Thermogenesis and thermoregulatory function of iron-deficient women without anemia

Physiological responses at 16 degrees C were studied in 11 women, age 28 +/- 2(mean +/- S.E.) years and 26 +/- 2% fat, after their body iron stores were depleted by diet (5.0 mg iron x 2,000 kcal-1 x d-1), phlebotomy and menstruation for about 80 d and were repleted by diet (13.7 mg iron x 2,000 kcal-1 x d-1) for about 100 d, including daily iron supplementation (50 mg of iron as ferrous sulfate) for the last 14 d of repletion. Iron depletion was characterized by a decline (p less than 0.05) in hemoglobin (12.0 +/- 0.2 g x dl-1), ferritin (5.5 +/- 0.5 ng x ml-1) and body iron balance (-9.1 +/- 2.6 mg x 6 d-1). Iron repletion, including supplementation, increased (p less than 0.05) hemoglobin (12.6 +/- 0.1 g x dl-1), ferritin (9.5 +/- 0.4 ng x ml-1) and iron balance (+67 +/- 6.7 mg x 6 d-1). Iron depletion reduced (p less than 0.05) metabolic heat production (49.6 +/- 1.1 vs 53.6 +/- 1.2 W x m-2) during acute cold exposure. The rates of cooling of the core and periphery were greater (p less than 0.05) during iron depletion than repletion. A shift in the lower core temperature threshold for shivering was paralleled by an earlier onset of shivering (p less than 0.05) in iron depletion indicating an adaptation in cold tolerance in an attempt to maintain core temperature. Iron depletion was associated with blunted post-exposure increases in plasma thyroid hormone concentrations and greater (p less than 0.05) increases in plasma norepinephrine concentrations as compared to iron repletion. In a subsample of the women, no significant effect of calcium or ascorbic acid supplementation was found on responses to cold exposure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of long-distance running on iron metabolism and hematological parameters

In 110 well-trained participants of a 1000-km running competition lasting for 20 days hematological parameters, iron metabolism, and their respective changes during the race were investigated. Thirty-nine men and 11 women were accustomed to wholesome vegetarian food (lacto-ovovegetarian), 52 men and 8 women consumed a conventional western diet. In each group 50% of the runners finished the race. Before the competition started red blood cell count, hematocrit, and hemoglobin were on average below the values observed in the normal population in all groups. Both male and female runners consuming the wholesome diet showed significantly lower ferritin values than those on a western diet. During the first days of the competition hemolysis occurred leading to increased serum concentrations of bilirubin and iron and decreased haptoglobin levels. Hb concentrations showed a constant decrease during the race. Serum ferritin concentration rose about twofold within the first days and then decreased again without reaching pre-race levels. Serum iron concentrations showed a significant decrease between days 3 and 6. Iron loss was caused by hematuria (25% of all urines tested), gastrointestinal blood loss (10% of all stool specimens tested), and by sweating (4.5 micrograms iron/dl sweat). Our results suggest that especially in female long-distance runners it may be difficult to supply sufficient quantities of iron with the diet.     

The effects of prelatent/latent iron deficiency on physical work capacity

In order to examine the effects of mild iron deficiency on physical work capacity, 40 prelatent iron-deficient female endurance runners were studied before and after 8 wk of supplementation with either oral iron (320 mg ferrous sulfate) or a matching placebo. Subjects underwent the following physical work capacity tests: the Wingate cycle ergometer test, the anaerobic speed test, the ventilatory threshold, VO2max, and maximal treadmill velocity during the VO2max test. Muscle biopsy samples pre- and post-treatment were obtained from 17 of the subjects, and these were assayed for citrate synthase and cytoplasmic alpha-glycerophosphate dehydrogenase activity. Subjects were randomly assigned to one of the treatment groups, and a double-blind method of administration of the supplements was used. The differences in improvement scores between the two groups on the work capacity and enzyme activity variables were statistically nonsignificant (P greater than 0.05). Serum ferritin values rose from a mean of 12.4 +/- 4.5 to 37.7 +/- 19.7 ng.ml-1 for the experimental group and from 12.2 +/- 4.3 to 17.2 +/- 8.9 ng.ml-1 for the controls (P = 0.0025), whereas hemoglobin levels remained fairly constant for both groups (P = 0.6). Eight weeks of iron supplementation to prelatent/latent iron-deficient, physically active females did not significantly enhance work capacity. Within the limitations of this study, the presence of a serum ferritin below 20 ng.ml-1 does not pose a significant handicap to physical work capacity.     

