Vitamin and mineral supplementation: effect on the running performance of trained athletes

High School Athletes' Use and Knowledge of (Safe) Nutritional Supplement Use: An Exploratory Study

The use of nutritional supplements can lead to doping risk and no data exist on high school athletes' use of certified third-party tested supplements. A cross-sectional cohort design was developed using an anonymous survey. Descriptive data for supplement use, use of third-party tested supplements, and knowledge in high school athletes were reported. A total of 225 high school athletes, ranging from 14-19 years of age, from a private high school in the western US, were included in the analysis of the results. A total of 94% (n=211) of athletes reported nutritional supplement use within the past year with an average of six (interquartile range: 3-9) individual supplements, ranging from 0-20 supplements per person. Most frequently reported were sports drinks (72%), vitamins (65%), sports bars (60%), protein powder (58%), caffeine (37%, as part of normal beverages, or 13% as a supplement), followed by creatine (23%). A total of 24% claimed to know for sure that all their supplements were third-party tested. In addition, the recognition of third-party testing organization icons was low (46% in supplement users vs. 14% in nonusers). Athletes also scored low in reporting how to find (22%) and how to order (25%) third-party tested supplements. In conclusion, almost all athletes in this study reported the use of multiple nutritional supplements annually. Only one-fourth of the athletes reported consistently using third-party tested supplements. Knowledge of where and how tested supplements could be purchased was limited in this high school athlete population.

Exploring the Relationship between Micronutrients and Athletic Performance: A Comprehensive Scientific Systematic Review of the Literature in Sports Medicine

The aim of this systematic review is twofold: (i) to examine the effects of micronutrient intake on athletic performance and (ii) to determine the specific micronutrients, such as vitamins, minerals, and antioxidants, that offer the most significant enhancements in terms of athletic performance, with the goal of providing guidance to athletes and coaches in optimizing their nutritional strategies. The study conducted a systematic search of electronic databases (i.e., PubMed, Web of Science, Scopus) using keywords pertaining to micronutrients, athletic performance, and exercise. The search involved particular criteria of studies published in English between 1950 and 2023. The findings suggest that vitamins and minerals are crucial for an athlete's health and physical performance, and no single micronutrient is more important than others. Micronutrients are necessary for optimal metabolic body's functions such as energy production, muscle growth, and recovery, which are all important for sport performance. Meeting the daily intake requirement of micronutrients is essential for athletes, and while a balanced diet that includes healthy lean protein sources, whole grains, fruits, and vegetables is generally sufficient, athletes who are unable to meet their micronutrient needs due to malabsorption or specific deficiencies may benefit from taking multivitamin supplements. However, athletes should only take micronutrient supplements with the consultation of a specialized physician or nutritionist and avoid taking them without confirming a deficiency.

International Society of Sports Nutrition Position Stand: nutritional considerations for single-stage ultra-marathon training and racing

Background

In this Position Statement, the International Society of Sports Nutrition (ISSN) provides an objective and critical review of the literature pertinent to nutritional considerations for training and racing in single-stage ultra-marathon. Recommendations for Training. i) Ultra-marathon runners should aim to meet the caloric demands of training by following an individualized and periodized strategy, comprising a varied, food-first approach; ii) Athletes should plan and implement their nutrition strategy with sufficient time to permit adaptations that enhance fat oxidative capacity; iii) The evidence overwhelmingly supports the inclusion of a moderate-to-high carbohydrate diet (i.e., ~ 60% of energy intake, 5–8 g·kg^− 1·d^− 1) to mitigate the negative effects of chronic, training-induced glycogen depletion; iv) Limiting carbohydrate intake before selected low-intensity sessions, and/or moderating daily carbohydrate intake, may enhance mitochondrial function and fat oxidative capacity. Nevertheless, this approach may compromise performance during high-intensity efforts; v) Protein intakes of ~ 1.6 g·kg^− 1·d^− 1 are necessary to maintain lean mass and support recovery from training, but amounts up to 2.5 g.kg^− 1·d^− 1 may be warranted during demanding training when calorie requirements are greater; Recommendations for Racing. vi) To attenuate caloric deficits, runners should aim to consume 150–400 Kcal·h^− 1 (carbohydrate, 30–50 g·h^− 1; protein, 5–10 g·h^− 1) from a variety of calorie-dense foods. Consideration must be given to food palatability, individual tolerance, and the increased preference for savory foods in longer races; vii) Fluid volumes of 450–750 mL·h^− 1 (~ 150–250 mL every 20 min) are recommended during racing. To minimize the likelihood of hyponatraemia, electrolytes (mainly sodium) may be needed in concentrations greater than that provided by most commercial products (i.e., > 575 mg·L^− 1 sodium). Fluid and electrolyte requirements will be elevated when running in hot and/or humid conditions; viii) Evidence supports progressive gut-training and/or low-FODMAP diets (fermentable oligosaccharide, disaccharide, monosaccharide and polyol) to alleviate symptoms of gastrointestinal distress during racing; ix) The evidence in support of ketogenic diets and/or ketone esters to improve ultra-marathon performance is lacking, with further research warranted; x) Evidence supports the strategic use of caffeine to sustain performance in the latter stages of racing, particularly when sleep deprivation may compromise athlete safety.

