Vitamin D receptor gene polymorphisms and colorectal cancer risk: A systematic meta-analysis

The role of vitamin D in reducing cancer risk and progression

Vitamin D is not really a vitamin but the precursor to the potent steroid hormone calcitriol, which has widespread actions throughout the body. Calcitriol regulates numerous cellular pathways that could have a role in determining cancer risk and prognosis. Although epidemiological and early clinical trials are inconsistent, and randomized control trials in humans do not yet exist to conclusively support a beneficial role for vitamin D, accumulating results from preclinical and some clinical studies strongly suggest that vitamin D deficiency increases the risk of developing cancer and that avoiding deficiency and adding vitamin D supplements might be an economical and safe way to reduce cancer incidence and improve cancer prognosis and outcome.

Vitamin D in the cancer patient

PURPOSE OF REVIEW

To briefly review recent work within the vitamin D and cancer field, whereas also providing context relating how these findings may impact clinical care and future research efforts.

RECENT FINDINGS

Vitamin D has now been convincingly shown both in vitro and in preclinical animal models to alter the differentiation, proliferation, and apoptosis of cancer cells. Whether vitamin D prevents cancer in humans or limits cancer progression, however, remain open questions. Epidemiologic and observational data relating circulating 25(OH)D levels and cancer risk suggest an inverse relationship for most cancers including breast, colorectal, leukemia and lymphoma, and prostate, although for each malignancy there also exist studies that have failed to demonstrate such an inverse relationship. Likewise, a more recent report failed to confirm a previously reported association of increased pancreatic cancer risk in patients with higher 25(OH)D levels. A large prospective study in which patients aged at least 50 years receive 2000 IU vitamin D3 daily for 5 years, with cancer as a primary endpoint, has recently been launched.

SUMMARY

Although much effort has attempted to delineate a causal relationship between vitamin D and a wide array of human cancers, we await large-scale randomized controlled trial data for definitive answers.

The VDR gene FokI polymorphism and ovarian cancer risk

The polymorphism of vitamin D receptor (VDR) gene is demonstrated to affect the activity of its encoding protein and the subsequent downstream effects mediated by vitamin D. Mutations in VDR gene FokI have been suggested in the development of various cancers. Whether the polymorphism of the VDR gene FokI confers risk to ovarian cancer still remains controversial across the published studies in different ethnicity. The aim of this meta-analysis was to determine the role of VDR gene FokI variant in the susceptibility to ovarian cancer. Six publications with 14 individual case-control studies involving a total of 10,964 subjects were finally included into our study after a comprehensive literature search of the PubMed, Embase, Web of Science, and Wanfang databases. The strength of the association between the VDR gene FokI polymorphism and ovarian cancer risk was estimated under the allelic (T vs. C), homozygous (TT vs. CC), additive (CT vs. CC), recessive (TT vs. CC + CT), and dominant (CT + TT vs. CC) gene models. The overall odds ratios (ORs) for the contrast models of T vs. C, TT vs. CC, CT vs. CC, and CT + TT vs. CC indicated that the VDR gene FokI variant was related to an increased risk of ovarian cancer (OR(T vs. C) = 1.09, 95 % confidence interval (CI) 1.03-1.15, P(OR) = 0.004; OR(TT vs. CC) = 1.17, 95 % CI 1.04-1.32, P(OR) = 0.011; OR(CT vs. CC) = 1.10, 95 % CI 1.01-1.20, P(OR) = 0.027; OR(CT + TT vs. CC) = 1.12, 95 % CI 1.03-1.21, P(OR) = 0.007). The stratified analysis among the Caucasians also identified a significant association between the VDR gene FokI polymorphism and the susceptibility to ovarian cancer. The present meta-analysis with large available published data has revealed that the VDR gene FokI polymorphism confers susceptibility to ovarian cancer, particularly among the Caucasian population.

