Once daily calcium (1000 mg) and vitamin D (1000 IU) supplementation during military training prevents increases in biochemical markers of bone resorption but does not affect tibial microarchitecture in Army recruits.

Basic combat training (BCT) is a period of novel physical training including load carriage resulting in higher risk of stress fracture compared to any other time during military service. Prior trials reported a 20% reduction in stress fracture incidence with Ca and vitamin D (Ca + D) supplementation (2000 mg Ca, 800 IU vitamin D), and greater increases in tibia vBMD during BCT compared to placebo. The primary objective of this randomized, double-blind, placebo-controlled trial was to determine the efficacy of a lower dose of Ca (1000 mg/d Ca, 1000 IU vit D) on PTH, bone biomarkers and tibial microarchitecture during BCT. One hundred volunteers (50 males, 50 females; mean age 21.8 ± 3.5 y) were block randomized by race and sex to receive a daily Ca + D fortified food bar or placebo. Anthropometrics, dietary intake, fasted blood draws and high resolution pQCT scans of the distal and mid-shaft tibia were obtained at the start of BCT and 8 wks later at the conclusion of training. As compliance was 98% in both treatment groups, an intent-to-treat analysis was used. At the distal tibia, total vBMD, Tb.vBMD, Tb.N, Th.Th and Tb.BV/TV increased (+1.07 to 2.12% for all, p < 0.05) and Tb.Sp decreased (0.96 to 1.09%, p < 0.05) in both treatment groups. At the mid-shaft, Ct.Pm increased (+0.18 to 0.21%, p = 0.01) and Ct.vBMD decreased (-0.48 to -0.77%, p < 0.001) in both groups. Ca + D prevented increases in CTX and TRAP, which were observed in the placebo group (group-by-time, p < 0.05). Mean circulating 25OHD, BAP, P1NP and iCa increased and PTH decreased in both treatment groups (p < 0.05). These results, in agreement with other studies, suggest that bone microarchitectural changes indicative of bone formation occur during BCT. While Ca + D supplementation at lower doses than those tested in previous studies prevented increases in biochemical markers of bone resorption in this study, there were no significant changes in bone tissue after 8 wks of Army BCT.

Divergent effects of sex and calcium/vitamin D supplementation on serum magnesium and markers of bone structure and function during initial military training.

Maintaining Mg status may be important for military recruits, a population that experiences high rates of stress fracture during initial military training (IMT). The objectives of this secondary analysis were to (1) compare dietary Mg intake and serum Mg in female and male recruits pre- and post-IMT, (2) determine whether serum Mg was related to parameters of bone health pre-IMT, and (3) whether Ca and vitamin D supplementation (Ca/vitamin D) during IMT modified serum Mg. Females (n 62) and males (n 51) consumed 2000 mg of Ca and 25 µg of vitamin D/d or placebo during IMT (12 weeks). Dietary Mg intakes were estimated using FFQ, serum Mg was assessed and peripheral quantitative computed tomography was performed on the tibia. Dietary Mg intakes for females and males pre-IMT were below the estimated average requirement and did not change with training. Serum Mg increased during IMT in females (0·06 ± 0·08 mmol/l) compared with males (-0·02 ± 0·10 mmol/l; P < 0·001) and in those consuming Ca/vitamin D (0·05 ± 0·09 mmol/l) compared with placebo (0·001 ± 0·11 mmol/l; P = 0·015). In females, serum Mg was associated with total bone mineral content (BMC, ß = 0·367, P = 0·004) and robustness (ß = 0·393, P = 0·006) at the distal 4 % site, stress-strain index of the polaris axis (ß = 0·334, P = 0·009) and robustness (ß = 0·420, P = 0·004) at the 14 % diaphyseal site, and BMC (ß = 0·309, P = 0·009) and stress-strain index of the polaris axis (ß = 0·314, P = 0·006) at the 66 % diaphyseal site pre-IMT. No significant relationships between serum Mg and bone measures were observed in males. Findings suggest that serum Mg may be modulated by Ca/vitamin D intake and may impact tibial bone health during training in female military recruits.

A prospective field study of U.S. Army trainees to identify the physiological bases and key factors influencing musculoskeletal injuries: a study protocol.

