What is the optimal vitamin D status for health?

The most objectively substantiated health-related reason for tanning is that it improves vitamin D status. The serum 25-hydroxyvitamin D concentration (25(OH)D) is the measure of vitamin D nutrition status. Human biology was probably optimized through natural selection for a sun-rich environment that maintained serum 25(OH)D higher than 100 nmol/L. These levels are now only prevalent in people who spend an above-average amount of time outdoors, with the sun high in the sky. The best-characterized criteria for vitamin D adequacy are based on randomized clinical trials that show fracture prevention and preservation of bone mineral density. Based upon these studies, 25(OH)D concentrations should exceed 75 nmol/L. This concentration is near the upper end of the 25(OH)D reference ("normal") range for populations living in temperate climates, or for people who practice sun-avoidance, or who wear head coverings. Officially mandated nutrition guidelines restrict vitamin D intake from fortified food and supplements to less than 25 mcg/day, a dose objectively shown to raise serum 25(OH)D in adults by about 25 nmol/L. The combined effect of current nutrition guidelines and current sun-avoidance advice is to ensure that adults who follow these recommendations will have 25(OH)D concentrations lower than 75 nmol/L. Therefore, advice to avoid UVB light should be accompanied by encouragement to supplement with vitamin D in an amount that will correct for the nutrient deficit that sun-avoidance will cause.     

Evaluation of serum parameters relevant to vitamin D status in tamarins

Serum levels of 25(OH)D, alkaline phosphatase (AP), and parathormone (PTH) were evaluated to investigate the vitamin D requirement of Saguinus fuscicollis. Diets with various vitamin D content were fed 4 weeks and longer. The values of 25(OH)D (30-300 nmol/l), AP (less than 300 U/l), and PTH (less than or equal to 1,000 equl/l) considered as normal were obtained with 2,000 IU D3/kg diet, or 33 IU/animal/day, which we regard as the level required. Animals depleted of vitamin D for 215 days developed a secondary hyperparathyroidism.     

Determinants of Vitamin D Status in Fair-Skinned Women of Childbearing Age at Northern Latitudes

Background and Objective

Poor vitamin D status during pregnancy has been associated with unfavorable outcomes for mother and child. Thus, adequate vitamin D status in women of childbearing age may be important. The aim of this study is to investigate the determinants of 25-hydroxyvitamin D (25(OH)D) serum concentrations in women of childbearing age living in Sweden, at latitude 57–58° north.

Method

Eighty four non-pregnant, non-lactating, healthy, fair-skinned women aged between 25–40 years were included. All subjects provided blood samples, four day food records and answered questionnaires about sun exposure and lifestyle. Total serum 25(OH)D was analyzed using Roche Cobas® electrochemoluminiescent immunoassay.

Results

Mean 25(OH)D was 65.8±19.9 nmol/l and 23% of the subjects had concentrations <50 nmol/l. Only 1% had concentrations <25 nmol/l. Determinants of 25(OH)D concentrations were recent sunbed use, recent travel to southern latitude, season, estrogen contraceptive use and use of supplementary vitamin D (R² = 0.27).

Conclusion

Every fifth woman had 25(OH)D concentrations <50 nmol/l. About 30% of the variation in vitamin D status was explained by sun exposure, use of vitamin D supplements and use of estrogen contraceptives. Cutaneous vitamin D synthesis seems to be a major contributor to vitamin D status, even at northern latitudes. Thus, recommendations on safe UV-B exposure could be beneficial for vitamin D status.     

Lipid status association with 25-hydroxy vitamin D: Cross sectional study of end stage renal disease patients

