Vitamin D and Dyslipidemia: Is There Really a Link? A Narrative Review

Nowadays, the interest in the extraskeletal effects of vitamin D is growing. In the literature, its several possible actions have been confirmed. Vitamin D seems to have a regulatory role in many different fields—inflammation, immunity, and the endocrine system—and many studies would demonstrate a possible correlation between vitamin D and cardiovascular disease. In this paper, we deepened the relationship between vitamin D and dyslipidemia by reviewing the available literature. The results are not entirely clear-cut: on the one hand, numerous observational studies suggest a link between higher serum vitamin D levels and a beneficial lipid profile, while on the other hand, interventional studies do not demonstrate a significant effect. Understanding the possible relationship between vitamin D and dyslipidemia may represent a turning point: another link between vitamin D and the cardiovascular system.


Introduction
Dyslipidemia is an imbalance of lipids such as total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), triglycerides (TGs), and high-density lipoprotein (HDL-C).It is a pathological condition found all around the world.Dyslipidemia is also a fundamental and modifiable cardiovascular risk factor.Genetic and environmental factors (obesity, incorrect diet, smoking) are both involved.Excessive cholesterol poses a risk, but it is essential in appropriate amounts for the human body; in fact, it maintains the integrity and fluidity of cell membranes and represents the precursor of hormones and bile acids.
Vitamin D undergoes an initial conversion to 25-hydroxyvitamin D (25OHD) in the liver, followed by a subsequent transformation into its active form, 1,25-dihydroxyvitamin D, or calcitriol, primarily occurring in the kidneys and various tissues.The synthesis of 1,25-dihydroxyvitamin D in the kidneys is regulated by levels of parathyroid hormone, as well as concentrations of calcium and phosphorus in the bloodstream.Vitamin D3, also referred to as cholecalciferol, shares structural similarities with steroids and is generated in the skin upon exposure to ultraviolet light from the sun.Circulating 25(OH)D is the most dependable indicator of vitamin D status in humans, reflecting dietary intake, supplements, and the skin synthesis of vitamin D.Moreover, 25OHD's functions do not stop only at the bone but involve the inflammatory, immune, and endocrine systems.Vitamin D deficiency is very common across numerous regions globally.In a recent study, the association between vitamin D deficiency and cardiovascular disease has been described [1].
How can vitamin D affect cholesterol levels?Actually, this is not entirely clear.Vitamin D and cholesterol share similarities in their biosynthesis processes: cholecalciferol is synthesized in the skin by UV-B irradiation from 7-dehydrocholesterol (7DHC); 7DHC is also converted to cholesterol by the action of the enzyme 7-Dehydrocholesterol reductase (DHCR7) [2].Zou and Porter [3] demonstrated in vitro that increased levels of cholecalciferol lead to a rapid decrease in DHCR7 activity and result in a lipid decrease.This represents a fundamental connection between lipids and vitamin D (Figure 1).However, the relationship between vitamin D and lipids has deep-seated roots, extending to the genetic level.Below, we summarize the mechanisms that link vitamin D and lipids.
How can vitamin D affect cholesterol levels?Actually, this is not entirely clear.Vitamin D and cholesterol share similarities in their biosynthesis processes: cholecalciferol is synthesized in the skin by UV-B irradiation from 7-dehydrocholesterol (7DHC); 7DHC is also converted to cholesterol by the action of the enzyme 7-Dehydrocholesterol reductase (DHCR7) [2].Zou and Porter [3] demonstrated in vitro that increased levels of cholecalciferol lead to a rapid decrease in DHCR7 activity and result in a lipid decrease.This represents a fundamental connection between lipids and vitamin D (Figure 1).However, the relationship between vitamin D and lipids has deep-seated roots, extending to the genetic level.Below, we summarize the mechanisms that link vitamin D and lipids.

