Vitamin D and the cardiovascular system: an overview of the recent literature

Native vitamin D in CKD and renal transplantation: meaning and rationale for its supplementation

Chronic kidney disease (CKD) poses a significant epidemiological challenge, necessitating effective patient management strategies. Nutritional intervention, particularly vitamin D supplementation, has garnered attention for its potential therapeutic utility in CKD. Despite widespread acknowledgment of the importance of vitamin D, particularly in bone and mineral metabolism, its supplementation in CKD patients for non-skeletal purposes remains contentious due to limited evidence. Hypovitaminosis D linked with CKD substantially contributes to disturbances in mineral and bone metabolism, increasing the risks of cardiovascular complications and skeletal disorders. Notably, CKD patients experience progressive vitamin D deficiency, exacerbating as the disease progresses. Guidelines recommend monitoring 25-hydroxyvitamin D (25 (OH)-D) levels due to their correlation with mineral metabolism parameters, although robust evidence for recommending supplementation is lacking. The primary aim of this paper is to focus on the main open questions regarding vitamin D supplementation in CKD, reporting the current evidence concerning the role of vitamin D supplementation in CKD and in renal transplant recipients.

Seasonal changes in free 25-(OH)D and vitamin D metabolite ratios and their relationship with psychophysical stress markers in male professional football players

Introduction: Novel markers of vitamin D status are currently being investigated, including free 25-(OH)D (25-(OH)DF) and the vitamin D metabolite ratio (24,25-(OH)2D3:25-(OH)D3; VMR). The VMR may provide additional functional information on vitamin D metabolism in athletes. Therefore, the main objective of the current study was to evaluate 25-(OH)DF, bioavailable 25-(OH)D (25-(OH)DB), VMR, and psychophysical stress markers during different training periods over a half-season. The second aim was to assess the association between vitamin D binding protein (VDBP), total and free 25-(OH)D, VMRs, and psychophysical stress markers in professional football players. Moreover, we examined the relationship between 25-(OH)D3 and vitamin D metabolites (24,25-(OH)2D3, 3-epi-25-(OH)D3) to determine if training loads in different training periods influenced the vitamin D metabolome. Methods: Twenty professional football players were tested at six different time points across half a year (V1-June; V2-July; V3-August; V4-October; V5-December; V6-January). Results: Analyses indicated a significant seasonal rhythm for VDBP, and total 25-(OH)D (25-(OH)DT), 25-(OH)DB, 24,25-(OH)2D3, 3-epi-25-(OH)D3, 25-(OH)D3:24,25-(OH)2D3, and 24,25-(OH)2D3:25-(OH)D3 VMRs throughout the training period. No correlation was detected between 25-(OH)DT, 25-(OH)DB, 25-(OH)DF, vitamin D metabolites, VMRs, VDBP, and ferritin, liver enzymes (aspartate transaminase [AST] and alanine transaminase [ALT]), creatine kinase (CK), cortisol, testosterone, and testosterone-to-cortisol ratio (T/C) in each period (V1-V6). However, there was a strong statistically significant correlation between 25-(OH)D3 and 24,25-(OH)D3 in each training period. Conclusion: In conclusion, a seasonal rhythm was present for VDBP, 25-(OH)DT, 25-(OH)DB, vitamin D metabolites (24,25-(OH)2D3, 3-epi-25-(OH)D3), and VMRs (25-(OH)D3:24,25-(OH)2D3, 25-(OH)D3:3-epi-25-(OH)D3). However, no rhythm was detected for 25-(OH)DF and markers of psychophysical stress (ferritin, liver enzymes, CK, testosterone, cortisol, and T/C ratio). Moreover, the relationships between free and total 25-(OH)D with psychophysical stress markers did not demonstrate the superiority of free over total measurements. Furthermore, training loads in different training periods did not affect resting vitamin D metabolite concentrations in football players.

Metabolism of vitamin D is not affected by sport activity

BACKGROUND

Higher levels of physical activity are related to higher 25-(OH)D levels. Total 25-(OH)D (25-(OH)DT) are routinely used in clinical practice to assess vitamin D, however novel biomarkers are currently being investigated as free 25-(OH)D (25-(OH)DF) or vitamin D metabolite ratios (VMRs). The primary aim of our study was to assess 25-(OH)DF, vitamin D metabolites and VMRs in inactive men and athletes. A secondary aim was to check whether regular physical activity influence on vitamin D metabolome. A tertiary aim was to determine the relationship between 25-(OH)DT, 25-(OH)DF, vitamin D binding protein (VDBP), vitamin D metabolites and VMRs in this cohort.

