Effects of antioxidant supplementation on bone mineral density, bone mineral content and bone structure in healthy men during 60 days of 6° head-down tilt bed rest: Results from a randomised controlled trial.

Dietary countermeasures to mitigate detrimental spaceflight-induced effects on bone health would alleviate the requirements and the consequences imposed by other types of countermeasures for this risk. We hypothesised that antioxidant supplementation during 60 days of 6° head-down tilt bed rest (HDBR), an analogue of spaceflight, would have a protective effect on bone mineral density (BMD), content (BMC) and bone structure parameters. An exploratory, randomised, controlled, single-blind intervention trial was conducted in a parallel design with 20 healthy male volunteers (age 34 ± 8 y, weight 74 ± 6 kg). The study included 14 days of baseline data collection (BDC) before bed rest, followed by 60 days of HDBR and a 14-day recovery period. Ten subjects in the antioxidant group received a supplement (741 mg/d polyphenols, 2.1 g/d omega-3 fatty acids, 168 mg/d vitamin E and 80 µg/d selenium) daily. Ten subjects in the control group received no supplement. The diet was consistent with dietary reference intakes, individually tailored based on the subject's bodyweight and strictly controlled. We measured whole-body, lumbar spine and femur BMD and BMC, as well as BMD of the cortical and trabecular compartments of the distal radius and tibia, and cortical and trabecular thickness during BDC, HDBR and recovery. Data were analysed using linear mixed models. The supplementation of an antioxidant cocktail did not mitigate the deteriorating effects of HDBR on BMD, BMC and bone structure parameters. Our findings do not support a recommendation for antioxidant supplementation for astronauts.

High resolution ancient sedimentary DNA shows that alpine plant diversity is associated with human land use and climate change.

The European Alps are highly rich in species, but their future may be threatened by ongoing changes in human land use and climate. Here, we reconstructed vegetation, temperature, human impact and livestock over the past ~12,000 years from Lake Sulsseewli, based on sedimentary ancient plant and mammal DNA, pollen, spores, chironomids, and microcharcoal. We assembled a highly-complete local DNA reference library (PhyloAlps, 3923 plant taxa), and used this to obtain an exceptionally rich sedaDNA record of 366 plant taxa. Vegetation mainly responded to climate during the early Holocene, while human activity had an additional influence on vegetation from 6 ka onwards. Land-use shifted from episodic grazing during the Neolithic and Bronze Age to agropastoralism in the Middle Ages. Associated human deforestation allowed the coexistence of plant species typically found at different elevational belts, leading to levels of plant richness that characterise the current high diversity of this region. Our findings indicate a positive association between low intensity agropastoral activities and precipitation with the maintenance of the unique subalpine and alpine plant diversity of the European Alps.

Antioxidant Supplementation Does Not Affect Bone Turnover Markers During 60 Days of 6° Head-Down Tilt Bed Rest: Results from an Exploratory Randomized Controlled Trial.

BACKGROUND: Immobilization and related oxidative stress are associated with bone loss. Antioxidants like polyphenols, omega-3 fatty acids, vitamins, and micronutrients may mitigate these negative effects on bone metabolism through scavenging of free radicals. OBJECTIVES: We hypothesized that antioxidant supplementation during 60 days of 6° head-down tilt bed rest (HDBR) would reduce bone resorption and increase bone formation compared to nonsupplemented controls. METHODS: This exploratory randomized, controlled, single-blind intervention study conducted in a parallel design included 20 healthy male volunteers (age, 34 ± 8 years; weight, 74 ± 6 kg). The study consisted of a 14-day adaptation phase [baseline data collection (BDC)], followed by 60 days of HDBR and a 14-day recovery period (R). In the antioxidant group, volunteers received an antioxidant cocktail (741 mg/d polyphenols, 2.1 g/d omega-3 fatty acids, 168 mg/d vitamin E, and 80 µg/d selenium) with their daily meals. In the control group, volunteers received no supplement. Based on their body weight, all volunteers received an individually tailored and strictly controlled diet, consistent with DRIs. We analyzed biomarkers of calcium homeostasis, bone formation, and bone resorption during BDC, HDBR, and R, as well as for 30 days after the end of HDBR. Data were analyzed by linear mixed models. RESULTS: The antioxidant supplement did not affect serum calcium, parathyroid hormone, urinary C-telopeptide of type I collagen (CTX), urinary N-telopeptide of type I collagen, serum ß-C-telopeptide of type I collagen (ß-CTX), bone alkaline phosphatase, aminoterminal propeptide of type I collagen, osteocalcin, or urinary calcium excretion. In both groups, typical bed rest-related changes were observed. CONCLUSIONS: Supplementation of an antioxidant cocktail to a diet matching the DRIs did not affect bone resorption or formation during 60 days of HDBR in healthy young men. This trial was registered at clinicaltrials.gov as NCT03594799.