Genetic Mechanisms
Vitamin D is involved in lipid metabolism through genetic mechanisms mediated by the vitamin D receptor (VDR).The VDR gene is located on chromosome 12 (q11-q13).Several studies have shown that, in some populations, certain VDR polymorphisms are associated with higher levels of triglycerides and cholesterol [4][5][6].Jia et al. [7] investigated the association between VDR polymorphism and dyslipidemia in a large Chinese population.Their work suggests that the presence of VDR rs2228570 polymorphism correlates with an increased risk of higher LDL-C and lower serum 25OHD levels in the study population.Additionally, it has been also proposed that VDR determines cholesterol levels by regulating the synthesis of bile acids at the genetic level: VDR inhibits liver

Genetic Mechanisms
Vitamin D is involved in lipid metabolism through genetic mechanisms mediated by the vitamin D receptor (VDR).The VDR gene is located on chromosome 12 (q11-q13).Several studies have shown that, in some populations, certain VDR polymorphisms are associated with higher levels of triglycerides and cholesterol [4][5][6].Jia et al. [7] investigated the association between VDR polymorphism and dyslipidemia in a large Chinese population.Their work suggests that the presence of VDR rs2228570 polymorphism correlates with an increased risk of higher LDL-C and lower serum 25OHD levels in the study population.Additionally, it has been also proposed that VDR determines cholesterol levels by regulating the synthesis of bile acids at the genetic level: VDR inhibits liver X receptor alpha (LXR-alpha) signaling, thereby regulating bile acid and cholesterol homeostasis [8,9].Li et al. demonstrated another important link between vitamin D and cholesterol trough VDR.Vitamin D deficiency reduces the transcriptional activity of VDR, leading to a down-regulation of insulin-induced gene-2 (Insig-2) expression and, consequently, the activation of its inhibitory effect on sterol regulatory element-binding protein 2 (SREBP-2).This cascade ultimately leads to an increase in 3-hydroxy-3-methylglutaryl-coenzyme A reductase expression, culminating in elevated cholesterol production [10].

Non-Genetic Mechanisms
There are also non-genetic mechanisms that link vitamin D and lipids (Figure 1).One of the main functions of vitamin D is to regulate calcium metabolism.Through this action, vitamin D interferes with lipid production in the following ways: (1) Increasing intestinal calcium absorption may play a role in modulating microsomal triglyceride transfer protein (MTP), thereby reducing the synthesis and secretion of triglycerides [11].(2) Increasing intestinal calcium levels reduces the intestinal absorption of fatty acids due to the formation of insoluble calcium-fat complexes.(3) Calcium may promote the conversion of cholesterol into bile acids, resulting in decreased cholesterol levels.(4) 25OHD regulates PTH; a previous paper on rats demonstrated that hyperparathyroidism is associated with increased triglycerides.Therefore, 25-OH-vitamin D (25OHD), by regulating PTH, could regulate triglyceride values [12].( 5) Hypovitaminosis D could affect beta cell function and insulin resistance, thereby influencing lipoprotein metabolism and resulting in increased triglyceride levels and reduced HDL-C levels [13].(6) Hypovitaminosis D is also associated with the pro-inflammatory state: inflammation, lipid metabolism, and atherosclerosis interact closely with each other [14].(7) Finally, calcitriol (1,25(OH)D) seems to arrest cholesterol uptake by macrophages, thus suppressing foam cell formation, which is involved in atherosclerosis [15].
In this narrative review, we aim to delve deeper into the relationship between vitamin D and lipids to understand their potential link by analyzing observational and interventional studies.

Materials and Methods
A literature review was conducted from inception to July 2023.The PubMed/Medline, Cochrane Library, ClinicalTrials.gov,and SCOPUS databases were searched using the following search terms: "dyslipidemia" or "cholesterol" or "lipids" or "triglyceride" AND "vitamin D".The process of selecting the studies for review in adherence to the PRISMA 2020 process is shown in Figure 2.

Observational Studies
On this topic, it is possible to find observational and interventional studies.First, we began by analyzing observational studies.However, it is worth noting that interest in this

