS)