Vitamin D receptor expression in human muscle tissue decreases with age

Falls are associated with decreased renal function and insufficient calcitriol production by the kidney

In a double blind placebo controlled 3-year osteoporosis study in elderly women, we collected prospective data on falls. The study population comprised 489 normal elderly women aged 65-77 years randomized to four groups: placebo, calcitriol 0.25 mcg b.i.d., conjugated equine estrogens (0.625 mg/day) and calcitriol+estrogen. Falls occurred in 57% of all women. Using a Poisson regression model, the placebo group with low GFR-creatinine clearance (CrCl<60 ml/min) had 60% more falls compared to the group with CrCl> or =60 ml/min. Further sub group analyses showed that there is no increased risk of falls with CrCl 60-70, 70-80 and >90 ml/min. Calcitriol treatment significantly reduced the number of falls by 50% (OR=0.5, 95% CI: 0.4-0.9, p=0.010) compared to placebo in the low CrCl group. The group with lower CrCl had lower calcium absorption (p<0.001), lower serum 1,25-dihydroxyvitamin D (1,25(OH)(2)D) (p<0.001) and normal serum 25OHD suggesting that there is decreased conversion of 25OHD to 1,25(OH)(2)D by the aging kidney. It is postulated that the decrease in falls on calcitriol therapy is related to an increase in serum 1,25(OH)(2)D, upregulation of VDR and improvement in muscle strength although one cannot exclude an effect on the central nervous system.

Superiority of a combined treatment of Alendronate and Alfacalcidol compared to the combination of Alendronate and plain vitamin D or Alfacalcidol alone in established postmenopausal or male osteoporosis (AAC-Trial)

A combined therapy with the strongly antiresorptive Alendronate and the pleiotropically acting D-hormone analogue Alfacalcidol may have additive effects on bone quality, falls and fracture risk in established osteoporosis. The aim of this study (Alfacalcidol Alendronate Combined-AAC) was to compare the efficacy and safety of a combined parallel therapy with Alendronate and Alfacalcidol to the treatment with either Alendronate in combination with plain vitamin D or Alfacalcidol alone in patients with established postmenopausal or male osteoporosis. Ninety patients were included as matched triplets to receive randomly either 1 microg Alfacalcidol daily + 500 mg calcium (group A, n = 30) or 70 mg Alendronate weekly + 1,000 mg calcium + 1,000 IU vitamin D daily (group B, n = 30) or 1 microg Alfacalcidol daily + 70 mg Alendronate weekly + 500 mg calcium daily (group C, n = 30). Patients were recruited in one centre and were followed up for 24 months. Analysis was intention-to-treat and the primary outcome was lumbar spine and total hip bone mineral density (measured observer blind). BMD was measured at the lumbar spine and at the proximal femur with dual energy X-ray absorptiometry (LUNAR Prodigy, GE, USA) at the beginning and after 12 and 24 months. During the 2-year-study we observed descriptively significant increases at the lumbar spine of 3.0% in group A compared to baseline, of 5.4% in group B and of 9.6% in group C, respectively. The superiority of the Alendronate + Alfacalcidol treatment group over Alfacalcidol alone and over Alendronate + vitamin D was of more than large rele-vance (both tests: MW > 0.71; CI-LB > 0.64; P < 0.001). We also observed median increases of the BMD at the total hip of 1.5% in group A, of 2.4% in group B and of 3.8% in group C, respectively. The superiority of group C over group A and over group B again was relevant and statistically significant in a descriptive sense. After 2 years there was a tendency towards higher rates of vertebral and non-vertebral fractures in group A and B as compared to C. Taking both fracture types together we observed 9, 10 and 2 "osteoporotic fractures" in groups A, B and C, respectively. The comparison of group C with pooled groups A and B and with each single group gave a relevantly lower fracture rate for the combination of Alendronate and Alfacalcidol. Furthermore a lower rate of falls was observed for the combination Alendronate plus Alfacalcidol versus Alendronate + vitamin D, but not versus Alfacalcidol alone. We found 80% of the patients in the Alendronate + Alfacalcidol group free from back pain at month 24, compared to 30% in the Alendronate + vitamin D and 43% in the Alfacalcidol monotherapy group. The superiority is relevant (both tests: MW > 0.64; CI-LB > 0.56; P < 0.003). Pain decrease also occurred more rapidly in the Alendronate + Alfacalcidol group than in the other groups. In general side effects in all groups were mild, and only four cases of moderate hypercalcuria in group A and one in group C were reported, but no case of hypercalcemia was documented. In conclusion, the combination therapy with Alendronate and Alfacalcidol exhibited superiority in terms of BMD, overall fractures, rate of falls and back pain over either Alendronate in combination with plain vitamin D or Alfacalcidol alone. The overall safety profiles of the three treatment regimens were found to be not different in this study.

