Vitamin D deficiency and risk of cardiovascular disease

The vitamin D deficiency pandemic and consequences for nonskeletal health: mechanisms of action

Vitamin D, the sunshine vitamin, is important for childhood bone health. Over the past two decades, it is now recognized that vitamin D not only is important for calcium metabolism and maintenance of bone health throughout life, but also plays an important role in reducing risk of many chronic diseases including type I diabetes, multiple sclerosis, rheumatoid arthritis, deadly cancers, heart disease and infectious diseases. How vitamin D is able to play such an important role in health is based on observation that all tissues and cells in the body have a vitamin D receptor, and, thus, respond to its active form 1,25-dihydroxyvitamin D. However, this did not explain how living at higher latitudes and being at risk of vitamin D deficiency increased risk of these deadly diseases since it was also known that the 1,25-dihydroxyvitamin D levels are normal or even elevated when a person is vitamin D insufficient. Moreover, increased intake of vitamin D or exposure to more sunlight will not induce the kidneys to produce more 1,25-dihydroxyvitamin D. The revelation that the colon, breast, prostate, macrophages and skin among other organs have the enzymatic machinery to produce 1,25-dihydroxyvitamin D provides further insight as to how vitamin D plays such an essential role for overall health and well being. This review will put into perspective many of the new biologic actions of vitamin D and on how 1,25-dihydroxyvitamin D is able to regulate directly or indirectly more than 200 different genes that are responsible for a wide variety of biologic processes.

Maternal plasma 25-hydroxyvitamin D concentrations and the risk for gestational diabetes mellitus

Background

Evidence is accumulating for a role of vitamin D in maintaining normal glucose homeostasis. However, studies that prospectively examined circulating concentrations of 25-hydroxyvitamin D (25-[OH] D) in relation to diabetes risk are limited. Our objective is to determine the association between maternal plasma 25-[OH] D concentrations in early pregnancy and the risk for gestational diabetes mellitus (GDM).

Methods

A nested case-control study was conducted among a prospective cohort of 953 pregnant women. Among them, 57 incident GDM cases were ascertained and 114 women who were not diagnosed with GDM were selected as controls. Controls were frequency matched to cases for the estimated season of conception of the index pregnancy.

Results

Among women who developed GDM, maternal plasma 25-[OH] D concentrations at an average of 16 weeks of gestation were significantly lower than controls (24.2 vs. 30.1 ng/ml, P<0.001). This difference remained significant (3.62 ng/ml lower on average in GDM cases than controls (P value = 0.018)) after the adjustment for maternal age, race, family history of diabetes, and pre-pregnancy BMI. Approximately 33% of GDM cases, compared with 14% of controls (P<0.001), had maternal plasma 25-[OH] D concentrations consistent with a pre-specified diagnosis of vitamin D deficiency (<20 ng/ml). After adjustment for the aforementioned covariates including BMI, vitamin D deficiency was associated with a 2.66-fold (OR (95% CI): 2.66 (1.01–7.02)) increased GDM risk. Moreover, each 5 ng/ml decrease in 25-[OH] D concentrations was related to a 1.29-fold increase in GDM risk (OR (95% CI): 1.29 (1.05–1.60)). Additional adjustment for season and physical activity did not change findings substantially.

Conclusions

Findings from the present study suggest that maternal vitamin D deficiency in early pregnancy is significantly associated with an elevated risk for GDM.

25-Hydroxyvitamin D deficiency is independently associated with cardiovascular disease in the Third National Health and Nutrition Examination Survey

OBJECTIVE

Serum 25-hydroxyvitamin D [25(OH)D] levels are inversely associated with important cardiovascular disease (CVD) risk factors. However, the association between 25(OH)D levels and prevalent CVD has not been extensively examined in the general population.

METHODS

We performed a cross-sectional analysis of data from the Third National Health and Nutrition Examination Survey (1988-1994) and examined the association between serum 25(OH)D levels and prevalence of CVD in a representative population-based sample of 16,603 men and women aged 18 years or older. Prevalence of CVD was defined as a composite measure inclusive of self-reported angina, myocardial infarction or stroke.

