Straight from D-Heart: vitamin D status and cardiovascular disease

Vitamin D and cardiovascular diseases: A narrative review

Cardiovascular diseases (CVD) and vitamin D deficiency are becoming highly prevalent among general populations. Despite plausible biological mechanisms for the role of vitamin D in cardio-protection, a cause-and-effect relationship has not yet been established. The interest in vitamin D as a potential therapeutic target to attenuate cardiovascular risk has been raised. The question about the benefit of vitamin D supplementation for cardiovascular outcomes cannot be answered certainly for the moment. The association between hypovitaminosis D and CVD has been proven by some studies while other studies deny any such link. The present narrative review gives a comprehensive overview of studies on the potential impact of hypovitaminosis D on CVD. The potential role of vitamin D supplementation in the management of CVD is also evaluated. Particular emphasis is paid to those studies that achieve a high level of scientific evidence.

Vitamin D and cardiovascular diseases: Causality

Vitamin D regulates blood pressure, cardiac functions, and endothelial and smooth muscle cell functions, thus, playing an important role in cardiovascular health. Observational studies report associations between vitamin D deficiency with hypertension and cardiovascular-related deaths. Peer-reviewed papers were examined in several research databases as per the guidelines of the Preferred Reporting Items for Systematic Reviews, using key words that address the relationship between vitamin D and cardiovascular disease. Correlations and interpretations were made considering the risks-benefits, broader evidence, and implications. This review analyzed current knowledge regarding the effects of vitamin D on the cardiovascular system. 1,25(OH)₂D and related epigenetic modifications subdue cellular inflammation, improve overall endothelial functions, reduce age-related systolic hypertension and vascular rigidity, and attenuate the actions of the renin-angiotensin-aldosterone system. Most observational and ecological studies support 25(OH)vitamin D having protective effects on the cardiovascular system. However, the association of vitamin D deficiency with cardiovascular diseases is based primarily on observational and ecological studies and thus, is a matter of controversy. Adequately powered, randomized controlled clinical trial data are not available to confirm these associations. Thus, to test the hypothesis that correction of vitamin D deficiency protects the cardiovascular system, well-designed, statistically powered, longer-term clinical trials are needed in persons with vitamin D deficiency. Nevertheless, the available data support that adequate vitamin D supplementation and/or sensible sunlight exposure to achieve optimal vitamin D status are important in the prevention of cardiovascular disease and other chronic diseases.

Associations of vitamin D with insulin resistance, obesity, type 2 diabetes, and metabolic syndrome

The aim of this study is to determine the relationships of vitamin D with diabetes, insulin resistance obesity, and metabolic syndrome. Intra cellular vitamin D receptors and the 1-α hydroxylase enzyme are distributed ubiquitously in all tissues suggesting a multitude of functions of vitamin D. It plays an indirect but an important role in carbohydrate and lipid metabolism as reflected by its association with type 2 diabetes (T2D), metabolic syndrome, insulin secretion, insulin resistance, polycystic ovarian syndrome, and obesity. Peer-reviewed papers, related to the topic were extracted using key words, from PubMed, Medline, and other research databases. Correlations of vitamin D with diabetes, insulin resistance and metabolic syndrome were examined for this evidence-based review. In addition to the well-studied musculoskeletal effects, vitamin D decreases the insulin resistance, severity of T2D, prediabetes, metabolic syndrome, inflammation, and autoimmunity. Vitamin D exerts autocrine and paracrine effects such as direct intra-cellular effects via its receptors and the local production of 1,25(OH)₂D₃, especially in muscle and pancreatic β-cells. It also regulates calcium homeostasis and calcium flux through cell membranes, and activation of a cascade of key enzymes and cofactors associated with metabolic pathways. Cross-sectional, observational, and ecological studies reported inverse correlations between vitamin D status with hyperglycemia and glycemic control in patients with T2D, decrease the rate of conversion of prediabetes to diabetes, and obesity. However, no firm conclusions can be drawn from current studies, because (A) studies were underpowered; (B) few were designed for glycemic outcomes, (C) the minimum (or median) serum 25(OH) D levels achieved are not measured or reported; (D) most did not report the use of diabetes medications; (E) some trials used too little (F) others used too large, unphysiological and infrequent doses of vitamin D; and (G) relative paucity of rigorous clinical data on the effects of vitamin D sufficiency on non-calcium endpoints. Although a large number of observational studies support improving T2D, insulin resistance, obesity, and metabolic syndrome with vitamin D adequacy, there is a lack of conclusive evidence from randomized control clinical trials that, these disorders are prevented following optimization of serum levels of 25(OH)D. However, none of the currently conducted clinical studies would resolve these issues. Thus, specifically designed, new clinical studies are needed to be conducted in well-defined populations, following normalizing the serum vitamin D levels in vitamin D deficient prediabetes subjects, to test the hypothesis that hypovitaminosis D worsens these disorders and correction would alleviate it.