An age-related decrease in creatinine clearance is associated with an increase in number of falls in untreated women but not in women receiving calcitriol treatment

CONTEXT

Decreased calcitriol production due to impaired renal function may be a significant risk factor for falls in normal aging population.

OBJECTIVE

The objective of the study was to examine the association between creatinine clearance (CrCl) and the incidence of falls and fallers in groups treated with placebo, calcitriol, estrogen therapy (ET)/estrogen + progestin therapy (HT), and calcitriol + ET/HT.

DESIGN

This was a 3-yr, double-blind, placebo-controlled study designed to test the efficacy of calcitriol and ET/HT on bone loss and falls with analysis by intention to treat and post hoc.

SETTING

The study was conducted at an academic outpatient center.

PARTICIPANTS

Four hundred eighty-nine normal elderly women aged 65-77 yr; 415 women completed the study.

INTERVENTION

Subjects were randomized to placebo, calcitriol 0.25 mug twice a day, ET daily (conjugated equine estrogens 0.625 mg), HT (conjugated equine estrogen 0.625 mg + medroxyprogesterone acetate 2.5 mg) and calcitriol + ET/HT.

MAIN OUTCOME MEASURES

Cumulative number of falls and fallers were compared between groups with 24-h urine CrCl less than 60 and 60 ml/min or greater.

RESULTS

Calcitriol treatment decreased the number of fallers and falls. Low CrCl less than 60 ml/min was a predictor of the number of falls per person but not fallers in the placebo group (P = 0.007). In the low CrCl group (<60 ml/min), the rate of falls decreased on calcitriol by 53% [95% confidence interval (CI) -71% to -22%; P = 0.003], calcitriol + ET/HT by 61% (95% CI -76% to -37%; P = 0.001), and ET/HT by 25% (95% CI: -55% to +24%; not significant). Calcitriol reduced the rate of falls by 30% (95% CI -49% to -4%; P = 0.027) in the CrCl 60 ml/min or greater group.

CONCLUSION

Calcitriol treatment decreases falls in all subjects but especially in elderly women with decreased renal function (<60 ml/min) and frequent fallers.

Smoking Is a Risk Factor for Decreased Physical Performance in Elderly Women

BACKGROUND

In 487 elderly women aged 65-77 years, we examined the association of smoking with physical performance measures of muscle function and whether the effect of smoking on physical performance measures is mediated through its effect on vitamin D or estrogen metabolism.

METHODS

Timed rise, timed walk at normal and fast speed, grip strength, and serum biochemical measurements were compared between smokers, past smokers, and nonsmokers. Analysis of covariance was used to compare physical performance variables while adjusting for confounding variables.

RESULTS

Compared to nonsmokers and past smokers, current smokers were significantly (p <.05) slower on timed rise and timed walk tests and had decreased grip strength. From multivariate analysis, smoking, age, total body fat, and serum 1,25(OH)(2)D examined as quartiles were predictors of physical performance measures. The effect of current smoking on physical performance was equivalent to a normal age-related decline in physical performance tests of 7-11 years depending on the test.