BackgroundSome observational studies indicate an association of 25-hydroxy vitamin D (25(OH)D) insufficiency and atherogenic cholesterol concentrations. The aim of this study was to investigate relationship between 25(OH)D concentrations and lipid parameters in end stage renal disease (ESRD) patients, separately for predialysis, hemodialysis and peritoneal dialysis patients.MethodsWe have adjusted 25(OH)D concentrations for seasonal variability with cosinor analysis, and performed all further analysis using these corrected 25(OH)D concentrations. Concentrations of 25(OH)D and the lipid parameters were determined in 214 ESRD patients and 50 control group participants. The analysis included the measurement of 25(OH)D by HPLC, apolipoprotein (Apo) AI, ApoB and Lp(a) by nephelometry, total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) and triglyceride (TG) by spectrophotometry and manually calculated ApoB/ApoAI and LDL-C/HDL-C ratio.ResultsESRD patients with adjusted 25(OH)D concentrations of 50 nmol/L had significantly higher TC (P = 0.005) and ApoAI (P = 0.049). Significantly higher HDLC (P = 0.011) and ApoAI (P = 0.020) were found in hemodialysis patients with the 25(OH)D concentrations of 50 nmol/L. The other analyzed lipid parameters differed significantly between predialysis, hemodialysis and peritoneal dialysis patients with 25(OH)D concentrations of < 50 nmol/L.ConclusionsOur study indicate the significant relationship between 25(OH)D repletion and optimal concentrations of lipid parameters in ESRD patients. Further research is necessary to explain whether joint evaluation of vitamin D status and lipid abnormalities could improve cardiovascular outcome in ESRD patients.     

1,25-Dihydroxyvitamin D and the Vitamin D Receptor Gene Polymorphism Apa1 Influence Bone Mineral Density in Primary Hyperparathyroidism

Objective

Parathyroid hormone (PTH) and vitamin D are the most important hormones regulating calcium metabolism. In primary hyperparathyroidism (PHPT) excessive amounts of PTH are produced. Bone turnover is enhanced, leading to reduced bone mineral density and elevated levels of serum calcium. The aim of this study was to investigate relations between serum levels of 25-hydroxyvitamin D (25(OH)D), 1,25-dihydroxyvitamin D (1,25(OH)₂D) and bone mineral density, as well as known genetic polymorphisms in the vitamin D receptor and enzymes metabolising vitamin D in patients with PHPT.

Design/Subjects

We conducted a cross-sectional study of 52 patients with PHPT.

Results

Mean level of 25(OH)D was 58.2 nmol/L and median 1,25(OH)₂D level was 157 pmol/L. Among our patients with PHPT 36.5% had 25(OH)D levels below 50 nmol/L. Serum 1,25(OH)₂D was inversely correlated to bone mineral density in distal radius (p = 0.002), but not to bone mineral density at lumbar spine or femoral neck. The vitamin D receptor polymorphism Apa1 (rs7975232) was associated with bone mineral density in the lumbar spine.

Conclusions

The results suggest that PHPT patients with high blood concentrations of 1,25(OH)₂D may have the most deleterious skeletal effects. Randomized, prospective studies are necessary to elucidate whether vitamin D supplementation additionally increases serum 1,25(OH)₂D and possibly enhances the adverse effects on the skeleton in patients with PHPT.     

Vitamin D and the Risk of Atrial Fibrillation - The Rotterdam Study

Atrial fibrillation (AF) is the most common chronic arrhythmia and it increases the risk of cardiovascular morbidity and mortality. Still there is not a complete understanding of its etiology and underlying pathways. Vitamin D might regulate renin-angiotensin-aldosterone system and might be involved in inflammation, both implicated in the pathophysiology of AF. The objective of this work was to investigate the association between vitamin D status with the risk of AF in the elderly. This study was conducted within the Rotterdam Study, a community-based cohort of middle-aged and elderly participants in Rotterdam, The Netherlands. We had 3,395 participants who were free of AF diagnosis at the start of our study and who had vitamin D data available. We analyzed the association between serum 25-hydroxivitamin D (25(OH)D) and incidence of AF using Cox regression models. Vitamin D deficiency was defined as serum 25(OH)D concentrations <50nmol/l, insufficiency between 50nmol/l and 75nmol/l, while serum 25(OH)D concentrations equal to and above 75nmol/l were considered as adequate. After mean follow-up of 12.0 years 263 (7.7%) participants were diagnosed with incident AF. Vitamin D status was not associated with AF in any of the 3 multivariate models tested (model adjusted for socio-demographic factors and life-style factors: HR per 10 unit increment in serum 25(OH)D 0.96, 95% CI: 0.91-1.02; HR for insufficiency: 0.82, 95%CI: 0.60-1.11,and HR for adequate status: 0.76, 95%CI: 0.52-1.12 compared to deficiency). This prospective cohort study does not support the hypothesis that vitamin D status is associated with AF.     

