内分泌疾病与钙代谢异常

钙是人体内含量最高的元素之一。骨骼系统储存着全身98％的钙,另外2％在血液中循环。血钙受甲状旁腺激素（PTH）、降钙素和活性维生素D[1,25-（OH）2D3]共同调节。当内分泌系统发生疾病时,内分泌腺分泌激素水平失调,钙代谢调控失衡,引起血钙水平波动。我们对内分泌疾病与钙代谢异常作一综述。     

2型糖尿病患者血清维生素D水平及影响因素分析

维生素D不仅调节钙磷代谢,还与糖尿病、代谢综合征、冠心病、高血压、外用血管病等疾病的发生发展有关。维生素D水平降低可能损伤胰岛B细胞功能,对2型糖尿病是一个潜在的危险因素。我们对2型糖尿病患者血清维生素D水平变化及影响因素进行分析。     

适量补充钙和维生素D是防治骨质疏松症的基础措施——评新英格兰医学杂志Jackson等"补充钙和维生素D与骨折危险"一文

对2006年2月16日新英格兰医学杂志(NEJM)发表的“补充钙和维生素D与骨折危险”一文进行评述。这是一项大样本的随机、对照临床试验,评价绝经后妇女长期补充钙和维生素D对预防骨质疏松性骨折的效果。结果显示,在健康的绝经后妇女中补充钙和维生素D后髋部骨密度少量增加,但未能显著减少髋部骨折的发生,而肾结石的危险增加。由于该研究在研究设计、人群的选择、依从性等方面存在明显的局限与缺陷,影响了研究结果的真实性、科学性和推广价值。本文的结论是:该研究没有提供充分可靠的证据否定补充钙和维生素D对防治骨质疏松的益处。基于以往的众多研究证据,继续推荐以钙和维生素D的适量补充作为防治骨质疏松的基础措施。     

钙剂加维生素D治疗对糖尿病患者钙代谢的影响

本文报道NIDDM患者在常规治疗的基础上加用钙剂和维生素D治疗后的钙代谢变化。糖尿病患者单纯用常规治疗控制血糖后,负钙平衡不能完全纠正,而加用钙剂和维生素D治疗后,负钙平衡能完全纠正,并且高于正常对照组平衡值(P<0.01)。说明钙剂加维生素D治疗对糖尿病性骨质疏松是有益的。     

老年骨质疏松

骨质疏松是老年人一种最常见、严重和花费昂贵的健康问题。随增龄矿物质代谢和骨骼完整性发生生理变化,其特点是肠道对钙的吸收减少,循环中甲状旁腺激素中等程度升高,而骨组织中则降低,随之骨折危险性增加。Tsai最近研究了年龄对维生素D代谢的作用。他们推测,老年人肾脏的25羟基维生素D羟化作用受损,使其有代谢活性的1,25二羟维生素D减少可能是钙吸收减少和甲状旁腺激素中等程度升高的原因。他们对正常绝经期前的妇女、初绝经的妇女、正常老年妇女和髋骨骨折的老年妇女四个组进行了比较,他们发现25羟基维生素D不受年龄影响。但老年组中1,25二羟基维生素D较低。甲状旁腺激素是肾脏1-α羟化酶的活化剂,输入24小时后,1,25二羟基维生素D增加,但老年组     

欧洲老年人的血清维生素D浓度

体内维生素D水平随年龄增长而下降,其原因主要是暴露在阳光下的时间受限、皮肤产生维生素D的能力下降、人体吸收日常饮食中维生素D的能力下降所致。血清中25(OH)D是最常用的检测维生素D水平的指标。25(OH)D浓度过低(<30nmol/L)可增加血清中甲状旁腺激素(PTH)浓度,导致骨骼中钙的再吸收,从而增加骨质疏松发生的可能性。     

妊娠哺乳相关性骨质疏松症诊治

妊娠及哺乳期是非绝经期妇女体内激素变化最大的两个时期,不同程度地影响着骨代谢,若这两个阶段缺少钙剂及维生素D的合理补充,同时伴发其他骨质疏松的危险因素,就可能发生妊娠哺乳相关性骨质疏松症。妊娠哺乳相关性骨质疏松症临床罕见,目前无明确的诊断标准,诊断多是根据特殊的发病时期、腰背部疼痛及同时存在脆性骨折为标准。治疗包括停止哺乳、合理补充钙剂及维生素D、应用抗骨质疏松药物,以及椎体成形术等手段。本文就妊娠哺乳期钙的代谢特征及妊娠哺乳相关性骨质疏松症的诊断治疗进展进行综述。     