Sweat iron loss of male and female runners during exercise

Male (n = 9) and female (n = 8) collegiate cross-country runners were studied during a training session to determine the amount of iron lost in the sweat. Sweat samples were collected from the arm using polyethylene bags. Total sweat loss was determined by weighing subjects before and after the runs. Average time of sweat collection was 42 min for males and 39 min for females. Sweat rate for the males (717.5 +/- 145.9 g/m2/h) was significantly greater than for the females (460.1 +/- 142.9 g/m2/h); however, the sweat rate per km was not significantly different. Females had a significantly greater sweat iron concentration (0.417 +/- 0.024 mg/l) than males (0.179 +/- 0.011 mg/l). Rate of sweat iron loss was not significantly different for females (0.276 +/- 0.140 mg/h) and males (0.21 +/- 0.13 mg/h). Sweat iron concentration was inversely related with sweat rate (r = -0.64). Our data suggest that although males lose more total sweat than females, the higher sweat iron concentration of females leads to similar rates of iron loss. For female runners, sweat iron loss coupled with a low dietary iron intake may result in a negative iron balance.     

The frequency of anemia and iron deficiency in the runner

The current consensus is that runners commonly experience a mild anemia influenced by iron deficiency. We compared hematologic parameters of 72 (35 males and 37 females) runners with 48 (27 males and 21 females) nonrunners and assessed the impact of iron supplementation. Male runners had lower hemoglobin (Hb) values than male nonrunners (14.8 vs 15.3 g.dl-1) (P less than 0.05) regardless of iron usage. Female runners had higher (P = 0.05) Hb values than female controls (13.5 vs 12.8 g.dl-1). Female runners off iron had Hbs similar to controls off iron (P = 0.30). Iron parameters (total serum iron, TSI; total iron-binding capacity, TIBC; percent saturation of the TIBC, %sat TIBC; and serum ferritin) of runners vs controls, runners vs runners (on or off iron), and nonrunners vs nonrunners (on or off iron) were comparable except 1) male runners off iron had lower (P less than 0.05) %sat TIBC values (26%) than male runners on iron (34%) and 2) female runners taking iron had ferritin values (32 ng.ml-1) similar to those of female nonrunners taking iron (39 ng.ml-1) but higher (P less than 0.05) than their counterparts off iron (15 and 15 ng.ml-1, respectively). This study concludes that running affects Hb in a variable manner and suggests that the runner's iron status is similar to that of the general population.     

Effect of iron supplementation on endurance capacity in iron-depleted female runners.

The purpose of this investigation was to examine the effects of oral iron supplementation on endurance performance in initially iron-depleted, nonanemic female distance runners. Eighteen iron-depleted (serum ferritin less than 20 ng.ml-1, hemoglobin greater than or equal to 12 g.dl-1) women (22-39 yr) performed a VO2max test and an endurance run to exhaustion. Subjects were pair-matched on the basis of endurance time and then randomly assigned to an iron supplement or a placebo group. Following supplementation, the iron group had a significantly higher (P = 0.03) mean serum ferritin concentration (23.4 vs 15.7 ng.ml-1) and lower (P = 0.04) mean total iron-binding capacity than the placebo group. Both groups increased their time to exhaustion (25.5% and 22.2% for the iron and placebo groups, respectively) but were not significantly different (P = 0.72) from each other. There were also no differences (P greater than 0.05) between the groups with respect to lactate concentrations and physiological measures taken during the two exercise tests. The results of this study suggest that 8 wk of oral iron supplementation improves iron status in iron-depleted female distance runners, but does not enhance endurance capacity.     