CONCLUSIONS

The results of this study suggest that current smoking is a risk factor for decreased muscle strength leading to decreased physical performance in elderly women. The effect of smoking on physical performance is in part mediated by its effect on 1,25(OH)(2)D metabolism. Smoking may also have an independent effect on physical performance possibly by a direct effect on muscle or through an effect on vascular function.

Relationship between vitamin D metabolites and bone mineral density in young males: a cross-sectional and longitudinal study

The purpose of this study was to investigate the association between vitamin D analogs and peak bone mineral density (BMD, g/cm(2)) in young men. The cohort consisted of 78 healthy young males with a mean age of 22.6 years at baseline. BMD of the total body, hip, and spine and lean body mass were measured at baseline and at follow-up 2 years later. Blood samples were assayed for 25-hydroxyvitamin D(2) (25OHD(2)), 25-hydroxyvitamin D(3) (25OHD(3)), and 25-hydroxyvitamin D (25OHD) at baseline using high-performance liquid chromatography. Levels of 25OHD(3) significantly correlated to BMD at all sites and to lean body mass (r = 0.23-0.35, P < 0.05). In contrast, levels of 25OHD(2) significantly negatively correlated with BMD of the total body (r = -0.28, P = 0.01) and spine (r = -0.27, P = 0.02). BMD was then adjusted for the influence of age, body weight, body height, and physical activity (hours/week). Level of 25OHD(3) was then found to be an independent predictor of BMD of the total body (beta = 0.24, P = 0.03) and spine (beta = 0.25, P = 0.03), while level of 25OHD(2) was an independent negative predictor at the same sites (beta = -0.23 for both, P = 0.03). There was a negative association between levels of 25OHD(3) and 25OHD(2) (r = -0.31, P = 0.006). In summary, our novel results suggest an inverse relationship between 25OHD(3) and 25OHD(2) and an opposite relationship of these vitamin D analogs to BMD in young men.

Calcium and vitamin D in the prevention and treatment of osteoporosis - a clinical update

Combined calcium and vitamin D supplementation is an essential component of the management of osteoporosis, supported by a strong scientific rationale. The types of individuals who should receive calcium and vitamin D supplements are those: (i) patients with documented osteoporosis receiving antiresorptive or anabolic treatment; (ii) patients receiving glucocorticoids; and (iii) individuals with or at high risk of calcium and/or vitamin D insufficiencies, in particular older women and men. This article describes the evidence base that supports targeting these groups. Benefits are most apparent when 800 IU day(-1) vitamin D is complemented with a dose of 1000-1200 mg day(-1) elemental calcium. Compliance is also key to optimizing clinical efficacy.

Addressing the musculoskeletal components of fracture risk with calcium and vitamin D: a review of the evidence

Osteoporotic fractures are an extremely common and serious health problem in the elderly. This article presents the rationale for calcium and vitamin D supplementation in the prevention and treatment of osteoporotic fractures and reviews the literature evidence on the efficacy of this strategy. Two musculoskeletal risk factors are implicated in osteoporotic fractures in the elderly: the loss of bone mass due to secondary hyperparathyroidism and the increased propensity to falls. Calcium and vitamin D reverse secondary hyperparathyroidism with resultant beneficial effects on bone mineral density (BMD). Additionally, calcium and vitamin D supplementation significantly improves body sway and lower extremity strength, reducing the risk of falls. The effects of combined calcium and vitamin D on parathyroid function and BMD provide a strong rationale for the use of this therapy in the prevention and treatment of osteoporosis and osteoporotic fractures. There is general agreement that, in patients with documented osteoporosis, calcium and vitamin D supplementation should be an integral component of the management strategy, along with antiresorptive or anabolic treatment. Frail elderly individuals constitute another major target population for calcium and vitamin D because evidence from randomized studies in institutionalized elderly subjects demonstrates that these supplements reduce osteoporotic fracture risk, particularly in the presence of dietary deficiencies. However, the results of trials in community-dwelling subjects have been equivocal. Within the primary-care setting, further research is required to establish appropriate target subgroups for calcium and vitamin D supplementation; overall, the data are consistent with a benefit individuals with insufficient calcium and/or vitamin D, although patients with documented osteoporosis will derive further benefit in terms of fracture prevention from the addition of an antiresorptive agent.