Serum 25-hydroxyvitamin D levels are associated with carotid atherosclerosis in normotensive and euglycemic Chinese postmenopausal women: the Shanghai Changfeng study

Background

The role of serum 25-hydroxyvitamin D (25 (OH) D) in atherogenesis is unclear. We investigated whether the 25 (OH) D is independently associated with the carotid intima–media thickness (CIMT) and carotid plaques in normotensive and euglycemic postmenopausal women.

Methods

A total of 671 normotensive and euglycemic postmenopausal women (mean age, 58.8 years) were enrolled from the Changfeng Study. A standard interview, anthropometrics measurements and laboratory analyses were performed for each participant. Bilateral CIMTs were measured using ultrasonography, and the presence of carotid plaques was assessed. The serum 25 (OH) D was measured using electrochemiluminescence immunoassay.

Results

Serum 25 (OH) D was 43.6 ± 18.2 nmol/L in the postmenopausal women. Compared with subjects with 25 (OH) D in the first, second and third quartiles, subjects with 25 (OH) D in the fourth quartile had decreased CIMT and prevalence of carotid plaque (0.684 ± 0.009 mm vs 0.719 ± 0.009 mm, 0.708 ± 0.009 mm and 0.709 ± 0.009 mm; 10.8% vs 19.0%, 14.8% and 16.8%, respectively). After adjusting for conventional CVD risk factors, PTH, liver and renal function, postmenopausal women with 25 (OH) D in the fourth quartile still had lower CIMT than those in the first, second and third quartiles (p = 0.039) and the subjects in the fourth quartile had a 0.421-fold decreased risk of carotid plaques relative to those in the lowest quartile (95% confidence interval 0.209 to 0.848).

Conclusions

These results suggest serum 25 (OH) D is independently and inversely associated with carotid atherosclerosis in postmenopausal women with normal blood pressure and normal glucose tolerance.

Relationships between 25-hydroxyvitamin D and nocturnal enuresis in five- to seven-year-old children

Background

Vitamin D has been recognized to contribute to various physiological processes. However, no study has investigated serum 25-hydroxyvitamin D [25(OH)D] concentrations in children with nocturnal enuresis (NE) in the English literature.

Objective

In the present study, serum 25(OH)D concentrations were measured in five- to seven-year-old children with NE and compared with those in non-enuretic children to investigate whether there was any relationship between 25(OH)D and NE as the first time in the literature.

Design

Two hundred forty-seven five- to seven-year-old children were recruited from Taizhou, Zhejiang Province, China. Serum 25(OH)D concentrations were measured, and the structured questionnaire was administered to the parents of all children. Low 25(OH)D was defined as serum 25(OH)D concentrations below 20 ng/ml.

