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J R Turnlund

Publications and source records attributed to J R Turnlund.

At least 37 records · Page 2Linked to original sources
PubMed1994

Future directions for establishing mineral/trace element requirements.

The amount of an element needed to prevent frank deficiency may not be sufficient to support optimal nutrition, but amounts to support optimal nutrition have not been established. Minerals and trace elements are toxic in excess and the interval between the required and toxic amount of some elements is narrow. Thus, lower and upper limits of an optimal range must be established. Before establishing dietary recommendations to support optimal nutriture for minerals, we need (1) sensitive and reliable methods for assessing status of most elements and (2) a better understanding of the influence of nutrient and non-nutrient components of diets upon requirements. Functions such as immune function, anti-oxidant status, muscle strength, glucose metabolism, and blood clotting can be affected by inadequate or excessive amounts of an element and may be more sensitive than specific status indices. Since such functions are not specific, studies must be designed so that a cause and effect relationship between the mineral and the functional index can be established. Two approaches to mineral status assessment may be both sensitive and specific: (1) tests of metalloenzyme function and (2) tracer studies using stable isotopes of minerals. Not only can stable isotopes be used to follow the metabolic fate of a mineral without exposure to radioactivity, they can be used in conjunction with compartmental modeling to predict kinetics and pool sizes in tissues not accessible in humans.

Absorption↗
PubMed1994

A compartmental model of zinc metabolism in adult men used to study effects of three levels of dietary copper.

The effect of dietary copper level on zinc metabolism in five healthy adult men was studied using compartmental modeling. The subjects were fed one level of dietary zinc (11.2 +/- 1.6 mg/day) and three levels of dietary copper (1.68, 0.785, and 7.52 mg/day). The stable isotope tracers 70Zn and 67Zn were administered intravenously (3 times) and orally (4 times), respectively. Plasma, urinary, and fecal 67Zn and 70Zn levels were measured. An existing model of zinc metabolism was used as a basis for our model. Model rate constants were modified to simulate multiple oral and intravenous doses of stable isotope tracers given during the 90-day study. Most rate constant changes occurred in the absorption and excretion pathways. The model predicted that movement of zinc through the gastrointestinal tract increased when the highest level of copper was fed and the urinary zinc excretion rate tended to increase. The fractional rate constant representing absorption of zinc decreased slightly when the highest level of copper was fed. Total body zinc was predicted to be approximately 2,000 mg, with 95% in tissues other than the liver, red blood cells, or plasma and approximately 2.25% in the blood (with 95% of that in the red blood cells), which follows expected zinc masses within the body and those predicted by previous models.

Adult↗
PubMed1993

Isotope ratios of molybdenum determined by thermal ionization mass spectrometry for stable isotope studies of molybdenum metabolism in humans.

Methods were developed to separate and purify Mo from biological samples and to measure isotopic ratios in 1 microgram of Mo. A magnetic sector, thermal ionization mass spectrometer was used with simultaneous collection of five isotopes. Isotopic ratios were corrected for mass fractionation by iterative normalization using the 96/98 ratio. Ion beam intensity was enhanced by using a double-filament configuration, loading samples onto evaporation filaments with silica gel and boric acid. A triple-isotope-dilution approach was used, so the method could be applied to two-tracer studies of Mo metabolism in human subjects. 94Mo was added to samples prior to purification to quantify the total Mo content of samples and to determine the amounts of enriched 97Mo and 100Mo appearing in urine and fecal samples of study participants. The three ratios, 94/98, 97/98, and 100/98, were determined with within-run precision of from 0.06 to 0.10% (RSD). Precision of the ratios between replicates was from 0.05 to 0.08%.

Boric Acids↗
PubMed1992

Vitamin B-6 depletion followed by repletion with animal- or plant-source diets and calcium and magnesium metabolism in young women.

An 84-98-d study was conducted in young women to determine the effect of vitamin B-6-deficient diets on calcium and magnesium metabolism. A vitamin B-6-deficient formula diet fed initially was followed by either animal- or plant-source protein food diets containing four increasing amounts of vitamin B-6. Calcium balance was negative during vitamin B-6 depletion. Serum calcium was higher and calcium balance negative with the plant protein diets. Magnesium balance was negative during vitamin B-6 depletion due to increased urinary magnesium excretion. Urinary calcium decreased during vitamin B-6 depletion and increased as dietary vitamin B-6 increased. Urinary oxalate was significantly higher at the end than at the beginning of vitamin B-6 depletion and was higher with plant than animal protein diets. The results suggest that vitamin B-6 depletion may alter calcium and magnesium metabolism and that dietary components associated with the protein source may influence calcium retention.