ISSN exercise & sports nutrition review update: research & recommendations

Background

Sports nutrition is a constantly evolving field with hundreds of research papers published annually. In the year 2017 alone, 2082 articles were published under the key words ‘sport nutrition’. Consequently, staying current with the relevant literature is often difficult.

Methods

This paper is an ongoing update of the sports nutrition review article originally published as the lead paper to launch the Journal of the International Society of Sports Nutrition in 2004 and updated in 2010. It presents a well-referenced overview of the current state of the science related to optimization of training and performance enhancement through exercise training and nutrition. Notably, due to the accelerated pace and size at which the literature base in this research area grows, the topics discussed will focus on muscle hypertrophy and performance enhancement. As such, this paper provides an overview of: 1.) How ergogenic aids and dietary supplements are defined in terms of governmental regulation and oversight; 2.) How dietary supplements are legally regulated in the United States; 3.) How to evaluate the scientific merit of nutritional supplements; 4.) General nutritional strategies to optimize performance and enhance recovery; and, 5.) An overview of our current understanding of nutritional approaches to augment skeletal muscle hypertrophy and the potential ergogenic value of various dietary and supplemental approaches.

Conclusions

This updated review is to provide ISSN members and individuals interested in sports nutrition with information that can be implemented in educational, research or practical settings and serve as a foundational basis for determining the efficacy and safety of many common sport nutrition products and their ingredients.

Nutritional behaviour and beliefs of ski-mountaineers: a semi-quantitative and qualitative study

BACKGROUND

Endurance athletes are advised to optimize nutrition prior to races. Little is known about actual athletes' beliefs, knowledge and nutritional behaviour. We monitored nutritional behaviour of amateur ski-mountaineering athletes during 4 days prior to a major competition to compare it with official recommendations and with the athletes' beliefs.

METHODS

Participants to the two routes of the 'Patrouille des Glaciers' were recruited (A, 26 km, ascent 1881 m, descent 2341 m, max altitude 3160 m; Z, 53 km, ascent 3994 m, descent 4090 m, max altitude 3650 m). Dietary intake diaries of 40 athletes (21 A, 19 Z) were analysed for energy, carbohydrate, fat, protein and liquid; ten were interviewed about their pre-race nutritional beliefs and behaviour.

RESULTS

Despite belief that pre-race carbohydrate, energy and fluid intake should be increased, energy consumption was 2416 ± 696 (mean ± SD) kcal · day(-1), 83 ± 17% of recommended intake, carbohydrate intake was only 46 ± 13% of minimal recommended (10 g · kg(-1) · day(-1)) and fluid intake only 2.7 ± 1.0 l · day(-1).

CONCLUSIONS

Our sample of endurance athletes did not comply with pre-race nutritional recommendations despite elementary knowledge and belief to be compliant. In these athletes a clear and reflective nutritional strategy was lacking. This suggests a potential for improving knowledge and compliance with recommendations. Alternatively, some recommendations may be unrealistic.

Redox modulation of mitochondriogenesis in exercise. Does antioxidant supplementation blunt the benefits of exercise training?

Physical exercise increases the cellular production of reactive oxygen species (ROS) in muscle, liver, and other organs. This is unlikely due to increased mitochondrial production but rather to extramitochondrial sources such as NADPH oxidase or xanthine oxidase. We have reported a xanthine oxidase-mediated increase in ROS production in many experimental models from isolated cells to humans. Originally, ROS were considered as detrimental and thus as a likely cause of cell damage associated with exhaustion. In the past decade, evidence showing that ROS act as signals has been gathered and thus the idea that antioxidant supplementation in exercise is always recommendable has proved incorrect. In fact, we proposed that exercise itself can be considered as an antioxidant because training increases the expression of classical antioxidant enzymes such as superoxide dismutase and glutathione peroxidase and, in general, lowering the endogenous antioxidant enzymes by administration of antioxidant supplements may not be a good strategy when training. Antioxidant enzymes are not the only ones to be activated by training. Mitochondriogenesis is an important process activated in exercise. Many redox-sensitive enzymes are involved in this process. Important signaling molecules like MAP kinases, NF-κB, PGC-1α, p53, heat shock factor, and others modulate muscle adaptation to exercise. Interventions aimed at modifying the production of ROS in exercise must be performed with care as they may be detrimental in that they may lower useful adaptations to exercise.

Polyphenol supplementation: benefits for exercise performance or oxidative stress?

