Vitamin D endocrine physiology

A review of vitamin D deficiency and vitamin D receptor polymorphisms in endocrine-related disorders

The endocrine system is a complex network of glands that produce and release hormones that regulate various physiological processes. In the past few decades, the human skin has been identified as an important peripheral endocrine organ that is the main site for the synthesis of vitamin D through exposure to sunlight. Mutations in downstream vitamin D-related gene pathways are associated with disease development. The vitamin D receptor (VDR) gene, which regulates the pleiotropic effects of vitamin D, has been extensively studied in adult populations. Several studies have reported the prevalence of vitamin D deficiency in children and adolescents. With changes in socioeconomic status and lifestyle, vitamin D-deficient individuals are prone to developing the disease at a young age. However, geographical and racial differences affect the association between VDR gene polymorphisms and vitamin D endocrine disorders, explaining the nonconsensus effects of polymorphisms and their association with disease development across populations. In this review, we discuss the connection between the vitamin D endocrine system and polymorphisms in the gene encoding VDR in children and adolescents, focusing on its effects on growth, puberty, insulin resistance, and the immune system.

Gluten-free diet attenuates the impact of exogenous vitamin D on thyroid autoimmunity in young women with autoimmune thyroiditis: a pilot study

Although both exogenous vitamin D and a gluten-free diet were found to reduce thyroid antibody titers, no study investigated interactions between gluten intake and vitamin D status in patients with autoimmune thyroid disorders. The aim of the present study was to assess whether the gluten-free diet determines the effect of vitamin D treatment on thyroid autoimmunity and thyroid function in young women with autoimmune (Hashimoto's) thyroiditis. The study compared two groups of euthyroid premenopausal women with this disorder, matched for thyroid antibody titers: 31 women with non-celiac gluten sensitivity complying for at least 12 months with the gluten-free diet and 31 unaffected sisters of women with non-celiac gluten sensitivity remaining without any dietary intervention. Plasma titers of thyroid peroxidase and thyroglobulin antibodies, as well as plasma concentrations of thyrotropin, free thyroid hormones, prolactin, 25-hydroxyvitamin D and high-sensitive C-reactive protein were measured at entry and after a six-month follow-up. Moreover, at both time points, the structure parameters of thyroid homeostasis were assessed. Although exogenous vitamin D decreased titers of thyroid peroxidase and thyroglobulin antibodies and increased 25-hydroxyvitamin D levels in each treatment group, this effect was less pronounced in patients on the gluten-free diet than in patients not following any dietary recommendations. Only in the latter group of patients, vitamin D increased SPINA-GT. Treatment-induced changes in thyroid peroxidase and thyroglobulin antibodies correlated with the impact of treatment on 25-hydroxyvitamin D levels. The obtained results suggest that gluten-free diet may impair beneficial effects of exogenous vitamin D in individuals with Hashimoto's thyroiditis.

Dietary calcium intake is associated with serum high-sensitivity C-reactive protein level in the general Japanese population

The beneficial effects of dietary calcium intake on high-sensitivity C-reactive protein levels, a risk factor of cardiovascular disease, have not been fully elucidated. This study investigated the associations between dietary calcium intake and serum high-sensitivity C-reactive protein levels in the general Japanese population. We analyzed the data of 2,019 subjects (1,194 men and 825 women) aged 35 to 69 years in a cross-sectional study of the Japan Multi-Institutional Collaborative Cohort Study. Nutrients intake including calcium were estimated using a validated food-frequency questionnaire. Analysis using a general linear model revealed that dietary calcium intake was inversely associated with serum high-sensitivity C-reactive protein levels (p for trend <0.001) after adjustment for age, sex, research group, leisure-time physical activity, smoking habit, drinking habit, dietary intakes (energy, dietary fiber, saturated fatty acids and vitamin D) and menopausal status. The association was slightly attenuated after additional adjustment for body mass index; however, remained significant (p for trend = 0.008). There were no significant interactions between dietary calcium intakes and sex, body mass index, or vitamin D intake for high-sensitivity C-reactive protein levels. This study have demonstrated that dietary calcium intake was inversely associated with serum high-sensitivity C-reactive protein levels in the general population.