Adult↗
PubMed1991

Bioavailability of dietary minerals to humans: the stable isotope approach.

A number of minerals contained in foods are essential nutrients for humans, animals, and/or plants. While most vitamins are very well absorbed, most essential minerals are not. Usual absorption of minerals ranges from less than 1% to over 90%. The bioavailability of dietary minerals must be considered when determining whether the diet contains enough, too little, or too much. By using stable isotope tracers as labels, the metabolic fate of minerals in a specific day's diet, a specific meal, or a food can be distinguished from minerals from other sources and followed. A number of mass spectrometric methods have been used to measure stable isotopes. Magnetic sector, thermal ionization mass spectrometry (TIMS) is used routinely in our laboratory to study bioavailability of Zn, Cu, and Fe. Other mass spectrometric methods that are less precise, but useful for many applications requiring isotopic determinations include quadrupole TIMS, inductively coupled plasma mass spectrometry (ICP/MS), and fast atom bombardment mass spectrometry (FAB/MS). One of the major advantages of stable isotope studies is that multiple isotopes of the same mineral can be used simultaneously and multiple minerals can be studied simultaneously. The use of stable isotopes for studies of bioavailability of minerals in foods has gained widespread interest in recent years. The approach is expected to be applied to an increasing number of food science and nutrition problems in the future.

Biological Availability↗
PubMed1991

A stable-isotope study of zinc, copper, and iron absorption and retention by young women fed vitamin B-6-deficient diets.

A 98-d study was conducted in young women to determine the effect of vitamin B-6-deficient diets on zinc, copper, and iron metabolism. Young women were fed vitamin B-6-deficient formula initially, followed by food diets containing four increasing amounts of vitamin B-6. Zinc, copper, and iron absorption, retention, and status were determined at intervals throughout the study. Zinc absorption and retention were greater during vitamin B-6 depletion but serum zinc declined, suggesting that absorbed zinc was not available for utilization. Copper absorption was lower during vitamin B-6 depletion but serum copper was not affected and balance was positive. Iron absorption was not impaired significantly by vitamin B-6-deficient diets but status may have declined. The results suggest that vitamin B-6 depletion of young women may alter zinc metabolism, inhibit copper absorption, and affect iron status. The effects of vitamin B-6 depletion differ markedly among these elements.

Absorption↗
PubMed1990

Copper status and urinary and salivary copper in young men at three levels of dietary copper.

Eleven young men were confined to a metabolic research unit for 90 d to determine the effect of the amount of dietary copper on copper nutriture. The study was divided into three metabolic periods (MP): 1) with an adequate-copper diet (1.68 mg/d) for 24 d, 2) with a low-copper diet (0.79 mg/d) for 42 d, and 3) with a high-copper diet (7.53 mg/d) for 24 d. Three indices of copper status, urinary copper, and salivary copper were determined at intervals throughout the study. Neither copper status, urinary copper, nor salivary copper differed among MPs. Sweat collections from three subjects suggested that losses of copper through sweat were very low and would not contribute significantly to copper balance. These results suggest that an amount of dietary copper slightly less than 0.8 mg/d is adequate to maintain copper status for greater than or equal to 42 d in normal, healthy men and that neither urinary nor salivary copper is affected by the amount of Cu in the diet.

Adult↗
PubMed1990

Milk's effect on the bioavailability of iron from cereal-based diets in young women by use of in vitro and in vivo methods.

A study was conducted in healthy young women to measure and compare the availability of iron from cereal-based diets with and without milk by use of in vivo and in vitro methods. In vitro iron-bioavailability tests demonstrated that the amounts of soluble and ionizable iron in cereal-based diets were increased two- and three-fold, respectively, when milk was added. 54Fe, a stable isotope of iron, and fecal monitoring were used to determine iron absorption in eight young women. Iron absorption was higher with milk than without milk in seven of the eight subjects but did not differ significantly between the two treatments. The results suggest that in vivo and in vitro effects differ and that the absorption of iron from cereal-based diets is neither enhanced nor inhibited by the addition of milk.