Supplement use among athletes is widespread, including non-traditional and biological compounds. Despite increasing research, a comprehensive and critical review on polyphenol supplementation and exercise is still lacking. This review is relevant for researchers directly involved in the topic, as well as those with a broad interest in athletic performance enhancement and sports nutrition. The purpose of this review is to present background information on groups of polyphenols and their derivatives because their differing chemical structures influence mechanisms of action; to discuss the potential of plant, fruit and vegetable-based biological supplements, high in polyphenol content, to affect exercise performance and biomarkers of oxidative stress and exercise-induced muscle damage; and to critically discuss the exercise studies and biomarkers used. Subjects in the studies reviewed were either sedentary, healthy individuals, or active, recreationally trained or well-trained athletes. Polyphenol supplementation in exercise studies included mainly extracts (multicomponent or purified), juices, infusions or an increased intake of polyphenol-rich foods. This review includes details of supplement doses and exercise test protocols. Many studies considered only the performance or one or two selected biomarkers of antioxidant capacity instead of a comprehensive choice of biomarkers to assess damage to lipids or proteins. Evidence is insufficient to make recommendations for or against the use of polyphenol supplementation (neither specific polyphenols nor specific doses) for either recreational, competitive or elite athletes. Polyphenols have multiple biological effects, and future exercise studies must be designed appropriately and specifically to determine physiological interactions between exercise and the selected supplement, rather than considering performance alone.

Chlorella-derived multicomponent supplementation increases aerobic endurance capacity in young individuals

Chlorella, a unicellular green alga, contains a variety of nutrients including amino acids, carbohydrates, vitamins, and minerals. A previous animal study found that maximal swimming time in mice increased after 14 days on a diet including Chlorella powder compared to no change in swimming performance on a normal diet. However, it is currently unknown whether Chlorella-derived multicomponent supplementation increases aerobic endurance capacity in humans. We investigated the effects of Chlorella-derived supplementation on peak oxygen uptake during incremental maximal cycling in young individuals using a double-blinded, placebo-controlled, crossover study design. Seven men and three women (mean age, 21.3 year) were allocated to placebo or Chlorella tablets (15 tablets × twice per day) for 4 weeks, with at least a 6-week washout period between trials, in a randomized order. Peak oxygen uptake significantly increased after Chlorella supplementation (before vs after, 37.9 ± 1.9 vs 41.4 ± 1.9 ml/kg/min, p = 0.003), but not with placebo (39.4 ± 2.2 vs 40.1 ± 2.1 ml/kg/min, p = 0.38). The change in peak oxygen uptake over the 4-week trial was significantly greater in the Chlorella trial than in the placebo trial (3.5 ± 0.9 vs 0.7 ± 0.8 ml/kg/min, p = 0.03). These results suggest that Chlorella-derived multicomponent supplementation increases aerobic endurance capacity in young individuals.

Antioxidant supplementation during exercise training: beneficial or detrimental?

High levels of reactive oxygen species (ROS) produced in skeletal muscle during exercise have been associated with muscle damage and impaired muscle function. Supporting endogenous defence systems with additional oral doses of antioxidants has received much attention as a noninvasive strategy to prevent or reduce oxidative stress, decrease muscle damage and improve exercise performance. Over 150 articles have been published on this topic, with almost all of these being small-scale, low-quality studies. The consistent finding is that antioxidant supplementation attenuates exercise-induced oxidative stress. However, any physiological implications of this have yet to be consistently demonstrated, with most studies reporting no effects on exercise-induced muscle damage and performance. Moreover, a growing body of evidence indicates detrimental effects of antioxidant supplementation on the health and performance benefits of exercise training. Indeed, although ROS are associated with harmful biological events, they are also essential to the development and optimal function of every cell. The aim of this review is to present and discuss 23 studies that have shown that antioxidant supplementation interferes with exercise training-induced adaptations. The main findings of these studies are that, in certain situations, loading the cell with high doses of antioxidants leads to a blunting of the positive effects of exercise training and interferes with important ROS-mediated physiological processes, such as vasodilation and insulin signalling. More research is needed to produce evidence-based guidelines regarding the use of antioxidant supplementation during exercise training. We recommend that an adequate intake of vitamins and minerals through a varied and balanced diet remains the best approach to maintain the optimal antioxidant status in exercising individuals.

Micronutrient supplementation improves physical performance measures in Asian Indian school-age children

Micronutrients are important in physical work capacity and therefore performance. The impact of a multi-micronutrient-fortified nutritional beverage on physical performance measures among clinically healthy school-age children was assessed in a double-blind (for test and placebo groups), placebo-controlled, randomized trial in children aged between 7 and 10.5 y (n = 300). The participants with height- and weight-for-age Z-scores between 0 and ≥ -3 were randomized to 1 of 3 study arms: fortified choco-malt beverage powder (F), matched energy equivalent unfortified placebo (U), and untreated control (C). Participants in the F and C groups were given 40 g fortified (19 key vitamins and minerals) and unfortified choco-malt beverage, respectively, daily for 120 d. Primary efficacy outcomes included endurance and aerobic capacity using a 20-m shuttle test and step test. Other physical performance measures included speed (40-m sprint), visual reaction time, maximal hand grip, and forearm static endurance. Micronutrient status included thiamin, riboflavin, folate, niacin, iron, pyridoxal phosphate, and vitamins B-12 and C. All measurements were made at baseline and the end of the intervention. There was a within-subject increase in aerobic capacity and whole body endurance (P < 0.05) accompanied by a significant improvement in the status of iron thiamin, riboflavin, pyridoxal phosphate, folate, and vitamins C and B-12 in the F group compared to the within-subject changes in the other 2 groups (P < 0.05). The study suggests that multiple micronutrient supplementation in similar populations may be beneficial in improving micronutrient status and enhancing aerobic capacity and endurance in children.