Results

The prevalence of NE was 7.3% in the group of children with 25(OH)D concentrations that exceeded 20 ng/ml; this prevalence was much lower than the 17.5% observed in the group of children with 25(OH)D concentrations below 20 ng/ml (p<0.05). After adjusting for potential confounders, serum 25(OH)D (≥20 ng/ml) was significantly associated with NE and represented a protective factor against NE (OR = 0.31, 95%CI = 0.092, 1.0, P<0.05). A nonlinear relationship between 25(OH)D and NE was observed. The prevalence of NE decreased with increasing 25(OH)D concentrations above 19 ng/ml. Additionally, children exhibiting higher frequencies of bedwetting had lower 25(OH)D concentrations [5–7 times/week: 18.3±4.8; 2–4 times/week: 20.9±4.1; 0–1 times/week: 23.6±6.4 (ng/ml), P<0.05)].

Conclusions

Low 25(OH)D was associated with an increased risk of NE in children aged five to seven years.

Dietary vitamin D inadequacy accelerates calcification and osteoblast-like cell formation in the vascular system of LDL receptor knockout and wild-type mice

Vitamin D insufficiency is highly associated with cardiovascular morbidity and mortality. We have demonstrated enhanced vascular calcification in LDL receptor knockout (LDLR(-/-)) mice fed a diet low in vitamin D. This study aimed to investigate the impact of a diet low in vitamin D on vascular calcification in wild-type (WT) mice lacking atherosclerotic plaques and the effects of a persistent and discontinuous vitamin D insufficiency on atherosclerotic plaque composition in LDLR(-/-) mice. The study was performed with 4-wk-old male WT and LDLR(-/-) mice that were fed a normal calcium/phosphate Western diet (210 g/kg fat, 1.5 g/kg cholesterol) containing either adequate (+D; 1000 IU/kg) or low (-D; 50 IU/kg) amounts of vitamin D-3 for 16 wk. Four groups of LDLR(-/-) mice received 1 of the 2 diets for additional 16 wk (total 32 wk) and were compared with mice fed the diets for only 16 wk. WT and LDLR(-/-) mice that were fed the -D diet for 16 wk tended to develop more calcified spots in the aortic valve than mice fed the +D diet (+50% and +56%, respectively; P < 0.10). In LDLR(-/-) mice, the extent of calcification increased from week 16 to week 32 and was higher in the -D than in the +D group (P < 0.05). The calcification, owing to the -D diet, was accompanied by highly expressed osteoblast differentiation factors, indicating a transdifferentiation of vascular cells to osteoblast-like cells. Feeding the +D diet subsequent to the -D diet reduced the vascular calcification (P < 0.05). LDLR(-/-) mice fed the -D diet for 32 wk had higher plaque lipid depositions (+48%, P < 0.05) and a higher expression of cluster of differentiation 68 (+31%, P < 0.05) and tumor necrosis factor α (+134%, P < 0.001) than the +D group. Collectively, the findings imply low vitamin D status as a causal factor for vascular calcification and atherosclerosis.

Plasma 25-hydroxyvitamin D and its genetic determinants in relation to incident myocardial infarction and stroke in the European prospective investigation into cancer and nutrition (EPIC)-Germany study

Circulating 25-hydroxyvitamin D (25(OH)D) has been associated with cardiovascular disease (CVD) risk in observational studies. Also, SNPs to explain variation in 25(OH)D have been identified by genome-wide association studies. Detection of direct associations between SNPs that significantly affect 25(OH)D and CVD risk would indicate a causal role of vitamin D, as reverse causation could be excluded and confounding could be better controlled. Thus, a combined analysis of candidate SNPs in relation to circulating 25(OH)D and CVD risk was carried out. A case-cohort study within the EPIC-Germany study was conducted comprising a randomly drawn subcohort of 2,132 subjects (57.9% women, mean age: 50.6 years) and incident cases of myocardial infarction (n=559) and stroke (n=471) that occurred during a mean follow-up duration of 7.6 years. 25(OH)D concentrations were measured by LC-MS/MS in baseline plasma samples. Additionally, eight candidate SNPs were assayed. Associations between 25(OH)D, SNPs and the risks of myocardial infarction and stroke were assessed by multivariable regression analyses. Mean 25(OH)D level was 47.2 nmol/L in the subcohort. Four SNPs were associated with 25(OH)D (p<0.05). In subjects with 25(OH)D levels <25 nmol/L, the risks of CVD as composite endpoint (Hazard Ratio: 1.53, 95% confidence interval: 1.12–2.09), myocardial infarction, and stroke were significantly increased compared to subjects with levels ≥50 nmol/L, while no significant linear associations were observed. A SNP score was not related to the risks of total CVD (Hazard Ratio: 1.0, 95% confidence interval: 0.71–1.42), myocardial infarction, or stroke. The same was true concerning single SNPs. Given the lack of association between SNPs and the risks of stroke and myocardial infarction, the present findings do not point to a major causal role of vitamin D in the development of these diseases. However, a detection of modest associations between genetic markers and CVD risk in larger consortia cannot be ruled out.

