The association between personal sun exposure, serum vitamin D and global methylation in human lymphocytes in a population of healthy adults in South Australia

A Population-Based Family Case-Control Study of Sun Exposure and Follicular Lymphoma Risk

BACKGROUND

Epidemiologic evidence suggests an inverse association between sun exposure and follicular lymphoma risk.

METHODS

We conducted an Australian population-based family case-control study based on 666 cases and 459 controls (288 related, 171 unrelated). Participants completed a lifetime residence and work calendar and recalled outdoor hours on weekdays, weekends, and holidays in the warmer and cooler months at ages 10, 20, 30, and 40 years, and clothing types worn in the warmer months. We used a group-based trajectory modeling approach to identify outdoor hour trajectories over time and examined associations with follicular lymphoma risk using logistic regression.

RESULTS

We observed an inverse association between follicular lymphoma risk and several measures of high lifetime sun exposure, particularly intermittent exposure (weekends, holidays). Associations included reduced risk with increasing time outdoors on holidays in the warmer months [highest category OR = 0.56; 95% confidence interval (CI), 0.42-0.76; Ptrend < 0.01], high outdoor hours on weekends in the warmer months (highest category OR = 0.71; 95% CI, 0.52-0.96), and increasing time outdoors in the warmer and cooler months combined (highest category OR = 0.66; 95% CI, 0.50-0.91; Ptrend 0.01). Risk was reduced for high outdoor hour maintainers in the warmer months across the decade years (OR = 0.71; 95% CI, 0.53-0.96).

CONCLUSIONS

High total and intermittent sun exposure, particularly in the warmer months, may be protective against the development of follicular lymphoma.

IMPACT

Although sun exposure is not recommended as a cancer control policy, confirming this association may provide insights regarding the future control of this intractable malignancy.

Time spent in the sun and the risk of developing non-Hodgkin lymphoma: a Canadian cohort study

PURPOSE

The objective was to explore the relationship of sun behavior patterns with the risk of developing non-Hodgkin lymphoma (NHL).

METHODS

Sun behavior information from Alberta's Tomorrow Project, CARTaGENE, and Ontario Health Study were utilized. The relationship between time in the sun during summer months and risk of NHL was assessed using Cox proportional hazard models with age as the time scale and adjustment for confounders. Cohorts were analyzed separately and hazard ratios (HR) pooled with random effects meta-analysis. Joint effects of time in the sun and use of sun protection were examined. Patterns of exposure were explored via combinations of weekday and weekend time in the sun.

RESULTS

During an average follow-up of 7.6 years, 205 NHL cases occurred among study participants (n = 79,803). Compared to < 30 min daily in the sun, we observed HRs of 0.84 (95% CI 0.55-1.28) for 30-59 min, 0.63 (95% CI 0.40-0.98) for 1-2 h, and 0.91 (95% CI 0.61-1.36) for > 2 h. There was suggestive evidence that > 2 h was protective against NHL with use of sun protection, but not without it. Compared to < 30 min daily, moderate exposure (30 min to 2 h on weekdays or weekend) was associated with a lower risk of NHL (HR 0.63, 95% CI 0.43-0.92), while intermittent (< 30 min on weekdays and > 2 h on weekends) and chronic (> 2 h daily) were not.

CONCLUSION

This study provides evidence of a protective effect of moderate time spent in the sun on NHL risk.

Epigenetic regulation of vitamin D deficiency

Tweetable abstract Epigenetic insights into vitamin D deficiency, a global health concern, are described here. This editorial illuminates the role of epigenetic mechanisms in understanding the molecular basis of vitamin D deficiency, shedding light on precision medicine.

Characterization of methylation patterns associated with lifestyle factors and vitamin D supplementation in a healthy elderly cohort from Southwest Sweden

Numerous studies have shown that lifestyle factors, such as regular physical activity and vitamin D intake, may remarkably improve overall health and mental wellbeing. This is especially important in older adults whose vitamin D deficiency occurs with a high prevalence. This study aimed to examine the influence of lifestyle and vitamin D on global DNA methylation patterns in an elderly cohort in Southwest of Sweden. We also sought to examine the methylation levels of specific genes involved in vitamin D's molecular and metabolic activated pathways. We performed a genome wide methylation analysis, using Illumina Infinium DNA Methylation EPIC 850kBeadChip array, on 277 healthy individuals from Southwest Sweden at the age of 70–95. The study participants also answered queries on lifestyle, vitamin intake, heart medication, and estimated health. Vitamin D intake did not in general affect methylation patterns, which is in concert with other studies. However, when comparing the group of individuals taking vitamin supplements, including vitamin D, with those not taking supplements, a difference in methylation in the solute carrier family 25 (SCL25A24) gene was found. This confirms a previous finding, where changes in expression of SLC25A24 were associated with vitamin D treatment in human monocytes. The combination of vitamin D intake and high physical activity increased methylation of genes linked to regulation of vitamin D receptor pathway, the Wnt pathway and general cancer processes. To our knowledge, this is the first study detecting epigenetic markers associated with the combined effects of vitamin D supplementation and high physical activity. These results deserve to be further investigated in an extended, interventional study cohort, where also the levels of 25(OH)D₃ can be monitored.