The Importance of Parathyroid Hormone and Vitamin D Status in the Treatment of Osteoporosis and Renal Insufficiency

Suboptimal vitamin D status is common in sick, elderly patients and is associated with secondary hyperparathyroidism, increased bone turnover, and accelerated bone loss. Nutritional supplementation of elderly patients with vitamin D and calcium has been associated with a reduction in fractures and falls. Recently, the National Kidney Foundation (NKF) recommended screening parathyroid hormone (PTH) levels in those with glomerular filtration rates (GFR) less than 60 mL/min. The PTH target range increases as renal failure progresses because of skeletal resistance. When PTH levels are above the target range, measurement of serum 25-hydroxyvitamin D (25-OH-D) is recommended. If the 25-OH-D level is less than 30 ng/mL, supplementation with vitamin D is recommended. Practitioners should consider supplementing most residents with vitamin D and calcium or follow NKF guidelines.

Vitamin D physiology

Vitamin D3 is synthesized in the skin during summer under the influence of ultraviolet light of the sun, or it is obtained from food, especially fatty fish. After hydroxylation in the liver into 25-hydroxyvitamin D (25(OH)D) and kidney into 1,25-dihydroxyvitamin D (1,25(OH)2D), the active metabolite can enter the cell, bind to the vitamin D-receptor and subsequently to a responsive gene such as that of calcium binding protein. After transcription and translation the protein is formed, e.g. osteocalcin or calcium binding protein. The calcium binding protein mediates calcium absorption from the gut. The production of 1,25(OH)2D is stimulated by parathyroid hormone (PTH) and decreased by calcium. Risk factors for vitamin D deficiency are premature birth, skin pigmentation, low sunshine exposure, obesity, malabsorption and advanced age. Risk groups are immigrants and the elderly. Vitamin D status is dependent upon sunshine exposure but within Europe, serum 25(OH)D levels are higher in Northern than in Southern European countries. Severe vitamin D deficiency causes rickets or osteomalacia, where the new bone, the osteoid, is not mineralized. Less severe vitamin D deficiency causes an increase of serum PTH leading to bone resorption, osteoporosis and fractures. A negative relationship exists between serum 25(OH)D and serum PTH. The threshold of serum 25(OH)D, where serum PTH starts to rise is about 75nmol/l according to most surveys. Vitamin D supplementation to vitamin D-deficient elderly suppresses serum PTH, increases bone mineral density and may decrease fracture incidence especially in nursing home residents. The effects of 1,25(OH)2D and the vitamin D receptor have been investigated in patients with genetic defects of vitamin D metabolism and in knock-out mouse models. These experiments have demonstrated that for active calcium absorption, longitudinal bone growth and the activity of osteoblasts and osteoclasts both 1,25(OH)2D and the vitamin D receptor are essential. On the other side, bone mineralization can occur by high ambient calcium concentration, so by high doses of oral calcium or calcium infusion. The active metabolite 1,25(OH)2D has its effects through the vitamin D receptor leading to gene expression, e.g. the calcium binding protein or osteocalcin or through a plasma membrane receptor and second messengers such as cyclic AMP. The latter responses are very rapid and include the effects on the pancreas, vascular smooth muscle and monocytes. Muscle cells contain vitamin D receptor and several studies have demonstrated that serum 25(OH)D is related to physical performance. The active metabolite 1,25(OH)2D has an antiproliferative effect and downregulates inflammatory markers. Extrarenal synthesis of 1,25(OH)2D occurs under the influence of cytokines and is important for the paracrine regulation of cell differentiation and function. This may explain that vitamin D deficiency can play a role in the pathogenesis of auto-immune diseases such as multiple sclerosis and diabetes type 1, and cancer. In conclusion, the active metabolite 1,25(OH)2D has pleiotropic effects through the vitamin D receptor and vitamin D responsive elements of many genes and on the other side rapid non-genomic effects through a membrane receptor and second messengers. Active calcium absorption from the gut depends on adequate formation of 1,25(OH)2D and an intact vitamin D receptor. Bone mineralization mainly depends on ambient calcium concentration. Vitamin D metabolites may play a role in the prevention of auto-immune disease and cancer.