Vitamin D Deficiency in Unselected Patients from Swiss Primary Care: A Cross-Sectional Study in Two Seasons

Background

As published data on 25-hydroxy-cholecalciferol (25(OH)D) deficiency in primary care settings is scarce, we assessed the prevalence of hypovitaminosis D, potential associations with clinical symptoms, body mass index, age, Vitamin D intake, and skin type in unselected patients from primary care, and the extent of seasonal variations of serum 25(OH)D concentrations.

Methodology/Principal Findings

25(OH)D was measured at the end of summer and/or winter in 1682 consecutive patients from primary care using an enzyme-linked immunosorbant assay. Clinical symptoms were assessed by self-report (visual analogue scale 0 to 10), and vitamin D deficiency was defined as 25(OH)D concentrations < 50 nmol/l. 25(OH)D deficiency was present in 995 (59.2%) patients. 25(OH)D deficient patients reported more intense muscle weakness (visual analogue scale 2.7, 95% confidence interval 2.5 to 2.9) and had a higher body mass index (25.9kg/m², 25.5 to 26.2) than non-deficient patients (2.5, 2.3 to 2.7; and 24.2, 23.9 to 24.5, respectively). 25(OH)D concentrations also weakly correlated with muscle weakness (Spearman’s rho -0.059, 95% confidence interval -0.107 to -0.011) and body mass index (-0.156, -0.202 to -0.108). Self-reported musculoskeletal pain, fatigue, and age were not associated with deficiency, nor with concentrations. Mean 25(OH)D concentrations in patients with vitamin D containing medication were higher (60.6 ± 22.2 nmol/l) than in patients without medication (44.8 ± 19.2 nmol/l, p < 0.0001) but still below the targeted level of 75 nmol/l. Summer and winter 25(OH)D concentrations differed (53.4 ± 19.9 vs. 41.6 ± 19.3nmol/l, p < 0.0001), which was confirmed in a subgroup of 93 patients who were tested in both seasons (p = 0.01).

Conclusion/Significance

Nearly 60% of unselected patients from primary care met the criteria for 25(OH)D deficiency. Self-reported muscle weakness and high body mass index were associated with lower 25(OH)D levels. As expected 25(OH)D concentrations were lower in winter compared to summer.     

Vitamin D deficiency in adult British Hindu Asians: a family disorder.

The vitamin D state of 60 apparently healthy adult Hindu Asian couples living in Britain was studied on a community basis. Twenty six (22%) of the Asian subjects had pronounced vitamin D deficiency, defined as 25-hydroxycholecalciferol concentrations below 10 nmol/l (4 ng/ml), while none of the white controls had such low concentrations. Asian men and women were equally affected, and plasma concentrations were similar in husbands and wives. Vitamin supplements were being taken by only 31 (26%) subjects, most of whom were women. It is suggested that the spouses of patients with osteomalacia should be screened for vitamin D deficiency.     

The High Prevalence of Vitamin D Deficiency and Its Related Maternal Factors in Pregnant Women in Beijing

Maternal vitamin D deficiency has been suggested to influence fetal and neonatal health. Little is known about vitamin D status in Chinese pregnant women. The purpose of this study was to assess the vitamin D status of pregnant women residing in Beijing in winter and evaluate the impact of maternal factors on serum 25-hydroxyvitamin D [25(OH)D] levels. The study was conducted on 125 healthy pregnant women. For each individual, data concerning pre-pregnancy weight, educational status, use of multivitamins and behavioral factors such as daily duration of computer use, walking and sun exposure were obtained. Serum concentrations of 25(OH)D were measured by enzyme-linked immunosorbent assay. The prevalence of vitamin D deficiency (25(OH)D < 50 nmol/L) was 96.8% and almost half (44.8%) of women were severely vitamin D deficiency (25(OH)D < 25 nmol/L). The concentration of 25(OH)D was lower in women with shorter duration of sun exposure (≤ 0.5 h/day, 25.3 ± 8.9 nmol/L) than that in women with longer duration of sun exposure (> 0.5 h/day; 30.3± 9.5 nmol/L; P = 0.003). Thirty six women (28.8%) had sun exposure duration ≥ 1.5h/day. The 25(OH)D concentration in these women was 31.5 ± 9.4 nmol/L which was also much lower than the normal level. Women who reported taking a multivitamin supplement had significantly higher 25(OH)D concentrations (32.3 ± 9.5 nmol/L) when compared with non-users (24.9 ± 8.2 nmol/L; P < 0.001). Pregnant women in Beijing are at very high risk of vitamin D deficiency in winter. Duration of Sun exposure and the use of multivitamin were the most important determinants for vitamin D status. However, neither prolonging the time of sunlight exposure nor multivitamin supplements can effectively prevent pregnant women from vitamin D deficiency. Other measures might have to be taken for pregnant women to improve their vitamin D status in winter.     