Absorption↗
PubMed1989

Protein utilization by young women consuming animal or plant protein diets at various levels of vitamin B-6 intake.

Eight young women consumed a vitamin B-6 depletion diet (egg albumen formula, less than 0.05 mg vitamin B-6/d) for 11-28 d. Subjects (n = 4) then consumed either animal protein (AP, mainly dairy and poultry products) or plant protein (PP, mainly various types of beans) diets with increasing vitamin B-6 intake (0.5, 1.0, 1.5, and 2.0 mg/d) for periods of 14-21 d. All diets provided 1.55 g protein/kg body wt. Apparent protein digestibility of AP (94.6%) was significantly higher than that of PP (88.4%) diets (p less than 0.001). Protein digestibility was not significantly affected by vitamin B-6 intake. Apparent nitrogen balance of subjects consuming AP diets was slightly, though not significantly, higher than that of subjects fed PP diets. N balance was not influenced by vitamin B-6 intake. Data suggest that short-term low vitamin B-6 intake does not affect protein utilization in humans as determined by digestibility and N balance.

Adult↗
PubMed1989

Copper absorption and retention in young men at three levels of dietary copper by use of the stable isotope 65Cu.

Eleven young men were confined to a metabolic research unit for 90 d to determine the effect of the level of dietary copper on absorption and retention. Cu absorption was determined by feeding the stable isotope 65Cu. Absorption and retention averaged 36.3 +/- 1.3% and 0.17 mg/d, respectively, with an adequate-Cu diet (1.68 mg/d). Absorption averaged 55.6 +/- 0.9% and retention averaged -0.316 mg/d for 6 d and 0.093 mg/d for the next 36 d of a low-Cu diet (0.785 mg/d). Absorption averaged 12.4 +/- 0.9% with a high-Cu diet (7.53 mg/d) and retention was strongly positive at first, decreasing linearly with time. The study demonstrated that Cu absorption is strongly dependent on dietary Cu level and that Cu balance can be achieved by most young men from a diet of 0.8 mg Cu/d. These results suggest that current dietary Cu recommendations may be higher than necessary. The apparent regulation of Cu absorption and endogenous losses would tend to protect humans from Cu deficiency and toxicity.

Adult↗
PubMed1989

The use of stable isotopes in mineral nutrition research.

Stable isotopes are valuable tools for research on mineral bioavailability and metabolism. They can be used as tracers with no exposure to radiation and they do not decay over time. Attempts to use stable isotopes of minerals as metabolic tracers were first described only 25 years ago. There were relatively few reports of their use over the next 15 years, but interest in stable isotopes has expanded markedly in the last 10 years. The advantages of stable isotope tracers are so great that scientists have been willing to accept the laborious and costly nature of mineral isotope analysis, and substantial progress has been made in the field. New applications for stable isotopes and new analytical methods have been introduced recently. However, limitations to the approach and methodological problems remain to be resolved. This review describes early work in the field and discusses the advantages and disadvantages of stable isotope tracers and of the various methods of analysis. Information discovered with stable isotopes is reviewed, and probable future applications are discussed.

Biological Availability↗
PubMed1988

Copper nutriture, bioavailability, and the influence of dietary factors.

Copper is known to be an essential nutrient for human beings, but a Recommended Dietary Allowance has not yet been established. A safe and adequate range of intake was established in 1980 for copper and five other trace elements. The range for copper, 2 to 3 mg/day, is higher than the usual dietary copper intake of many individuals in this country. On the basis of balance studies, a requirement of 1.3 mg/day has been suggested. Recent data on copper intake and bioavailability should aid in reevaluating the dietary copper requirement. Copper deficiency symptoms have seldom been observed in human beings. When copper deficiency has been recognized, it has been under unusual conditions, such as in patients receiving parenteral nutrition. Interactions between copper and other dietary components may alter copper status, but the impact of those interactions is not yet well understood. Dietary factors that may affect the bioavailability of copper include the levels of copper, zinc, and molybdenum in the diet; iron deficiency; ascorbic acid intake; intake of carbohydrates, including fructose, glucose, and starch; and fiber and phytate intakes. Some drugs may also affect copper bioavailability.

Copper↗
PubMed1987

Effect of varying ascorbic acid intakes on copper absorption and ceruloplasmin levels of young men.