METHODS

A total of 69 participants (27 inactive men, 18 indoor and 24 outdoor athletes) participated in the study. Vitamin D metabolites (25-(OH)DT, 24,25-(OH)2D3, 3-epi-25-(OH)D3, and 1,25-(OH)2D) were assessed using LC-MS/MS. The 25-(OH)DF concentration was calculated based on serum albumin and VDBP levels.

RESULTS

There were no differences in vitamin D metabolites and VMRs between inactive men and between the two groups of athletes. We showed a strong relationship between 25-(OH)DT, 25-(OH)DF and 24,25-(OH)D3, 3-epi-25(OH)D3, 24,25-(OH)2D3:25-(OH)D3 VMR in each group. Analysis showed that 25-(OH)DT, 25-(OH)DF inversely associated with 25-(OH)D3:24,25-(OH)2D3, 25-(OH)D3:3-epi-25-(OH)D3, 1,25-(OH)2D:24,25-(OH)2D3 ratios in inactive men and athletes (indoor and outdoor).

CONCLUSIONS

On the basis of our results, we concluded that regular long-term physical activity has no effect on the concentration of vitamin D metabolites at rest. Furthermore, free vitamin D does not correlate more strongly with vitamin D metabolites and VMRs compared to total.

Vitamin D and Calcium Supplementation and Urolithiasis: A Controversial and Multifaceted Relationship

Patients with urolithiasis, and particularly those with hypercalciuria, frequently have a marked reduction of bone mineral content up to the levels of osteoporosis, with a significant increase in bone fracture risk. For these reasons, the indication to prescribe vitamin D and/or calcium supplementations is very frequent in such patients. On the other hand, both calcium supplementation, and even more vitamin D therapy, can worsen the risk of developing urolithiasis by increasing calcium, phosphate, and oxalate urinary excretion. Despite the clinical and practical relevance of this issue, the evidence on this topic is scarce and contradictory. Therefore, some concerns exist about how and whether to prescribe such supplements to a patient with a history of kidney stones. In this narrative review, we resume some pivotal pathophysiological concepts strictly related to the dealt topic, and we draw some considerations and personal opinions on the pros and cons of such prescriptions. Finally, we share with the reader our pragmatic algorithm for handling the urolithiasis risk in patients who have strong indications to be prescribed vitamin D and calcium supplementations.

Correlation between Serum 25-Hydroxyvitamin D Level and Depression among Korean Women with Secondary Amenorrhea: A Cross-Sectional Observational Study

Vitamin D deficiency is considered a major public health problem worldwide and has been reported as having an association with depression. However, studies on the association between vitamin D deficiency and depressive symptoms in secondary amenorrhea (SA) patients are still scarce. This study examined the relationship between serum 25-hydroxyvitamin D (25(OH)D) levels and depressive symptoms among Korean women with SA. In this cross-sectional observational study, 78 patients with SA were initially recruited. Clinical and biochemical parameters, including serum 25(OH)D level, were measured. Data from 63 SA patients who met the study inclusion criteria and completed psychiatric assessments were finally analyzed. We analyzed their association with depression using a hierarchical regression model. The average serum 25(OH)D level was 34.40 ± 24.02 ng/mL, and 41.3% of the women with SA were vitamin D-deficient (<20 ng/mL). The total score of the Korean version of the Hamilton Depression Rating Scale (K-HDRS) was negatively related to serum 25(OH)D levels, free testosterone, and serum anti-Müllerian hormone (AMH) after adjusting for age and BMI (r = −0.450, p < 0.001; r = −0.258, p = 0.045; and r = −0.339, p = 0.006, respectively). Serum 25(OH)D levels and AMH levels were the most powerful predictors of depressive severity when using the K-HDRS in SA patients (β = −0.39, p < 0.005; β = −0.42, p < 0.005, respectively). This study showed that low serum 25(OH)D levels were associated with the severity of depressive symptoms in SA patients. This observation suggests that the evaluation of vitamin D deficiency for the risk of depression may be necessary in patients with SA.

Vitamin D and subclinical cardiac damage in a cohort of kidney transplanted patients: a retrospective observational study

In 178-kidney transplanted patients (KTxp), the prevalence of hypovitaminosis-D, the presence and novel development of left ventricular hypertrophy(LVH) and the correlations between native Vitamin-D (25OHD) and LVH were evaluated during the 1st year of transplantation (KTx). Clinical and instrumental data were recorded at pre-KTx and at one (T1) and 12 (T12) months after KTx. 25OHD levels were considered sufficient (s25OHD, ≥ 30 ng/dL) or insufficient (i25OHD, < 30 ng/dL). 25OHD correlated at T1 with parathormone(PTH), and at T12 with 25OHD-T1 and PTH-(T1,T12). At T12, s25OHD (15%) had higher 25OH and alkaline phosphatase (ALP), lower Ca, at T1, and lower PTH-(T1, T12) than i25OH-T12. At T1, KTxp with LVH (LVH-T1pos, 42%) were older and with longer dialysis vintage than LVH-T1neg. At T12, KTxp with LVH (LVH-T12pos, 53%) were older, with higher systolic blood pressure (SBP) at T12 than LVH-T12neg. No relation between 25OHD and LVH were found. Novel LVH was found in 14% of KTxp. They were older, had higher SBP-T12 and lower serum albumin-T12 than the others. LVH-modifications and 25OHD were not correlated. Hypovitaminosis-D is highly prevalent in KTxp. LVH correlates with different risk factors according to the time elapsed from KTx. However, during the 1st year of KTx, no relationship between LVH and 25OHD was observed.