RESULTS

In the whole population, there were 1308 (8%) subjects with self-reported CVD. Participants with CVD had a greater frequency of 25(OH)D deficiency [defined as serum 25(OH)D levels <20 ng/mL] than those without (29.3% vs. 21.4%; p<0.0001). After adjustment for age, gender, race/ethnicity, season of measurement, physical activity, body mass index, smoking status, hypertension, diabetes, elevated low-density lipoprotein cholesterol, hypertriglyceridemia, low high-density lipoprotein cholesterol, chronic kidney disease and vitamin D use, participants with 25(OH)D deficiency had an increased risk of prevalent CVD (odds ratio 1.20 [95% confidence interval (CI) 1.01-1.36; p=0.03]).

CONCLUSIONS

These results indicate a strong and independent relationship of 25(OH)D deficiency with prevalent CVD in a large sample representative of the US adult population.

Nutrient supplements and cardiovascular disease: a heartbreaking story

Observational data have identified associations between carotenoids, folic acid, and vitamin E, or metabolites altered by these nutrients, and cardiovascular disease (CVD) risk. Despite biological plausibility, for the most part, data derived from nutrient supplement trials using moderate to high doses of single nutrients or nutrient combinations (exceeding amounts to avoid nutrient deficiency) have been disappointing. The data for vitamin D is not yet adequate to evaluate; observational data suggest were a relationship to exist it would be related to nutrient insufficiency. There is some evidence that use of nutrient supplements intended to decrease CVD risk has resulted in unanticipated adverse consequences. Potential discrepancies between observational and interventional data include concerns of residual confounding by diet and lifestyle patterns, publication bias against studies with null or negative outcomes, reliance on secondary rather than primary prevention trials, and unaccounted for contribution of genotypic variations. At this time there are insufficient data to recommend the routine use of nutrient supplements to prevent or treat CVD. In the recent past we have learned a great deal about anticipated and unanticipated consequences of nutrient supplementation and cardiovascular outcomes. As a result, we are in a better position to adjudicate new potential relationships as data emerge.

Heart Failure Is a Risk Factor for Orthopedic Fracture

Background— Heart failure (HF) is associated with factors that may contribute to accelerated bone loss and subsequent fractures. Whether it leads to an increased fracture risk is unknown.

Methods and Results— A population-based cohort of consecutive patients ≥65 years of age with cardiovascular disease presenting to all emergency rooms between 1998 and 2001 in Alberta, Canada (n=16294 patients), was used. The 2041 patients with a new diagnosis of HF were compared with a control group of 14 253 patients with non-HF cardiovascular diagnoses. The primary outcome was any orthopedic fracture requiring hospital admission in the year after the emergency room visit. Patients with HF had a median age of 78 years (interquartile range, 72 to 84 years), and 51.9% were female; control subjects had a median age of 73 years (interquartile range, 68 to 79 years), and 53.2% were female. In the first year after the emergency room visit, 4.6% of the HF cohort (n=93) and 1.0% of patients without HF (n=147) sustained an orthopedic fracture ( P <0.001). Hip fractures occurred in 26 HF patients (1.3%) and 18 patients (0.1%) without HF ( P <0.001). After multivariable adjustment, HF was independently associated with a greater risk of any orthopedic fracture (adjusted odds ratio, 4.0; 95% CI, 2.9 to 5.3) or hip fracture (adjusted odds ratio, 6.3; 95% CI, 3.4 to 11.8).

Conclusions— HF is associated with an increased risk of subsequent orthopedic fracture, particularly hip fracture. This suggests that screening for and treatment of osteoporosis to reduce fracture risk need to be considered in those with HF.

Vitamin D in the prevention and treatment of coronary heart disease

PURPOSE OF REVIEW

The pathogenesis of coronary heart disease is of multifactorial origin. Probably, not all risk factors are satisfactorily understood. This article outlines beneficial vitamin D effects on cardiac function and the vasculature. In addition, human data associating serum vitamin D metabolite levels or oral vitamin D dosages or both with coronary heart disease outcome parameters are reviewed.

RECENT FINDINGS

There is accumulating evidence that the vitamin D hormone calcitriol exerts important physiological effects in cardiomyocytes, vascular smooth muscle cells, and the vascular endothelium. Low levels of the calcitriol precursor 25-hydoxyvitamin D are associated with myocardial infarction, congestive heart failure, and calcific aortic stenosis. Deficient calcitriol concentrations probably contribute to the massive vascular calcification seen in chronic kidney disease. In patients with end-stage renal disease and end-stage heart failure, very low-circulating calcitriol levels or nonuse of active vitamin D or both are independently associated with high mortality rates.