The vitamin D questions: How much do you need and how should you get it?

UV radiation is a well-documented human carcinogen, indisputably linked to the current continued increased rate of skin cancer. UV radiation is also responsible for cutaneous synthesis of vitamin (vit) D3, a substance that is then sequentially hydroxylated in the liver and kidney to yield 1,25(OH)2 vit D, a hormone critical for calcium homeostasis and skeletal maintenance. Because the UV action spectra for DNA damage leading to skin cancer and for vit D photosynthesis are virtually identical, the harmful and beneficial effects of UV irradiation are inseparable. This has given rise to the argument that sun avoidance, with a goal of skin cancer prevention, may compromise vit D sufficiency. Public interest in this matter has been heightened in recent years by multiple studies correlating the level of 25-OH vit D, the readily measurable "storage" precursor form of the vit, with a variety of benefits separate from skeletal health. Although the studies are of variable quality and all alleged treatment benefits are based on dietary supplementation with vit D, not on increased sun exposure, they have been interpreted by some as support for advocating increased sun exposure of the public at large. The goal of this review is to provide a detailed, balanced, and referenced discussion of the complex literature underlying the current popular interest in vit D and sun exposure for the purpose of increasing vit D photosynthesis. We review the nomenclature, metabolism, and established functions of vit D; the evidence supporting the less well-established but purported vit D effects; the concept of vit D insufficiency; populations at risk for vit D deficiency; and finally the risk/benefit of obtaining vit D from cutaneous photosynthesis versus diet or supplementation.

Higher 1,25-dihydroxyvitamin D3 concentrations associated with lower fall rates in older community-dwelling women

INTRODUCTION

The purpose of this study was to examine the relationships of vitamin D supplementation and serum concentrations of vitamin D metabolites and parathyroid hormone (PTH) with neuromuscular function and falls in older community-dwelling women.

METHODS

We examined these relationships using a 4-year prospective multi-center study among 9,526 community-dwelling women enrolled in the Study of Osteoporotic Fractures (median age: 70 years; interquartile range: 67-75) and a subset of 389 women (97%) out of 400 who were randomly selected from the entire cohort for serum measures. Measurements included: vitamin D supplementation, serum 25-hydroxyvitamin D(3) [25(OH)D(3)], serum 1,25-dihydroxyvitamin D(3) [1,25(OH) (2)D(3)], and serum intact parathyroid hormone (iPTH); grip and quadriceps strength, chair-stand time, walking speed, reaction time, and balance-walk time (including changes in grip strength, chair-stand time, walking speed and balance-walk time over approximately 3.7 years); and incident fall rates (number of falls/woman-years).

RESULTS

In 9,526 women, vitamin D supplementation was not associated with any measures of neuromuscular function, change in neuromuscular function, or fall rates (p>0.01 for all). In a subgroup of 389 women, there was a trend of higher 25(OH)D(3) concentration with slightly weaker grip strength (p=0.007), and women in the fourth quartile of 1,25(OH)(2)D(3) had a faster chair-stand time (p=0.017) than women in the first quartile; still, in general, concentrations of 25(OH)D(3), 1,25(OH)(2)D(3), and iPTH were not associated with either neuromuscular function or changes in neuromuscular function (p>0.05 for all). However, higher 1,25(OH)(2)D(3) concentration was associated with lower fall rates (p=0.039).

CONCLUSIONS

Higher 1,25(OH)(2)D(3) concentration is associated with a lower fall risk in older community-dwelling women, but vitamin D supplementation, and 25(OH)D(3) and iPTH concentrations are not associated with either neuromuscular function or falls.