Low calcium diet increases 4T1 mammary tumor carcinoma cell burden and bone pathology in mice

Breast cancer metastasizes to bone in the majority of patients with advanced disease. We investigated the effects of inadequate dietary calcium (Ca) on bone turnover, tumor growth, and bone response to tumor in tibia inoculated with 4T1 mammary carcinoma cells. Nine-month-old female Balb/c mice were placed on an adequate Ca (5 g/kg diet, n = 30) or low Ca (80 mg/kg diet, n = 31) diet for 14 days, then injected intratibially with 1,000 4T1 cells (transfected with luciferase for bioluminescence imaging), and sacrificed at 5, 10, or 21 days post-inoculation (n = 7–10 mice/group). Control mice (n = 6/group) were injected with carrier and sacrificed at 10 days post-inoculation. Tibiae with muscle intact were excised and evaluated by microcomputed tomography and histology. In vivo bioluminescent imaging revealed that 4T1 cells metastasized to lung. Therefore, lungs were removed for quantification of tumor. Mice fed low Ca exhibited higher bone turnover and higher tibial lesion scores than mice fed adequate Ca. Lesion severity, manifested as cortical osteolysis and periosteal woven bone formation, and tumor cell infiltration to muscle, increased with time, irrespective of diet. However, for most skeletal endpoints the rates of increase were greater in mice consuming low Ca compared to mice consuming adequate Ca. Infiltration of tumor cells into adjacent muscle, but not metastasis to lung, was also greater in mice consuming low Ca diet. The findings suggest that high bone turnover due to Ca insufficiency results in greater local mammary tumor cell growth, cortical osteolysis, woven bone formation, and invasion to muscle in mice.

A rare case of a non-traumatic neck of femur fracture in a 17-year-old boy associated with vitamin D deficiency

Hip fractures in the young, healthy population are rare and often the result of high-energy trauma. A previously healthy 17-year-old patient presented to our institution with a 5-week history of left hip and knee pain in the absence of any trauma. Pelvic radiograph revealed a subacute left femoral neck fracture. He subsequently underwent surgical fixation and made an uneventful recovery. Further endocrine evaluation revealed isolated vitamin D deficiency to be the likely underlying cause for this fracture. Multiple previous opportunities were missed to identify the cause for this patient's symptoms. An intracapsular fracture in a young adult requires early recognition and prompt anatomical reduction. This case emphasises the need to maintain a high index of suspicion for atraumatic fractures in healthy adolescents with unexplained joint pain. Further endocrine and metabolic investigations are warranted, and isolated vitamin D deficiency must be considered as a potential causative factor.

Safety and Efficacy of High-dose Daily Vitamin D3 Supplementation in Children and Young Adults With Sickle Cell Disease

Suboptimal vitamin D (vit D) status (<32 ng/mL) is ubiquitous among African American children with type SS sickle cell disease (SCD-SS). The vit D supplemental dose to normalize vit D status is unknown. Five to 20-year-old African American children with (n=21) and without (n=23) SCD-SS were randomized to vit D3 supplementation (4000 or 7000 IU/d) and evaluated at 6 and 12 weeks for changes in vit D and SCD status. A dose was considered unsafe if serum calcium was elevated associated with elevated serum 25 hydroxyvitamin D (25(OH)D). At baseline 95% of subjects with SCD-SS and 87% of healthy controls had suboptimal vit D status (mean±SD, 19.2±7.2 and 22.3±9.3 ng/mL, respectively). After 12 weeks supplementation, both D3 doses were safe and well tolerated. Neither group achieved the a priori efficacy criterion of 25(OH)D≥32 ng/mL in >80% of subjects (45% in SCD-SS and 63% in controls). However, for both subjects with SCD-SS and healthy subjects by 12 weeks, deficient (<20 ng/mL) vit D status was eliminated only in those receiving 7000 IU/d. For subjects with SCD-SS, by 12 weeks there was a significant (all P<0.05) increase in fetal hemoglobin, decrease in high-sensitivity C-reactive protein, and reduction in the percentage of subjects with a high platelet count.