Intestinal copper absorption and blood measures of copper status were studied in healthy young men receiving varying intakes of ascorbic acid (AA) over 14 wk in a live-in nutrition suite. Copper absorption and retention were assessed by measuring absorption of a stable isotope of copper and total fecal copper during four AA intake periods: 2 wk x 65 mg AA/d, 4 wk x 5 mg/d, 3 wk x 605 mg/d and 4 wk x 5 mg/d. Measures of copper status were serum copper and serum ceruloplasmin determined by both enzymatic and immunochemical methods. Copper absorption, copper retention, total serum copper and the serum level of ceruloplasmin protein were not affected significantly by the changes in AA intake; however, the oxidase activity of serum ceruloplasmin was decreased an average of 21% during the high (605 mg/d) AA intake period. The results suggest that in adult men moderate supplemental intakes of AA reduce ceruloplasmin oxidase activity specifically but do not depress intestinal copper absorption or overall body copper status.

Adult↗
PubMed1987

Zinc protoporphyrin. Past, present, and future.

The course of zinc protoporphyrin research has progressed at an increasingly rapid pace on several fronts. A variety of biochemical and clinical evidence viewed in toto now suggests that ferrochelatase catalyzes zinc protoporphyrin formation in states of relative iron-deficient erythropoiesis and in lead-inhibited iron metabolism. Furthermore, a redefinition of the relationship of zinc protoporphyrin to certain other parameters of iron status has been made based upon changes during the earliest states of iron depletion. These clinical studies show that the zinc protoporphyrin level and the ferritin level vary in concert but that changes in the percent transferrin saturation and in the hematocrit results are less consistent. Thus zinc protoporphyrin and ferritin are closely linked metabolically such that iron-deficient erythropoiesis becomes an initial manifestation of iron depletion. The measurement and expression of results as mumoles zinc protoporphyrin/mole heme have improved the quality of results, partly by the elimination of the assumed hematocrit designed into existing instruments. Other refinements in hematofluorometry technology have permitted exploration of the potentially extensive applications of zinc protoporphyrin measurements for lead surveillance and diagnosis, blood banking, pediatrics, obstetrics, sports medicine, and other clinical situations where a very sensitive, cost-effective indication of iron status is required.

Erythrocytes↗
PubMed1986

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.

Absorption↗
PubMed1986

Effect of chlorthalidone on zinc levels, testosterone, and sexual function in man.

This study was designed to test the hypothesis that chlorthalidone, a diuretic used to treat hypertension, depletes body zinc enough to interfere with testosterone production and thereby cause sexual dysfunction. Serum and hair zinc, serum testosterone, and sexual function were measured in 19 middle-aged hypertensive men who had been taking chlorthalidone in average daily doses of between 11 and 50 mg per day for at least 6 months, and a control group of 31 unmedicated middle-aged normotensive men. Although the medicated group had a higher incidence of sexual dysfunction (42% as compared to 16% in the control group), use of chlorthalidone did not significantly affect serum testosterone levels. When other variables were controlled for, medicated men had significantly higher serum zinc levels, and men on the highest dosage of chlorthalidone had higher hair zinc levels than all other men. There was no significant correlation between hair zinc, serum zinc, testosterone, and sexual function. Serum zinc decreased significantly with age (p = 0.043) and with ethanol intake after controlling for age (p = 0.032). Sexual dysfunction occurred more often in older men (p = 0.002). In the unmedicated controls, prevalence of dysfunction increased slightly with increasing serum potassium levels.

Adult↗
PubMed1985

A stable isotope study of copper absorption in young men: effect of phytate and alpha-cellulose.

A sixty-three day study was conducted with young men confined to a metabolic unit to study the effects of alpha-cellulose and phytate on copper absorption. Copper absorption was determined with 65Cu, a stable isotope of copper, during each of 3 dietary treatments (basal diet, basal diet + alpha-cellulose, or basal diet + phytate). The addition of alpha-cellulose or phytate to the basal diet did not affect copper absorption. Average copper absorption was 35.0% from the basal diet, 34.1% from the diet with 0.5 g alpha-cellulose per kg body weight added, and 31.4% from the diet with 2.34 g of phytate as sodium phytate added to the diet. Copper absorption was significantly different between subjects and averaged 44.1%, 26.8%, 33.4%, and 29.5% in individual subjects. The results suggest that high levels of either alpha-cellulose or phytate do not have marked effects on copper absorption, but copper absorption differs between individuals.

Adult↗