Adverse effects of dietary and furosemide-induced sodium depletion on thermoregulation

In this study, the diuretic furosemide was used in combination with dietary sodium (Na) restriction to quantify the effects of moderate to severe Na depletion on heat tolerance in a validated model of heat stress in rats. Rats were subjected to an Na depletion regimen as follows: a control group (I, n = 17) had free access to a normal diet and tap water; group II (n = 20) consumed the same normal diet and tap water, but was treated with the diuretic furosemide at a dose of 10 mg.kg-1.d-1, ip; group III (n = 18) had free access to an Na-free diet and deionized drinking water; group IV (n = 21) consumed the same Na-free diet and electrolyte-free water, but was also treated with furosemide. Both the dietary and drug manipulations affected significant (p less than 0.05) negative electrolyte and water balances. Group IV consistently exhibited the greatest decrements. Following the 4-d depletion all four groups were acutely exposed to a 42 degrees C, 25-30% rh environmental heat stress during which time core body temperature increased. The time required for rectal temperature to reach 42.6 degrees C was significantly (p less than 0.05) decreased from a time of 242 +/- 8 min in the control group to 176 +/- 14, 181 +/- 8, and 111 +/- 11 min in groups II, III and IV, respectively. We concluded that Na deprivation and diuretic treatment can elicit a 25-50% reduction in heat tolerance due to electrolyte depletion and dehydration. These data confirm that during environmental heat stress uncompensated negative Na balance may predispose an individual to heat illnesses.     

Changes in selected blood measures during repeated days of intense training and carbohydrate control

Ten runners were studied to determine whether selected blood measures were useful indices of the metabolic stress associated with intense training and dietary carbohydrate (CHO) deficiency. The runners performed two diet/training regimens, involving 5 repeated days of intense training approximately 80 min/d, approximately 80% VO2max) and dietary CHO control (8.0 g.kg-1.d-1, EQ-CHO; 3.9 g.kg-1.d-1, LO-CHO). Resting blood samples were obtained after a 3-day control period, after 3 and 5 days of intense training, and after 3 days of rest. Resting uric acid levels were significantly higher (P less than 0.05) after 3 and 5 days of training during the LO-CHO vs EQ-CHO regimen (353 +/- 21 vs 309 +/- 24, and 345 +/- 26 vs 302 +/- 26 mol.l-1, respectively). Resting thyroxine (T4) levels were higher (P less than 0.05) after 5 days of training during the LO-CHO vs EQ-CHO regimen (102.2 +/- 6.2 vs 83.7 +/- 4.5 nmol.l-1, respectively). While creatine kinase levels were elevated after both regimens (P less than 0.05), there was no difference between regimens. Serum cortisol (C) levels were reduced by 10% for both regimens (P less than 0.05), possibly due to an expansion in plasma volume (7.6 and 7.3% for the LO-CHO and EQ-CHO regimens, respectively). Resting FFA levels were increased (P less than 0.05) during both regimens, but there was no difference between the regimens.(ABSTRACT TRUNCATED AT 250 WORDS)     

Iron status of women distance runners, sprinters, and control women

Fasting blood samples from 11 women distance runners, 12 sprinters, and 11 moderately active women were examined to determine iron status. Dietary iron intake and bioavailability were analyzed from 3-day food diaries. Both distance runners and sprinters had lower hematocrits and haptoglobins than moderately active women. Distance runners had significantly lower ferritin (15.8 micrograms/l) than sprinters (32.8 micrograms/l), but moderately active women's ferritin (26.1 micrograms/l) was not significantly different than in the other groups. Five distance runners, two sprinters, and one moderately active woman had ferritins below 12 micrograms/l, which suggests iron depletion. Differences in hemoglobin, plasma iron, transferrin, and food iron intake were not significant among the three groups. Absorbable iron and heme iron intake were significantly lower for the distance runners and control women than the sprinters. The results suggest that low ferritin is more common among women who train for distance events than for sprints. This difference may by due to differences in bioavailability of food iron intake.     

