Vitamin B-6 requirement and status assessment: young women fed a depletion diet followed by a plant- or animal-protein diet with graded amounts of vitamin B-6.

The vitamin B-6 requirement of young women consuming a high-protein diet (1.55 g/kg body wt) and the effect of protein quality on this requirement was studied. In addition, the response of clinical, functional, and biochemical measures of vitamin B-6 nutriture to short-term depletion and step-wise repletion of vitamin B-6 were evaluated. Eight healthy young women resided in a metabolic unit and were fed a formula depletion diet (< 0.05 mg vitamin B-6/d) for 11-28 d followed by either an animal-protein (AP) or plant-protein (PP) diet with successively increasing vitamin B-6 intakes (0.5, 1.0, 1.5, and 2.0 mg/d) for periods of 14-21 d. Animal proteins were primarily from dairy and poultry sources and plant proteins were primarily from legumes. Vitamin B-6 status measures were assessed at weekly intervals. Results showed that a PP diet does not elevate the vitamin B-6 requirement over that required for an AP diet given the high amount of dietary protein used in this study. It was also found that 0.015 mg vitamin B-6/g protein intake normalized most biochemical indexes of vitamin B-6 status (including those indicative of functional status), and that 0.020 mg/g protein normalized all biochemical measures except total urinary vitamin B-6. Adding a margin of safety to either the 0.015 or 0.020 mg/g protein intake would raise the vitamin B-6 requirement for young women above the currently recommended dietary allowance of 0.016 mg/g protein.

Insensitivity of the tryptophan-load test to marginal vitamin B-6 intake in rats.

The tryptophan-load test for vitamin B-6 nutritional status was administered to adult female Long-Evans rats fed graded levels of pyridoxine hydrochloride (PN.HCl) in two experiments, and its sensitivity to marginal vitamin B-6 intake was evaluated. In Experiment 1, rats were 4-h meal-fed an AIN-76A (20% casein) diet devoid of PN.HCl for 3 wk, then repleted (n = 12) for 6 wk with 4-h pair-fed meals of either 0.25, 0.5, 1.0 or 7.0 (control) mg PN.HCl/kg diet. In Experiment 2, rats (n = 16) were pair-fed for 10 wk either 0.0, 0.5, 1.0 or 7.0 (control) mg PN.HCl/kg diet, with 24-h access to food. Vitamin B-6 nutritional status was assessed at the end of each experiment. Except in rats fed 0 mg PN.HCl/kg diet, mean body weights were not significantly different among diet groups of either experiment. Plasma pyridoxal phosphate (PLP), pyridoxal and total vitamin B-6 concentrations, determined by HPLC, were very sensitive to gradations in dietary PN.HCl concentrations (P less than 0.05). Red blood cell endogenous and PLP-stimulated alanine and aspartate aminotransferase activity did not statistically differentiate all levels of dietary vitamin B-6, although the calculated activity coefficient for each enzyme (stimulated/endogenous activity) did. Urinary xanthurenic acid excretion following a tryptophan load [24.5 mumol (5 mg) L-tryptophan/100 g body weight, injected intraperitoneally] was significantly (P less than 0.05) elevated compared with controls only in the group fed 0 mg PN/HCl/kg diet. At the tryptophan dose used here, the tryptophan-load test was not useful in detecting marginal vitamin B-6 intake in rats.

Ascorbic acid and erythorbic acid metabolism in nonpregnant women.

Ascorbic acid (AA) metabolism and requirements were studied in 11 adult nonpregnant women maintained in a metabolic unit and fed a formula diet devoid of AA for 54 d. After depletion for 24 d, the subjects received increasing supplements of AA in the presence or absence of 600 mg/d of erythorbic acid (EA). Various analytical procedures were used to measure AA concentrations in blood components. The depletion period resulted in a marked decrease in AA in all blood indices. During the study scorbutic signs developed in some of the subjects. AA supplements of 30 mg/d for 10 d failed to increase plasma ascorbate concentrations; 60 mg/d for 10 d produced a small increase; 90 mg/d resulted in a mean AA concentration of 29 mumol/L. EA did not present any adverse effects, but rather had a small sparing effect. Vitamin C requirements for adult nonsmoking, nonpregnant women would be marginally met by an intake of 60 mg/d of AA whereas 90 mg/d would provide an allowance for body storage.

Evaluation of vitamin B-6 status and function of rats fed excess pyridoxine.