BACKGROUND: Musculoskeletal injuries (MSKIs) are common in military trainees and present a considerable threat to occupational fitness, deployability, and overall military readiness. Despite the negative effects of MSKIs on military readiness, comprehensive evaluations of the key known and possible risk factors for MSKIs are lacking. The U.S. Army Research Institute of Environmental Medicine (ARIEM) is initiating a large-scale research effort, the ARIEM Reduction in Musculoskeletal Injury (ARMI) Study, to better understand the interrelationships among a wide range of potential MSKI risk factors in U.S. Army trainees in order to identify those risk factors that most contribute to MSKI and may be best targeted for effective mitigation strategies. METHODS: This prospective study aims to enroll approximately 4000 (2000 male and 2000 female) U.S. Army trainees undergoing Basic Combat Training (BCT). Comprehensive in-person assessments will be completed at both the beginning and end of BCT. Participants will be asked to complete surveys of personal background information, medical history, physical activity, sleep behaviors, and personality traits. Physical measurements will be performed to assess anthropometrics, tibial microarchitecture and whole body bone mineral density, muscle cross-sectional area, body composition, and muscle function. Blood sampling will be also be conducted to assess musculoskeletal, genetic, and nutritional biomarkers of risk. In addition, participants will complete weekly surveys during BCT that examine MSKI events, lost training time, and discrete risk factors for injury. Participants' medical records will be tracked for the 2 years following graduation from training to identify MSKI events and related information. Research hypotheses focus on the development of a multivariate prediction model for MSKI. DISCUSSION: Results from this study are expected to inform current understanding of known and potential risk factors for MSKIs that can be incorporated into solutions that optimize Soldier health and enhance military readiness.

Effects of vitamin D supplementation on salivary immune responses during Marine Corps basic training.

Vitamin D's role in regulating immune responses may increase during periods of elevated psychological and physiological stress. Due to the high demands placed on US Marine Corps recruits undergoing 12 weeks of basic military training, we hypothesized that vitamin D status would be related to markers of innate mucosal immunity, and daily vitamin D supplementation would augment immune responses during training. Males (n = 75) and females (n = 74) entering recruit basic training during the summer and winter volunteered to participate in a randomized, double-blind, placebo-controlled study. Subjects received either 1000 IU vitamin D3  + 2000 mg calcium/d (n = 73) or placebo (n = 76) for 12 weeks. Saliva samples were collected pre-training, during (weeks 4 and 8), and post-training (week 12) in order to determine salivary SIgA and cathelicidin (indices of mucosal immunity) and α-amylase (indicator of stress). Initial (baseline) and post-training serum 25(OH)D levels were measured. Results were as follows: serum 25(OH)D levels were 37% higher in recruits entering training in summer compared with winter. A positive relationship was observed between baseline 25(OH)D levels and SIgA secretion rates (-SR). When stress levels were high during summer training, baseline 25(OH)D levels contributed to an increase in salivary secretory immunoglobulin A secretion rates (SIgA-SR) and cathelicidin-SR, the latter only in males. Vitamin D supplementation contributed to the changes in SIgA-SR and cathelicidin-SR, specifically SIgA-SR was higher in the treatment group. These data highlight the importance of vitamin D and mucosal immune responses during arduous basic military training when stress levels are increased.

Calcium and vitamin D supplementation and bone health in Marine recruits: Effect of season.

Stress fractures are common overuse injuries caused by repetitive bone loading. These fractures are of particular concern for military recruits and athletes resulting in attrition in up to 60% of recruits that sustain a fracture. Army and Navy recruits supplemented with daily calcium and vitamin D (Ca + D) demonstrated improved bone strength and reduced stress fractures. The aim of the current study was to evaluate whether Ca + D supplementation improves measures of bone health in recruits undergoing United States Marine Corps initial military training (IMT), and whether the effect of supplementation on indices of bone health varied by season. One-hundred ninety-seven Marine recruits (n = 107 males, n = 90 females, mean age = 18.9 ±â€¯1.6 y) were randomized to receive either Ca + D fortified snack bars (2000 mg Ca and 1000 IU vitamin D per day) or placebo divided into twice daily doses during 12 weeks of IMT. Anthropometrics, fasted blood samples, and peripheral quantitative computed tomography (pQCT) scans of the tibial metaphysis and diaphysis were collected upon entrance to- and post-training (12 weeks later). Half of the volunteers entered training in July and the other half started in February. Time-by-group interactions were observed for vitamin D status (25OHD) and the bone turnover markers, BAP, TRAP and OCN. 25OHD increased and BAP, TRAP and OCN all decreased in the Ca + D group (p < .05). Training increased distal tibia volumetric BMD (+1.9 ±â€¯2.8%), BMC (+2.0 ±â€¯3.1%), and bone strength index (BSI; +4.0 ±â€¯4.0%) and diaphyseal BMC (+1.0 ±â€¯2.2%) and polar stress strain index (SSIp; +0.7 ±â€¯2.1%) independent of Ca + D supplementation (p < .05 for all). When analyzed by season, change in BSI was greater in the Ca + D group as compared to placebo in the summer iteration only (T*G; p < .05). No other effects of supplementation on bone tissue were observed. When categorized by tertile of percent change in BSI, recruits demonstrating the greatest changes in BSI and 25OHD entered training with the lowest levels of 25OHD (p < .05). Over all, these results suggest that Ca + D supplementation reduced some markers of bone formation and resorption and the decline in 25OHD over training in volunteers that started training in the summer was prevented by supplementation. Baseline 25OHD and trajectory may impact bone responses to IMT, but little effect of Ca + D supplementation was observed at the investigated doses.