Safety and Efficacy of High-Dose Daily Vitamin D3 Supplementation in Children and Young Adults Infected With Human Immunodeficiency Virus

BACKGROUND

Suboptimal vitamin D (vitD) status is common in children and young adults infected with human immunodeficiency virus (HIV). The vitD supplemental dose needed to normalize vitD status in this population is unknown.

METHODS

In this double-blind trial, subjects infected with HIV ages 8.3 to 24.9 years were randomized to vitD3 supplementation of 4000 IU/day or 7000 IU/day and evaluated at 6 and 12 week for changes in vitD status and HIV indicators. A dose was considered unsafe if serum calcium was elevated (above age and sex-specific range) associated with elevated serum 25 hydroxyvitamin D (25(OH)D); >160 ng/mL).

RESULTS

At baseline, 95% of subjects (n = 44; 43% with perinatally acquired HIV, 57% with behaviorally acquired HIV) had a suboptimal serum 25(OH)D concentration of <32 ng/mL (mean ± standard deviation, 19.3 ± 7.4; range, 4.4-33.6 ng/mL). After 12 weeks (main outcome) of D3 supplementation, both D3 doses were safe and well tolerated, with no evidence of elevation of serum calcium concentrations or deterioration in HIV immunologic or virologic status. Sufficient vitD status, defined as serum 25(OH)D ≥32 ng/mL, was achieved in 81% of all subjects, and only the 7000 IU/day group (86%) achieved this a priori efficacy criterion in >80% of subjects. Change in serum 25(OH)D did not differ between HIV acquisition groups.

CONCLUSIONS

A 7000 IU/day D3 supplementation was safe and effective in children and young adults infected with HIV.

Vitamin D and bone disease

Vitamin D is important for normal development and maintenance of the skeleton. Hypovitaminosis D adversely affects calcium metabolism, osteoblastic activity, matrix ossification, bone remodeling and bone density. It is well known that Vit. D deficiency in the developing skeleton is related to rickets, while in adults is related to osteomalacia. The causes of rickets include conditions that lead to hypocalcemia and/or hypophosphatemia, either isolated or secondary to vitamin D deficiency. In osteomalacia, Vit. D deficiency leads to impairment of the mineralisation phase of bone remodeling and thus an increasing amount of the skeleton being replaced by unmineralized osteoid. The relationship between Vit. D and bone mineral density and osteoporosis are still controversial while new evidence suggests that Vit. D may play a role in other bone conditions such as osteoarthritis and stress fractures. In order to maintain a “good bone health” guidelines concerning the recommended dietary intakes should be followed and screening for Vit. D deficiency in individuals at risk for deficiency is required, followed by the appropriate action.

[Hungarian consensus regarding the role of vitamin D in the prevention and treatment of diseases]

The metabolism of vitamin D is unique in the human body and its diverse effects are present in almost every organ. Vitamin D deficiency is one of the most prominent health issues in the civilized world. For the solution of this concern an extensive collaboration is imperative. Recognizing this necessity the most prominent Hungarian medical associations fighting with the effects of vitamin D deficiency worked out a collective consensus on the importance, diagnosis, prevention and suggested therapy of vitamin D deficiency. Along with the clinical guidelines of the different associations, the result of this consensus could serve as guidance for the practicing doctors in the prevention and therapy of vitamin D deficiency. In addition the consensus aims to direct the attention of decision-makers and the general public on the significance of this issue.