SUMMARY

Despite these exciting data, it is still too early to recommend exact dosages for the prevention or therapy of coronary heart disease. Prospective, randomized controlled trials with different amounts of vitamin D and probably with its active form calcitriol are needed to determine whether vitamin D can prevent coronary heart disease events and mortality.

Recovery of hyperphosphatoninism and renal phosphorus wasting one year after successful renal transplantation

BACKGROUND AND OBJECTIVES

In the first months after successful kidney transplantation, hypophosphatemia and renal phosphorus wasting are common and related to inappropriately high parathyroid hormone (PTH) and fibroblast growth factor-23 (FGF-23) levels. Little is known about the long-term natural history of renal phosphorus homeostasis in renal transplant recipients.

DESIGN, SETTING, PARTICIPANTS

We prospectively followed parameters of mineral metabolism (including full-length PTH and FGF-23) in 50 renal transplant recipients at the time of transplantation (Tx), at month 3 (M3) and at month 12 (M12). Transplant recipients were (1:1) matched for estimated GFR with chronic kidney disease (CKD) patients.

RESULTS

FGF-23 levels (Tx: 2816 [641 to 10665] versus M3: 73 [43 to 111] versus M12: 56 [34 to 78] ng/L, median [interquartile range]) and fractional phosphorus excretion (FE(phos); M3: 45 +/- 19% versus M12: 37 +/- 13%) significantly declined over time after renal transplantation. Levels 1 yr after transplantation were similar to those in CKD patients (FGF-23: 47 [34 to 77] ng/L; FE(phos) 35 +/- 16%). Calcium (9.1 +/- 0.5 versus 8.9 +/- 0.3 mg/dl) and PTH (27.2 [17.0 to 46.0] versus 17.5 [11.7 to 24.4] ng/L) levels were significantly higher, whereas phosphorus (3.0 +/- 0.6 versus 3.3 +/- 0.6 mg/dl) levels were significantly lower 1 yr after renal transplantation as compared with CKD patients.

CONCLUSIONS

Data indicate that hyperphosphatoninism and renal phosphorus wasting regress by 1 yr after successful renal transplantation.

Effects of vitamin D supplementation on the calcium-phosphate balance in renal transplant patients

Low serum levels of 25-hydroxy vitamin D frequently occur after renal transplantation, but few studies have evaluated the effects of normalizing this on serum parathyroid hormone and calcium levels or urinary calcium excretion. To determine this we compared the outcomes of 94 renal transplant patients with low 25-hydroxy vitamin D and normal serum calcium levels who were either treated or not with cholecalciferol every 2 weeks for 2 months (intensive phase) followed by an every other month maintenance phase. The biological characteristics of the two equally divided patient groups did not differ before treatment. After the intensive phase, serum 25-hydroxy vitamin D levels were normalized in all but 3 patients and the serum parathyroid hormone decreased and calcium levels increased with no severe adverse effects. During the maintenance phase, the serum 25-hydroxy vitamin D level decreased but remained significantly higher than in controls. In the control group, the serum 25-hydroxy vitamin D concentration increased slightly but became normal in only three patients. Serum 25-hydroxy vitamin D levels were significantly higher and parathyroid hormone levels were lower in treated patients compared to controls one year following transplant. Hence, cholecalciferol treatment significantly increased serum 25-hydroxy vitamin D and decreased parathyroid hormone levels with no adverse effects in 25-hydroxy vitamin D-deficient renal transplant patients.

The link between vitamin D deficiency and systemic lupus erythematosus

Vitamin D deficiency is highly prevalent and is increasingly thought to be an important risk factor in many diseases that have high morbidity and mortality, including lupus. Vitamin D is an immunomodulatory hormone with effects on T cells, B cells, and dendritic cells. Animal models of autoimmune disease and epidemiologic studies suggest a role for vitamin D as a modifiable environmental factor in autoimmune disease. Recommendations are available regarding screening for and repletion of vitamin D deficiency. More research is needed to understand the role of vitamin D as an immunomodulator and to determine the optimal range of serum 25-hydroxyvitamin D for musculoskeletal, cardiovascular, and immune health.