Observational Studies
On this topic, it is possible to find observational and interventional studies.First, we began by analyzing observational studies.However, it is worth noting that interest in this topic is not recent.One of the earliest papers in 1992 was a Belgian study conducted on a group of 358 subjects.In this study, a blood sample was performed for the determination of total serum calcium, 25OHD, TC, HDL-C, apolipoprotein A-I (apoA1), apolipoprotein B (apoB), and total protein.The study determined the existence of a significant positive relation between serum 25OHD and both HDL-C and apo A-I [16].It is well known that high HDL-C has a protective effect, unlike LDL-C and TGs.Cross-sectional studies with very large populations have reported an inversely significant correlation between the values of 25OHD, TGs, and LDL-C and a positive correlation with HDL-C, as reported by Aumerx et al. [16].Similarly, Jiang too in 2018, in a cross-sectional study carried out on 3788 subjects, found an inversely significant correlation between 25OHD, TGs, and LDL-C, while there was a positive correlation with HDL-C [17].These results further underline the possible protective role of vitamin D in reducing cardiovascular risk.Other studies confirmed the inverse correlation between 25OHD and TG or LDL-C serum levels [18][19][20].In 2007, Botella-Carretero led a transversal observational study on 73 patients with morbid obesity.Anthropometric variables, 25OHD, lipid profiles (TC, HDL-C, LDL-C, TGs), glucose and insulin levels, and insulin resistance were measured for each patient.Vitamin D deficiency was present in 37 of 73 patients (50.7%) and was more prevalent in morbidly obese patients with metabolic syndrome.HDL-C was lower and TGs were higher in the hypovitaminosis D group [21].Similar positive associations have been observed in numerous other studies conducted across various populations [22][23][24][25][26][27][28][29][30][31][32].A recent cross-sectional study confirmed that the percentage of individuals with dyslipidemia and dysglycemia was higher in subjects with low levels of vitamin D [33].Results from some studies suggested a possible correlation with gender.In a study by Wang et al. [34], vitamin D deficiency seemed to be associated with an increased risk of dyslipidemia more in men than in women.However, in a more recent paper by AlQuaiz et al., it was observed that hypovitaminosis D was associated with lower HDL-C levels in men and higher TG levels in women [35].Many authors studied vitamin D and lipid profiles in young adults and children; also in these groups, vitamin D deficiency seemed to be associated with an increased risk of dyslipidemia [36][37][38][39][40][41][42][43][44][45].A study by Al-Ajlan et al. analyzed the relationship between vitamin D and lipids in Saudi pregnant women, who had higher incidence of obesity, diabetes, and cardiovascular disease during the course of pregnancy.Surprisingly, serum vitamin D levels positively correlated with serum levels of TC and TGs [46].Conversely, a prospective study carried out on a large cohort of Brazilian women reported that low 25OHD concentrations during early pregnancy were associated with higher TC, LDL-C, and TC/HDL-C ratios throughout pregnancy [47].This correlation was recently confirmed in a study carried out on 2479 pregnant Chinese women in the second trimester.Serum 25OHD levels were inversely associated with TC, TG, HDL-C, LDL-C, and hs-CRP levels, suggesting that higher levels of vitamin D during pregnancy may improve lipid levels and inhibit the rise of hs-CRP [48].
The effect of vitamin D on lipid profile has also been studied in subpopulations with higher cardiovascular risk, such as patients with type 2 diabetes mellitus (T2DM), finding significant correlations [49][50][51][52].Insulin resistance has effects on lipids [53]; therefore, vitamin D, having a regulatory role on insulin resistance [54], could also act on lipids in diabetic patients through this mechanism.
A meta-analysis conducted by Jafari et al. aimed to clarify the effect of vitamin D on serum TC, TGs, LDL-C, and HDL-C in T2DM patients; 17 studies comparing an intervention group (which received vitamin D) with a control group (which received a placebo) were enrolled in the study.The meta-analysis demonstrated that vitamin D improved serum levels of TC, TGs, and LDL-C in patients with T2DM, although changes in serum HDL-C levels were not significant [55].
One of the most influential studies on vitamin D and lipids was conducted by Ponda et al. in 2012 [56].In this study, 4.06 million laboratory test results from September 2009 to February 2011 were analyzed.The study was both a cross-sectional study and a retrospective cohort analysis.While vitamin D deficiency was associated with an unfavorable lipid profile in cross-sectional analyses, replenishing vitamin D deficiency up to normal levels did not change lipid concentrations.Thus, although observational studies suggest that vitamin D deficiency impacts lipoprotein levels, Ponda's study reported that this effect was not confirmed in interventional studies.Table 1 describes the main characteristics of observational studies.