Vegetarian diets : nutritional considerations for athletes

The quality of vegetarian diets to meet nutritional needs and support peak performance among athletes continues to be questioned. Appropriately planned vegetarian diets can provide sufficient energy and an appropriate range of carbohydrate, fat and protein intakes to support performance and health. The acceptable macronutrient distribution ranges for carbohydrate, fat and protein of 45-65%, 20-35% and 10-35%, respectively, are appropriate for vegetarian and non-vegetarian athletes alike, especially those who perform endurance events. Vegetarian athletes can meet their protein needs from predominantly or exclusively plant-based sources when a variety of these foods are consumed daily and energy intake is adequate. Muscle creatine stores are lower in vegetarians than non-vegetarians. Creatine supplementation provides ergogenic responses in both vegetarian and non-vegetarian athletes, with limited data supporting greater ergogenic effects on lean body mass accretion and work performance for vegetarians. The potential adverse effect of a vegetarian diet on iron status is based on the bioavailability of iron from plant foods rather than the amount of total iron present in the diet. Vegetarian and non-vegetarian athletes alike must consume sufficient iron to prevent deficiency, which will adversely affect performance. Other nutrients of concern for vegetarian athletes include zinc, vitamin B12 (cyanocobalamin), vitamin D (cholecalciferol) and calcium. The main sources of these nutrients are animal products; however, they can be found in many food sources suitable for vegetarians, including fortified soy milk and whole grain cereals. Vegetarians have higher antioxidant status for vitamin C (ascorbic acid), vitamin E (tocopherol), and beta-carotene than omnivores, which might help reduce exercise-induced oxidative stress. Research is needed comparing antioxidant defences in vegetarian and non-vegetarian athletes.     

Poor iron status of women runners training for a marathon

The iron status of nine female marathon runners was evaluated during 11 weeks of training for a marathon race and following a marathon race. Venous blood samples were obtained at the start of the training period, weekly during training, and 1, 2, 3, and 4 days post-race. The subjects completed menstrual and dietary histories, and the diet content of energy, protein, iron, and ascorbic acid was calculated. Serum iron, total iron binding capacity, and transferrin saturation showed no significant change at weeks 1, 7, and 11 during training. The mean values of serum iron and transferrin saturation were low. During training, eight of the nine women averaged serum ferritin levels below 50 ng/ml, one of the eight having values consistently less than 10 ng/ml. Ferritin values were significantly elevated for 3 days after the marathon. No subject reported abnormally heavy menstrual bleeding, and nutrient intakes were near recommended levels, except for iron. Thus, the iron status of these women marathon runners was poor, suggesting that women runners may have higher dietary needs for iron than sedentary women. Serum ferritin levels were also elevated after a marathon run and may not adequately reflect iron stores.     

Changes in the protein nutritional status of adolescent wrestlers

The protein nutritional status of adolescent wrestlers was studied to determine whether changes occur during a season of competition and weight loss. Subjects (N = 18) were measured prior to the start of the season (PRE), twice in the midseason, and once during late season (LATE) for weight, percent body fat, and height. At each of these times, a venous blood sample was obtained from the subjects, who were fasted, and analyzed for concentrations of albumin, prealbumin, retinol binding protein (RBP), blood urea nitrogen (BUN), hemoglobin, hematocrit, and 23 amino acids. Diet records were kept by subjects to assess daily energy, protein, fat, and carbohydrate intake. Data were analyzed by repeated measures ANOVA. Results showed that wrestlers decreased weight by an average of 6.6 +/- 0.9% and that percent body fat, fat-free weight, plasma levels of prealbumin and RBP, the ratio of total essential amino acids to total amino acids, and dietary energy nutrient intakes were significantly lower at LATE compared to PRE. RBP decreased during midseason and averaged (+/- SE) 3.21 +/- 0.15 mg.100 ml-1 at LATE; prealbumin was significantly lower at LATE with a mean value of 19.8 +/- 1.0 mg.100 ml-1. Total energy intake decreased from PRE values by 35%, to approximately 27 kcal.kg-1.d-1 during the season. In conclusion, in these high school wrestlers who lost approximately 6.6% of weight, there were adverse effects on some of the indices of protein nutritional status.     