Evidence in favor of a severely impaired net intestinal calcium absorption in patients with (early-stage) chronic kidney disease

INTRODUCTION

Calcium and phosphorus are essential to many vital physiological processes. Little is known about the net and fractional intestinal absorption of calcium and phosphorus in patients with chronic kidney disease (CKD) and their clinical and hormonal determinants.

METHODS

Blood and 24-hour urine samples were collected in 20 healthy volunteers (HV) and 72 stable CKD stage 1-4 patients and analyzed for parameters of mineral metabolism including calcidiol, calcitriol, and parathyroid hormone (PTH). Dietary intake was assessed by dietary history.

RESULTS

The 24-hour urinary calcium excretion, as opposed to the phosphorus excretion, showed a stepwise decrease across CKD stages (median of 219, 84, 40, and 22 mg/day in HV and patients with CKD stages 1-2, 3 and 4, respectively). Younger age, high serum calcitriol, and high estimated GFR were associated with a high 24-hour urinary calcium excretion. High serum calcitriol levels and dietary phosphorus intake were associated with a high 24-hour urinary phosphorus excretion. The fractional intestinal calcium absorption, as estimated by the urinary-to-ingested calcium ratio, decreased across CKD stages.

CONCLUSIONS

The 24-hour urinary excretion of calcium, as opposed to phosphorus, is markedly decreased in CKD, even in early-stage disease. This is partly explained by low calcitriol levels and older age. Assuming a neutral calcium balance at the time of urine collection, we infer that net intestinal calcium absorption may be severely impaired in CKD.

Vitamin D and respiratory infection in adults

Vitamin D insufficiency is a global issue that has significant implications for health. The classical role of vitamin D in bone mineralisation is well known; vitamin D deficiency leads to rickets, osteomalacia or osteoporosis. The role of vitamin D in an immune system is less known. Vitamin D is not an actual vitamin but a secosteroid hormone produced in the skin from 7-dehydrocholesterol after exposure to sunlight UVB radiation. Nutrition and supplements are main sources of vitamin D in wintertime in northern countries as sunlight exposure is inadequate for the production. For activation vitamin D needs to be hydroxylated in liver to form 25-hydroxyvitamin D and in kidney to 1,25-dihydroxyvitamin D, the most active hormone in Ca absorption in the gut. For determination of vitamin D status serum 25-hydroxyvitamin D level, the major circulating form of the hormone is to be measured. Vitamin D regulates gene expression through binding with vitamin D receptors, which dimerises with retinoid X receptor. This complex binds to vitamin D-responsive elements inside the promoter regions of vitamin D-responsive genes. Vitamin D has a key role in innate immunity activation; the production of antimicrobial peptides (cathelicidin and defensins) following Toll-like receptor stimulation by pathogen lipopeptides is dependent on sufficient level of 25-hydroxyvitamin D. Clinically, there is evidence of the association of vitamin D insufficiency and respiratory tract infections. There is also some evidence of the prevention of infections by vitamin D supplementation. Randomised controlled trials are warranted to explore this preventive effect.

Vitamin D supplementation in the pediatric rheumatology clinic

Vitamin D is capturing the attention of healthy and chronically ill populations for its potential skeletal and nonskeletal benefits. New information suggesting a role in immune modulation has led to a surge of interest among rheumatologists. Although the epidemiologic data are limited, it appears that many children with rheumatic conditions are at risk of vitamin D deficiency. However, understanding this phenomenon requires an appreciation for how vitamin D status is assessed, and options for supplementation. Although a “more-is-better” attitude is tempting when considering the medicinal effects of a nutritional supplement, we suggest a cautious approach and suggest that further studies are needed to clarify the potential benefits and risks among children with rheumatic conditions.