Magnesium sulfate enhances exercise performance and manipulates dynamic changes in peripheral glucose utilization

The effect of magnesium supplementation on exercise performance remains controversial. In the present study, the effects of magnesium sulfate on exercise performance and blood glucose metabolism were examined. In order to provide a non-invasive measure of continuous exercise, we developed an auto-blood sampling system was coupled to a microdialysis analyzer to detect the dynamic changes in glucose metabolism in conscious and freely moving gerbils subjected to forced swimming. Gerbils were pretreated with saline or magnesium sulfate (90 mg kg(-1), ip) 30 min before exercise. The duration times were significantly increased by 71% in the magnesium sulfate-treated groups (p < 0.01) when compared with those in the control. Another group of gerbils were subjected to blood sampling assay. A catheter was implanted in the jugular vein of each gerbil for collecting blood samples by the computer-aided blood sampler. The basal levels of plasma glucose, lactate, and magnesium were 6,245 +/- 662, 1,067 +/- 309, and 590 +/- 50 microM, respectively, with no significant difference between groups. Plasma glucose, lactate, and magnesium levels increased to 134 and 204%, 369 and 220%, and 155 and 422% of basal levels during swimming in both the control and magnesium sulfate-treated groups, respectively (p < 0.05). Pretreatment with magnesium sulfate elevated glucose and magnesium levels to 175 and 302% of the basal levels (p < 0.05), respectively, whereas pretreatment with magnesium sulfate reduced the lactate levels 150% of the basal level (p < 0.05) during swimming. Furthermore, the magnesium levels increased to about 152-422% of basal levels during forced swimming and the recovery period (p < 0.05). The present study demonstrates that magnesium sulfate improved the duration time of forced swimming exercise. In addition, magnesium raised glucose levels and attenuated lactate levels during forced swimming. These results indicate that positive effects of magnesium supplementation may contribute to the enhancement of exercise performance in athletes.

Multivitamins do not improve radiation therapy-related fatigue: results of a double-blind randomized crossover trial

BACKGROUND

Fatigue is a common symptom in cancer patients receiving radiation therapy.

PATIENTS AND METHODS

We conducted a double-blind randomized crossover trial of multivitamins versus placebo in patients with breast cancer undergoing radiation therapy to evaluate fatigue and quality of life.

RESULTS

: We randomized 40 patients to either placebo or Centrum Silver. At the middle of the radiation treatments, patients were switched from placebo to multivitamins and vice versa. Patients answered the EORTC QLQ C-30 quality of life (QOL) and Chalder fatigue questionnaires at the beginning, middle, and end of radiation therapy. Both groups experienced decreases in general (P = 0.009; P = 0.001) and physical fatigue scores (P = 0.031; P = 0.029) at the end of the course of placebo compared with the assessment prior to this treatment. We also observed significant improvements in functional (P = 0.026) and symptoms (P = 0.016) score scales of the QOL questionnaire in the patients on placebo. No significant changes were elicited with the use of multivitamins. We also observed significantly lower rates of fatigue in the patients who had just finished a course of placebo as compared with patients finishing a course of multivitamins (0 vs. 25% P = 0.035).

CONCLUSION

Multivitamins do not improve radiation-related fatigue in patients with breast cancer.

Effect of A Liquid Multivitamin/Mineral Supplement on Anaerobic Exercise Performance

The purpose of this study was to determine if supplementation with a liquid multi-vitamin/mineral would improve anaerobic exercise performance. Fourteen resistance-trained men performed a 30-second cycle sprint and one set of squat exercise on 2 separate days before and following 8 weeks of supplementation with either a liquid multi-vitamin/ mineral or a placebo. Heart rate, perceived exertion, blood lactate, peak and mean power, and rate of fatigue were determined for all tests. No differences were noted for any variable (P > 0.05). When controlling for presupplementation values, however, a decreased rate of fatigue was noted for both exercise tests following the multi-vitamin/mineral supplementation. These data suggest that in resistance trained men consuming a nutritionally sound diet, supplementation with a liquid multi-vitamin/mineral does not favorably impact most anaerobic exercise performances. Such supplementation, however, may result in a minor decreased rate of fatigue. It appears that, in terms of improved short duration anaerobic exercise performance, supplemental micronutrients may not be efficient ergogenic agents for well-trained individuals consuming an adequate diet.