Effect of chronic endurance exercise on retention of dietary protein

On two separate occasions, five well-trained endurance runners (VO2max = 71 +/- 5 ml/kg/min; means +/- SD) consumed a meat-free diet for 6 days. For one trial the subjects consumed the recommended dietary allowance (RDA) of protein (REC-PRO = 0.86 +/- 0.23 g/kg body wt/day). Protein intake for the other trial was 1.7 times higher (HI-PRO = 1.49 +/- 0.29 g/kg body wt/day). Each subject followed his regular training program (12-16 km running/day), and on day 5 of each diet completed a treadmill run at a similar intensity and duration (75 min at 72% VO2max). Seventy-two hour urinary urea N loss (days 4, 5, and 6 of each diet) and day 5 exercise sweat urea N excretion were measured. Serum urea N and creatinine increased significantly during the treadmill run under both dietary conditions (P less than 0.05). No significances between diet differences were observed in sweat or urinary urea N excretion; however, excretion of both tended to be higher on the REC-PRO diet than on the HI-PRO diet. The differences in protein intake combined with the nitrogen excretion measures resulted in significant differences in estimated whole-body nitrogen retention between the two treatments. Nitrogen retention (means +/- SE) remained positive during the HI-PRO trial (2.41 +/- 1.99 g/day) but was significantly (P less than 0.005) reduced to -5.29 +/- 2.58 g/day during the REC-PRO trial. These results suggest that the current protein RDA may be inadequate for athletes engaging in chronic high-intensity endurance exercise. Future studies are needed to confirm this observation.     

Zinc and copper status in women by physical activity and menstrual status

Zinc and copper status of 33 eumenorrheic and 12 amenorrheic runners and 19 eumenorrheic and 8 amenorrheic nonrunners was studied. Three-day diet records and fasting blood samples were collected and analyzed. No indices of zinc or copper status differed as a function of menstrual status. Although zinc intakes of runners tended to be higher than nonrunners, plasma zinc concentrations tended to be lower. Runners had significantly higher erythrocyte zinc concentrations than nonrunners (12.4 +/- 0.2 vs 11.5 +/- 0.3 micrograms/g; p less than 0.05). Copper intakes of runners also tended to be higher than nonrunners. Mean plasma copper concentration of runners was significantly higher than nonrunners (18.8 +/- 0.5 vs 16.1 +/- 0.6 mumol/L; p less than 0.01) but erythrocyte copper was significantly lower (1.06 +/- 0.02 vs 1.26 +/- 0.03 micrograms/g; p less than 0.01). The observed differences between runners and nonrunners suggest that chronic exercise may induce redistribution of zinc and copper.     