Vitamin D supplementation and serum heat shock protein 60 levels in patients with coronary heart disease: a randomized clinical trial

BACKGROUND

The aim in this study was to investigate the effect of vitamin D (25(OH)D3) supplementation on heat shock protein 60 (HSP 60) and other inflammatory markers (IL-17, TNF-α, PAB) in patients with coronary heart disease (CHD).

METHODS

In this double-blind, randomized clinical trial, we recruited 80 male and female patients aged 30-60 with CHD and 25(OH)D3 serum levels < 30 ng/ml from Rasool-e-Akram Hospital in Tehran, Iran. Serum levels of HSP 60 as primary outcome, and 25(OH)D3, IL-17, TNF-α, PAB, lipid profiles and parathyroid hormone (PTH) as secondary outcomes were measured at baseline and post-intervention. We randomly assigned eligible participants to a placebo group (N = 40) or an intervention group (N = 40) (50,000 IU/wk. vitamin D supplement) for eight weeks.

RESULTS

The results demonstrated that vitamin D supplementation resulted in a significant increase in 25(OH) D3 serum levels in the intervention group compared to the placebo group (46.86 vs. 7.28 ng/ml). PTH levels decreased in the intervention group compared to the placebo group (- 19.81 vs. 2.92 pg/ml) after eight weeks of supplementation. Furthermore, we observed a significant change in waist circumference (- 0.97 vs. -0.26 cm), fat percentage (-.13 vs. 0.1%), systolic blood pressure (- 3.85 vs. -2.11 mmHg) and diastolic blood presure (- 4 vs. -1.86 mmHg) in the vitamin D group compared to the placebo group (all P values < 0.05). Other variables did not significantly change after the intervention.

CONCLUSION

Based on our findings, weekly vitamin D supplementation of 50,000 IU for eight weeks in patients with CHD resulted in decreased systolic and diastolic blood pressure, waist circumference and fat percentage. No significant effect on HSP 60, inflammatory markers or lipid profiles was observed.

TRIAL REGISTRATION

IRCT, IRCT201612122365N14. Registered 12 December 2016.

Clinical diagnostic tools for vitamin D assessment

Vitamin D deficiency has been implicated in a plethora of diseases including rheumatoid arthritis, Parkinson's disease, Alzheimer's disease, and osteoporosis. Deficiency of this vitamin is a global epidemic affecting both developing and developed nations. Within a clinical context, the qualitative and quantitative analysis of vitamin D is therefore vital. The main metabolic markers for assessing vitamin D status in humans are the hydroxylated forms of vitamin D, 25OHD₃ and 25OHD₂ on account of their long half-lives within the body and excellent stability. An adequate level for healthy individuals of these hydroxylated forms is estimated to be around 20-40ng/ml of blood. There are three main analytical techniques for determining the levels of 25OHD₃ and 25OHD₂. The first technique is immunoassay-based and can be performed in a rapid, high throughput, automated manner, allowing as many as 240 tests per hour with the duration of each assay as little as 18min. Furthermore, it offers excellent sensitivity with a detection range of 3.4-156ng/ml. A major downside of immunoassays is that they are unable to distinguish between the various forms of vitamin D. While HPLC is a highthroughput low cost instrument it is not a very sensitive technique and cannot quantify the down stream metabolites of vitamin D. The third technique, namely liquid chromatography-mass spectrometry (LC-MS/), provides excellent sensitivity with a wide dynamic range from 0.068pg/ml to 100ng/ml. Additionally, it offers a high level of separation and permits identification of vitamin D-related metabolites. However, a huge limitation with LC/MS/MS is their poor throughput for sample analyses. As yet, there is no analytical technique which combines the fine detection capabilities of LC/MS/MS and the rapid, automated format of immunoassay, for vitamin D analyses. Future attention therefore needs to be given to this area if the current clinical diagnostic tools for vitamin D analysis are to be further improved.