Interventional Studies
In addition to observational studies on the link between vitamin D and lipids, several interventional studies on this topic are available in the literature.One of the earliest studies dates back to 1970 by Carlson et al., who examined the effect of vitamin D supplementation for 6 weeks on lipid profiles.The study concluded that replenishing vitamin D had no impact on lipid concentrations [57].Yousefi Rad carried out a study on 58 diabetic patients, where for 2 months, 28 subjects received 100 micrograms (4000 IU) of vitamin D while 30 subjects received a placebo.HDL-C levels increased significantly in both groups; no difference was observed in the replenishment group [58].A double-blind randomized placebo-controlled trial on 70 diabetic patients, who received vitamin D or a placebo for 12 weeks, showed a significant reduction in TC, LDL-C, and TGs, in both groups.HDL-C level decreased significantly only in the placebo group; however, the variables did not all achieve statistical significance [59].Moreover, numerous studies over time have shown that there is no change in TC, LDL-C, HDL-C, and TGs after treatment with different doses of vitamin D .A prospective, randomized, open-label trial carried out on healthy Indian men compared the effect of increased sunlight exposure versus vitamin D supplementation on 25OHD status and lipid profile in subjects with vitamin D deficiency.In the sunlight exposure group, an increase in vitamin D levels significantly reduced TC, LDL-C, and HDL-C concentrations, while in the cholecalciferol supplementation group, TC and HDL-C levels increased [91].However, these data are not unique.In fact, there are also studies which have demonstrated that vitamin D supplementation can have effects on lipids.This is the case of the paper of Farag et al. [92], in which daily vitamin D supplementation for 12 weeks associated with moderate physical activity led to a significant reduction in lipid profile in patients with metabolic syndrome.In the paper of Salekzamani [93], vitamin D replenishment seemed to have positive effects only on TGs.Also, Asemi et al. demonstrated a significant decrease in TGs and VLDL-C in a population who received calcium and vitamin D [94].This reduction in TG levels was also observed in other studies [95][96][97][98][99][100].
In the study by Imga et al., carried out on 122 overweight or obese women who underwent to vitamin D replenishment, it was concluded that vitamin D supplementation led to an improvement in HOMA-IR and LDL-C values [101].The same results were demonstrated in a group of 120 adult Saudi patients with controlled T2DM who received 2000 IU of vitamin D daily for 18 months.The vitamin D replenishment brought about an improved lipid profile (a decrease in LDL-C and TC) and an improvement in HOMA-β function [102].Shab-Bidar et al., in a study carried out into T2DM, found a decrease in LDL-C and TC along with a significative increase in HDL-C after vitamin D supplementation [103].Replenishment with vitamin D was also associated with decreased TC in a T2DM Spanish study [104].A recent study by Sacheck JM et al. found that replenishment with vitamin D had positive effects on HDL-C, LDL-C, and TC [105] in young people.Significant improvements in serum HDL-C in a vitamin D group was also found by Liyanage [106] in subjects with T2DM and early-stage nephropathy.An Iranian randomized controlled trial carried out on 168 subjects with prediabetes showed significantly increased HDL-C levels in the co-supplementation group (with omega 3 and vitamin D) compared to the other three groups (placebo group, only omega 3 group, only vitamin D group) [107].
Samimi et al. carried out a double-blind, placebo-controlled trial on 60 women at risk for pre-eclampsia from 20 to 30 weeks of gestation; in particular, 30 women received 50,000 IU of cholecalciferol every 2 weeks plus 1000 mg of calcium per day, and 30 women received a placebo [108].The study demonstrated that vitamin D plus calcium administration for 12 weeks had beneficial effects on HDL-C, glycemic status, and blood pressure among women at risk for pre-eclampsia.In 2018, Riek et al. studied the potential role of vitamin D in cardiovascular risk in diabetic patients, with very interesting results [109].This study was based on the fact that vitamin D and its metabolites have effects on atherogenesis, acting on macrophages and peripheral blood monocytes in patients with diabetes [110].Riek randomized 26 diabetic patients to receive either vitamin D at a dosage of 4000 IU/day or a placebo for 4 months.Monocytes of the patients were isolated; in 2TDM patients who received vitamin D, levels of oxidized LDL uptake in cultured monocytes had a reduction >50%.These data would support the positive effect of vitamin D on atherosclerosis and lipid carriers [110].Moreover, in a group of 181 subjects with mild cognitive impairment, a replenishment for 12 months with 400 UI/day of vitamin D showed decreased levels of TC, TGs, and LDL-C as well as increased HDL-C [111].In a very recent interventional study, the correction of vitamin D deficiency in Arab adults seemed to improve their 10-year risk of atherosclerotic cardiovascular disease (ASCVD).This result is very interesting; once optimal vitamin D levels were achieved, there was a modest improvement in glucose and HDL-C levels, resulting in a decrease in ASCVD risk scores [112].However, a study by Schwetz et al. demonstrated that vitamin D supplementation significantly increased TC, TGs, VLDL-C, LDL-C, HDL-C, ApoB, and ApoB, indicating a negative effect on lipid profile [113].An increase in LDL-C levels after replenishment was observed also by Zittermann in 2009 [114].The non-univocal interpretation of the results on the relationship between vitamin D and lipids is evident in the studies of Jorde.In a cross-sectional study from 2010 carried out on 1762 nonsmoking and 397 smoking subjects, Jorde [115] found a significative decrease in TGs with an increase in vitamin D. In the same year, Jorde randomized 438 overweight or obese subjects to receive (a) 40,000 IU of vitamin D weekly, (b) 20,000 IU of vitamin D weekly, or (c) a placebo for one year; the result was that replenishment with vitamin D had no effect on serum lipid levels.In 2016, in a randomized placebo-controlled trial conducted on 511 subjects with prediabetes, Jorde also found a significant decrease in LDL-C in the vitamin D supplementation group [116].Moreover, the most recent papers show conflicting results on the effect of vitamin D supplementation on dyslipidemia [117][118][119].Table 2 describes the main characteristics of interventional studies.
In Figure 3, we report the number of studies presenting responses to treatment with vitamin D.
Nutrients 2024, 16, x FOR PEER REVIEW 7 of 37 studies of Jorde.In a cross-sectional study from 2010 carried out on 1762 nonsmoking and 397 smoking subjects, Jorde [115] found a significative decrease in TGs with an increase in vitamin D. In the same year, Jorde randomized 438 overweight or obese subjects to receive (a) 40,000 IU of vitamin D weekly, (b) 20,000 IU of vitamin D weekly, or (c) a placebo for one year; the result was that replenishment with vitamin D had no effect on serum lipid levels.In 2016, in a randomized placebo-controlled trial conducted on 511 subjects with prediabetes, Jorde also found a significant decrease in LDL-C in the vitamin D supplementation group [116].Moreover, the most recent papers show conflicting results on the effect of vitamin D supplementation on dyslipidemia [117][118][119].Table 2 describes the main characteristics of interventional studies.
In Figure 3, we report the number of studies presenting responses to treatment with vitamin D. Out of the 64 interventional studies examined, 35 (55%) indicated no significant effects on lipid profiles following vitamin D supplementation, whereas 29 (45%) demonstrated a significant alteration in lipid profile.Taking into consideration the studies carried out on patients with T2DM, we have observed that treatment with vitamin D gave positive answers in a greater number of studies (57%).Also, in the group of studies Out of the 64 interventional studies examined, 35 (55%) indicated no significant effects on lipid profiles following vitamin D supplementation, whereas 29 (45%) demonstrated a significant alteration in lipid profile.Taking into consideration the studies carried out on patients with T2DM, we have observed that treatment with vitamin D gave positive answers in a greater number of studies (57%).Also, in the group of studies conducted in patients with metabolic syndrome or who were overweight/obese, it was found that the number of studies with positive results was slightly higher than those with negative results.On the other hand, in studies conducted on healthy subjects, the response rate was markedly lower.
In Figure 4 we reported the effect of Vitamin D supplementation on lipid profile in different categories of patients.
With regard to the effect on individual classes of the lipid profile, we observed that in patients with T2DM, the most frequent variation concerns TC and LDL-C, while in studies with MetS and overweight (OW) subjects, the effect on the reduction in TGs prevails.