Vitamin D Status among Thai School Children and the Association with 1,25-Dihydroxyvitamin D and Parathyroid Hormone Levels

In several low latitude countries, vitamin D deficiency is emerging as a public health issue. Adequate vitamin D is essential for bone health in rapidly growing children. In the Thai population, little is known about serum 25-hydroxyvitamin D [25(OH)D] status of infants and children. Moreover, the association between 25(OH)D and the biological active form of 1,25-dihydroxyvitamin D [1,25(OH)]₂D is not clear. The specific aims of this study were to characterize circulating serum 25(OH)D, 1,25(OH)₂D and their determinants including parathyroid hormone (PTH), age, sex, height and body mass index (BMI) in 529 school-aged Thai children aged 6–14 y. Adjusted linear regression analysis was performed to examine the impact of age and BMI, and its interaction with sex, on serum 25(OH)D concentrations and 1,25(OH)₂D concentrations. Serum 25(OH)D, 1,25(OH)₂D and PTH concentrations (geometric mean ± geometric SD) were 72.7±1.2 nmol/L, 199.1±1.3 pmol/L and 35.0±1.5 ng/L, respectively. Only 4% (21 of 529) participants had a serum 25(OH)D level below 50 nmol/L. There was statistically significant evidence for an interaction between sex and age with regard to 25(OH)D concentrations. Specifically, 25(OH)D concentrations were 19% higher in males. Moreover, females experienced a statistically significant 4% decline in serum 25(OH)D levels for each increasing year of age (P = 0.001); no decline was seen in male participants with increasing age (P = 0.93). When BMI, age, sex, height and serum 25(OH)D were individually regressed on 1,25(OH)₂D, height and sex were associated with 1,25(OH)₂D with females exhibiting statistically significantly higher serum 1,25(OH)₂D levels compared with males (P<0.001). Serum 1,25(OH)₂D among our sample of children exhibiting fairly sufficient vitamin D status were higher than previous reports suggesting an adaptive mechanism to maximize calcium absorption.     

Circulating vitamin D3 and 25-hydroxyvitamin D in humans: An important tool to define adequate nutritional vitamin D status

Circulating 25-hydroxyvitamin D [25(OH)D] is generally considered the means by which we define nutritional vitamin D status. There is much debate, however, with respect to what a healthy minimum level of circulation 25(OH)D should be. Recent data using various biomarkers such as intact parathyroid hormone (PTH), intestinal calcium absorption, and skeletal density measurements suggest this minimum level to be 80 nmol (32 ng/mL). Surprisingly, the relationship between circulating vitamin D₃ and its metabolic product—25(OH)D₃ has not been studied. We investigated this relationship in two separate populations: the first, individuals from Hawaii who received significant sun exposure; the second, subjects from a lactation study who received up to 6400 IU vitamin D₃/day for 6 months.

Results (1) the relationship between circulating vitamin D₃ and 25(OH)D in both groups was not linear, but appeared saturable and controlled; (2) optimal nutritional vitamin D status appeared to occur when molar ratios of circulating vitamin D₃ and 25(OH)D exceeded 0.3; at this point, the V_max of the 25-hydroxylase appeared to be achieved. This was achieved when circulating 25(OH)D exceeded 100 nmol.

We hypothesize that as humans live today, the 25-hydroxylase operates well below its V_max because of chronic substrate deficiency, namely vitamin D₃. When humans are sun (or dietary) replete, the vitamin D endocrine system will function in a fashion as do these other steroid synthetic pathways, not limited by substrate. Thus, the relationship between circulating vitamin D and 25(OH)D may represent what “normal” vitamin D status should be.     

