CPQ Nutrition (2020) 4:1Review Article
Deciphering Controversies About the Effect of Vitamin D in
Marina Ruxandra Otelea1*, Oana Sandulescu1,2 & Isabela Tarcomnicu2
1Clinical Department 2, University of Medicine and Pharmacy Carol Davila, Bucharest, Romania
2National Institute for Infectious Diseases “Prof. Dr. Matei Bals”, Bucharest, Romania
*Correspondence to: Dr. Marina Ruxandra Otelea, Clinical Department 2, University of Medicine and
Pharmacy Carol Davila, Bucharest, Romania.
Copyright © 2020 Dr. Marina Ruxandra Otelea et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Received: 17 January 2020
Published: 03 February 2020
Keywords: Vitamin D; Hepatitis B; Vitamin D Binding Protein; Vitamin D Receptor
Chronic infection with hepatitis B virus has a major public health impact. Current antiviral
therapy in chronic hepatitis B keeps the infection under control, but does not cure the disease;
therefore, different areas of research aiming to reduce the risk of progressive disease are open.
Despite numerous experimental data showing a benefit from vitamin D supplementation, clinical
studies do not consistently support this finding. This review covers the possible explanations for
these controversies, highlighting the complexity of vitamin D metabolism and of hepatitis B virus
biology that should be considered for proper comparison of the results of the clinical studies.
The global prevalence of hepatitis B virus (HBV) infection is estimated to almost 3 million cases  and the
lack of access to suitable treatment or to prevention programs in certain areas contributes to the maintenance
of these high figures. The consequences of this infection are enormous, as the cumulative 5-year incidence
of cirrhosis is 8-17%  and the 5-year risk of developing hepatocellular carcinoma is estimated to be
between 10-15% . Even in the absence of significant cirrhosis, HBV is capable of leading to hepatocellular carcinoma at any time during disease evolution. Current antiviral therapy in chronic hepatitis B keeps
the infection under control, but does not cure the disease, with rare exceptions; therefore, different areas
of research aiming to reduce the risk of progressive disease are open. One of these directions explores the
positive reported effects of vitamin D in the immune response against HBV infection [3,4]. The bone
metabolism is frequently modified in hepatitis B. The hepatic osteodystrophy is found in 20% of patients with
chronic hepatitis and reaches up to 50% in viral-induced cirrhosis . The excessive chronic production of
inflammatory cytokines (interleukin-1, interleukin-6, tumor necrosis factor-alpha) increases the expression
of the receptor activator of nuclear factor kappa-B ligand (RANKL), which stimulates osteoclastogenesis
along with bone resorption. Low vitamin K, low level of insulin growth factor 1, hypogonadism, malabsorption
and low body mass index are contributing factors. The significance of the vitamin D insufficiency should
not be ignored but the relation between vitamin D and liver pathology is far more complex, exceeding the
domain of the bone metabolism.
Role of Vitamin D in Hepatitis B Virus Infection
Experimental data show that vitamin D is active in the inflammatory process, in the innate and in the
adaptative response. In the hepatic stellate cells, vitamin D has an inhibitory effect on transforming growth
factor (TGF) β  and reduces the matrix deposition , subsequently delaying the fibrosis evolution. The
anti-proliferative effects of vitamin D rely on the prevention of the initiation process: the nuclear binding of
vitamin D receptors (VDR)-vitamin D increases the expression of tumor suppressor genes, promoting the
DNA repair process  stabilizing the cells and preventing oncogenesis.
A recent systematic review and meta-analysis showed that low vitamin D levels were inversely correlated to
viral load . Before further considerations, it is important to underline that current practice of vitamin D
status evaluation is plasma or serum measurement of the total 25-hydroxyvitamin D2/D3 (25(OH)D) by
immunoassay tests or by liquid chromatography tandem mass spectrometry (LC/MS). The arguments for
considering 25(OH)D as representative for the vitamin D status are the short plasma half time (limited to
a couple of hours) of the active metabolite, 1,25-dihydroxyvitamin D2/D3 (1,25(OH)2D), and the response
of the parathormone (PTH) axis that rapidly increases the 1,25(OH)2D after a deficiency level is attained
Several prospective studies confirmed that serum levels of vitamin D are inversely associated with the
incidence  and prognosis of HBV-related hepatocellular carcinoma , but a Cochrane review did
not find a benefit from vitamin D supplementation . Some promising results concerning the vitamin
D immunomodulation of hepatitis B evolution were found in a large multicentric study , but were not
confirmed in another . Other studies suggest that polymorphisms of the genes involved in vitamin D
metabolism might even predict the efficacy of the current treatment for HBV infection [16,17]. Hence,
although experimental data are rather consistent on vitamin D role, clinical data on supplementation are not,
at least not to the same extent.