Diabetes and the vitamin d connection

Vitamin D deficiency, which is common in children and adults, causes rickets, osteomalacia, and osteoporosis. Most organs and immune cells have a vitamin D receptor, and some also have the capacity to metabolize 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D. 1,25-Dihydroxyvitamin D is a potent immunomodulator that also enhances the production and secretion of several hormones, including insulin. Vitamin D deficiency has been associated with increased risk of type 1 diabetes. Glycemic control and insulin resistance are improved when vitamin D deficiency is corrected and calcium supplementation is adequate. 25-Hydroxyvitamin D (measure of vitamin D status) of less than 20 ng/mL is vitamin D deficiency and 21 to 29 ng/mL is insufficiency. Children and adults need at least 1000 IU of vitamin D per day to prevent deficiency when there is inadequate sun exposure.

Baseline serum 25-hydroxy vitamin d is predictive of future glycemic status and insulin resistance: the Medical Research Council Ely Prospective Study 1990-2000

OBJECTIVE

Accumulating epidemiological evidence suggests that hypovitaminosis D may be associated with type 2 diabetes and related metabolic risks. However, prospective data using the biomarker serum 25-hydroxyvitamin D [25(OH)D] are limited and therefore examined in the present study.

RESEARCH DESIGN AND METHODS

A total of 524 randomly selected nondiabetic men and women, aged 40-69 years at baseline, with measurements for serum 25(OH)D and IGF-1 in the population-based Ely Study, had glycemic status (oral glucose tolerance), lipids, insulin, anthropometry, and blood pressure measured and metabolic syndrome risk (metabolic syndrome z score) derived at baseline and at 10 years of follow-up.

RESULTS

Age-adjusted baseline mean serum 25(OH)D was greater in men (64.5 nmol/l [95% CI 61.2-67.9]) than women (57.2 nmol/l [54.4,60.0]) and varied with season (highest late summer). Baseline 25(OH)D was associated inversely with 10-year risk of hyperglycemia (fasting glucose: beta = -0.0023, P = 0.019; 2-h glucose: beta = -0.0097, P = 0.006), insulin resistance (fasting insulin beta = -0.1467, P = 0.010; homeostasis model assessment of insulin resistance [HOMA-IR]: beta = -0.0059, P = 0.005), and metabolic syndrome z score (beta = -0.0016, P = 0.048) after adjustment for age, sex, smoking, BMI, season, and baseline value of each metabolic outcome variable. Associations with 2-h glucose, insulin, and HOMA-IR remained significant after further adjustment for IGF-1, parathyroid hormone, calcium, physical activity, and social class.

CONCLUSIONS

This prospective study reports inverse associations between baseline serum 25(OH)D and future glycemia and insulin resistance. These associations are potentially important in understanding the etiology of abnormal glucose metabolism and warrant investigation in larger, specifically designed prospective studies and randomized controlled trials of supplementation.

Enzyme-independent NO stores in human skin: quantification and influence of UV radiation

Nitric oxide (NO) has many functions in the skin, including the mediation of inflammation and antimicrobial defense, wound healing, regulation of keratinocyte homeostasis, and regulation of apoptosis following UV radiation. NO is synthesized by a family of NO synthase enzymes, but its rapid release following UV exposure suggests the existence of preformed stores. NO can be converted into nitrite or nitrosothiols that are stable until cleaved by UV to release NO. Using dermal microdialysis, suction blister epidermal samples, and sweat collection, we demonstrated cutaneous concentrations of total NO-related products of 12+/-5.97 microM, 0.03+/-0.03 micromol mg(-1) epidermal protein, and 22+/-9.34 microM, respectively. The predominant oxyanion was nitrate (60-75%) followed by nitrite. S-Nitrosothiols were barely detectable. Serum total NO-related products correlated directly with those of the upper dermis and sweat (R(2)=0.62 and 0.3, respectively). UVA irradiation (10 mW cm(-2)) increased the yield of NO-related products by microdialysis, peaking after 30 minutes. Dialysis with noradrenaline abrogated this rise. Both the skin and the dermal vasculature contain biologically significant stores of NO, particularly nitrite, which can be directly mobilized by UVA irradiation. The level of circulating NO-related products probably determines skin-bound stores.