Effectiveness of Resistive Vibration Exercise and Whey Protein Supplementation Plus Alkaline Salt on the Skeletal Muscle Proteome Following 21 Days of Bed Rest in Healthy Males.

Muscle atrophy is a deleterious consequence of physical inactivity and is associated with increased morbidity and mortality. The aim of this study was to decipher the mechanisms involved in disuse muscle atrophy in eight healthy men using a 21 day bed rest with a cross-over design (control, with resistive vibration exercise (RVE), or RVE combined with whey protein supplementation and an alkaline salt (NEX)). The main physiological findings show a significant reduction in whole-body fat-free mass (CON -4.1%, RVE -4.3%, NEX -2.7%, p < 0.05), maximal oxygen consumption (CON -20.5%, RVE -6.46%, NEX -7.9%, p < 0.05), and maximal voluntary contraction (CON -15%, RVE -12%, and NEX -9.5%, p < 0.05) and a reduction in mitochondrial enzyme activity (CON -30.7%, RVE -31.3%, NEX -17%, p < 0.05). The benefits of nutrition and exercise countermeasure were evident with an increase in leg lean mass (CON -1.7%, RVE +8.9%, NEX +15%, p < 0.05). Changes to the vastus lateralis muscle proteome were characterized using mass spectrometry-based label-free quantitative proteomics, the findings of which suggest alterations to cell metabolism, mitochondrial metabolism, protein synthesis, and degradation pathways during bed rest. The observed changes were partially mitigated during RVE, but there were no significant pathway changes during the NEX trial. The mass spectrometry proteomics data have been deposited to the ProteomeXchange Consortium with the dataset identifier PXD006882. In conclusion, resistive vibration exercise, when combined with whey/alkalizing salt supplementation, could be an effective strategy to prevent skeletal muscle protein changes, muscle atrophy, and insulin sensitivity during medium duration bed rest.

Putative Effects of Nutritive Polyphenols on Bone Metabolism In Vivo-Evidence from Human Studies.

For the prevention and treatment of bone loss related diseases, focus has been put on naturally derived substances such as polyphenols. Based on human intervention studies, this review gives an overview of the effects of dietary significant polyphenols (flavonoids, hydroxycinnamic acids, and stilbenes) on bone turnover. Literature research was conducted using PubMed database and articles published between 01/01/2008 and 31/12/2018 were included (last entry: 19/02/2019). Randomized controlled trials using oral polyphenol supplementation, either of isolated polyphenols or polyphenols-rich foods with healthy subjects or study populations with bone disorders were enclosed. Twenty articles fulfilled the inclusion criteria and the average study quality (mean Jadad score: 4.5) was above the pre-defined cut-off of 3.0. Evidence from these studies does not allow an explicit conclusion regarding the effects of dietary important polyphenols on bone mineral density and bone turnover markers. Differences in study population, habitual diet, lifestyle factors, applied polyphenols, used doses, and polyphenol bioavailability complicate the comparison of study outcomes.

Alkalinization with potassium bicarbonate improves glutathione status and protein kinetics in young volunteers during 21-day bed rest.