Nutritional Vitamin D in Renal Transplant Patients: Speculations and Reality

Reduced levels of nutritional vitamin D are commonly observed in most chronic kidney disease (CKD) patients and particularly in patients who have received a kidney transplant (KTx). In the complex clinical scenario characterizing the recipients of a renal graft, nutritional vitamin D deficiency has been put in relation not only to the changes of mineral and bone metabolism (MBM) after KTx, but also to most of the medical complications which burden KTx patients. In fact, referring to its alleged pleiotropic (non-MBM related) activities, vitamin D has been claimed to play some role in the occurrence of cardiovascular, metabolic, immunologic, neoplastic and infectious complications commonly observed in KTx recipients. Furthermore, low nutritional vitamin D levels have also been connected with graft dysfunction occurrence and progression. In this review, we will discuss the purported and the demonstrated effects of native vitamin D deficiency/insufficiency in most of the above mentioned fields, dealing separately with the MBM-related and the pleiotropic effects.

Role of Vitamin D deficiency in extraskeletal complications: predictor of health outcome or marker of health status?

The relationship of vitamin D with extraskeletal complications, such as cardiovascular disease, cancer, and autoimmune disease, is of major interest considering its roles in key biological processes and the worldwide high prevalence of vitamin D deficiency. However, the causal relationships between vitamin D and most extraskeletal complications are weak. Currently, a heated debate over vitamin D is being conducted according to two hypotheses. In this review, we first present the different arguments that suggest a major role of vitamin D in a very broad type of extraskeletal complications (hypothesis #1). We then present results from recent meta-analyses of randomized controlled trials indicating a lack of association of vitamin D with major extraskeletal complications (hypothesis #2). We discuss different issues (e.g., causality, confounding, reverse causation, misclassification, and Mendelian randomization) that contribute to the favoring of one hypothesis over the other. While ultimately only one hypothesis is correct, we anticipate that the results from the ongoing randomized controlled trials will be unlikely to reconcile the divided experts.

Effects of combined vitamin D--calcium supplements on the cardiovascular system: should we be cautious?

Despite the growing body of evidence on the potential effects of calcium and vitamin D as monotherapies on different cardiovascular (CV) parameters, the combined supplementation with calcium and vitamin D (CaD), which is most frequently encountered in clinical practice, has not received the attention it deserves. A literature search was conducted via EMBASE and Medline and identified 14 randomised controlled trials (RCTs) and 2 meta-analyses reporting on effects of combined supplementation with CaD on CV events, CV death, blood pressure, lipids, glucose metabolism and weight. Overall, the existing evidence does not support beneficial properties of supplementation with CaD on the CV system, nor does it suggest that a re-appraisal of the use of CaD is necessary due to adverse effects, although increased risk of CV events has been reported by some authors. The guidelines for the use of CaD supplementation need not change until well-conducted RCTs that have CV effects as primary outcomes and adjust for major confounders indicate otherwise.

Vitamin D status in chronic dialysis patients with depression: a prospective study

BACKGROUND

Depression is the most widely acknowledged psychological problem among end-stage renal disease (ESRD) patients. Depression may be associated with VD deficiency. The aims of this study are to (a) elucidate the prospective association between HsCRP, VD contents and depressive symptoms in the dialyzed population, and (b) find the effect of calcitriol supplementation on depression in dialyzed patients.

METHODS

In this prospective study, 484 dialysis patients (382 hemodialysis [HD] cases and 102 peritoneal dialysis [PD] cases; aged 18-60 years) from two hospitals in southeast China were included. The depression in these patients was evaluated using the Chinese version of Beck's Depression Inventory (BDI). All subjects answered the BDI-I questionnaire for assessment of depression levels in summer. A cut-off value of 16 was set to include dialysis patients with depression. All patients were divided into two groups depending on the absence (Group 1) or presence (Group 2) of depression. The two groups took 0.5 μg/day 1,25-Dihydroxyvitamin D orally for one year. BDI Scores were recalculated for all patients. Sociodemographic, clinical data, and serum VD contents were also collected.

RESULTS

A total of 484 participants (247 men [51.0%] and 237 women [49.0%]) were surveyed. Depressive symptoms were found in 213 (44.0%) patients. The baseline serum VD level (VD2 + VD3) was 17.6 ± 7.7 nmol/L. Patients with depressive symptoms have significantly higher serum HsCRP level and significantly lower serum VD level compared with the control group. After one-year follow-up, the supplementation of 0.5 μg/day calcitriol slightly improved the microinflammatory state such as lowering mean serum HsCRP level and improving serum VD level, but not in significantly enhancing the depressive symptoms.

CONCLUSIONS

Calcitriol supplementation did not significantly enhance the depressive symptoms in our dialyzed population although patients with low levels of serum VD were more depressed. Therefore, more prospective randomized controlled trials are necessary to reveal the exact cause-and-effect relationship between VD status and depressive symptoms or VD status related to some specific subtypes in dialyzed patients.