Vitamin D3 fortification, quantification, and long-term stability in Cheddar and low-fat cheeses

Considering the widespread insufficiency of vitamin D, the fortification of additional foods with vitamin D is warranted. The objective of this research was to assess the feasibility of vitamin D3 fortification in natural hard cheeses. We examined the recovery, distribution, long-term retention, and heat stability of the vitamin in industrially made fortified Cheddar and low-fat cheeses. The results indicated that the vitamin D3 did not degrade during processing, over 1 year of ripening (3-8 degrees C), or after thermal treatment at 232 degrees C for 5 min. Vitamin D3 recovery in the fortified Cheddar and low-fat cheeses were, respectively, 91 and 55% of the vitamin D3 added to the milk used to make each cheese. The remaining vitamin D3 was entrained in the whey. The vitamin D3 was uniformly distributed throughout the blocks of cheese. The fortification process did not alter the yield, chemical composition, or flavor of the Cheddar cheese. We conclude that industrially manufactured Cheddar and low-fat cheeses are suitable for vitamin D3 fortification.

The noncalciotropic actions of vitamin D: recent clinical developments

PURPOSE OF REVIEW

This review summarizes recently described actions of 1,25-dihydroxyvitamin D beyond its function in calcium homeostasis and bone metabolism.

RECENT FINDINGS

1,25-Dihydroxyvitamin D stimulates the innate immune system, facilitating the clearance of infections such as tuberculosis. Hypovitaminosis D has been associated with several autoimmune disorders, various malignancies, and cardiovascular risk factors in a number of recent epidemiologic reports. Based on these observational reports, vitamin D and its analogues are being evaluated for the prevention and treatment of a variety of conditions, with early findings showing mixed results.

SUMMARY

The broad tissue distribution of the 25-hydroxyvitamin D 1alpha-hydroxylase enzyme and the vitamin D receptor establish a role for 1,25-dihydroxyvitamin D in the pathophysiology of various disease states and provide new therapeutic targets for vitamin D and its analogues.

The bioavailability of vitamin D from fortified cheeses and supplements is equivalent in adults

There is a need to increase the options for vitamin D fortification. We have developed a method to fortify hard cheese with vitamin D. Our aim was to characterize the bioavailability of vitamin D from fortified cheeses. Eighty adults were randomized to weekly servings of fortified cheddar cheese (DC) (34 g; n = 20); fortified low-fat cheese (DLF) (41 g; n = 10); liquid vitamin D supplement (1 mL), taken with food (DS+) (n = 20) or without food (DS-) (n = 10); placebo cheddar cheese (n = 10); or placebo supplement (n = 10). The treatments contained 28,000 IU cholecalciferol (vitamin D3), equivalent to 4000 IU (100 microg/d). The primary outcome was the comparison of vitamin D bioavailability, as measured by the serum 25-hydroxyvitamin D [25(OH)D] response, between fortified cheeses and supplement. In the placebo groups, initial 25(OH)D, 55.0 +/- 25.3 nmol/L, declined over the 8-wk winter protocol, to 50.7 +/- 24.2 nmol/L (P = 0.046). In the vitamin D-treated groups, the mean increases in 25(OH)D over 8 wk were: 65.3 +/- 24.1 (DC), 69.4 +/- 21.7 (DLF), 59.3 +/- 23.3 (DS+), and 59.3 +/- 19.6 nmol/L (DS-); these changes differed from the placebo groups (P < 0.0001) but not from one another (P = 0.62). Compared with baseline, serum parathyroid hormone decreased with both fortification (P = 0.003) and supplementation (P = 0.012). These data demonstrate that vitamin D is equally bioavailable from fortified hard cheeses and supplements, making cheese suitable for vitamin D fortification.

Vitamin D and osteogenic differentiation in the artery wall

Vascular calcification is widespread, particularly in patients with chronic kidney disease, who receive, among other treatments, active vitamin D supplements. Emerging evidence indicates that vascular calcification is a regulated process that resembles embryonic endochondral osteogenesis, involving osteoblastic differentiation of vascular smooth muscle cells. In experimental animal models, high dosages of vitamin D consistently promote vascular calcification. In particular, the vitamin D-fed rat is frequently used as a model to assess putative regulators of calcific vasculopathy. The artery wall calcification in these animals most likely results from multiple mechanisms involving systems physiology of the complex, bone-vascular-renal-endocrine axis. Genetically engineered mice with upregulated vitamin D signaling pathways have also shed light on the molecular intermediaries, including fibroblast growth factor-23 and transcriptional intermediary factor 1-alpha. In contrast to the studies of animals, studies of humans show that vitamin D has an inverse relationship or little effect. This difference between in vitro and in vivo findings is most likely, again, due to the complex, systemic feedback regulatory mechanisms that control calcium-phosphate metabolism. Recent epidemiologic evidence suggests that there is a narrow range of vitamin D levels in which vascular function is optimized. Levels above or below this range seem to confer a significant increase in risk for cardiovascular disease. There is some evidence to suggest that dietary vitamin D may be carried by lipoprotein particles into cells of the artery wall and atherosclerotic plaque, where it may be converted to active form by monocyte-macrophages. These findings raise interesting questions regarding the effects of vitamin D intake on atherosclerotic calcification and cardiovascular risk.