Vitamin D receptor FokI gene polymorphisms may be associated with colorectal cancer among African American and Hispanic participants

BACKGROUND

Vitamin D plays a role in cancer tumorogenesis and acts through the vitamin D receptor (VDR). Although African Americans have the lowest serum vitamin D levels, supplementation has not yielded a significant improvement in cancer. Gene polymorphisms in VDR may play a role. There is a dearth of information on VDR gene polymorphisms and colorectal cancer (CRC) among under-represented ethnic groups. In this study, the authors examined whether VDR gene single nucleotide polymorphisms (SNPs) were associated with CRC in predominately African American and Hispanic study participants.

METHODS

Blood samples were collected from 378 participants, including a group of 78 patients with CRC (cases), a group of 230 noncancer participants without polyps (controls without polyps), and a group of 70 noncancer participants with polyps (controls with polyps). The 4 polymorphic SNPs in VDR (FokI, BsmI, TaqI, and ApaI) were assessed using the polymerase chain reaction-restriction fragment length polymorphism method.

RESULTS

There was a significant association of the VDR-FokI FF genotype with CRC cases (odds ratio, 2.9; P= .036) compared with the controls without polyps. The most common VDR-FokI genotype in the overall study population was the FF genotype (46%). However, upon breakdown by ethnicity, the FF genotype was the most common in African American participants (61%), and the Ff genotype was the most common in Hispanic/Latino participants (49%). When the association was assessed in a multivariate model, there was no significant association with any VDR polymorphism and CRC cases (P> .05). The other 3 polymorphic variants of VDR (BsmI, TaqI, and ApaI) were not associated with CRC.

CONCLUSIONS

The results from this study suggest that genetic variation of the VDR-FokI SNPs may influence CRC risk, particularly in African American cohorts.

Systematic review and meta-analysis on vitamin D receptor polymorphisms and cancer risk

The vitamin D receptor (VDR) can influence cancer susceptibility through binding to vitamin D. However, the previous studies were contradictory. Therefore this meta-analysis was conducted to clarify the association between VDR polymorphisms (BsmI, TaqI, FokI, and ApaI) and cancer risk. One hundred twenty-six studies were enrolled through PubMed. For VDR BsmI polymorphism, significantly increased cancer risks were observed in the overall analysis. In the further stratified analysis, increased risks were observed in colorectal and skin cancer, especially in Caucasian population. However, no significant associations were observed in other VDR polymorphisms in the overall analysis. In the further subgroup analysis, increased risks were found in oral, breast, and basal cell cancer while decreased risk was found in prostate cancer in t allele carriers of TaqI polymorphism. For VDR FokI polymorphism, increased risks were found in ovarian and skin cancer while decreased risk in glioma in f allele carriers. For VDR ApaI polymorphism, increased risk was observed in basal cell cancer, especially in Asian population in a allele carriers. In conclusion, these results indicated that b allele of BamI polymorphism was a risk factor for cancer susceptibility. Meanwhile, t allele of TaqI polymorphism was a risk factor for oral, breast, and basal cell cancer and a protective factor for prostate cancer. Moreover, f allele of FokI polymorphism was a risk factor for ovarian and skin cancer and a protective factor for glioma. Finally, a allele of ApaI polymorphism was a risk factor for basal cell cancer in Asian population.

Systematic review and meta-analysis on vitamin D receptor polymorphisms and cancer risk

The vitamin D receptor (VDR) can influence cancer susceptibility through binding to vitamin D. However, the previous studies were contradictory. Therefore this meta-analysis was conducted to clarify the association between VDR polymorphisms (BsmI, TaqI, FokI, and ApaI) and cancer risk. One hundred twenty-six studies were enrolled through PubMed. For VDR BsmI polymorphism, significantly increased cancer risks were observed in the overall analysis. In the further stratified analysis, increased risks were observed in colorectal and skin cancer, especially in Caucasian population. However, no significant associations were observed in other VDR polymorphisms in the overall analysis. In the further subgroup analysis, increased risks were found in oral, breast, and basal cell cancer while decreased risk was found in prostate cancer in t allele carriers of TaqI polymorphism. For VDR FokI polymorphism, increased risks were found in ovarian and skin cancer while decreased risk in glioma in f allele carriers. For VDR ApaI polymorphism, increased risk was observed in basal cell cancer, especially in Asian population in a allele carriers. In conclusion, these results indicated that b allele of BamI polymorphism was a risk factor for cancer susceptibility. Meanwhile, t allele of TaqI polymorphism was a risk factor for oral, breast, and basal cell cancer and a protective factor for prostate cancer. Moreover, f allele of FokI polymorphism was a risk factor for ovarian and skin cancer and a protective factor for glioma. Finally, a allele of ApaI polymorphism was a risk factor for basal cell cancer in Asian population.