Discussion
The relationship between vitamin D and cardiovascular risk is very popular today.In most studies, the conclusions are quite consistent: observational studies have shown inverse associations between vitamin D concentration and cardiovascular disease, but the same results are not always replicable in intervention studies.Considering these data, which unfortunately often accompany vitamin D studies, we conducted our analysis.
From the review of the literature on vitamin D and dyslipidemia, the same paradox clearly emerges: while observational studies give mostly unambiguous results and support an evident association between increased serum vitamin D levels and a favorable lipid profile, interventional studies show contrasting data or no effect.So, it would seem that hypovitaminosis D could predispose to dyslipidemia rather than replenishment leading to a significant improvement in lipid levels.Observational studies do not allow us to find a cause-and-effect link between vitamin D and dyslipidemia; however, from the consistent results, it would seem, as in many other fields, that vitamin D deficiency represents a risk marker-in this case, a possible marker of cardiovascular risk.Similarly, inconclusive results have been obtained in several studies involving vitamin D treatment for patients with diabetes [120] or COVID-19 infection [121].
The interventional studies we considered in our review exhibit significant heterogeneity regarding population characteristics (such as age and pathologies) as well as doses, methods of administration, and duration of vitamin D intervention.Nevertheless, upon analyzing these studies, it does not seem that age influenced the results.Surprisingly, positive effects of vitamin D supplementation on lipids were observed across various age groups, including adults (aged over 60) and younger patients, including children.
In most studies where vitamin D supplementation was administered to individuals with vitamin D deficiency, beneficial effects on lipid profiles were observed.Interestingly, the dosage of vitamin D supplementation does not appear to significantly impact these effects.However, there remains a critical gap in knowledge regarding the optimal dose of vitamin D for pleiotropic effects.Discrepancies in study outcomes may also stem from variations in the methods used to assess vitamin D levels; some studies employed validated schemes for assessment, while others did not specify their methods.This discrepancy represents a notable limitation.Indeed, intervention studies with meticulous vitamin D assessment tend to demonstrate positive effects on lipid profiles as a result of vitamin D supplementation.
Some of the most interesting data that emerge from this review show that supplementation with vitamin D is particularly effective in improving and the lipid profile in patients with T2DM, MetS, or OW.
Therefore, diabetic and metabolic patients would have a greater advantage, compared to healthy subjects, in the administration of vitamin D in terms of lipids.This positive effect of vitamin D on dyslipidemia in these patients could be explained by the action of vitamin D on improving insulin resistance (IR).Insulin resistance is an important metabolic component in metabolic syndrome, prediabetes, PCOS, and T2DM and is associated with risk of micro-and macrovascular complications.Insulin resistance is also involved in lipid metabolism, leading to atherogenic dyslipidemia; therefore, vitamin D, by improving IR, would probably have an indirect effect on lipids.Indirectly, also through the control of inflammation, vitamin D could lead to action on lipids.A recent review showed how the administration of vitamin D to patients with T2DM determines a significant reduction in inflammatory markers (CRP and IL-6), with a positive effect on the lipid profile [122].
Similar to other hormones, vitamin D supplementation is beneficial for individuals with deficiency but may not be necessary for everyone.This phenomenon is also evident in addressing bone fragility: while vitamin D supplementation significantly reduces fragility fractures in individuals who are deficient and at risk, administering high doses to healthy individuals does not show a significant effect in preventing such fractures.
Furthermore, the inconsistent outcomes of interventional studies might also stem from variations in dosage, frequency, or duration of vitamin D supplementation.Also, other variables could influence the results of interventional studies, such as physical activity, obesity, VDR polymorphisms, or the heterogeneity of populations.Let us not forget that vitamin D is partly taken with food; this component was not considered in interventional works.Furthermore, cholesterol also depends on diet as well as physical activity.So, in order to carry out more truthful studies, all of these components should be taken into consideration, as they could influence the results of interventional studies.