Deficiency of sunlight and vitamin D

Fortification of foods and advice on sensible sun exposure are urgently needed

Vitamin D in health and disease

Vitamin D functions in the body through both an endocrine mechanism (regulation of calcium absorption) and an autocrine mechanism (facilitation of gene expression). The former acts through circulating calcitriol, whereas the latter, which accounts for more than 80% of the metabolic utilization of the vitamin each day, produces, uses, and degrades calcitriol exclusively intracellularly. In patients with end-stage kidney disease, the endocrine mechanism is effectively disabled; however, the autocrine mechanism is able to function normally so long as the patient has adequate serum levels of 25(OH)D, on which its function is absolutely dependent. For this reason, calcitriol and its analogs do not constitute adequate replacement in managing vitamin D needs of such patients. Optimal serum 25(OH)D levels are greater than 32 ng/mL (80 nmol/L). The consequences of low 25(OH)D status include increased risk of various chronic diseases, ranging from hypertension to diabetes to cancer. The safest and most economical way to ensure adequate vitamin D status is to use oral dosing of native vitamin D. (Both daily and intermittent regimens work well.) Serum 25(OH)D can be expected to rise by about 1 ng/mL (2.5 nmol/L) for every 100 IU of additional vitamin D each day. Recent data indicate that cholecalciferol (vitamin D(3)) is substantially more potent than ergocalciferol (vitamin D(2)) and that the safe upper intake level for vitamin D(3) is 10,000 IU/d.

Serum 25-hydroxyvitamin D levels and the prevalence of peripheral arterial disease: results from NHANES 2001 to 2004

OBJECTIVE

The purpose of this study was to determine the association between 25-hydroxyvitamin D (25(OH)D) levels and the prevalence of peripheral arterial disease (PAD) in the general United States population.

METHODS AND RESULTS

We analyzed data from 4839 participants of the National Health and Nutrition Examination Survey 2001 to 2004 to evaluate the relationship between 25(OH)D and PAD (defined as an ankle-brachial index < 0.9). Across quartiles of 25(OH)D, from lowest to highest, the prevalence of PAD was 8.1%, 5.4%, 4.9%, and 3.7% (P trend < 0.001). After multivariable adjustment for demographics, comorbidities, physical activity level, and laboratory measures, the prevalence ratio of PAD for the lowest, compared to the highest, 25(OH)D quartile (< 17.8 and > or = 29.2 ng/mL, respectively) was 1.80 (95% confidence interval: 1.19, 2.74). For each 10 ng/mL lower 25(OH)D level, the multivariable-adjusted prevalence ratio of PAD was 1.35 (95% confidence interval: 1.15, 1.59).

CONCLUSIONS

Low serum 25(OH)D levels are associated with a higher prevalence of PAD. Several mechanisms have been invoked in the literature to support a potential antiatherosclerotic activity of vitamin D. Prospective cohort and mechanistic studies should be designed to confirm this association.