A dietary pattern rich in calcium, potassium, and protein is associated with tibia bone mineral content and strength in young adults entering initial military training.

Background: Stress fracture risk is elevated during initial military training (IMT), particularly in lower-extremity bones such as the tibia. Although the etiology of stress fractures is multifactorial, lower bone strength increases risk. Objective: The objective of this study was to assess, through the use of peripheral quantitative computed tomography, whether adherence to a dietary pattern rich in calcium, potassium, and protein before IMT is positively associated with bone indexes in young adults entering IMT. Design: A cross-sectional analysis was performed with the use of baseline data from 3 randomized controlled trials in Army, Air Force, and Marine recruits (n = 401; 179 men, 222 women). Dietary intake was estimated from a food-frequency questionnaire. A dietary pattern characterized by calcium, potassium, and protein was derived via reduced rank regression and a pattern z score was computed for each volunteer, where higher scores indicated greater adherence to the pattern. At the 4% (metaphysis) and 14% (diaphysis) sites of the tibia, bone mineral content (BMC), volumetric bone mineral density, robustness, and strength indexes were evaluated. Associations between dietary pattern z score as the predictor variable and bone indexes as the response variables were evaluated by multiple linear regression. Results: Pattern z score was positively associated with BMC (P = 0.004) and strength (P = 0.01) at the metaphysis and with BMC (P = 0.0002), strength (P = 0.0006), and robustness (P = 0.02) at the diaphysis when controlling for age, sex, race, energy, smoking, education, and exercise. Further adjustment for BMI attenuated the associations, except with diaphyseal BMC (P = 0.005) and strength (P = 0.01). When height and weight were used in place of body mass index, the association with BMC remained (P = 0.046). Conclusions: A dietary pattern rich in calcium, potassium, and protein is positively associated with measures of tibia BMC and strength in recruits entering IMT. Whether adherence to this dietary pattern before IMT affects injury susceptibility during training remains to be determined. These trials were registered at clinicaltrials.gov as NCT01617109 and NCT02636348.

Dietary Intake in Relation to Military Dietary Reference Values During Army Basic Combat Training; a Multi-center, Cross-sectional Study.

INTRODUCTION: The military dietary reference intakes (MDRIs), outlined in Army Regulation 40-25, OPNAVINST 10110.1/MCO10110.49, AFI 44-141, establish standards intended to meet the nutrient requirements of Warfighters. Therefore, the purpose of this study was to comprehensively compare the revised MDRIs, published in 2017, with estimated dietary intakes in U.S. military personnel. MATERIALS AND METHODS: During this cross-sectional study, Block food frequency questionnaires were administered at the end of the 9-week basic combat training course to estimate dietary intake during basic combat training in male (n = 307) and female (n = 280) recruits. The cut-point method was used to determine nutrient adequacy in comparison to the MDRIs. This study was approved by the Institutional Review Board of the U.S. Army Research Institute of Environmental Medicine. RESULTS: Recruits consumed an adequate amount of vitamins A, C and K, as well as the B-vitamins, and phosphorus, selenium, zinc, and protein and carbohydrate as a percentage of total calories when compared with MDRI standards. Vitamin D was the short-fall nutrient affecting the greatest number of participants, as 55 and 70% of males and females, respectively, consumed less than 33% of the MDRI. In addition, less than 50% of males met the MDRI for linoleic and α-linolenic acid, fiber, vitamin E, magnesium, and potassium, and less than 50% of females met the MDRI for α-linolenic acid, fiber, vitamin E, calcium, iron, magnesium, and potassium. In contrast, fat and sodium were over-consumed by both males (78 and 87%, respectively) and females (73 and 72%, respectively). CONCLUSION: The main findings of this study were that vitamins D and E, magnesium, potassium, α-linolenic acid, and fiber were under consumed by male and female recruits while males also did not consume adequate linoleic acid and females did not consume adequate calcium and iron. Future prospective research studies are needed to determine possible health and performance impacts that may be associated with suboptimal intake of these nutrients.