Make Vitamin D While the Sun Shines,Take Supplements When It Doesn′t: A Longitudinal,Observational Study of Older Adults in Tasmania,Australia

Low vitamin D status has been associated with a number of chronic conditions, particularly in older adults. The aim of this study was to identify how best to maintain optimum vitamin D status throughout the year in this high-risk population. The main objectives of the study were to assess seasonal vitamin D status; identify the main determinants of vitamin D status; determine if taking part in the study led to alterations in participant behaviour and vitamin D status. A longitudinal design across four consecutive seasons observed ninety-one 60–85 year old community-dwelling adults in Tasmania (41π S) over 13 consecutive months, with a follow-up assessment at next winter''s end. Associations between solar UVB exposure, sun protection behaviours, dietary and supplemental vitamin D with serum 25(OH)D concentrations were assessed. Variation in serum 25(OH)D demonstrated an identical pattern to solar UVB, lagging 8–10 weeks. Serum 25(OH)D was positively associated with summer UVB (mean 15.9 nmol/L; 95%CI 11.8–19.9 nmol/L, p<0.001) and vitamin D supplementation (100–600 IU/day: 95%CI 10.2 nmol/L; 0.8–19.6 nmol/L; p = 0.03; 800 IU/day: 21.0 nmol/L; 95%CI 8.1–34.0 nmol/L; p = 0.001). Seasonal variation in serum 25(OH)D was greatly diminished in supplement users. The most common alteration in participant behaviour after the study was ingesting vitamin D supplements. Post-study vitamin D supplementation ℘800 IU/day was seven times more likely than during the study resulting in mean difference in serum 25(OH)D between supplement and non-supplement users of 30.1 nmol/L (95%CI 19.4–40.8 nmol/L; p<0.001). The main limitation was homogeneity of participant ethnicity. Solar exposure in summer and ingestion of vitamin D supplements in other seasons are the most effective ways of achieving and maintaining year-round vitamin D sufficiency in older adults in the Southern hemisphere. Vitamin D supplementation has greatest effect on vitamin D status if ingested during and after winter, i.e. between the autumn and spring equinoxes.     

Which circulating level of 25-hydroxyvitamin D is appropriate?

Moderate Vitamin D deficiency causes secondary hyperparathyroidism and bone loss, leading to osteoporosis and fractures. Controversy exists which circulating level of 25-hydroxyvitamin D (25OH)D is appropriate. The high incidence of hip fractures at northern latitudes suggest a relationship with Vitamin D deficiency. However, international studies show lower serum 25(OH)D levels in southern than in northern Europe. Serum 25(OH)D was not a risk factor for hip fractures in several epidemiological studies. The required serum 25(OH)D is usually established by assessing the point where serum parathyroid hormone (PTH) starts to rise. This point varied in several studies between 30 and 78 nmol/l. However, interlaboratory variation may also influence the apparent required serum 25(OH)D level. Dietary calcium intake influences serum PTH and serum PTH may influence the turnover of Vitamin D metabolites. A low calcium intake causes an increase of serum PTH and serum 1,25(OH)2D thereby decreasing the half life of serum 25(OH)D. While a low calcium intake may aggravate Vitamin D deficiency, a high calcium intake may have a Vitamin D sparing effect. With current knowledge, a global estimate for the appropriate serum 25(OH)D is 50 nmol/l.     

Vitamin D in Overweight/Obese Women and Its Relationship With Dietetic and Anthropometric Variables

Overweight/obese persons usually have an inadequate vitamin D status, a situation commonly made worse by an inadequate intake of this vitamin. For this reason, the aim of this study was to analyze dietetic and anthropometric differences in a group of young, overweight/obese Spanish women with respect to their vitamin D status. The study subjects were 66 white Spanish women (aged 20–35 years) with a BMI of 24–35 kg/m². Dietetic, anthropometric, and biochemical data were collected. Women were divided into two groups depending on their serum vitamin D concentrations: LD (women with <90 nmol/l 25(OH)D) and HD (women with ≥90 nmol/l 25(OH)D). The intakes of vitamin D, calcium, and supplements were similar in both groups. The body weight, BMI, and waist circumference of the HD subjects were smaller than those recorded for the LD subjects (68.6 ± 4.2 kg, 26.0 ± 1.3 kg/m², and 79.4 ± 3.4 cm compared to 76.2 ± 9.8, 28.6 ± 3.2 kg/m², and 86.2 ± 9.3 cm, respectively; P < 0.05). The hip circumference and the waist/hip ratio were similar in both groups. A BMI of <27.7 kg/m² (P50) was associated with serum vitamin D concentrations of ≥90 nmol/l (odds ratio = 0.1313; confidence interval: 0.0149–1.1599; P < 0.05). Overweight/obese women are at higher risk of vitamin D deficiency, largely due to excess adiposity rather than inadequate intake.     