Is fall prevention by vitamin D mediated by a change in postural or dynamic balance?

INTRODUCTION

The objectives were:(1) to validate a quantitative balance assessment method for fall risk prediction; (2) to investigate whether the effect of vitamin D and calcium on the risk of falling is mediated through postural or dynamic balance, as assessed by this method.

MATERIALS AND METHODS

A secondary analysis of a double blind randomized controlled trial was employed, which included 64 institutionalized elderly women with complete balance assessment (age range: 65-97; mean 25-hydroxyvitamin D levels: 16.4 ng/ml (SD +/-9.9). Participants received 1,200 mg calcium plus 800 IU cholecalciferol (n=33) or 1,200 mg calcium (n=31) per day over a 3-month treatment period. Using an electronic device attached to the lower back of the participant, balance was assessed as the degree of trunk angular displacement and angular velocity during a postural task (standing on two legs, eyes open, for 20 s) and a dynamic task (get up from a standard height chair with arm rests, sit down and then stand up again and remain standing).

RESULTS

It was found that both postural and dynamic balance independently and significantly predicted the rate of falling within the 3-month follow-up. Vitamin D plus calcium reduced the rate of falls by 60% [relative risk (RR)=0.40; 95% CI: 0.17, 0.94] if compared with calcium alone. Once postural and dynamic balance were added to the regression analysis, they both attenuated the effect of vitamin D plus calcium on the rate of falls. For postural balance, the RR changed by 22% from 0.40 to 0.62 if angular displacement was added to the model, and by 9% from 0.40 to 0.49 if angular velocity was added. For dynamic balance, it changed by 1% from 0.40 to 0.41 if angular displacement was added, and by 14% from 0.40 to 0.54 if angular velocity was added.

DISCUSSION

Thus, balance assessment using trunk angular displacement is a valid method for the prediction of falls in older women. Of the observed 60% reduction in the rate of falls by vitamin D plus calcium supplementation compared with calcium alone, up to 22% of the treatment effect was explained by a change in postural balance and up to 14% by dynamic balance.

In elderly men and women treated for osteoporosis a low creatinine clearance of <65 ml/min is a risk factor for falls and fractures

Recently, a low creatinine clearance (CrCl) of < 65 ml/min was described as a new significant and independent risk factor for the number of fallers and falls in a community-dwelling elderly population. In this study we investigated if a low creatinine clearance of < 65 ml/min is also a risk factor for falls and fractures in elderly men and women treated for osteoporosis. In a cross-sectional study with the help of questionnaires we assessed the prevalence of having experienced falls within the last 12 months according to renal function in 5,313 German men and women receiving treatment for osteoporosis. The CrCl was calculated using the established Cockcroft-Gault formula. The prevalence of falls and fractures was assessed in multivariate-controlled logistic regression models according to a CrCl cut off of 65 ml/min. The P-values were two-sided. In this study of elderly men and women treated for osteoporosis (n=5,313), 60.9% (n=3,238) had a CrCl of < 65 ml/min, which was associated in multivariate controlled analyses, compared to a CrCl of > or = 65 ml/min (n=2,075), with a significant increased risk of experiencing falls (1,775/3,238 vs. 773/2,075, OR 1.69, 95% CI 1.50-1.91, P<0.0001) and an increased risk for multiple falls (37.1 vs. 22.6%, OR 1.63, 95% CI 1.42-1.87, P<0.0001). Furthermore, compared to a creatinine clearance of > or = 65 ml/min, a creatinine clearance of < 65 ml/min was also associated with a significant increased multivariate controlled risk for hip fractures (OR 1.57, 95%CI 1.18-2.09, P=0.002), for radial fractures (OR 1.79, 95%CI 1.39-2.31, P=<0.0001), for total vertebral fractures (OR 1.31, 95%CI 1.19-1.55, P=0.003) and for fall-associated vertebral fractures (OR 1.24, 95% CI 1.03-1.54, P=0.031). Similar to community-dwelling elderly, in elderly men and women treated for osteoporosis a CrCl of less than 65 ml/min is a significant and independent risk factor for falls. Furthermore, we could show for the first time that a low creatinine clearance in elderly men and women treated for osteoporosis is also associated with a significantly increased risk of vertebral, hip and radial fractures.