Dietary supplements and sports performance: introduction and vitamins

Sports success is dependent primarily on genetic endowment in athletes with morphologic, psychologic, physiologic and metabolic traits specific to performance characteristics vital to their sport. Such genetically-endowed athletes must also receive optimal training to increase physical power, enhance mental strength, and provide a mechanical advantage. However, athletes often attempt to go beyond training and use substances and techniques, often referred to as ergogenics, in attempts to gain a competitive advantage. Pharmacological agents, such as anabolic steroids and amphetamines, have been used in the past, but such practices by athletes have led to the establishment of anti-doping legislation and effective testing protocols to help deter their use. Thus, many athletes have turned to various dietary strategies, including the use of various dietary supplements (sports supplements), which they presume to be effective, safe and legal.

Vitamin and mineral status: effects on physical performance

Public health recommendations encourage the selection of a balanced diet and increasing physical activity to foster health and well-being. Whereas the adverse effects of restricted intakes of protein, fat, and carbohydrate on physical performance are well known, there is limited information about the impact of low intakes of vitamins and minerals on the exercise capacity and performance of humans. Physically active people generally consume amounts of vitamins and minerals consistent with the recommendations for the general public. However, when intakes are less than recommendations, some noticeable functional impairments occur. Acute or short-term marginal deficiencies, identified by blood biochemical measures of vitamin B status, had no impacts on performance measures. Severe deprivation of folate and vitamin B12 result in anemia and reduce endurance work performance. Evidence of vitamin A and E deficiencies in athletic individuals is lacking apparently because body storage is appreciable. In contrast to vitamins, marginal mineral deficiencies impair performance. Iron deficiency, with or without anemia, impairs muscle function and limits work capacity. Magnesium deprivation increases oxygen requirements to complete submaximal exercise and reduces endurance performance. Use of vitamin and mineral supplements does not improve measures of performance in people consuming adequate diets. Young girls and individuals participating in activities with weight classifications or aesthetic components are prone to nutrient deficiencies because they restrict food intake and specific micronutrient-rich foods. This information will be useful to professionals who counsel physically active people and scientific groups who make dietary recommendations to improve health and optimize genetic potential.

Medication use in athletes selected for doping control at the Sydney Olympics (2000)

During the Olympic Games held in Sydney in September, 2000 Doping Control was undertaken as specified in the International Olympic Code. During this process information about the medications taken by athletes was collected as a routine and formed part of the paperwork associated with a urine test. In their Post Games Report the World Anti-Doping Agency (WADA) recommended that the information about medications be collated with a view to assessing their use by athletes. Mandatory doping control for winners of events as well as random selection of athletes both during competition and out of competition allowed data to be collected about medications and supplements used by athletes. At the Doping Control Stations all competitors selected for a test, after providing a urine sample for analysis, were asked the same question: "what medications have you taken in the past three days?" The answer was to include all prescription drugs, over-the-counter medications, any other substances taken by mouth, injection, inhalation, ointment or by suppository, as well as vitamins, minerals, and all other supplements. This paper reviews the data from the 2758 Declaration Forms obtained at doping control. The prevalence of use of medications, the number used by an individual, and the pattern of use by these elite sports people were examined. The trends seen in this survey point to a dangerous overuse of nonsteroidal anti-inflammatory agents and an unnecessary overuse of vitamins in this population, while pointing out the increased prevalence of asthma and the dangers of drug interactions.

OBJECTIVE

The main objective here is to review some of the medications used by athletes in the Olympic Games in Sydney 2000.

DATA SOURCES

During these Games Doping Control was undertaken as specified by the International Olympic Committee. As well as a urine test, information about medications routinely taken was collected. Mandatory doping control for winners of events as well as random selection of athletes both during competition and out of competition required data to be collected about medications and supplements used by athletes as part of the sample collection protocol. At the Doping Control Stations all competitors selected for a test, after providing a urine sample for analysis, were asked the same question: "what medications have you taken in the past three days?" The answer was to include all prescription drugs, over-the-counter medications, any other substances taken by mouth, injection, inhalation, ointment or by suppository, as well as vitamins, minerals, and all other supplements.

DATA SELECTION

In this article we review the data from the laboratory copy of the 2758 Declaration Forms obtained at doping control. The cut down version of the Declaration Form submitted to the laboratory had all information identifying the athlete removed. Thus all information used in this article is completely anonymous. The prevalence of use of medications, the number used by an individual, and the pattern of use by these elite sports people were examined at the request of the IOC.

CONCLUSIONS

In their Post-Games Report, the World Anti-Doping Agency (WADA) acting as independent observers of the anti-doping process recommended to the IOC that the information obtained in the Athlete Declaration Forms concerning medications be collated with a view to assessing their use by athletes. The trends in their use seen in this survey point to an overuse of supplements as well as a dangerous overuse of drugs such as nonsteroidal anti-inflammatory agents together with multiple drug use emphasising the dangers of drug interactions and points out the increased prevalence of asthma in this population.

The effects of magnesium supplementation on exercise performance

PURPOSE

To determine the effects of magnesium (Mg2+) supplementation on performance and recovery in physically active women using the sensitive and recently advanced measure of ionic Mg2+ (iMg).