We compared the vitamin B-6 status of 12-wk-old rats (n = 12) fed excess (1400 mg/kg diet) or the recommended level (7 mg/kg diet, control) of pyridoxine (PN) hydrochloride to test if excess vitamin B-6 would cause tissue depletion of pyridoxal phosphate (PLP), the active coenzyme form of vitamin B-6. Plasma PLP, tryptophan-load test results, food intake, and tissue and body weights were not different at wk 6. Red blood cell endogenous alanine aminotransferase activity and PLP concentration were elevated (P less than 0.01) in rats fed 1400 mg PN.HCl/kg diet. In contrast, PLP concentration in muscle was significantly lower (P = 0.01) in rats fed excess vitamin B-6 (9.7 +/- 0.8 nmol/g, mean +/- SEM) than in controls (14.9 +/- 1.4). PLP concentration in other tissues, including plasma, was not affected. In rats fed excess vitamin B-6, pyridoxal was increased in all tissues examined (P less than 0.05), and total vitamin B-6 was increased in plasma, red blood cells and kidneys (P less than 0.05). Total glycogen phosphorylase (a + b) activity in the gastrocnemius was not affected, but phosphorylase a activity was increased in rats fed excess vitamin B-6 (P = 0.025). Concentrations of dopamine and metabolites in the caudate nucleus of the basal ganglia were not affected. A transient, but significant, elevation in acoustic startle response, a central nervous system reflex, was observed in rats fed excess vitamin B-6. The depletion in muscle PLP could not hae been predicted by either plasma or red blood cell PLP concentration, although the latter did reflect vitamin B-6 intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Folate requirement and metabolism in nonpregnant women.

Folate metabolism and requirements were studied in 10 adult nonpregnant women maintained for 92 d in a metabolic unit. After a folate depletion period of 28 d, the subjects received increasing supplements of folate from food items or as pteroylmonoglutamic acid (PGA). Plasma folate levels fell 60% during the depletion period and continued to fall until 200 micrograms/d of naturally occurring food folates were provided. Supplements of 300 micrograms/d of naturally occurring folates produced a small rise in plasma folate levels although erythrocyte folate levels continued to fall. Lymphocyte deoxyuridine suppression, neutrophil hypersegmentation, and other measurements related to folate metabolism were performed. When compared with PGA, dietary folates appeared to be no more than 50% available. A daily intake of 200-250 micrograms of dietary folates appears to meet the folate requirements of nonpregnant adult women whereas an intake of 300 micrograms/d provides an allowance for storage.

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.

Biochemical indices of human vitamin C status.

Biochemical indicators of ascorbic acid (AA) status were studied in eleven young adult males fed the same AA deficient diet for 14 wk in a live-in metabolic unit. Supplements of AA were added to the diet to give AA-intake periods of 65 mg/d (2 wk), 5 mg/d (4 wk), 605 mg/d (3 wk), 5 mg/d (4 wk), 605 mg/d (4 d), and 65 mg/d (3 d). Blood plasma, erythrocyte, and leukocyte AA levels all reflected AA intake, however, plasma AA showed less variability than red cell AA levels and was considerably easier to determine than leukocyte AA. Plasma AA values less than 0.40 mg/dL (23 mumol/L) reflected marginal AA status. The daily AA intake calculated to maintain plasma AA levels of at least 0.4 mg/dL (23 mumol/L) in healthy young men was 41 mg. The average AA intake estimated to maximize the total body pool was 138 mg/d. Urine and salivary AA levels were not useful indicators of AA status because urinary AA levels did not discriminate well between adequate and deficient AA intakes and salivary AA levels did not consistently reflect AA intake.

Simple method for bleeding the unanaesthetized rat by tail venipuncture.

A technique is described for the intermittent collection of blood from the rat tail. By using commonly available equipment, blood samples can easily be obtained from rats without the need for anaesthesia. The development of this technique makes the rat more readily available as an animal model for repeated withdrawals of small blood samples for pharmacokinetic or bioavailability evaluations.

Experimental vitamin C depletion and supplementation in young men. Nutrient interactions and dental health effects.

Biochemical indices of AA clearly showed that the young men in this study were brought into various states of AA depletion and repletion according to their dietary AA intakes. While previous studies have postulated that supplemental intakes of AA may adversely affect body status of vitamins B6 and B12, we found no changes in the B vitamin status of the young men receiving varying AA intakes. Moderate AA supplementation (605 mg/day) showed no antagonistic effect on markers of vitamins B6 and B12. Blood markers of fat-soluble vitamins A and E and iron status were not affected by AA intakes. The propensity of the gingiva to become inflamed or bleed on probing was reduced after normal (65 mg/day) AA intakes as compared to deficient (5 mg/day) intakes and upon supplementary (605 mg/day) AA intakes as compared to normal intakes. The results suggest that AA status may influence early stages of gingival inflammation and crevicular bleeding, and warrant further study of the relationship between AA and periodontal health.