Association Between Single Gene Polymorphisms and Bone Biomarkers and Response to Calcium and Vitamin D Supplementation in Young Adults Undergoing Military Training.

Initial military training (IMT) is associated with increased stress fracture risk. In prior studies, supplemental calcium (Ca) and vitamin D provided daily throughout IMT reduced stress fracture incidence, suppressed parathyroid hormone (PTH), and improved measures of bone health compared with placebo. Data were analyzed from a randomized, double-blind, placebo-controlled trial to determine whether single-nucleotide polymorphisms (SNPs) in Ca and vitamin D-related genes were associated with circulating biomarkers of bone metabolism in young adults entering IMT, and whether responses to Ca and vitamin D supplementation were modulated by genotype. Associations between SNPs, including vitamin D receptor (VDR), vitamin D binding protein (DBP), and 1-alpha-hydroxylase (CYP27B1), and circulating biomarkers were measured in fasting blood samples from volunteers (n = 748) starting IMT. Volunteers were block randomized by race and sex to receive Ca (2000 mg) and vitamin D (1000 IU) or placebo daily throughout Army or Air Force IMT (7 to 9 weeks). Total Ca and vitamin D intakes were calculated as the sum of supplemental intake based on intervention compliance and dietary intake. Relationships between SNPs, Ca, and vitamin D intake tertile and change in biomarkers were evaluated in trial completers (n = 391). At baseline, the minor allele of a DBP SNP (rs7041) was positively associated with both 25OHD (B = 4.46, p = 1.97E-10) and 1,25(OH)2 D3 (B = 9.63, p < 0.001). Combined genetic risk score (GRS) for this SNP and a second SNP in the VDR gene (rs1544410) was inversely associated with baseline 25OHD (r = -0.28, p < 0.001) and response to Ca and vitamin D intake differed by GRS (p < 0.05). In addition, presence of the minor allele of a second VDR SNP (rs2228570) was associated with lower P1NP (B = -4.83, p = 0.04) and osteocalcin (B = -0.59, p = 0.03). These data suggest that VDR and DBP SNPs are associated with 25OHD status and bone turnover and those with the highest GRS require the greatest vitamin D intake to improve 25OHD during IMT. © 2016 American Society for Bone and Mineral Research.

Optimizing Performance, Health, and Well-being: Nutritional Factors.

Nutrition is essential for maintaining peak health and performance of Warfighters. This review will focus on a series of nutrients of concern for female Warfighters. Biological function, dietary sources, and requirements will be reviewed, and recommendations for women in combat roles will be provided. Iron, essential for physical and cognitive performance, is critical for female Warfighters because of elevated dietary requirements as compared to male Warfighters, as well as declines in iron status that may occur in response to physical activities, such as military training. Calcium and vitamin D are essential for bone health, and should be considered in efforts to prevent stress fractures, which occur with greater frequency in female Warfighters as compared to their male counterparts. Folate, essential for the prevention of neural tube defects during pregnancy and gestation, is critical for female Warfighters because of elevated dietary requirements before pregnancy. Providing optimal levels of these nutrients will facilitate readiness as women prepare to serve in combat roles.

Consumption of a calcium and vitamin D-fortified food product does not affect iron status during initial military training: a randomised, double-blind, placebo-controlled trial.

Ca/vitamin D supplementation maintains bone health and decreases stress fracture risk during initial military training (IMT); however, there is evidence that Ca may negatively affect the absorption of other critical micronutrients, particularly Fe. The objective of this randomised, double-blind, placebo-controlled trial was to determine whether providing 2000 mg/d Ca and 25 µg/d vitamin D in a fortified food product during 9 weeks of military training affects Fe status in young adults. Male (n 98) and female (n 54) volunteers enrolled in US Army basic combat training (BCT) were randomised to receive a snack bar with Ca/vitamin D (n 75) or placebo (snack bar without Ca/vitamin D; n 77) and were instructed to consume 2 snack bars/d between meals throughout the training course. Circulating ionised Ca was higher (P0·05) in markers of Fe status between placebo and Ca/vitamin D groups. Collectively, these data indicate that Ca/vitamin D supplementation through the use of a fortified food product consumed between meals does not affect Fe status during IMT.