Serum vitamin D metabolites and intestinal calcium absorption efficiency in women

BACKGROUND

Vitamin D sufficiency may be determined by the serum concentration of 25-hydroxyvitamin D [25(OH)D] that results in maximal intestinal calcium absorption efficiency. However, some investigators questioned whether 25(OH)D concentrations above the concentrations associated with rickets or osteomalacia influence calcium absorption.

OBJECTIVE

We determined whether calcium absorption efficiency is related to serum 25(OH)D or serum 1,25-dihydroxyvitamin D [1,25(OH)(2)D] concentrations.

DESIGN

We measured calcium absorption efficiency in 492 black and white healthy women (age range: 20-80 y) by the single-isotope method with (45)Ca. Serum 25(OH)D concentrations were measured by a radioreceptor assay. Other relevant measurements included concentrations of serum 1,25(OH)(2)D, serum parathyroid hormone, serum creatinine, and serum estradiol, calcium intake, and bone mineral density.

RESULTS

There was no relation between serum 25(OH)D concentrations and calcium absorption efficiency. In development of a multivariate model, the 4 major determinants of calcium absorption efficiency were menopausal status, calcium intake, and serum estradiol and serum 1,25(OH)(2)D concentrations. There was an interaction between serum 25(OH)D and 1,25(OH)(2)D concentrations on calcium absorption efficiency. The relation between calcium absorption and 1,25(OH)(2)D was positive, and this relation was stronger for lower concentrations of 25(OH)D than for higher concentrations of 25(OH)D.

CONCLUSION

The relation of serum 25(OH)D to calcium absorption is not useful as an indicator of vitamin D sufficiency.

Extraskeletal effects of vitamin D in older adults: cardiovascular disease, mortality, mood, and cognition

BACKGROUND

Vitamin D insufficiency is prevalent among older adults and may be associated with higher risk for cardiovascular (CV) disease, mortality, depression, and cognitive deficits.

OBJECTIVE

The aim of this article was to review published observational and experimental studies that explored the association between vitamin D insufficiency and CV disease, mortality, mood, and cognition with an emphasis on older adults.

METHODS

PubMed and Web of Science databases were searched for English-language articles from January 1966 through June 2009 relating to vitamin D, using the following MeSH terms: aged, vitamin D deficiency, physiopathology, drug therapy, cardiovascular diseases, blood pressure, mortality, delirium, dementia, cognitive disorders, depression, depressive disorder, seasonal affective disorder, mental disorders, and vitamin D/therapeutic use. Publications had to include patients > or =65 years of age who had > or =1 recorded measurement of 25-hydroxyvitamin D (25[OH]D) or were receiving vitamin D supplementation. All case-control, cohort, and randomized studies were reviewed.

RESULTS

Forty-two case-control, cohort, and randomized trials were identified and included in the review. Based on these publications, the prevalence of vitamin D insufficiency (25[OH]D concentration <30 ng/mL) in communitydwelling older adults (> or =65 years of age) ranged from 40% to 100%. Epidemiologic data and several small randomized trials found a potential association between vitamin D deficiency (25[OH]D concentration <10 ng/mL) and CV disease, including hypertension and ischemic heart disease. Although subgroup analyses of data from the Women's Health Initiative Randomized Trial (the largest randomized, placebo-controlled trial of vitamin D plus calcium therapy) did not find reductions in blood pressure, myocardial infarction, or CV disease-related deaths, intervention contamination limited the findings. Observational studies and a meta-analysis of randomized controlled trials found a mortality benefit associated with higher serum 25(OH)D concentrations or vitamin D(2) or D(3) supplementation (mean dose, 528 IU/d). Observational and small randomized trials found a potential benefit of sunlight or vitamin D on symptoms of depression and cognition, but the findings were limited by methodologic problems.

CONCLUSIONS

Vitamin D insufficiency appears to be highly prevalent among older adults. Evidence from epidemiologic studies and small clinical trials suggests an association between 25(OH)D concentrations and systolic blood pressure, risk for CV disease-related deaths, symptoms of depression, cognitive deficits, and mortality. The Women's Health Initiative Randomized Trial did not find a benefit of vitamin D supplementation on blood pressure, myocardial infarction, or mortality in postmenopausal women.