Impact of activated vitamin D and race on survival among hemodialysis patients

Contrary to most examples of disparities in health outcomes, black patients have improved survival compared with white patients after initiating hemodialysis. Understanding potential explanations for this observation may have important clinical implications for minorities in general. This study tested the hypothesis that greater use of activated vitamin D therapy accounts for the survival advantage observed in black and Hispanic patients on hemodialysis. In a prospective cohort of non-Hispanic white (n = 5110), Hispanic white (n = 979), and black (n = 3214) incident hemodialysis patients, higher parathyroid hormone levels at baseline were the primary determinant of prescribing activated vitamin D therapy. Median parathyroid hormone was highest among black patients, who were most likely to receive activated vitamin D and at the highest dosage. One-year mortality was lower in black and Hispanic patients compared with white patients (16 and 16 versus 23%; P < 0.01), but there was significant interaction between race and ethnicity, activated vitamin D therapy, and survival. In multivariable analyses of patients treated with activated vitamin D, black patients had 16% lower mortality compared with white patients, but the difference was lost when adjusted for vitamin D dosage. In contrast, untreated black patients had 35% higher mortality compared with untreated white patients, an association that persisted in several sensitivity analyses. In conclusion, therapy with activated vitamin D may be one potential explanation for the racial differences in survival among hemodialysis patients. Further studies should determine whether treatment differences based on biologic differences contribute to disparities in other conditions.

Prevalence and severity of disordered mineral metabolism in Blacks with chronic kidney disease

Disorders of mineral metabolism develop early in chronic kidney disease, but it appears that Blacks with stage-5 disease have more severe secondary hyperparathyroidism than other races. We measured levels of parathyroid hormone, calcium, phosphorus, 25-hydroxyvitamin D (25D) and 1,25-dihydroxyvitamin D (1,25D) in 227 Black and 1633 non-Black participants in the SEEK study, a multi-center cohort of patients with early chronic kidney disease. Overall, Blacks had similar 1,25D levels compared with non-Blacks, but significantly lower levels of 25D with higher levels of calcium, phosphorus, and parathyroid hormone, and were significantly more likely to have hyperphosphatemia than non-Blacks. In multivariable analyses adjusted for age, gender, estimated glomerular filtration rate, body mass index, and diabetes, Blacks had significantly lower 25D and higher parathyroid hormone levels than non-Blacks, with the latter parameter remaining significant after further adjustment for calcium, phosphorus, 25D, and 1,25D. The association between Black race and secondary hyperparathyroidism, independent of known risk factors, suggests that novel mechanisms contribute to secondary hyperparathyroidism in Blacks with chronic kidney disease.

Relationships of low serum vitamin D3 with anthropometry and markers of the metabolic syndrome and diabetes in overweight and obesity

Low serum 25 hydroxyvitamin D₃ (vitamin D₃) is known to perturb cellular function in many tissues, including the endocrine pancreas, which are involved in obesity and type II diabetes mellitus (TIIDM). Vitamin D₃ insufficiency has been linked to obesity, whether obesity is assessed by body mass index (BMI) or waist circumference (waist). Central obesity, using waist as the surrogate, is associated with the metabolic syndrome (MetSyn), insulin resistance, TIIDM and atherosclerotic cardiovascular disease (CVD). We tested how vitamin D₃ was related to measures of fat mass, MetSyn markers, haemoglobin A_1c (HbA_1c) and MetSyn in a cross-sectional sample of 250 overweight and obese adults of different ethnicities. There were modest inverse associations of vitamin D₃ with body weight (weight) (r = -0.21, p = 0.0009), BMI (r = -0.18, p = 0.005), waist (r = -0.14, p = 0.03), [but not body fat % (r = -0.08, p = 0.24)], and HbA_1c (r = -0.16, p = 0.01). Multivariable regression carried out separately for BMI and waist showed a decrease of 0.74 nmol/L (p = 0.002) in vitamin D₃ per 1 kg/m² increase in BMI and a decrease of 0.29 nmol/L (p = 0.01) per 1 cm increase in waist, with each explaining approximately 3% of the variation in vitamin D₃ over and above gender, age, ethnicity and season.

The similar relationships of BMI and waist with vitamin D₃ may have been due to associations between BMI and waist, or coincidental, where different mechanisms relating hypovitaminosis D₃ to obesity occur concurrently. Previously reviewed mechanisms include that 1) low vitamin D₃, may impair insulin action, glucose metabolism and various other metabolic processes in adipose and lean tissue 2) fat soluble-vitamin D₃ is sequestered in the large adipose compartment, and low in serum, 3) obese people may be sensitive about their body shape, minimising their skin exposure to view and sunlight (not tested). We showed evidence for the first theory but no evidence to support the second.

In the current study, serum vitamin D₃ was inversely related to weight, BMI and markers of TIIDM (large waist, raised HbA_1c) but not to adipose mass nor to MetSyn per se.