METHODS

Participants (N = 121) were screened for [iMg] in plasma, with 44 (36.4%) exhibiting [iMg] below the normal range of 0.53-0.67 mmol.L-1 (4). Thirty-two subjects (21 +/- 3 yr) representing a broad range of [iMg] (0.54 +/- 0.04 mmol.L-1) completed the main 14-wk study. At baseline, participants submitted to a resting blood pressure measurement, and they completed both an anaerobic treadmill test and an incremental (aerobic) treadmill test. For the latter, values for workload, oxygen uptake, and heart rate were obtained at both anaerobic threshold and maximal effort. Blood samples for iMg, total serum Mg2+ (TMg), erythrocyte Mg2+ (EMg), Ca2+, K+, Na+, hemoglobin, hematocrit, lactate, and glucose were also collected pretest, and 4, 10, 30 min, and 24 h posttest. Subjects received 212 mg.d-1 Mg oxide or placebo in a double-blind fashion and were retested after 4 wk. After a 6-wk washout period, the testing was repeated with a treatment crossover.

RESULTS

Ionic Mg2+ increased with Mg2+ treatment versus placebo (P < 0.05); however, performance and recovery indices were not significantly affected.

CONCLUSION

Four weeks of 212 mg.d-1 Mg oxide supplementation improves resting [iMg] levels but not performance or recovery in physically active women.

The effects of magnesium supplementation on exercise performance

OBJECTIVES

Magnesium (Mg) status, although difficult to assess, is suspected to be marginal in many individuals, especially athletes, and this has led to the common use of Mg supplements. The purpose of this article is to critique research that has addressed Mg supplementation in athletes.

DATA SOURCES

The primary database was Medline, which was searched for English articles from 1966 to June 1999 using the words "magnesium" and "supplementation."

STUDY SELECTION

Only experimental studies dealing with human subjects, Mg supplementation, and exercise performance were critiqued (n = 12).

DATA EXTRACTION

Quality of critiqued articles was based on 1) use of cross-over designs, 2) how and if Mg status was assessed, 3) whether treatment was solely Mg supplementation, 4) duration of supplementation, 5) subject number, and 6) degree of experimental control. Articles were classified into "no effect" and "positive effect," and also were examined in regard to the type of performance outcome (strength, anaerobic-lactacid, and aerobic).

DATA SYNTHESIS

Mg is a cofactor to over 325 enzymatic reactions, and a deficiency of the mineral therefore has many physiological and exercise performance implications. Low dietary intakes, as found in many female athletes, coupled with increased urinary losses with exercise, may eventually lead to an Mg deficiency. Strength of evidence favors those studies finding no effect of Mg supplementation, regardless of whether the performance outcome was strength, anaerobic-lactacid, or aerobic. Analysis was confounded due to: 1) variable exercise modes, intensities, and durations, 2) variable training states and ages of subjects, 3) subject selection favoring males and gender differences has not been probed, 4) Mg dosage has ranged from 1 day to 3 months and from 116 mg/day to 500 mg/day, 5) multivitamins/minerals have been ingested with the Mg, 6) with one exception, Mg status was either not reported or reliant on total Mg (TMg), 7) lack of a cross-over design, 8) only one study made note of controlling exercise prior to exercise testing and blood assay, and 9) typical Mg intake measured was only measured in three of the studies.

CONCLUSIONS

Most evidence indicates no effect of Mg supplementation on performance (strength, anaerobic-lactacid, and aerobic). When only peak treadmill speed during a VO2 max test is examined, the strength of evidence is equivocal. Trained subjects appear to benefit less than untrained subjects, but this observation requires further study. Little research has focused on physically active females who may be at the highest risk for Mg deficiency. Research has been confounded by numerous factors.

Indicators of vitamin and mineral status in athletes' blood: a review

This review examines the hypothesis that vitamin and mineral status in athletes is inadequate for optimal sports performance. The review is based on indicators determined from blood and on studies published since 1980. Most of the studies did not find micronutrient status in athletes to be different from untrained controls. The serum ferritin concentration in females was lower than in males (27 vs. 78 micrograms.L-1), and the prevalence of low serum ferritin concentration was higher in female athletes than in untrained female controls (37 vs. 23%). Supplementation of water-soluble vitamins and iron was associated with an improvement in the corresponding indicators. Excluding a few studies with mildly anemic subjects, improvements in indicators of micronutrient status were not associated with enhanced athletic performance. Consequently, the levels of indicators of micronutrient status seen in athletes' blood were apparently compatible with optimal physical performance.

Overtraining: consequences and prevention

Overtraining refers to prolonged fatigue and reduced performance despite increased training. Its roots include muscle damage, cytokine actions, the acute phase response, improper nutrition, mood disturbances, and diverse consequences of stress hormone responses. The clinical features are varied, non-specific, anecdotal and legion. No single test is diagnostic. The best treatment is prevention, which means (1) balancing training and rest, (2) monitoring mood, fatigue, symptoms and performance, (3) reducing distress and (4) ensuring optimal nutrition, especially total energy and carbohydrate intake.