Vitamin D receptor and colorectal cancer

Colorectal cancer (CRC) is the third cause of cancer-related morbidity and mortality in America following lung cancer and stomach cancer. In China and other Asian countries, increasingly Westernized diets have led to a high incidence of CRC. The vitamin D receptor (VDR) can mediate 1,25(OH)₂D₃ to regulate cell growth and differentiation in a variety of normal tissues or tumor tissues. VDR gene polymorphisms are closely related to the occurrence and development of CRC. This article summarizes the recent progress in understanding the relationship between VDR and CRC in terms of the structure and function of VDR, mechanisms of CRC inhibition, correlation between VDR polymorphisms and CRC, and the development of analogs of VDR ligands.

Vitamin D receptor polymorphism and colorectal cancer-specific and all-cause mortality

BACKGROUND

The vitamin D receptor (VDR) gene is present in colorectal cancer (CRC) cells and its genetic variants have been associated with an increased risk of CRC. The association with colorectal cancer prognosis remains widely unexplored.

METHODS

1397 colorectal cancer patients participating in two cancer cohorts (ESTHER II and VERDI) and in a population-based case-control study (DACHS) were followed for 5 years. Unadjusted and adjusted hazard ratios for all-cause mortality (469 events) and CRC-specific mortality (336 events) were estimated for VDR variants rs731236 (TaqI), rs2228570 (FokI), rs11568820 (Cdx2), and rs1989969 (VDR-5132).

RESULTS

No association was found between VDR polymorphism and CRC specific and all-cause mortality. Adjusted hazard ratios ranged from 0.79 (95% CI 0.57-1.12) to 1.14 (95% CI 0.89-1.46) for CRC-specific mortality and from 0.89 (95% CI 0.67-1.18) to 1.22 (95% CI 0.99-1.50) for all-cause mortality. All 95% confidence intervals included the null value.

CONCLUSIONS

Our findings do not support the hypothesis that the common VDR gene variants investigated in this study are of clinical relevance with respect to CRC prognosis.

Vitamin D3 insufficiency and colorectal cancer

Traditionally the main recognized function of vitamin D has been calcium and phosphate homeostasis. Nevertheless, recent evidences have highlighted the importance of vitamin D3 as a protective agent against various cancers. The association between CRC and vitamin D3 was first suggested in ecologic studies, but further was confirmed by observational studies in humans and experimental studies in both animal models and cellular lines. The protective role of vitamin D3 against cancer has been attributed to its influence of on cell proliferation, differentiation, apoptosis, DNA repair mechanisms, inflammation and immune function. In its active (calcitriol) form (1,25-dihydroxyvitamin D3[1α,25-(OH)2D3]) vitamin D3 and the nuclear vitamin D receptor (VDR) regulate hundreds of genes including those coding for proteins involved in cell differentiation and cell proliferation. The current review addresses some of the key mechanisms that influence the biological actions of vitamin D and its metabolites. The insights derived from these mechanisms may aid in designing new uses for this hormone and its non-hypercalcemic derivatives in the treatment and/or prevention of CRC.