The Effect of a Whey Protein Supplement on Bone Mass in Older Caucasian Adults.

CONTEXT: It has been assumed that the increase in urine calcium (Ca) that accompanies an increase in dietary protein was due to increased bone resorption. However, studies using stable Ca isotopes have found that dietary protein increases Ca absorption without increasing bone resorption. OBJECTIVE: The objective of the study was to investigate the impact of a moderately high protein diet on bone mineral density (BMD). DESIGN: This was a randomized, double-blind, placebo-controlled trial of protein supplementation daily for 18 months. SETTING: The study was conducted at two institutional research centers. PARTICIPANTS: Two hundred eight older women and men with a body mass index between 19 and 32 kg/m(2) and a self-reported protein intake between 0.6 and 1.0 g/kg participated in the study. INTERVENTION: Subjects were asked to incorporate either a 45-g whey protein or isocaloric maltodextrin supplement into their usual diet for 18 months. MAIN OUTCOME MEASURE: BMD by dual-energy x-ray absorptiometry, body composition, and markers of skeletal and mineral metabolism were measured at baseline and at 9 and 18 months. RESULTS: There were no significant differences between groups for changes in L-spine BMD (primary outcome) or the other skeletal sites of interest. Truncal lean mass was significantly higher in the protein group at 18 months (P = .048). C-terminal telopeptide (P = .0414), IGF-1 (P = .0054), and urinary urea (P < .001) were also higher in the protein group at the end of the study period. There was no difference in estimated glomerular filtration rate at 18 months. CONCLUSION: Our data suggest that protein supplementation above the recommended dietary allowance (0.8 g/kg) may preserve fat-free mass without adversely affecting skeletal health or renal function in healthy older adults.

Calcium and vitamin D supplementation maintains parathyroid hormone and improves bone density during initial military training: a randomized, double-blind, placebo controlled trial.

Calcium and vitamin D are essential nutrients for bone health. Periods of activity with repetitive mechanical loading, such as military training, may result in increases in parathyroid hormone (PTH), a key regulator of Ca metabolism, and may be linked to the development of stress fractures. Previous studies indicate that consumption of a Ca and vitamin D supplement may reduce stress fracture risk in female military personnel during initial military training, but circulating markers of Ca and bone metabolism and measures of bone density and strength have not been determined. This randomized, double-blind, placebo-controlled trial sought to determine the effects of providing supplemental Ca and vitamin D (Ca+Vit D, 2000mg and 1000IU/d, respectively), delivered as 2 snack bars per day throughout 9weeks of Army initial military training (or basic combat training, BCT) on PTH, vitamin D status, and measures of bone density and strength in personnel undergoing BCT, as well as independent effects of BCT on bone parameters. A total of 156 men and 87 women enrolled in Army BCT (Fort Sill, OK; 34.7°N latitude) volunteered for this study. Anthropometric, biochemical, and dietary intake data were collected pre- and post-BCT. In addition, peripheral quantitative computed tomography was utilized to assess tibia bone density and strength in a subset of volunteers (n=46). Consumption of supplemental Ca+Vit D increased circulating ionized Ca (group-by-time, P=0.022), maintained PTH (group-by-time, P=0.032), and increased the osteoprotegerin:RANKL ratio (group-by-time, P=0.006). Consistent with the biochemical markers, Ca+Vit D improved vBMD (group-by-time, P=0.024) at the 4% site and cortical BMC (group-by-time, P=0.028) and thickness (group-by-time, P=0.013) at the 14% site compared to placebo. These data demonstrate the benefit of supplemental Ca and vitamin D for maintaining bone health during periods of elevated bone turnover, such as initial military training. This trial was registered with ClincialTrials.gov, NCT01617109.

The efficacy of vitamin D supplementation during a prolonged submarine patrol.