N-acetylcysteine inhibits muscle fatigue in humans

N-acetylcysteine (NAC) is a nonspecific antioxidant that selectively inhibits acute fatigue of rodent skeletal muscle stimulated at low (but not high) tetanic frequencies and that decreases contractile function of unfatigued muscle in a dose-dependent manner. The present experiments test the hypothesis that NAC pretreatment can inhibit acute muscular fatigue in humans. Healthy volunteers were studied on two occasions each. Subjects were pretreated with NAC 150 mg/kg or 5% dextrose in water by intravenous infusion. The subject then sat in a chair with surface electrodes positioned over the motor point of tibialis anterior, an ankle dorsiflexor of mixed-fiber composition. The muscle was stimulated to contract electrically (40-55 mA, 0.2-ms pulses) and force production was measured. Function of the unfatigued muscle was assessed by measuring the forces produced during maximal voluntary contractions (MVC) of ankle dorsiflexor muscle groups and during electrical stimulation of tibialis anterior at 1, 10, 20, 40, 80, and 120 Hz (protocol 1). Fatigue was produced using repetitive tetanic stimulations at 10 Hz (protocol 1) or 40 Hz (protocol 2); intermittent stimulations subsequently were used to monitor recovery from fatigue. The contralateral leg then was studied using the same protocol. Pretreatment with NAC did not alter the function of unfatigued muscle; MVC performance and the force-frequency relationship of tibialis anterior were unchanged. During fatiguing contractions stimulated at 10 Hz, NAC increased force output by approximately 15% (P < 0.0001), an effect that was evident after 3 min of repetitive contraction (P < 0.0125) and persisted throughout the 30-min protocol. NAC had no effect on fatigue induced using 40 Hz stimuli or on recovery from fatigue. N-acetylcysteine pretreatment can improve performance of human limb muscle during fatiguing exercise, suggesting that oxidative stress plays a causal role in the fatigue process and identifying antioxidant therapy as a novel intervention that may be useful clinically.

Vitamin-mineral supplement use and nutritional status of athletes

Dietary, anthropometric, and chronic disease risk factors (CDRF) including blood lipids and blood pressure (BP), were measured in 91 vitamin-mineral supplement users (SU) and nonusers (NU) representing a wide range of athletic interests. Supplements were used by 46 (51%) subjects; 100% of female athletes and 51% of male athletes used supplements while none of a group of 15 control female subjects currently used supplements. Both dietary intake and energy expenditure were measured using 7-day records. Adiposity was determined from body weight, body mass index, and skinfolds. Total cholesterol, high-density lipoprotein cholesterol, serum ferritin, hemoglobin, hematocrit, zinc, copper, and vitamin C were based on 12-hour fasting blood samples. Dietary intake (excluding supplements) for SU tended to be greater than NU for vitamin C, thiamin, riboflavin, niacin, B6, B12, folate, calcium, iron and magnesium. Plasma vitamin C levels were significantly higher among SU than NU of both gender groups (p < 0.05). Although SU may exhibit additional healthy lifestyle practices, lipid profiles for many of these athletes were unfavorable with regard to CDRF.

The effect of exercise on the riboflavin status of adult men

Six sedentary to moderately active men with biochemical signs of riboflavin deficiency were studied under metabolic ward conditions to examine the effects of physical activity on riboflavin status. All participants were subjected to additional exercise (EXER) for an 18 d period between two maintenance (M1 and M2) periods (16 and 13 d respectively) of habitual physical activity. Energy balance and riboflavin intake were maintained throughout the study. Riboflavin status, as judged by a significant reduction in erythrocyte glutathione reductase (EC 1.6.4.2) activation coefficient (EGR-AC), improved on changing from home (1.53 (SD 0.14)) to period M1 (1.36 (SD 0.21)) diets. The exercise period, however, resulted in a significant deterioration in riboflavin status (1.57 (SD 0.31)) which persisted in the subsequent period M2 (1.54 (SD 0.15)). There was a concomitant fall in the urinary excretion of riboflavin only in the EXER period, when results were expressed as a percentage of the dietary intake of riboflavin. These results suggest an increased demand for the vitamin for selective biochemical functions during exercise. However, the energy cost of walking (treadmill 4 km/h), 50 W and 100 W work-loads (bicycle ergometer) as well as delta mechanical efficiency (DME) did not change during the three metabolic periods. The urinary excretion of riboflavin was inversely related to DME (r -0.49; P < 0.05) and directly correlated with haemoglobin levels (r 0.63; P < 0.005). The present study suggests that riboflavin status further deteriorates during a short period of increased physical activity in individuals whose riboflavin status is marginal.