Vitamin D levels for preventing acute coronary syndrome and mortality: evidence of a nonlinear association

CONTEXT

Low serum calcidiol has been associated with multiple comorbidities and mortality but no "safe" range has been found for the upper concentration.

OBJECTIVE

We aim to establish the upper threshold of serum calcidiol, beyond which there is an increased risk for acute coronary syndrome and/or mortality.

DESIGN, SETTING, AND PARTICIPANTS

We extracted data for 1,282,822 Clalit Health Services members aged >45 between July 2007 and December 2011. Records of mortality or acute coronary syndrome were extracted during the follow-up period. Kaplan-Meier analysis calculated time to episode and Cox regression models generated adjusted hazard ratios for episode by calcidiol group (<10, 10.1-20, 20.1-36, and >36.1 ng/mL).

OUTCOME MEASURES

Acute coronary syndrome subsuming all-cause mortality.

RESULTS

During the 54-month study period, 422,822 Clalit Health Services members were tested for calcidiol, of which 12,280 died of any cause (905 with acute coronary syndrome) and 3933 were diagnosed with acute coronary syndrome. Compared to those with 20-36 ng/mL, the adjusted hazard ratios among those with levels of <10, 10-20, and >36 ng/mL were 1.88 (confidence interval [CI]: 1.80-1.96), 1.25 (CI: 1.21-1.30), and 1.13 (CI: 1.04-1.22) (P < .05), respectively.

LIMITATIONS

The study cohort comprised only 30% of the population, those tested for vitamin D. The small sample size of those with calcidiol >36 ng/mL prevented further analysis of this group.

CONCLUSIONS

Vitamin D in the 20-36 ng/mL range was associated with the lowest risk for mortality and morbidity. The hazard ratio below and above this range increases significantly.

Dietary fats and other nutrients on stroke

PURPOSE OF REVIEW

This review summarizes current epidemiologic evidence regarding the associations of dietary fat and other nutrients with risk of stroke.

RECENT FINDINGS

Recent epidemiologic studies show no association of total fat intake or absolute intakes of saturated, monounsaturated, or polyunsaturated fat with risk of stroke. Data on long-chain omega-3 polyunsaturated fatty acids in relation to stroke risk are inconclusive but may favor fewer strokes in women. Insufficient evidence exists for trans fatty acids, other fatty acids, and dietary cholesterol intake. Present evidence indicates that high dietary magnesium and potassium intakes may lower the risk of stroke, whereas a high sodium (salt) intake and a low dietary vitamin D intake likely increase stroke risk. Calcium does not prevent stroke in populations with moderate-to-high calcium intakes but might play a role in populations with low calcium intakes. Supplementation with single vitamins likely has no protective effect on stroke in well nourished populations.

SUMMARY

Available epidemiologic evidence indicates that diets high in magnesium and potassium may play a role in the prevention of stroke, whereas a high sodium intake is a risk factor. It remains unclear whether specific fatty acids, dietary cholesterol, and combinations of vitamins affect the risk of stroke.