Vitamin D deficiency and risk of cardiovascular disease

BACKGROUND

Vitamin D receptors have a broad tissue distribution that includes vascular smooth muscle, endothelium, and cardiomyocytes. A growing body of evidence suggests that vitamin D deficiency may adversely affect the cardiovascular system, but data from longitudinal studies are lacking.

METHODS AND RESULTS

We studied 1739 Framingham Offspring Study participants (mean age 59 years; 55% women; all white) without prior cardiovascular disease. Vitamin D status was assessed by measuring 25-dihydroxyvitamin D (25-OH D) levels. Prespecified thresholds were used to characterize varying degrees of 25-OH D deficiency (< 15 ng/mL, < 10 ng/mL). Multivariable Cox regression models were adjusted for conventional risk factors. Overall, 28% of individuals had levels < 15 ng/mL, and 9% had levels < 10 ng/mL. During a mean follow-up of 5.4 years, 120 individuals developed a first cardiovascular event. Individuals with 25-OH D < 15 ng/mL had a multivariable-adjusted hazard ratio of 1.62 (95% confidence interval 1.11 to 2.36, P=0.01) for incident cardiovascular events compared with those with 25-OH D > or = 15 ng/mL. This effect was evident in participants with hypertension (hazard ratio 2.13, 95% confidence interval 1.30 to 3.48) but not in those without hypertension (hazard ratio 1.04, 95% confidence interval 0.55 to 1.96). There was a graded increase in cardiovascular risk across categories of 25-OH D, with multivariable-adjusted hazard ratios of 1.53 (95% confidence interval 1.00 to 2.36) for levels 10 to < 15 ng/mL and 1.80 (95% confidence interval 1.05 to 3.08) for levels < 10 ng/mL (P for linear trend=0.01). Further adjustment for C-reactive protein, physical activity, or vitamin use did not affect the findings.

CONCLUSIONS

Vitamin D deficiency is associated with incident cardiovascular disease. Further clinical and experimental studies may be warranted to determine whether correction of vitamin D deficiency could contribute to the prevention of cardiovascular disease.

The link between osteoporosis and cardiovascular disease

Cardiovascular disease (CVD) and osteoporosis are common age-related conditions associated with significant morbidity, mortality, and disability.Traditionally, these two conditions were considered unrelated and their coexistence was attributed to independent age-related processes. However, an increasing body of biological and epidemiological evidence has provided support for a link between the two conditions that cannot be explained by age alone. Several hypotheses have been proposed to explain the link between osteoporosis and CVD including: 1) shared risk factors, 2) common pathophysiological mechanisms, 3) common genetic factors, or 4) a causal association.This review highlights the epidemiologic literature on the association of bone density with cardiovascular mortality, cardiovascular morbidity, and subclinical measures of atherosclerosis. It also summarizes the different potential mechanisms involved in the link between osteoporosis and CVD.

Trout ova, an alternative source of anti-B

Background

The reasons Blacks have higher mortality rates from colorectal cancer (CRC) than non-Hispanic Whites are not fully understood. Blacks have higher rates of vitamin D deficiency than non-Hispanic Whites, and vitamin D deficiency has been associated with CRC. We investigated the association of vitamin D deficiency with excess risk for CRC mortality for Blacks in the third National Health and Nutrition Examination Survey (NHANES III) 1988-1994.

Methods

We examined the association of serum 25(OH) D levels with CRC mortality and its contribution to elevated risk among Blacks using baseline data from NHANES III and CRC mortality through 2006 from the National Death Index. Using survival models, we examined the adjusted risk for African Americans for CRC death with and without adjusting for vitamin D deficiency, defined as less 25(OH)D < 20 ng/dl.

Results

Black race (Hazard Ratio [HR] 2.03; 95% Confidence Interval [CI] 1.04-3.95), age (HR 1.12; 95% CI 1.09-1.15), not having health insurance (HR 2.45; 95% CI 1.12-5.36), and history of CRC (HR 7.22; 95% CI 2.12-24.6) predicted CRC mortality. When added to the model, vitamin D deficiency was significantly associated with CRC mortality (HR 2.11; 95% CI 1.11-4.00) and the effect of race was decreased (HR 1.60; 95% 0.87-2.93); the 40% attenuation was statistically significant (F[1, 49] = 4.85, p = 0.03). Similar results were seen when participants with a history of CRC were excluded from the analysis.

Conclusion

Our findings are consistent with the hypothesis that vitamin D deficiency contributes to excess African American mortality from CRC.