TaqI polymorphism of VDR gene contributes to breast cancer risk

Previous studies on the association of Vitamin D receptor (VDR) TaqI gene polymorphism with breast carcinogenesis have yielded inconsistent and inconclusive findings. The current meta-analysis was performed to provide a more precise assessment on the role of VDR TaqI polymorphism in breast cancer risk. 20 eligible case-control studies involving 9,055 cases and 10,516 controls were identified after a comprehensive literature search of the PubMed, Embase, Web of Science, and Wanfang databases. The pooled odds ratio (OR) with corresponding 95% confidence interval (95% CI) was calculated. Stratified analyses by ethnicity and study quality were conducted for further estimation. All statistical analyses were conducted by use of STATA (STATA Corporation, College Station, TX, Version 11.0). The overall ORs showed that the variant t allele and tt genotype were related to an increased risk of breast cancer (OR(t vs. T) = 1.05, 95% CI 1.01-1.10, P(OR) = 0.025; OR(tt vs. TT) = 1.12, 95% CI 1.03-1.23, P(OR) = 0.011; OR(tt vs. Tt + TT) = 1.10, 95% CI 1.01-1.20, P(OR) = 0.023). Stratified analyses of studies in Caucasians and with high-quality further confirmed the results. However, no significant relationship was observed among Asians. This meta-analysis suggests that the VDR TaqI polymorphism confers risk effect on the breast cancer development, particularly in Caucasians.

Polymorphisms in the vitamin D Receptor (VDR) and the risk of ovarian cancer: a meta-analysis

The vitamin D receptor (VDR) principally mediates the anticancer activities of vitamin D. Various epidemiological studies have investigated the associations of VDR gene polymorphisms with ovarian cancer; however, the results have been inconclusive. In the current study, we evaluated, in a meta-analysis, the association of five common single nucleotide polymorphisms (SNPs) in the VDR gene (ApaI, BsmI, Cdx-2, FokI, and TaqI) with the risk of ovarian cancer. Six eligible studies, with a total of 4,107 cases and 6,661 controls, which evaluated the association of these variants and ovarian cancer risk, were identified from the MEDLINE and PubMed databases. The meta-analysis indicated that FokI was associated with an increased ovarian cancer risk, with a pooled odds ratio (OR) of 1.10 [95% confidence intervals (95% CI) = 1.00-1.20] for CT heterozygotes and 1.16 (95% CI = 1.02-1.30) for TT homozygotes relative to common CC carriers. Carriers of the T allele (also known as the f allele) showed an 11% (pooled OR = 1.11, 95% CI = 1.02-1.21; TT/CT vs. CC) increased risk of ovarian cancer relative to CC carriers. For FokI, no significant heterogeneity between the studies was found (I(2) = 0%, P = 0.62 for the Q test). There was no statistically significant association between the other four variants (ApaI, BsmI, Cdx-2 and TaqI) and risk of ovarian cancer. These data indicate that the polymorphism FokI on the VDR is a susceptibility factor for ovarian cancer. Nevertheless, more studies are warranted to elucidate the underlying mechanisms of the VDR in development of ovarian cancer.

The association between the poly(A) polymorphism in the VDR gene and cancer risk: a meta-analysis

The poly(A) polymorphism (L/S) in the VDR gene has been implicated in susceptibility of cancer, but a number of studies have reported inconclusive results. The aim of this study is to investigate the relationship between the poly(A) polymorphism in the VDR gene and cancer risk by meta-analysis. We searched PubMed database, EMBASE database, CNKI database, and Wanfang database, covering all studies until January 22, 2013. Statistical analysis was performed by using the software Revman4.2 and STATA 10.0. A total 8,186 cancer cases and 8,685 controls in 19 case-control studies from 15 studies were identified for data analysis. The results suggested that the S allele carriers (SS+SL) did not have an increased or decreased risk of cancer when compared with the homozygote LL carriers (odds ratio (OR) =0.96, 95 % CI=0.87-1.06, P=0.43 for SS+SL vs. LL). In addition, in the subgroup analysis by ethnicity and cancer type, no significant association was found among Caucasians, African-Americans, prostate cancer, or breast cancer. This current meta-analysis suggested that the poly(A) polymorphism in the VDR gene may not contribute to the risk of cancer. Future studies are needed to validate our findings.

Vitamin D receptor gene BsmI and FokI polymorphisms in relation to ovarian cancer risk in the Polish population

BACKGROUND

The role of vitamin D receptor (VDR) single-nucleotide polymorphisms (SNPs) in ovarian cancer has been studied in various populations; however, these results are discordant between different ethnicities.

METHOD

Using the polymerase chain reaction-restriction fragment length polymorphism method, we studied the prevalence of the VDR FokI (rs2228570) and BsmI (rs1544410) SNPs in women with ovarian cancer (n=168) and controls (n=182) in a Polish population.