BACKGROUND & AIMS: Physical inactivity is associated with lean body mass wasting, oxidative stress and pro-inflammatory changes of cell membrane lipids. Alkalinization may potentially counteract these alterations. We evaluated the effects of potassium bicarbonate supplementation on protein kinetics, glutathione status and pro- and anti-inflammatory polyunsaturated fatty acids (PUFA) in erythrocyte membranes in humans, during experimental bed rest. METHODS: Healthy, young, male volunteers were investigated at the end of two 21-day bed rest periods, one with, and the other without, daily potassium bicarbonate supplementation (90 mmol × d-1), according to a cross-over design. Oxidative stress in erythrocytes was evaluated by determining the ratio between reduced (GSH) and oxidized glutathione (GSSG). Glutathione turnover and phenylalanine kinetics, a marker of whole body protein metabolism, were determined by stable isotope infusions. Erythrocyte membranes PUFA composition was analyzed by gas-chromatography. RESULTS: At the end of the two study periods, urinary pH was 10 ± 3% greater in subjects receiving potassium bicarbonate supplementation (7.23 ± 0.15 vs. 6.68 ± 0.11, p < 0.001). Alkalinization increased total glutathione concentrations by 5 ± 2% (p < 0.05) and decreased its rate of clearance by 38 ± 13% (p < 0.05), without significantly changing GSH-to-GSSG ratio. After alkalinization, net protein balance in the postabsorptive state improved significantly by 17 ± 5% (p < 0.05) as well as the sum of n-3 PUFA and the n-3-to-n-6 PUFA ratio in erythrocyte membranes (p < 0.05). CONCLUSIONS: Alkalinization during long-term inactivity is associated with improved glutathione status, anti-inflammatory lipid pattern in cell membranes and reduction in protein catabolism at whole body level. This study suggests that, in clinical conditions characterized by inactivity, oxidative stress and inflammation, alkalinization could be a useful adjuvant therapeutic strategy.

A nutrient cocktail prevents lipid metabolism alterations induced by 20 days of daily steps reduction and fructose overfeeding: result from a randomized study.

Physical inactivity and sedentary behaviors are independent risk factors for numerous diseases. We examined the ability of a nutrient cocktail composed of polyphenols, omega-3 fatty acids, vitamin E, and selenium to prevent the expected metabolic alterations induced by physical inactivity and sedentary behaviors. Healthy trained men ( n = 20) (averaging ∼14,000 steps/day and engaged in sports) were randomly divided into a control group (no supplementation) and a cocktail group for a 20-day free-living intervention during which they stopped exercise and decreased their daily steps (averaging ∼3,000 steps/day). During the last 10 days, metabolic changes were further triggered by fructose overfeeding. On days 0, 10, and 20, body composition (dual energy X-ray), blood chemistry, glucose tolerance [oral glucose tolerance test (OGTT)], and substrate oxidation (indirect calorimetry) were measured. OGTT included 1% fructose labeled with (U-13C) fructose to assess liver de novo lipogenesis. Histological changes and related cellular markers were assessed from muscle biopsies collected on days 0 and 20. While the cocktail did not prevent the decrease in insulin sensitivity and its muscular correlates induced by the intervention, it fully prevented the hypertriglyceridemia, the drop in fasting HDL and total fat oxidation, and the increase in de novo lipogenesis. The cocktail further prevented the decrease in the type-IIa muscle fiber cross-sectional area and was associated with lower protein ubiquitination content. The circulating antioxidant capacity was improved by the cocktail following the OGTT. In conclusion, a cocktail of nutrient compounds from dietary origin protects against the alterations in lipid metabolism induced by physical inactivity and fructose overfeeding. NEW & NOTEWORTHY This is the first study to test the efficacy of a novel dietary nutrient cocktail on the metabolic and physiological changes occurring during 20 days of physical inactivity along with fructose overfeeding. The main findings of this study are that 1) reduction in daily steps leads to decreased insulin sensitivity and total fat oxidation, resulting in hyperlipemia and increased de novo lipogenesis and 2) a cocktail supplement prevents the alterations on lipid metabolism.

Sensitivity of serum concentration of cartilage biomarkers to 21-days of bed rest.

The objective of the study was to test the hypothesis that serum levels of cartilage oligomeric matrix protein (COMP) would decrease and serum levels of tumor-necrosis factor alpha (TNF-α) and selected matrix metalloproteinases (MMPs) would increase in response to bed rest (BR) and that these changes are unaffected by the intake of potassium bicarbonate or whey protein. Seven and nine healthy male subjects participated in two 21-day 6° head down tilt crossover BR-studies with nutrition interventions. Serum samples were taken before, during, and after BR and biomarker concentrations were measured using commercial enzyme-linked immunosorbent assays. MMP-3 during BR was significantly lower than at baseline (reduction greater 20%; p < 0.001). MMP-3 increased significantly from 14 to 21 days of BR (+7%; p = 0.049). COMP during BR was significantly lower than at baseline (reduction greater 20%; p < 0.001). MMP-3 and COMP returned to baseline within 1 day after BR. MMP-9 on day 3 of BR was significantly lower than at baseline (-31%; p < 0.033) and on days 3, 5, and 14 of BR significantly lower than at the end of and after BR (reduction greater 35%; p < 0.030). The nutritional countermeasures did not affect these results. The observed changes in cartilage biomarkers may be caused by altered cartilage metabolism in response to the lack of mechanical stimulus during BR and inflammatory biomarkers may play a role in changes in biomarker levels. CLINICAL RELEVANCE: Immobilization independently from injury can cause altered cartilage biomarker concentration. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1465-1471, 2018.