The vitamin D epidemic and its health consequences

Vitamin D deficiency is now recognized as an epidemic in the United States. The major source of vitamin D for both children and adults is from sensible sun exposure. In the absence of sun exposure 1000 IU of cholecalciferol is required daily for both children and adults. Vitamin D deficiency causes poor mineralization of the collagen matrix in young children's bones leading to growth retardation and bone deformities known as rickets. In adults, vitamin D deficiency induces secondary hyperparathyroidism, which causes a loss of matrix and minerals, thus increasing the risk of osteoporosis and fractures. In addition, the poor mineralization of newly laid down bone matrix in adult bone results in the painful bone disease of osteomalacia. Vitamin D deficiency causes muscle weakness, increasing the risk of falling and fractures. Vitamin D deficiency also has other serious consequences on overall health and well-being. There is mounting scientific evidence that implicates vitamin D deficiency with an increased risk of type I diabetes, multiple sclerosis, rheumatoid arthritis, hypertension, cardiovascular heart disease, and many common deadly cancers. Vigilance of one's vitamin D status by the yearly measurement of 25-hydroxyvitamin D should be part of an annual physical examination.

Papel da vitamina D na função neuro-muscular

A vitamina D, através de suas ações no intestino, rim, osso e glândulas paratiróides, é um hormônio fundamental para a homeostase do cálcio e para o desenvolvimento de um esqueleto saudável. Além disso, receptores deste hormônio podem ser encontrados em quase todos os tecidos do organismo e outras ações não relacionadas ao metabolismo mineral têm sido imputadas a ele. Na célula muscular esquelética, a vitamina D atua através do mecanismo clássico de ligação a um receptor nuclear e também através da ligação a um receptor de membrana, realizando ações que envolvem o transporte de cálcio, a síntese protéica e a velocidade de contração muscular. Clinicamente, a deficiência de vitamina D, que é bastante comum em idosos, inclusive em nosso país, tem sido relacionada a um aumento da incidência de quedas, a uma diminuição da força muscular e a uma deterioração do equilíbrio, avaliada pela oscilação do corpo na postura ereta. Por outro lado, tem sido demonstrado que a suplementação associada de cálcio e vitamina D em idosos deficientes contribui para melhoria destes aspectos da função neuro-muscular. Nesta revisão, serão discutidos os mecanismos conhecidos envolvidos na associação entre vitamina D e função neuro-muscular, e também a suplementação de vitamina D e cálcio na prevenção de fraturas osteoporóticas não-vertebrais sob a perspectiva dos efeitos neuro-musculares.

Vitamin D in the aging musculoskeletal system: An authentic strength preserving hormone

Until recently, vitamin D was only considered as one of the calciotrophic hormones without major significance in other metabolic processes in the body. Several recent findings have demonstrated that vitamin D plays also a role as a factor for cell differentiation, function and survival. Two organs, muscle and bone, are significantly affected by the presence, or absence, of vitamin D. In bone, vitamin D stimulates bone turnover while protecting osteoblasts of dying by apoptosis whereas in muscle vitamin D maintains the function of type II fibers preserving muscle strength and preventing falls. Furthermore, two major changes associated to aging: osteoporosis and sarcopenia, have been also linked to the development of frailty in elderly patients. In both cases vitamin D plays an important role since the low levels of this vitamin seen in senior people may be associated to a deficit in bone formation and muscle function. In this review, the interaction between vitamin D and the musculoskeletal components of frailty are considered from the basic mechanisms to the potential therapeutic approach. We expect that these new considerations about the importance of vitamin D in the elderly will stimulate an innovative approach to the problem of falls and fractures which constitutes a significant burden to public health budgets worldwide.