RESULTS

We found a significant contribution of the BsmI SNP Bb+BB-versus-bb dominant inheritance model to ovarian cancer development (p=0.0221, p(corr)=0.0442, odds ratio [OR]=1.648 [95% confidence intervals, CI=1.073-2.532]). However, we did not observe an association of the BsmI SNP BB versus Bb+bb recessive inheritance model in patients (p=0.8059, OR=1.093 [95% CI=0.538-2.218]). Moreover, there was no association of FokI SNPs either in Ff+ff versus FF dominant or ff versus Ff+FF recessive inheritance models with ovarian cancer development (p=0.9924, OR=1.002 [95% CI=0.628-1.599] and p=0.1123, OR=1.542 [95% CI=0.901-2.638], respectively). The p-values of the trend test observed for the VDR BsmI and FokI SNPs in patients with ovarian cancer were p(trend)=0.0613 and p(trend)=0.3655, respectively.

CONCLUSION

Our study indicates that the VDR B gene variant might be a moderate risk factor of ovarian cancer development in the Polish population.

Vitamin D and overall mortality

Vitamin D is a steroid molecule, mainly produced in the skin that regulates the expression of a large number of genes. Several meta-analyses of epidemiological studies support the evidence that low vitamin D serum level, which is highly prevalent worldwide, could be a 'new' risk factor for many chronic diseases including cancer, and for all-cause mortality. A meta-analysis in healthy subjects suggested that current doses of vitamin D supplements could be associated with decrease in total mortality rates. However, these associations are insufficient to establish causality between vitamin D and all-cause mortality. Furthermore, long-term health effects of high doses of vitamin D, that is, prolonged supplementation and association with different baseline vitamin D levels, remain to be investigated. Several trials are ongoing but population-based, placebo-controlled randomized trials with total mortality as the main endpoint should be planned to confirm a real beneficial effect of vitamin D for non-skeletal diseases and to prove causality.

Vitamin D: health panacea or false prophet?

Vitamin D deficiency, diagnosed when the serum 25-hydroxyvitamin D (25-OHD(3)) concentration is less than 20 ng/mL, has joined vitamin A deficiency as two of the most common nutrition-responsive medical conditions worldwide. There have been more scientific articles published about vitamin D in the 21st century than about any other vitamin, reflecting the massive expansion of the field of vitamin D research. Adequate vitamin D status has been linked to decreased risks of developing specific cancers, including cancers of the esophagus, stomach, colon, rectum, gallbladder, pancreas, lung, breast, uterus, ovary, prostate, urinary bladder, kidney, skin, thyroid, and hematopoietic system (e.g., Hodgkin's lymphoma, non-Hodgkin's lymphoma, multiple myeloma); bacterial infections; rheumatoid arthritis; Crohn's disease; periodontal disease; multiple sclerosis; asthma; type 2 diabetes; cardiovascular disease; stroke; peripheral artery disease; hypertension; chronic kidney disease; muscle weakness; cognitive impairment; Alzheimer's disease; clinical depression; and premature death. On the other hand, inadequate vitamin D status during human pregnancy may be associated with increased risk for the development of type 1 diabetes in the offspring. However, this point of view may be excessively optimistic. There also is evidence that despite the current heavy reliance on serum 25-OHD(3) concentration for the diagnosis of an individual's vitamin D status, local tissue vitamin D intoxication may be present in individuals with much lower serum 25-OHD(3) concentrations than are currently appreciated. Only rarely are the symptoms of local tissue vitamin D intoxication associated with vitamin D status or intake. An individual's serum 25-OHD(3) concentration may appear to be "low" for reasons totally independent of sunlight exposure or vitamin D intake. Serum 25-OHD(3) concentration is only poorly responsive to increases in vitamin D intake, and the prolonged routine consumption of thousands of international units of vitamin D may interfere with the regulation of phosphate homeostasis by fibroblast growth factor-23 (FGF23) and the Klotho gene product, with consequences that are detrimental to human health. In light of these counterbalancing observations, curbing excessive enthusiasm for universally increasing vitamin D intake recommendations may be in order.