Glucocorticoid activity and metabolism with NaCl-induced low-grade metabolic acidosis and oral alkalization: results of two randomized controlled trials.

Low-grade metabolic acidosis (LGMA), as induced by high dietary acid load or sodium chloride (NaCl) intake, has been shown to increase bone and protein catabolism. Underlying mechanisms are not fully understood, but from clinical metabolic acidosis interactions of acid-base balance with glucocorticoid (GC) metabolism are known. We aimed to investigate GC activity/metabolism under alkaline supplementation and NaCl-induced LGMA. Eight young, healthy, normal-weight men participated in two crossover designed interventional studies. In Study A, two 10-day high NaCl diet (32 g/d) periods were conducted, one supplemented with 90 mmol KHCO3/day. In Study B, participants received a high and a low NaCl diet (31 vs. 3 g/day), each for 14 days. During low NaCl, the diet was moderately acidified by replacement of a bicarbonate-rich mineral water (consumed during high NaCl) with a non-alkalizing drinking water. In repeatedly collected 24-h urine samples, potentially bioactive-free GCs (urinary-free cortisol + free cortisone) were analyzed, as well as tetrahydrocortisol (THF), 5α-THF, and tetrahydrocortisone (THE). With supplementation of 90 mmol KHCO3, the marker of total adrenal GC secretion (THF + 5α-THF + THE) dropped (p = 0.047) and potentially bioactive-free GCs were reduced (p = 0.003). In Study B, however, GC secretion and potentially bioactive-free GCs did not exhibit the expected fall with NaCl-reduction as net acid excretion was raised by 30 mEq/d. Diet-induced acidification/alkalization affects GC activity and metabolism, which in case of long-term ingestion of habitually acidifying western diets may constitute an independent risk factor for bone degradation and cardiometabolic diseases.

Alkaline salts to counteract bone resorption and protein wasting induced by high salt intake: results of a randomized controlled trial.

High sodium chloride (NaCl) intake can induce low-grade metabolic acidosis (LGMA) and may thus influence bone and protein metabolism. We hypothesized that oral potassium bicarbonate (KHCO(3)) supplementation may compensate for NaCl-induced, LGMA-associated bone resorption and protein losses. Eight healthy male subjects participated in a randomized trial with a crossover design. Each of two study campaigns consisted of 5 d of dietary and environmental adaptation followed by 10 d of intervention and 1.5 d of recovery. In one study campaign, 90 mmol KHCO(3)/d were supplemented to counteract NaCl-induced LGMA, whereas the other campaign served as a control with only high NaCl intake. When KHCO(3) was ingested during high NaCl intake, postprandial buffer capacity ([HCO(3)(-)]) increased (P = 0.002). Concomitantly, urinary excretion of free potentially bioactive glucocorticoids [urinary free cortisol (UFF) and urinary free cortisone (UFE)] was reduced by 14% [∑(UFF,UFE); P = 0.024]. Urinary excretion of calcium and bone resorption marker N-terminal telopeptide of type I collagen was reduced by 12 and 8%, respectively (calcium, P = 0.047; N-terminal bone collagen telopeptide, P = 0.044). There was a trend of declining net protein catabolism when high NaCl was combined with KHCO(3) (P = 0.052). We conclude that during high salt intake, the KHCO(3)-induced postprandial shift to a more alkaline state reduces metabolic stress. This leads to decreased bone resorption and protein degradation, which in turn might initiate an anticatabolic state for the musculoskeletal system in the long run.

Effects of whey protein supplements on metabolism: evidence from human intervention studies.

PURPOSE OF REVIEW: Epidemiological studies indicate that the consumption of milk and dairy products is inversely associated with a lower risk of metabolic disorders and cardiovascular diseases. In particular, whey protein seems to induce these effects because of bioactive compounds such as lactoferrin, immunoglobulins, glutamine and lactalbumin. In addition, it is an excellent source of branch chained amino acids. This review summarizes recent findings on the effects of whey protein on metabolic disorders and the musculoskeletal system. RECENT FINDINGS: We identified 25 recently published intervention trials examining chronic and/or acute effects of whey protein supplementation on lipid and glucose metabolism, blood pressure, vascular function and on the musculoskeletal system. Whey protein appears to have a blood glucose and/or insulin lowering effect partly mediated by incretins. In addition, whey protein may increase muscle protein synthesis. In contrast there are no clear-cut effects shown on blood lipids and lipoproteins, blood pressure and vascular function. For bone metabolism the data are scarce. SUMMARY: In summary, whey protein may affect glucose metabolism and muscle protein synthesis. However, the evidence for a clinical efficacy is not strong enough to make final recommendations with respect to a specific dose and the duration of supplementation.