Severe Vitamin D Deficiency in Arab-American Women Living in Dearborn,Michigan

ObjectiveTo determine the prevalence and degree of 25-hydroxyvitamin D deficiency in a group of Arab- American women in the largest, most-concentrated Arab- American settlement in the United States and to search for correlations with dress, diet, and use of vitamin D–fortified foods and vitamin supplements.MethodsIn this cross-sectional study, Arab-American women, 18 years and older, who attended an ethnic market on April 7 or 14, 2007, were recruited. Participants were interviewed by bilingual English- and Arabic-speaking investigators using a semi-structured interview to assess dress; demographic variables; medical history; medication use; clinical symptoms associated with vitamin D deficiency (eg, joint or bone pain, muscle weakness); and dietary intake of vitamin D from fortified orange juice, milk, and vitamin supplementation. Blood samples were drawn to measure concentrations of serum calcium, creatinine, phosphorus, alkaline phosphatase, parathyroid hormone, and 25-hydroxyvitamin D. Participants were initially divided into 2 groups based on whether the woman was veiled and further subdivided into 3 groups on the basis of vitamin D intake from supplemented food sources (milk or vitamin D–fortified orange juice) and vitamin pills: unveiled, veiled and taking supplements, and veiled and taking no supplements.ResultsEighty-seven women participated. Serum 25-hydroxyvitamin D levels were uniformly low, with the highest levels in the unveiled group (median [interquartile range]) (8.5 ng/mL [5.75-13.5 ng/mL]) followed by the veiled, supplemented group (7 ng/mL [4-11.5 ng/mL]) and the veiled, unsupplemented group (4 ng/mL [2-6.8 ng/ mL]). 25-Hydroxyvitamin D levels were lower in women with less experience in the United States and in those with less education. Vitamin D–fortified orange juice consumption had a greater positive predictive effect on serum 25- hydroxyvitamin D levels than either milk or vitamin pills and may possibly serve as a surrogate marker for vitamin D awareness.ConclusionsVitamin D deficiency, as assessed by 25-hydroxyvitamin D concentrations, is endemic in a sample of Arab-American women living in Dearborn, Michigan. These findings potentially identify an important health problem in the largest, most-concentrated Arab- American population in the United States. (Endocr Pract. 2009;15:35-40)     

Vitamin D,Parathyroid Hormone,and Heart Failure in A Chinese Elderly Population

ObjectiveHeart failure (HF) is a major cause of morbidity and mortality worldwide. Low vitamin D status has been shown to be associated with increased risk of developing cardiovascular disease. In this study, we examined the association between vitamin D and parathyroid hormone (PTH) levels and HF in and elderly population in China.MethodsA population-based cross-sectional study was conducted in the spring of 2013 among 2,047 community-dwelling healthy individuals, aged 60 to 101 years. 25-Hydroxyvitamin D (25[OH]D) was measured using a chemiluminescence assay. PTH levels were measured with an electrochemiluminescence immunoassay.ResultsA total of 2,047 participants, including 1,121 women (54.7%), were evaluated in 2013. The median concentrations of serum 25(OH)D and PTH for the entire group were 16.1 ng/mL and 41.5 pg/mL, respectively. Serum 25(OH)D and PTH levels were associated with serum N-terminal pro-brain natriuretic peptide levels and left ventricular ejection fraction in a multivariate adjusted linear regression analysis (P < .05). In logistic regression analyses, serum 25(OH)D and PTH levels were associated with a risk of HF in single and multiple regression models (P < .05). Compared with patients with 25(OH)D levels between 30.0 and 44.9 ng/mL, patients with 25(OH)D levels less than 10 ng/mL had a higher mean hazard ratio for HF (2.88; 95% confidence interval, 1.59 to 4.38).ConclusionSerum 25(OH)D and PTH levels are independently associated with risk of HF in a Chinese elderly population. (Endocr Pract. 2014;21:30-40)     

High Prevalence of Vitamin D Insufficiency in China: Relationship with the Levels of Parathyroid Hormone and Markers of Bone Turnover