Submariners spend prolonged periods submerged without sunlight exposure and may benefit from vitamin D supplementation to maintain vitamin D status. The primary objective of this study was to determine the efficacy of daily vitamin D supplementation on maintenance of 25-hydroxyvitamin D (25(OH)D) during a 3-month submarine patrol. Submariners were randomly divided into three groups: placebo (n = 16), 1,000 IU/day (n = 20), or 2,000 IU/day (n = 17). Anthropometrics, self-reported dietary calcium and vitamin D intake, serum markers of vitamin D and bone metabolism, and peripheral quantitative computed tomography (pQCT) parameters of the tibia were determined before and after the patrol. Prior to departure, 49 % of the subjects were vitamin D insufficient (<50 nmol/L). Following the patrol, 25(OH)D increased in all groups (p < 0.001): 3.3 ± 13.1 (placebo), 4.6 ± 11.3 (1,000 IU/day), and 13 ± 14 nmol/L (2,000 IU/day). The changes in 25(OH)D levels were dependent upon the baseline concentration of 25(OH)D and body mass (p < 0.001). Osteocalcin increased by 38 % (p < 0.01), and pQCT analyses revealed small, yet significant increases in indices of tibial structure and strength (p < 0.05) that were independent of supplementation. These data suggest that vitamin D status was low prior to the patrol, and the subsequent changes in vitamin D status were dependent on the baseline 25(OH)D levels and body mass. Furthermore, short-term skeletal health does not appear to be negatively affected by 3 months of submergence in spite of a suboptimal response to vitamin D supplementation.

Female athletes: a population at risk of vitamin and mineral deficiencies affecting health and performance.

Adequate vitamin and mineral status is essential for optimal human health and performance. Female athletes could be at risk for vitamin and mineral insufficiency due to inadequate dietary intake, menstruation, and inflammatory responses to heavy physical activity. Recent studies have documented poor iron status and associated declines in both cognitive and physical performance in female athletes. Similarly, insufficient vitamin D and calcium status have been observed in female athletes, and may be associated with injuries, such as stress fracture, which may limit a female athlete's ability to participate in regular physical activity. This review will focus on recent studies detailing the prevalence of poor vitamin and mineral status in female athletes, using iron, vitamin D, and calcium as examples. Factors affecting the dietary requirement for these vitamins and minerals during physical training will be reviewed. Lastly, countermeasures for the prevention of inadequate vitamin and mineral status will be described.

Inflammation and diminished iron status: mechanisms and functional outcomes.

PURPOSE OF REVIEW: To summarize recent findings regarding the effects of inflammation on iron (Fe) metabolism and to review studies detailing the influence of poor Fe status on physical and cognitive performance. RECENT FINDINGS: Hepatic expression and release of hepcidin, a negative regulator of Fe status, is increased by the actions of the inflammatory cytokine interleukin-6. Inflammation associated with chronic disease, obesity, and exercise is associated with elevated interleukin-6 and hepcidin levels, which may result in diminished Fe status. SUMMARY: Decrements in Fe status due to insufficient dietary Fe intake and/or the inflammatory response may degrade physical and cognitive performance. Future studies should clarify whether dietary or other therapeutic interventions to mitigate inflammation attenuate hepcidin-mediated declines in Fe status.

Increasing dietary protein requirements in elderly people for optimal muscle and bone health.

Osteoporosis and sarcopenia are degenerative diseases frequently associated with aging. The loss of bone and muscle results in significant morbidity, so preventing or attenuating osteoporosis and sarcopenia is an important public health goal. Dietary protein is crucial for development of bone and muscle, and recent evidence suggests that increasing dietary protein above the current Recommended Dietary Allowance (RDA) may help maintain bone and muscle mass in older individuals. Several epidemiological and clinical studies point to a salutary effect of protein intakes above the current RDA (0.8 g/kg per day) for adults aged 19 and older. There is evidence that the anabolic response of muscle to dietary protein is attenuated in elderly people, and as a result, the amount of protein needed to achieve anabolism is greater. Dietary protein also increases circulating insulin-like growth factor, which has anabolic effects on muscle and bone. Furthermore, increasing dietary protein increases calcium absorption, which could be anabolic for bone. Available evidence supports a beneficial effect of short-term protein intakes up to 1.6 to 1.8 g/kg per day, although long-term studies are needed to show safety and efficacy. Future studies should employ functional measures indicative of protein adequacy, as well as measures of muscle protein synthesis and maintenance of muscle and bone tissue, to determine the optimal level of dietary protein. Given the available data, increasing the RDA for older individuals to 1.0 to 1.2 g/kg per day would maintain normal calcium metabolism and nitrogen balance without affecting renal function and may represent a compromise while longer-term protein supplement trials are pending.