Conclusions
The prospect of vitamin D supplementation contributing to the improvement of lipid parameters and reducing cardiovascular risk is truly fascinating.Vitamin D is readily available and generally without side effects when taken in recommended doses.The possibility that its replenishment could play a role in cardiovascular risk is very intriguing and warrants further analysis.
Currently, data in the literature confirm that, at the molecular level, there is a close link between lipid metabolism and vitamin D; numerous observational studies suggest a possible association between vitamin D and serum lipid levels, but the data do not appear to be completely confirmed in interventional studies.However, it was certainly interesting to observe how, in interventional studies on metabolic and diabetic patients, the effects of vitamin D replenishment were positive on lipids.
In the future, this relationship should be further explored in large, well-designed, randomized controlled trials (RCTs).The results of such studies could be truly surprising and could help us better understand the role of vitamin D in cardiovascular prevention.

Figure 1 .
Figure 1.Mechanisms involved in the relationship between vitamin D and dyslipidemia.

Figure 1 .
Figure 1.Mechanisms involved in the relationship between vitamin D and dyslipidemia.

Nutrients 2024 , 37 Figure 2 .
Figure 2. Flow chart of the studies identified and included in this review.

Figure 2 .
Figure 2. Flow chart of the studies identified and included in this review.

Figure 3 .
Figure 3.The effect of vitamin D supplementation on lipid profiles in interventional studies.

Figure 3 .
Figure 3.The effect of vitamin D supplementation on lipid profiles in interventional studies.

Figure 4 .
Figure 4.The effect of Vitamin D supplementation on lipid profile in different categories of patients.

Figure 4 .
Figure 4.The effect of Vitamin D supplementation on lipid profile in different categories of patients.

Table 1 .
Main characteristics of observational studies.

Table 2 .
Main characteristics of the interventional studies.