Determinants of 25-hydroxyvitamin D levels in African-American and Caucasian male veterans

SUMMARY

Among 307 males seen in VA Medical Center, independent determinants (p < 0.01 for all) of serum 25-hydroxyvitamin D [25(OH)D] levels included race, vitamin D supplements, BMI, dietary calcium intake and smoking, but not age. Negative association between 25(OH)D and parathyroid hormone (PTH) was similar for Caucasian and African-American men.

INTRODUCTION

In this prospective cohort study, we examined determinants of serum 25-hydroxyvitamin D [25(OH)D] levels and the relationship between 25(OH)D and PTH levels and body mass index (BMI).

METHODS

Male veterans (n = 307) were recruited at a VA Medical Center. Serum levels of PTH and 25(OH)D were obtained. Surveys and chart reviews were completed. Vitamin D insufficiency was defined as 25(OH)D <30 ng/ml. Univariate and multivariate regression analyses were performed.

RESULTS

Among 232 African-American (AA) men (mean +/- SD), 25(OH)D level (21.4 +/- 10.4 ng/ml) was lower and prevalence of insufficiency (80%) was higher than among 75 Caucasians (C; 28.5 +/- 11.1 ng/ml and 53%, respectively, p < 0.01 for both). In multivariate regression analysis, independent determinants (p < 0.01 for all) of 25(OH)D levels included AA race, vitamin D supplements, BMI, dietary calcium intake, and smoking. Despite lower 25(OH)D levels in African-Americans, PTH levels were similar to those seen in Caucasians. There was a significant (p < 0.02) negative linear association between 25(OH)D and PTH in African-American (r(2) = 0.05) and Caucasian (r(2) = 0.08) men, and there was no difference between the slopes of the relationship.

CONCLUSIONS

25(OH)D levels are determined by modifiable risk factors such as vitamin D supplementation in both AA and C males. The negative association between 25(OH)D and PTH is similar between the two races.

Comparison of daily, weekly, and monthly vitamin D3 in ethanol dosing protocols for two months in elderly hip fracture patients

BACKGROUND

Different dosing protocols have been used for vitamin D supplementation, but there has been a lack of comparative data among them.

OBJECTIVE

Our objective was to determine whether the same cumulative dose of vitamin D3 produces different effects if it is given daily, weekly, or monthly.

DESIGN

Women, age 81 +/- 8 yr (+/- sd, n = 48), who had undergone surgery to repair hip fracture were randomized to vitamin D3-supplementation protocols at 1,500 IU daily, or 10,500 IU once weekly, or 45,000 IU once every 28 d. The primary outcome measure was the serum 25-hydroxyvitamin D [25(OH)D] concentration attained.

RESULTS

Initially, serum 25(OH)D concentrations for daily, weekly, and monthly groups were, respectively, 15.13 +/- 6.9, 15.7 +/- 10.1, and 16.2 +/- 10.1 ng/ml. By d 7, these had increased significantly in all the groups (P < 0.001). On the first day after the monthly dose, both serum 25(OH)D and serum 1,25-dihydroxyvitamin D had increased significantly (P < 0.012 each), whereas these did not change significantly on the day after daily or weekly doses. After 2 months, serum 25(OH)D with daily, weekly, and monthly dosing were, respectively, 33.2 +/- 8.5, 29.2 +/- 8.9, and 37.1 +/- 10.3 ng/ml; there were no significant differences among these values.

CONCLUSIONS

Supplementation with vitamin D can be achieved equally well with daily, weekly, or monthly dosing frequencies. Therefore, the choice of dose frequency can be based on whichever approach will optimize an individual's adherence with long-term vitamin D supplementation.