Possible Explanations for the Controversy of the Clinical Results
This inconsistency might be explained by various factors: the virus genotype, the variations in vitamin D
metabolism, and the biases related to technique of the vitamin D determination.
a) In what concerns the virus genotype, the genotype D and E of the HBV were associated with lower
vitamin D levels . The major hydrophilic region of the HBsAg contains sequences of amino acids that
are targets for the neutralizing antibodies and mutations in this area, called “escape mutations”, and have
critical role in the infection reactivation and in chronic evolution of the hepatitis . It is significant to
notice that mutations of these epitopes were found in vitamin D deficient or insufficient patients infected
with HBV  and they might explain, on one side, the severity of the evolution, and on the other side, the
lack of benefit from standard treatment, as these mutations are frequently associated with drug resistance
. As there is no proof of immune-escape mutations compensation by vitamin D supplementation, there
are no clear benefits of the adjuvant therapy with respect to immunologic response or viral load.
b) The vitamin D metabolism. Hepatic cells convert both vitamin D2 and D3 in 25-hydroxyvitamin D2/
D3 (25(OH)D). The process is catalyzed mainly by CYP2R1 in the endoplasmic reticulum and, in less
significant quantity, in the mitochondria by CYP27A1. Variation in CYP2R1 polymorphisms influences
the level of the circulating vitamin D . Some polymorphisms also influence the results of vitamin
D supplementation , but others do not . In the liver, 25(OH)D3 can be further metabolized to
23,25(OH)2D3 or to 25,26(OH)D3 by CYP3A4  or sent into the circulation. Under physiological
conditions, about 85% of the 25(OH)D in plasma is bound to vitamin D binding protein (DBP), about 15%
is bound to albumin and only 0.03% is free (bioavailable form) . The expression of the DBP, including
the response to supplementation with vitamin D and the affinity of vitamin D binding seem to be genetically
determined . These variations of DBP have consequences on the vitamin D distribution and on the
active form availability, affecting the clinical significance of the total vitamin D level currently measurement.
They also influence the efficacy of the vitamin D treatment, in general. In hepatitis, this influence is even
more significant, as the most important source of DPB is the liver. The diminished synthesis of the DBP and
the reduced conversion of D2 and D3 in D2/D3 25(OH)D, which can occur in chronic hepatitis or hepatic
cirrhosis, would lead to lower levels of total 25(OH)D, but will not necessarily reduce the level of the active
form 1,25 (OH)2D3 (calcitriol), produced by the kidney and regulated by specific mechanisms (described
bellow). It is, however, reasonable to presume that DBP synthesis is not equally affected in all patients, and
therefore, the interpretation of 25(OH)D values should take into account the DBP level. According to the
free hormone theory, stipulating that the biological functions of the vitamin D (as any other hormone)
are ensured by the free level of 25(OH)D and 1,25(OH)2D, a lower level of DBP should be considered
biologically beneficial. In fact, a multicentric study published in 2018 found higher levels of free but also of
total 25(OH)D in patients with cirrhosis than in healthy subjects, medically-stable outpatients, prediabetes
patients or pregnant women . In a graphical representation, the relationship between free and total
25(OH)D has the steepest slope among the studied groups, suggesting higher bioavailability of Vitamin
D in patients with cirrhosis. As the biologically active 1,25(OH)2D is generally not measured in clinical
studies, the clinical significance of the results based on the total 25(OH)D determination could be biased.
The kidney is the main source of the major vitamin D active form, by converting 25(OH)D3 to 1,25(OH)2D3.
The reaction is mediated in mitochondria by 1α-hydroxylase, the product of CYP27B1, highly regulated
by PTH and the fibroblast growth factor 23 (FGF-23). Genetic variations of CYP27B1 could create an
apparently normal level of serum vitamin D, with an abnormal, low level of the active form and could also
lead to misinterpretation of the results .