2型糖尿病患者血清25-羟维生素D与椎骨骨折的相关性

维生素D是骨代谢的一个重要调节因子。既往研究对于维生素D缺乏与骨质疏松性骨折的关系尚存在争议。部分前瞻性队列研究显示,老年人血清25-羟维生素D[25-（OH）D]的水平与骨质疏松性骨折相关,然而目前对于血清25-（OH）D的水平与糖尿病患者椎骨骨折的相关性尚不明确。     

健身操结合钙和骨化三醇对中老年女性髋部骨量的影响

除了与绝经相关的雌激素水平下降有关外,体内钙调节系统紊乱在加速骨量丢失、导致骨质疏松的发生中也起重要作用.骨化三醇是活性维生素D代谢物中最具活性的药物,对钙平衡的调节有着重要作用.     

维生素D新功效:防止骨质疏松

正一项最新研究表明联合补充维生素D及某些食物可以保护防止发生衰老相关骨质疏松。研究人员解释道,只有在同时补充维生素D的情况下,食用牛奶、酸奶和奶酪才与老年人更高的脊柱骨密度、更少的髋部骨质疏松有关。哈佛大学附属Hebrew Senior Life及马萨诸塞大学的研究人员说道,维生素D可以刺激钙吸收,帮助形成骨组织并防止骨质疏松。     

Relative value of plain vitamin D and of biologically active vitamin D in the prevention and treatment of osteoporosis

Vitamin D metabolism has an important role in the pathogenesis of osteoporosis. Vitamin D deficiency is very common in elderly people in central Europe. This leads to secondary hyperparathyroidism and to increased bone resorption, resulting in osteoporosis. Combined with the elevated risk of falling that results from vitamin D deficiency, this increases the frequency of bone fractures. Severe vitamin D deficiency also causes impaired bone mineralization (osteomalacia). Controlled intervention trials with native vitamin D (and calcium) yielded no consistent results in terms of the prevention of extravertebral fractures. It appears likely that treatment with plain vitamin D is effective only in populations with vitamin D deficiency. Treatment with active vitamin D (1-alpha-hydroxylated metabolites such as alfacalcidol) has to be considered a pharmacological intervention that exerts pleiotropic effects on the gut (calcium absorption), bone (stimulation of formation), muscle (decreasing of the risk of falling), and immune system. Target groups are patients with disturbed vitamin D metabolism (renal insufficiency, glucocorticoid therapy, inflammatory disease such as rheumatoid arthritis). Alfacalcidol can prevent glucocorticoid-induced bone loss (high-grade evidence). In comparative studies alfacalcidol was superior to plain vitamin D.     

Vitamin D deficiency and osteoporosis

Osteoporosis is a disease of disequilibrium between bone formation and bone loss, and vitamin D is one of the key hormones in the regulation of bone metabolism, the major role of which is to provide the proper micro‐environment for bone mineralization. Vitamin D deficiency which has been defined by most experts as circulating 25‐hydroxyvitamin D levels of less than 20 ng/mL (50 nmol/L) is widespread all over the world. As shown by the results of recent studies, vitamin D deficiency could increase the risk of low bone mineral density or osteoporosis, muscle disorders, falls, and as a matter of course, fractures due to both osteoporosis and falls. Long‐term supplementation of vitamin D and calcium are good prevention measures for osteoporosis, falls and fractures. At the same time, they are essential components of osteoporosis management. Many studies show that sufficient vitamin D intake could increase bone mass, and decrease the risk of falls and fractures.     