Effect of short-term fat adaptation on high-intensity training

PURPOSE: To determine the effect of short-term (3-d) fat adaptation on high-intensity exercise training in seven competitive endurance athletes (maximal O2 uptake 5.0 +/- 0.5 L x min(-1), mean +/-SD). METHODS: Subjects consumed a standardized diet on d-0 then, in a randomized cross-over design, either 3-d of high-CHO (11 g x kg(-1)d(-1) CHO, 1 g x kg(-1) x d(-1) fat; HICHO) or an isoenergetic high-fat (2.6 g CHO x kg(-1) x d(-1), 4.6 g FAT x kg(-1) x d(-1); HIFAT) diet separated by an 18-d wash out. On the 1st (d-1) and 4th (d-4) day of each treatment, subjects completed a standardized laboratory training session consisting of a 20-min warm-up at 65% of VO2peak (232 +/- 23W) immediately followed by 8 x 5 min work bouts at 86 +/- 2% of VO2peak (323 +/- 32 W) with 60-s recovery. RESULTS: Respiratory exchange ratio (mean for bouts 1, 4, and 8) was similar on d-1 for HIFAT and HICHO (0.91 +/- 0.04 vs 0.92 +/- 0.03) and on d-4 after HICHO (0.92 +/- 0.03) but fell to 0.85 +/- 0.03 (P < 0.05) on d-4 after HIFAT. Accordingly, the rate of fat oxidation increased from 31 +/- 13 on d-1 to 61 +/- 25 micromol x kg(-1) x min(-1) on d-4 after HIFAT (P < 0.05). Blood lactate concentration was similar on d-1 and d-4 of HICHO and on d-1 of HIFAT (3.5 +/- 0.9 and 3.2 +/- 1.0 vs 3.7 +/- 1.2 mM) but declined to 2.4 +/- 0.5 mM on d-4 after HIFAT (P < 0.05). Ratings of perception of effort (legs) were similar on d-1 for HIFAT and HICHO (14.8 +/- 1.5 vs 14.1 +/- 1.4) and on d-4 after HICHO (13.8 +/- 1.8) but increased to 16.0 +/- 1.3 on d-4 after HIFAT (P < 0.05). CONCLUSIONS: 1) competitive endurance athletes can perform intense interval training during 3-d exposure to a high-fat diet, 2) such exercise elicited high rates of fat oxidation, but 3) compared with a high-carbohydrate diet, training sessions were associated with increased ratings of perceived exertion.     

MR evaluation of liver iron overload

Children and young adults with hemolytic anemias requiring frequent transfusions develop increased liver iron content. We evaluated 15 chronically transfused children with sickle cell disease to determine whether spin-echo magnetic resonance (MR) imaging was useful in assessing the degree of iron overload. Quantitative MR parameters were correlated with liver biopsy iron determinations and serum ferritin levels. The best predictor of liver iron was the ratio of the intensities between the liver and paraspinal musculature on somewhat T1 weighted sequence (repetition time 0.5 s, echo time 28 ms), R2 = 0.58. Magnetic resonance was able to separate those patients with liver iron levels greater than 100 micrograms/mg (intensity ratios approximately 0.4), from those with levels less than 100 micrograms/mg (intensity ratios near 1). However, MR was unable to quantitate liver iron in patients with values ranging from 100 to 400 micrograms/mg since similar intensity ratios were present in this range. Thus, MR provides a qualitative rather than quantitative assessment of liver iron overload.     

Training for cross-country skiing and iron status

Effects of iron supplements and training for cross-country skiing on hematological and iron status were studied in nine men and ten women from the U. S. Nordic ski team. Four men and five women received a multiple vitamin, multiple mineral supplement containing 18 mg iron for 8 months while five men and five women received a placebo. Fasting blood samples were taken from all skiers prior to supplementation (May) and in August, November, and January. Hemoglobin, hematocrit, plasma iron, total iron binding capacity (TIBC), percentage of transferrin saturation, serum ferritin, free erythrocyte porphyrin, and haptoglobin were measured on each sample. Hemoglobin, hematocrit, and TIBC were higher in November when both men and women skiers trained at altitude than in August. In January TIBC was further increased, haptoglobin was increased, hemoglobin for the men fell below May levels, and hematocrit returned to May levels. Skiers receiving iron had lower TIBC levels in November and January than the placebo group. Six women and two men had ferritin levels below 28 ng X ml-1, which suggests prelatent iron deficiency. Free erythrocyte porphyrin levels above 100 micrograms X dl-1 RBC were found in all skiers at some point during training. The results suggest that multivitamin, multimineral supplements containing iron have little effect on the iron status of cross-country skiers.     