Vitamin supplementation and physical exercise performance

Vitamins, just as minerals and trace elements, meet with great interest in the world of sports because of their supposed role in enhancing physical performance. Of the 13 compounds now considered as vitamins, most water-soluble vitamins and vitamin E are involved in mitochondrial energy metabolism. The influence of vitamin supplementation on mitochondrial metabolism is largely unknown. The principal argument for vitamin supplementation is the assumed increased vitamin requirement of athletes. Theoretically, an increased requirement can be caused by decreased absorption by the gastrointestinal tract, increased excretion in sweat, urine and faeces, increased turnover, as well as biochemical adaptation to training. Of course, a marginal low vitamin status can simply be the consequence of a long-term inadequate intake. However, considering the RDAs there are no indications that long-term vitamin intake among athletes is insufficient. Neither are there indications that vitamin excretion or turnover is increased in athletes. However, it is very likely that the (apparently) increased requirement is the consequence of biochemical adaptation to training and does not indicate a decreased intake. Although a marginal vitamin status, induced by inadequate vitamin intake, may have a negative effect on performance, there is no evidence to support the view that this occurs in trained athletes. Moreover, vitamin supplementation in athletes with an adequate vitamin status has no effect on physical working capacity. Possibly, exceptions have to be made for the use of vitamin E at high altitudes and for the use of vitamin C and multiple B-vitamin supplements in hot climates.

Vitamin and mineral supplementation to athletes

Vitamin and mineral supplements are frequently used by competitive and recreational athletes. Dietary deficiencies of most vitamins are not very common among athletes except in those who restrict their food intake in order to maintain body weight. Vitamins most likely to be deficient in the diet are folate, B6, B12, and E. Biochemical evidence of vitamin deficiencies in some athletes have been reported for thiamine, riboflavin, and B6. When the diet is deficient, vitamin supplements may improve performance but are not likely to be effective if the dietary intake is adequate. Some female athletes' diets are low in calcium, iron, and zinc. Low calcium intake may reduce peak bone mass in young women. Iron deficiency may impair performance and needs to be corrected with an iron supplement. Zinc supplements that exceed the RDA interfere with the absorption of copper and lower HDL-cholesterol.

Skeletal muscle limits the exercise tolerance of renal transplant recipients: effects of a graded exercise training program

Sixteen renal transplant recipients were studied before and after they had participated in a 24-week exercise training program to determine (1) the nature of the factors explaining their impaired exercise tolerance, and (2) their adaptative responses to exercise training. During progressive treadmill exercise to exhaustion prior to training, renal transplant recipients stopped exercising at lower peak rates of oxygen consumption (VO2max) (29.0 +/- 7.8 47.9 +/- 9.1 mL O2.kg-1.min-1; P less than 0.001) and ventilation (55.9 +/- 13.2 v 124.0 +/- 22.2 L.min-1; P less than 0.0001), and at lower peak heart rates (169 +/- 22 v 196 +/- 9 beats.min-1; P less than 0.05) and peak blood lactate concentrations (5.0 +/- 2.1 v 11.5 +/- 4.0 mmol.L-1; P less than 0.001) than did controls. None showed a plateau in oxygen consumption with increasing workload. Exercise time to exhaustion was also significantly shorter in renal transplant recipients (9.5 +/- 1.8 v 16.0 +/- 1.3 min; P less than 0.0001). After training, exercise time to exhaustion (12.0 +/- 2.0 min; P less than 0.001), VO2max (37.5 +/- 4.8 mL O2.kg-1.min-1; P less than 0.05), maximum ventilation rate (68.5 +/- 14.0 L.min-1; P less than 0.05), peak blood lactate concentrations (7.8 +/- 1.8 mmol-L-1; P less than 0.001), and the rate of oxygen consumption at a blood lactate concentration of 2.0 mmol.L-1 (22.5 +/- 2.5 v 16.5 +/- 2.2 mL O2.kg-1.min-1; P less than 0.001) had all increased significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

A survey of pharmacists recommendations for food supplements in the U.S.A. and U.K

A survey was sent to 1,000 pharmacists in metropolitan Detroit U.S.A. (19.7% responded) and 750 pharmacists in the U.K. (57.9% responded) to assess the frequency of recommendations for health food stores, minerals, multivitamins, natural vitamins, protein supplements, Stresstabs, and weight-reduction products. Pharmacists were also asked about their five most common reasons for recommending vitamins and minerals from a list of 16 items, which included alcoholism, anaemia, arthritis, athletically active, children, colds, dieting, fatigue, feeling nervous, headaches, old age, pain, pregnancy, prophylaxis, skin problems, stress or other. About 40% of the U.S.A. community pharmacists recommended multivitamins more than five times a week compared to 28.6% of U.K. community pharmacists. Anaemia (48.6%), dieting (44.8%), alcoholism (42.3%), pregnancy (40.0%), and fatigue (36.8%) were the five most common reasons for pharmacists to recommend vitamins and minerals, this was consistent, for the most part, with the American Medical Association's Council on Scientific Affairs report, however, a large number of pharmacists placed the non-specific symptoms of fatigue and stress in the five most common reasons for which they recommend vitamins or minerals.