Expression of CYP27B1 is not limited to the renal cells. A significant circulating level of 1,25(OH)2D3
through non-renal cells output reflects a pathophysiological status, being reached only from activated tissue
macrophages and placenta . Inflammatory cytokines upregulate CYP27B1 expression in macrophages
 and other immune cells in an autocrine or paracrine manner with apparently neither PTH nor FGF-23
feedback. Due to this lack of a systemic control, at least in theory, this mechanism of conversion to calcitriol
is unlimited in inflammation , a reason why 25(OH)D might not be reliable enough for the estimation
of the treatment results.
Vitamin D receptors are present in a variety of tissues. Evolutionarily, the VDR are closely related to receptors
involved in xenobiotic detoxification and elimination, such as the pregnane X receptor, or the farnesoid X
receptor . The VDR recognizes a specific DNA sequence, the vitamin D response element (VDRE). The
VDRE is composed by 2 hexameric nucleotide half-sites separated by 3 base pairs that are recognized by
the heterodimer formed by one molecule of VDR and one of retinoid X receptor (RXR). It is estimated that
as much as 5% of the human genome is regulated by calcitriol, via VDR-RXR link to the VDRE or by the
ability of the VDR to facilitate the recruitment, in a gene-specific manner, of large and diverse co-regulatory
complexes. Epigenetic modifications enlarge the influence of the vitamin D on the gene expression .
VDR is not present in the hepatocytes from normal human liver but is strongly expressed in hepatic stellate
cells, sinusoidal endothelial cells and Kupffer cells . In inflammation, the VDR expression increases in
hepatic stellate cells and Kupffer cells, but also in hepatocytes . The literature regarding the impact of the
genetic variation of VDR in hepatic disorders is rather consistent, showing an increase in the susceptibility of
progression to liver cirrhosis and portal hypertension for some polymorphisms , or to hepatic carcinoma
associated to chronic hepatitis B virus infection [34,35]. Other polymorphisms led to some protective effects
c) The vitamin D determination in plasma. As previously mentioned, in order to assess the current practice
is to determine the total 25(OH)D concentration in plasma by immunoassay or LC/techniques. The 25(OH)
D3 is the major circulating form of vitamin D3, but numerous other metabolites of vitamin D3 were
measured in serum . The most significant in terms of quantity are 3-epi-25(OH)D, the 24R,25(OH)2D3,
the 1,25(OH)2D3 and 1,25(OH)2D2, the 25-hydroxyvitamin D3-3-sulfate and the D-hydroxyderivatives
(20S(OH)D3 and 22(OH)D3 and their metabolites). The active forms of vitamin D are 1,25(OH)2D3 and
1,25(OH)2D2, which bind to the VDR and produce both the calcemic and the non-calcemic effects. The
functional role of the other compounds is not enough characterized and its clinical significance is not yet
well understood. An exception are the D-hydroxyderivatives; they bind to the VDR, without inducing the
calcemic effects; instead, they are almost as potent as 1,25(OH)2D3 in the extra-osseous effects, including
the antifibrogenic one .
The total level of 25(OH)D is also the only therapeutic target of the vitamin D substitution, although there
are reports showing that free 25(OH)D would better reflect the achievement of the normal vitamin D status
[39,40]. The liver produces both DBP and albumin, the carriers of vitamin D in the blood stream; depending
on the severity of the liver disease, both proteins might be significantly reduced. The free form of vitamin
D is less dependent on the hepatic function and therefore the measurement of the total vitamin D is not a
good reflection of the real status of this hormone in hepatic disorders. Even more, results could be biased
by an increased percentage of free serum 25(OH)D in patients with vitamin D deficiency . Due to difficulties in the measurement of the free 25(OH)D level, the latter is rarely communicated in clinical
studies. However, a recent extensive review of the published studies related to free vitamin D measurement
strongly recommends the measurement of the free 25(OH)D in liver diseases .
There are no large studies addressing all these issues in a systematic manner and therefore the results are difficult
to compare. Without considering the complex biology of the vitamin D metabolism and the biology
of the HBV it is impossible to obtain reliable results and to conclude on the vitamin D supplementation in
Due to this diversity, it is not yet well established what specific profiles of patients are suitable for treatment,
and a patient-centered approach still waits to be defined.
Conflicts of Interests
Nothing to declare.
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