Influence of iron status and iron supplements on natural killer cell activity in trained women runners

Twenty-two trained women runners (.VO2peak 48.1 + 1.2 ml x kg -1 x min -1) were divided into an iron supplement (n = 13) or placebo group (n = 9) based on initial serum ferritin concentration (24.2 +/- 2.9 and 58.5 +/- 4.0 microg x l -1, respectively). Exercise consisted of a 35-min run (80 % .VO2peak) and was performed at week 0 (WK0), after two weeks of intensified training (WK2) and after eight weeks recovery training (WK10). The eight weeks recovery training were concomitant with subjects taking iron supplements or placebo in a double blind fashion. Concentrations of serum ferritin, serum iron and total iron binding capacity were assessed pre-exercise and complete blood count, natural killer cell activity (NKACT), and cell surface markers for CD3+, CD4+, CD3+,CD8+, CD3-, CD16+, CD56+ cells were determined both pre- and post-exercise. Serum ferritin concentrations were significantly (p < 0.05) increased on WK10 compared to WK2 (time effect). NKACT (%lysis) and NK cell number was lower (p < 0.05) at WK0 for supplement (42.9 +/- 1.9 % and 305.5 +/- 15.0 x 10 6 x l -1, respectively) compared to placebo groups (50.9 +/- 2.0 and 406.1 +/- 25.6, respectively). Two weeks of intensified training did not alter indices of host defense. In conclusion, NKACT and NK cell numbers were lower in subjects with greater body mass and lower iron stores (p < 0.05), but were not significantly altered after two weeks of intensified training or when serum ferritin levels increased.     

Dietary intake of women runners

One hundred and three women who were habitual distance runners and 74 age-matched physically inactive women provided three-day diet records. Intergroup differences in intakes of energy nutrients, micronutrients, cholesterol and fiber were evaluated via analysis of variance and, to assess qualitative differences, via analysis of covariance with total caloric intake entered as the covariate. Women runners reported consuming more carbohydrate (192.4 vs 165.0 g.d-1) and less fat (57.5 vs 66.1 g.d-1) than did the inactive women (p less than .05). After controlling for the non-significant intergroup difference in caloric intake, these differences persisted and protein intake was lower in the runners. Cholesterol and saturated fat intakes were lower and fiber intake was greater in the runners, with and without control for differences in caloric intake. These data suggest that female runners, when compared to inactive counterparts, tend to follow dietary practices that conform more closely to the current recommendations of health authorities.     

Hypothalamic-pituitary-testicular axis function in endurance-trained males

The hypothalamic-pituitary-testicular (H-P-T) axis was evaluated in groups of endurance-trained (TRG) and untrained (UNT) males. Each group was subjected to: 1) a 4-h resting hormonal profile [testosterone (T), free-testosterone (FT), estradiol (E2), luteinizing hormone (LH), prolactin (PRL), and cortisol (C)], 2) a dopamine antagonist (DA; 10 micrograms.kg-1 body weight) challenge to the pituitary-testes, and 3) a gonadotropin-releasing hormone (GnRH; 120 micrograms.kg-1 body weight) challenge to the pituitary-testes. Compared to UNT, the TRG resting T (4.8 +/- 0.7 vs 7.1 +/- 1.2 ng.ml-1, p = 0.05) and PRL (3.3 +/- 1.4 vs 7.0 +/- 2.3 ng.ml-1, p = 0.09) were lower while LH was elevated (15.0 +/- 1.8 vs 11.8 +/- 1.5 mIU.ml-1, p = 0.06). The DA challenge produced a greater integrated PRL response in the TRG (2962.7 +/- 265.1 ng +/- ml-1.min) than in the UNT (1735.3 +/- 282.0 ng.ml-1.min; p = 0.01). No significant changes were observed in T following the DA-induced PRL rise. The TRG had a blunted LH response (817.2 +/- 111.6 mIU.ml-1.min) following the GnRH injection as compared to the UNT (1493.7 +/- 213.4 mIU.ml-1.min; P less than 0.02). T levels were significantly (p less than 0.03) increased in both groups by the LH rise after the GnRH challenge (TRG = 9.9 +/- 5.0%; UNT = 8.6 +/- 9.9%, respectively), but no significant between group differences were observed. Results suggest endurance training produces an enhanced PRL and attenuated LH release by the pituitary.(ABSTRACT TRUNCATED AT 250 WORDS)