Wholesomeness of Irradiated Foods.

The history and applications of food irradiation are reviewed. The term wholesomeness when applied to food irradiation, embodies the concepts of microbiological and toxicological safety, and nutritional adequacy. The status of these areas of concern is reviewed. Nutritional studies have addressed the effects of irradiation on nutrient content and bioavailability, and evaluation of potential consequences of changes in either. Results of rat studies are presented in which we tested for the presence of anti-thiamin and anti-pyridoxine activity in radappertized chicken and beef. Test meats were analyzed for thiamin and pyridoxine to establish a basis for incorporation into repletion diets. Thiamin levels in gamma- and electron-irradiated, and thermally processed (commercial canning) chicken were 74, 34 and 78%, respectively, of the vitamin level in a frozen meat reference; the levels in beef were 77, 56 and 79%, respectively. Pyridoxine levels in chicken were 50, 38 and 17%, respectively, of the reference level. Rats were depleted in each vitamin, then repleted at two vitamin levels with diets containing test meats. Activities of transketolase, aspartate aminotransferase and alanine aminotransferase in erythrocytes from these rats provided no consistent evidence of antivitamin presence. It was concluded that these irradiated meats pose no problem regarding vitamins B1 and B6 if part of a complete diet.

Plasma ascorbic acid in adult males: effects of depletion and supplementation.

We investigated effects of moderately elevated oral doses of ascorbic acid (AS) on plasma AS turnover in healthy men after abrupt alterations in AS intake. Subjects ate a basal diet of conventional food in which only AS intake was changed. Blood specimens were collected from fasted subjects twice each week during depletion periods. Deproteinized plasma was analyzed after derivatization with 2,4-dinitrophenylhydrazine. Subjects remained healthy and never became frankly scorbutic. The kinetics of log-converted plasma AS values for the depletion periods demonstrated that the slopes calculated by least squares were up to 56% higher for six of nine subjects after 600 mg AS/day. The difference between the mean slopes (M) for loss of plasma AS was significantly different (p less than 0.05, n = 6) after 60 mg AS (M = -0.0222 +/- 0.0145) than after 600 mg AS (M = -0.0246 +/- 0.0003). Leukocyte AS concentration decreased 44.6% in the first depletion period and 77.1% in the second.

Comparison of hemoglobin values in black and white male U.S. military personnel.

Black and white male military personnel were studied to determine if hemoglobin (Hb) differences existed between the two groups, and if so, whether they were due to dissimilar nutrient intakes or to different patterns of vitamin and mineral self-therapy. Data analyses showed that black males (n = 331) had a 0.27 g/dl lower mean Hb than white males (n = 2268, P = 0.006). However, when only black (n = 60) and white (n = 371) subjects with known iron intakes at or above the recommended level were compared, the differences in the Hb of the two groups became smaller. The serum ferritin values of both of the latter groups appeared adequate for unimpaired Hb synthesis. The use of vitamin and mineral supplements did not differ significantly between the two groups. Adequate intakes of the hemopoietic nutrients resulted in higher Hb levels for both black and white males; at these levels of nutrient intakes the differences in the Hb values of black and white subjects were smaller than those previously reported. Studies comparing the Hb levels of black and white personnel should consider the level of iron intake of the two groups before drawing conclusions about the magnitude and implications of observed differences in Hb concentrations.

Protein metabolism during intensive physical training in the young adult.

Two groups of men consumed two levels of protein (1.4 and 2.8 g/kg body weight) during a 40-day experimental period. Physical activity and the sweat rates were fairly high during the entire experimental phase. Urinary nitrogen excretions remained fairly constant for both groups during the training and heavy physical activity periods. Nitrogen balances were positive exclusive or inclusive of the daily sweat nitrogen losses showing nitrogen retention. The essentially unchanged blood hemoglobin and serum protein levels showed that the control group was receiving an adequate protein intake to maintain nitrogen equilibrium, under conditions of fairly heavy physical acitvity. Although others may have suggested some compensatory reductions in the urinary excretion of nitrogen under conditions of profuse sweating, our data have not supported these conclusions. It appears that sweat losses of nutrients become relevant in determining requirements and will increase in importance as sweat rates are increased. The data again demonstrate that the nutrient losses during profuse sweating consitute an error that could seriously invalidate the accuracy of metabolic balance studies. In this study, although the men did increase body protein stores and muscle mass with high-protein diets, the additional body protein did not enhance physiological work performance. It is suggested that in this sutdy 100 g of protein/day was adequate for men performing fairly heavy work.