There is a lack of large-scale studies on vitamin D status and its relationship to parathyroid hormone (PTH) and bone turnover markers in adults living in Shanghai. The objectives were to determine the prevalence of vitamin D insufficiency in Shanghai and to investigate the relationship of 25(OH)D with parathyroid function and bone turnover markers. This cross-sectional study involved 649 men and 1939 women aged 20–89 years who were randomly sampled in Shanghai. Serum concentrations of 25(OH)D, PTH, albumin, and bone turnover markers were measured. During the winter season, the prevalence of vitamin D insufficiency (<30 ng/mL) was 84% in males and 89% in females. The prevalence of vitamin D deficiency (<20 ng/mL) was 30% in males and 46% in females. With increasing serum 25(OH)D concentrations categorized as <10, 10–20, 20–30, and ≥30 ng/mL, the mean PTH and bone turnover markers levels gradually decreasd in both sexes (p<0.001). There was an inverse relationship between the serum 25(OH)D and PTH concentrations in both genders, but no threshold of 25(OH)D at which PTH levels plateaued was observed. There were modest but significantly inverse relationships between the levels of 25(OH)D and bone turnover markers, but no plateau was observed for serum 25(OH)D levels up to 40 ng/mL.     

Inhibitory effects of 1 alpha, 25-dihydroxycholecalciferol on parathyroid hormone secretion in rats

In an attempt to study the influence of vitamin D metabolites on PTH secretion, serum calcium and urinary excretion of cAMP were sequentially measured in conscious perfused rats, and the effects of a single iv injection of the metabolites on these parameters were examined. Four hours after the administration of 0.25 microgram/kg (0.6 nmol/kg, probably a physiological dose) of 1 alpha, 25-dihydroxycholecalciferol [1 alpha, 25 (OH)2D3], the urinary excretion of cAMP decreased to a level compatible with that of parathyroidectomized rats (approximately 60% of the initial value; P less than 0.05) and this level was sustained for nearly 24 h. Serum concentrations of calcium (total and ionized) did not change. In parathyroidectomized rats which were continuously infused with bovine PTH (1 U/h), the vitamin D metabolite had no significant effect on the urinary excretion of cAMP. 24 R, 25-dihydroxcholecalciferol (12.5 microgram/kg) had no significant effect either on the urinary excretion of cAMP or on serum calcium. These results suggest that in rats, a physiological dose of 1 alpha, 25(OH)2D3 inhibits PTH secretion without causing a significant rise iu serum calcium, reflecting a feed-back mechanism between active vitamin D metabolite, 1 alpha, 25(OH)2D3 and the parathyroid glands.     

Effect of vitamin D3 administration on serum 25-hydroxyvitamin D3, 1,25-dihydroxyvitamin D3 and osteocalcin in vitamin D-deficient elderly people

In elderly institutionalized people, confined to bedroom and receiving no vitamin D supplementation, the frequency of vitamin D deficiency is found very high. Systematic administration of vitamin D has, therefore, been proposed to correct vitamin D deficiency. Within this context, we studied 40 elderly institutionalized subjects (mean age 80.5 + 7.2 yr) with low 25(OH)D3 concentrations (4.4 + 1.8 micrograms/l). Sixteen of them (Group I) had low serum calcium concentrations (less than 2.3 mmol/l) and 24 (Group II) had normal serum calcium concentrations (from 2.3 to 2.6 mmol/l). As hypocalcemia has been shown to regulate 1,25(OH)D3 production independent of PTH in animals and in humans, we compared their respective responses to the administration of vitamin D3. Subjects received a total dose of 15 mg (600,000 IU) of vitamin D3 divided into 3 i.m. injections at one month intervals and were explored before therapy and one and 6 months after the last dose of vitamin D3. The treatment induced a similar marked rise in 25(OH)D3 levels (from 4.1 + 1.7 to 24.4 + 8.7 micrograms/l for group I and from 5.1 + 1.8 to 27.2 + 8.0 micrograms/l for group II) in both groups but increased the 1,25(OH)2D3 concentrations only in group I (from 22.9 + 6.9 to 32.6 + 11.3 ng/l). Meanwhile serum calcium concentrations rose in group I (to low normal range i.e. 2.31 + 0.07 mmol/l) and were unaffected in group II. These results suggest that hypocalcemia is a potent stimulator of renal 1-hydroxylase in elderly people. Furthermore, a transient significant (P less than 0.01) increase in serum osteocalcin (from 10.6 + 4.1 to 14.1 + 5.9 micrograms/l) could be observed in group I which demonstrates for the first time that the osteocalcin response of osteoblasts to stimulation by 1,25(OH)2D3 is retained in very old people.