Newly discovered endocrine functions of the liver

The liver, the largest solid visceral organ of the body, has numerous endocrine functions, such as direct hormone and hepatokine production, hormone metabolism, synthesis of binding proteins, and processing and redistribution of metabolic fuels. In the last 10 years, many new endocrine functions of the liver have been discovered. Advances in the classical endocrine functions include delineation of mechanisms of liver production of endocrine hormones [including 25-hydroxyvitamin D, insulin-like growth factor 1 (IGF-1), and angiotensinogen], hepatic metabolism of hormones (including thyroid hormones, glucagon-like peptide-1, and steroid hormones), and actions of specific binding proteins to glucocorticoids, sex steroids, and thyroid hormones. These studies have furthered insight into cirrhosis-associated endocrinopathies, such as hypogonadism, osteoporosis, IGF-1 deficiency, vitamin D deficiency, alterations in glucose and lipid homeostasis, and controversially relative adrenal insufficiency. Several novel endocrine functions of the liver have also been unraveled, elucidating the liver’s key negative feedback regulatory role in the pancreatic α cell-liver axis, which regulates pancreatic α cell mass, glucagon secretion, and circulating amino acid levels. Betatrophin and other hepatokines, such as fetuin-A and fibroblast growth factor 21, have also been discovered to play important endocrine roles in modulating insulin sensitivity, lipid metabolism, and body weight. It is expected that more endocrine functions of the liver will be revealed in the near future.     

Vitamin D: More than just affecting calcium and bone

Vitamin D is a fat-soluble steroid that is essential for maintaining normal calcium metabolism. In vitamin D deficiency, calcium absorption is insufficient and cannot satisfy the body's needs. Consequently, parathyroid hormone production increases and calcium is mobilized from bones and reabsorbed in the kidneys to maintain normal serum calcium levels--a condition defined as secondary hyperparathyroidism. Most organs, including the gut, brain, heart, pancreas, skin, kidneys, and immune system have receptors for 1,25 (OH)vitamin D. Furthermore, all of these organs have the capacity to synthesize 1,25 (OH)vitamin D from vitamin D. Extensive research suggests that vitamin D deficiency is common and represents a global health problem. Clinical consequences related to low vitamin D levels include not only osteomalacia, osteoporosis, and rickets, but also neuro-muscular dysfunction and fractures. Falls related to neuromuscular dysfunction lead to 40% of all nursing home admissions and are the largest single cause of injury-related deaths in elderly people. About one-third of all persons 65 and older fall at least once a year, resulting in more than 1.5 million emergency room treatments and more than 300,000 hospitalizations. Falls cause more than 11,000 deaths per year, most of them in elderly patients (> or = 75 years) who suffer hip fractures. It is well established that vitamin D deficiency not only has serious consequences for bone health, but also for other organ systems. Previous studies have shown that vitamin D supplementation reduces the number of fractures and directly improves neuromuscular function, thus helping to prevent falls and subsequent fractures. In addition, vitamin D appears to have other important functions as a regulator of cell differentiation and cell growth.     

Osteoporosis in Thailand

Osteoporosis is a health problem which is becoming more prevalent in Thailand. A number of differences compared to Caucasian populations, however, exist which include the burden and the diagnosis of osteoporosis, genetics of osteoporosis, vitamin D status and calcium intake. Thai postmenopausal women suffer less hip fractures despite lower bone mineral density (BMD). Other environmental or genetic factor are likely to play modulatory role on the determination of osteoporotic fractures besides BMD. Distal renal tubular acidosis is prevalent in certain parts of Thailand. The disorder in which low BMD is a clinical feature needs to be excluded before the diagnosis of osteoporosis based on bone densitometry can be made. Genetic factors play important role in the determination of osteoporosis and osteoporotic fractures. The cohort of genes involved in osteoporosis and their impact are likely to be different among populations with different ethnic background. Besides genetic factors, environmental factors such as calcium intake and vitamin status are also crucial. Thailand is situated in a geographic area with abundant sunlight exposure and vitamin D deficiency is not commonly found in our elderly who are still active and ambulatory. Due to adequate vitamin D status, favorable vitamin D receptor genotype and less urinary calcium loss because of smaller body built, the optimal calcium in Thais may not be as high as that recommended in Caucasians.     

The optimum amount of vitamin D for osteoporosis: in case of activated vitamin D treatment

Since the resistance factors for the effect of vitamin D increases by aging, ingestion of various nutrition factors, such as calcium, and vitamin D is important for prevention and medical treatment of osteoporosis. 1 alpha 25-dihydroxyvitamin D(3) known as active form of vitamin D can stimulate calcium absorption from intestine and also it is used for the medical treatment of osteoporosis. The vitamin D action for the regulation of bone and mineral metabolism changes with the sufficiency states or the amounts of ingestion of vitamin D. Therefore, the action as a medicine is not simple. This article reviews the effect and its optimum ingestion amount of activated vitamin D in osteoporosis medical treatment.     