The effect of L-arginine administration on muscle force and power in postmenopausal women.

Previously published data (J Bone Miner Res (2005); 20: 471) did not give evidence that the administration of the nitric oxide precursor L-arginine increases bone formation and decreases bone resorption in postmenopausal women. Data of this trial were reanalysed for putative effects of L-arginine on muscle mass and muscular function. Therefore, 11 females of the former study group (n=15; age 54.5+/-4.1 years; daily oral administration of 18 g L-arginine hydrochloride (equivalent of 14.2 g L-arginine) over 6 months) and 12 females of the control group (n=15; age 55.3+/-4.4 years; daily administration of 18 g dextrose over 6 months) were analysed for biomechanical parameters (MIGF, maximal isometric grip force; PJF, peak jump force; PJP, peak jump power) and for the cross-sectional muscle area (MA) and fat area (FA) at forearm and leg (calf) measured by peripheral quantitative computed tomography. The study was performed in a double-blind design. The assessment of muscular and biomechanical parameters was undertaken before and after 6 months of L-arginine versus placebo administration. L-arginine-supplemented females had a significant increase of PJF/kg in comparison with the control group. PJP/kg, MIGF, MA and FA were not significantly influenced by the administration of L-arginine. In conclusion, the administration of L-arginine increased maximal force in mechanographic analyses and may prevent a decline of muscle force in postmenopausal women.

L-arginine, the natural precursor of NO, is not effective for preventing bone loss in postmenopausal women.

UNLABELLED: NO is an important regulator of bone turnover. L-Arginine, the natural precursor of NO, can enhance NO production. However, no effect of L-arginine hydrochloride supplementation was found on bone metabolism or on BMD, bone mass, or bone structure of healthy postmenopausal women. INTRODUCTION: Recent studies indicate that NO exerts an anabolic effect on bone cell activity. The NO level of the human body can be elevated by administering pharmacological NO donors. Animal studies and the first human trial showed that NO donor administration had a positive effect on bone formation and a negative effect on bone resorption. L-arginine, the natural precursor of NO, can enhance NO production. This study was conducted to examine the effect of an oral L-arginine supplement on bone metabolism of healthy postmenopausal women. MATERIALS AND METHODS: The participants in this study were 30 healthy, age-matched postmenopausal women, divided into two groups. For 6 months, one group (54.5 +/- 4.1 years; 66.3 +/- 10.5 kg) received a daily oral supplement with 18 g L-arginine hydrochloride (14.8 g free L-arginine). The other 15 volunteers (55.3 +/- 4.4 years; 64.2 +/- 9.1 kg) received 18 g dextrose as a placebo. To verify compliance, 24-h urinary excretion of nitrogen was analyzed for 2 consecutive days at baseline and after 2, 4, and 6 months. At baseline and after 2, 4, and 6 months of supplementation, blood was drawn for analysis of insulin-like growth factor-I (IGF-I) and biomarkers of bone metabolism. At baseline, after 6 months, and after 1 year, pQCT measurements were performed at trabecular and cortical sites of the radius and tibia. The two groups of subjects were compared by repeated measures ANOVA. RESULTS: As expected, in the group with L-arginine hydrochloride supplementation, nitrogen excretion rose, and in the placebo group, it remained constant. Only bone formation marker, procollagen type I propeptides (PICP), increased significantly (p < 0.05) after 6 months of L-arginine supplementation. The results from pQCT showed no significant changes at any site in either group. No significant change in IGF-I concentration, which might have been caused by the L-arginine hydrochloride supplementation, was evident. CONCLUSIONS: We conclude from these results that supplementation with L-arginine hydrochloride is not effective for improving bone mass in humans.

Bone turnover during inpatient nutritional therapy and outpatient follow-up in patients with anorexia nervosa compared with that in healthy control subjects.