Bone and mineral metabolism in African Americans.

Important differences exist in the metabolism of bone and mineral and the vitamin D endocrine system between whites and African Americans and include rate o f skeletal remodeling, bone mass, and vitamin D metabolism. A higher bone mineral density (BMD) in African Americans is associated with a diminished incidence o f osteoporosis and fractures. Serum 17beta-estradiol and the rate of GH secretion are higher in black than in white men, but there is no racial difference in women in this regard. The mechanisms for reduced rate o f skeletal remodeling and for greater BMD in blacks are not known, but diminished rate of skeletal remodeling could be a contributing factor for greater bone mass. Reduction in serum 25-hydroxyvitamin D in blacks is attributed to increased skin pigment and to diminished dermal production of vitamin D(3) and consequent decreased hepatic synthesis o f the metabolite. There is no evidence that alteration of the vitamin D endocrine system contributes to or is responsible for racial differences in skeletal remodeling and bone mass. Black infants, however, are at risk for developing vitamin D-deficient rickets, particularly when breast-fed.     

Vitamin D levels and potential impact in systemic sclerosis

Vitamin D is essential not only for calcium and bone metabolism, but it also may exert other biological activities, including immunomodulation through the expression of vitamin D receptor in antigen-presenting cells and activated T cells. Evidence from animal models and human prospective studies of rheumatoid arthritis, multiple sclerosis, type I diabetes, and systemic lupus erythematosus, indeed suggested an important role for vitamin D as a modifiable environmental factor in autoimmune diseases. In systemic sclerosis (SSc), this role has not been completely dissected, although recent studies clearly evidenced a high prevalence of vitamin D deficiency. Moreover, some degree of association between vitamin D deficiency and disease activity or phenotype characteristics has also been observed. Vitamin D deficiency in SSc may be related to several factors: insufficient sun exposure due to disability and skin fibrosis, insufficient intake because of gut involvement and malabsorption. Although it is advisable to regularly check vitamin D status in these patients, there is no consensus about which vitamin D supplementation regimen might be sufficient to modulate immunological homeostasis, and possibly reduce disease activity or severity, thus further prospective studies are needed. Moreover, novel vitamin D analogues with more pronounced immune modulatory effect and lower activity on calcium metabolism are in the pipeline, and might represent a great innovative opportunity for the treatment of vitamin D deficiency in such autoimmune disorders.     

The Role of Vitamin D Deficiency in the Pathogenesis of Osteoporosis and in the Modulation of the Immune System in HIV-Infected Patients

Vitamin D deficiency is widespread among HIV-infected adults and children. Vitamin D deficiency may contribute to the risk of developing the long-term complications of HIV infection, such as osteoporosis. Vitamin D is also known to play an important role in the immune system and may affect HIV disease progression and/or CD4 cell counts. This article will review the current data on the role of vitamin D deficiency in the pathogenesis of osteoporosis and in the modulation of the immune system in HIV-infected patients.     

Advantages of active vitamin D metabolites in the treatment of osteoporosis as compared with calciferol

Vitamin D is one of the most important regulating agents in the development of bone mass. Therefore administration of calciferol along with calcium in patients with nutritional vitamin D deficiency leads to improvement of bone density. In patients with osteoporosis who do not respond to vitamin D, insensitivity of osseous tissue to the active metabolite of vitamin D--1,25(OH)2 D3--is involved or inadequate synthesis of active metabolites in the liver or kidneys. Administration of 1alpha-OH vitamin D3 and in particular 1,25(OH) 2D3 improves the general calcium balance in the organism and increases by direct osteoforming action the value of bone mass and improves its quality. Administration of active vitamin D metabolites is unequivocally better in treatment of involutional osteoporosis, either along with calcium or in combination with some antiresorption substance, in osteoporosis associated with chronic inflammatory diseases, after organ transplantation or glukcocorticoid treatment. Even patients with postmenopausal osteoporosis respond better to 1,25(OH)2D3.