BACKGROUND: Osteopenia and osteoporosis are among the most frequent and severe complications in adolescents with anorexia nervosa. OBJECTIVE: The aim of this study was to assess the influence of nutritional therapy on bone metabolism during adolescent anorexia nervosa. DESIGN: We studied 19 anorectic patients aged 14.1 +/- 1.4 y (x +/- SD) with a body mass index (BMI; in kg/m(2)) of 14.2 +/- 1.4 and 19 age-matched control subjects aged 15.1 +/- 2.3 y with a BMI of 20.8 +/- 1.9 for 1 y. Blood samples were taken for the measurement of bone markers, insulin-like growth factor I (IGF-I), and leptin. RESULTS: BMI rose significantly from 14.2 +/- 1.4 at baseline to 17.4 +/- 0.6 (P < 0.0001) at week 15. Compared with concentrations in the control subjects, concentrations of the bone formation markers procollagen type I propeptide (PICP) and bone alkaline phosphatase (bAP) in the anorectic patients were lower at baseline (PICP: P = 0.0071; bAP: P = 0.0012), increased with nutritional therapy (PICP: P = 0.0060, bAP: P = 0.0147), and were no longer significantly different (P > 0.05) during the follow-up period. Concentrations of IGF-I and leptin were significantly lower (P < 0.0001 for both) in the anorectic patients than in the control subjects at baseline. IGF-I increased with nutritional therapy but was still significantly lower (P = 0.0036) than that in the control group and decreased again during the follow-up period (P = 0.0126). In contrast, serum C-telopeptide decreased with nutritional therapy (P = 0.0446). CONCLUSION: Nutritional therapy improves concentrations of bone formation markers in adolescent patients with anorexia nervosa.

Nutritional interventions related to bone turnover in European space missions and simulation models.

Low energy intake, low calcium intake, low plasma 25-hydroxy-vitamin D or low calcitriol levels, and high salt intake might support the development of space osteoporosis. Therefore, my colleagues and I monitored the daily energy and calcium intakes in eight astronauts during their respective space missions (Spacelab D2, Euromir 94, Euromir 95). In most of these astronauts, energy intake was reduced by more than 20% compared with their calculated energy expenditure. In all three missions, the average daily calcium intake of the eight astronauts was 25% lower than the German recommended daily allowances of 900 mg/d for healthy people without osteoporosis risk. In some astronauts, the calcium intake was extremely low at 53 and 74 mg/d. Sodium intake in these astronauts varied from 39 mEq/d to a very high intake of 462 mEq/d. As a consequence of these results, we examined in the 21-d Mir 97 mission a preventative dietary approach of high calcium intake of at least 1000 mg/d with vitamin D supplementation (650 IU/d of Ergocalciferol) and constant sodium intake (180 mEq/d). Total serum calcium concentration and urinary calcium excretion significantly increased during this mission. Synthesis of 25-OH-cholecalciferol synthesis was markedly reduced because of inadequate ultraviolet light, whereas total 25-OH-Vitamin D levels were unchanged. However, parathyroid hormone and calcitriol levels decreased significantly. Sodium excretion decreased significantly, resulting in positive sodium balances. Based on these results, dietary calcium and vitamin D do not stabilize bone turnover because markers of bone formation were reduced and markers of bone resorption were increased. We concluded that, in contrast to terrestrial conditions, adequate or even high calcium and vitamin D intakes during microgravity do not efficiently counteract the development of space osteoporosis. Conversely, vitamin K (Konakion) seemed to counteract microgravity-induced reduction of bone formation markers. In the 179-d Euromir 95 mission, investigators administered 10 mg of vitamin K from inflight day 86 to day 136 in one astronaut. During and after supplementation, bone formation markers increased significantly during this part of the mission. Therefore, vitamin K seems to play a significant role in bone turnover during space flight.

Effects of L-arginine supplementation on bone metabolism.

Recent experimental studies indicate that nitric oxide (NO) is an important regulator of bone turnover in humans by exerting an anabolic effect on bone cell activity. NO is synthesised from the nonessential amino acid L-arginine. Therefore, a supplementation with oral L-arginine might be highly potent to affect bone cell activity via NO synthesis from L-arginine. In our study we examined the effect of a six months oral supplementation with L-arginine-hydrochloride (18 g) on bone metabolism in 15 healthy postmenopausal women. We analysed nitrogen excretion, markers of bone turnover and calcium concentration. The results show neither a change in serum calcium concentration nor in bone turnover as shown by bone markers. In conclusion, L-arginine-hydrochloride supplementation at that concentration seems to have no effect on bone cell activity in healthy postmenopausal women.