More Than Effects in Skin: Ultraviolet Radiation-Induced Changes in Immune Cells in Human Blood

Cells of the skin and circulation are in constant two-way communication. Following exposure of humans to sunlight or to phototherapy, there are alterations in the number, phenotype and function of circulating blood cells. In this review, only data obtained from human studies are considered, with changes induced by UV radiation (UVR) exposure described for phagocytic leukocytes and peripheral blood mononuclear cells plus their component T and B cells, natural killer cells and dendritic cells. These immune modulations illustrate the potential of UVR to have therapeutic effects beyond the skin, and that sunlight exposure is an important environmental influence on human health.

High-dose vitamin D supplementation to prevent prostate cancer progression in localised cases with low-to-intermediate risk of progression on active surveillance (ProsD): protocol of a phase II randomised controlled trial

INTRODUCTION

Active surveillance (AS) for patients with prostate cancer (PC) with low risk of PC death is an alternative to radical treatment. A major drawback of AS is the uncertainty whether a patient truly has low risk PC based on biopsy alone. Multiparametric MRI scan together with biopsy, appears useful in separating patients who need curative therapy from those for whom AS may be safe. Two small clinical trials have shown short-term high-dose vitamin D supplementation may prevent PC progression. There is no substantial evidence for its long-term safety and efficacy, hence its use in the care of men with PC on AS needs assessment. This protocol describes the ProsD clinical trial which aims to determine if oral high-dose vitamin D supplementation taken monthly for 2 years can prevent PC progression in cases with low-to-intermediate risk of progression.

METHOD AND ANALYSIS

This is an Australian national multicentre, 2:1 double-blinded placebo-controlled phase II randomised controlled trial of monthly oral high-dose vitamin D supplementation (50 000 IU cholecalciferol), in men diagnosed with localised PC who have low-to-intermediate risk of disease progression and are being managed by AS. This trial will assess the feasibility, efficacy and safety of supplementing men with an initial oral loading dose of 500 000 IU cholecalciferol, followed by a monthly oral dose of 50 000 IU during the 24 months of AS. The primary trial outcome is the commencement of active therapy for clinical or non-clinical reason, within 2 years of AS.

ETHICS AND DISSEMINATION

This trial is approved by Bellberry Ethics Committee (2016-06-459). All results will be reported in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

ACTRN12616001707459.

Epigenetic Clock and Leukocyte Telomere Length Are Associated with Vitamin D Status but not with Functional Assessments and Frailty in the Berlin Aging Study II

DNA methylation (DNAm) age acceleration, a parameter derived via the epigenetic clock, has recently been suggested as a biomarker of aging. We hypothesized that accelerated biological aging, measured by both this new and the established biomarker of aging, relative leukocyte telomere length (rLTL), are associated with vitamin D deficiency. Moreover, we tested for an association between rLTL/DNAm age acceleration and different clinical assessments for functional capacity, including the Fried frailty score. Cross-sectional data of 1,649 participants of the Berlin Aging Study II was available (~50% female, age: 22-37 and 60-84 years). A seven cytosine-phosphate-guanine clock was estimated to calculate the DNAm age acceleration. rLTL was measured by quantitative real-time polymerase chain reaction (PCR). 25-hydroxyvitamin D (25(OH)D) serum levels <25 nmol/L was defined as vitamin D deficiency and <50 nmol/L as vitamin D insufficiency. Vitamin D-sufficient individuals had a 1.4 years lower mean DNAm age acceleration (p < .05, analysis of variance [ANOVA]) and a 0.11 longer rLTL (p < .001, ANOVA) than vitamin D-deficient participants. Likewise, vitamin D-sufficient participants had lower DNAm age acceleration (β = 1.060, p = .001) and longer rLTL (β = -0.070; p < .001) than vitamin D nonsufficient subjects in covariate-adjusted analysis. Neither DNAm age acceleration nor rLTL were significantly associated with the Fried frailty score or the functional assessments. Only the clock drawing test was associated with DNAm age acceleration (subgroup of older men: β = 1.898, p = .002). Whether the analyzed biomarkers of aging can be used to predict an individual's functional capacity or will be associated with frailty in the advanced course of aging, will be clarified by future longitudinal analyses.

Vitamin D and its Effects on DNA Methylation in Development, Aging, and Disease

DNA methylation is increasingly being recognized as a mechanism through which environmental exposures confer disease risk. Several studies have examined the association between vitamin D and changes in DNA methylation in areas as diverse as human and animal development, genomic stability, chronic disease risk, and malignancy. In many cases, they have demonstrated clear associations between vitamin D and DNA methylation in candidate disease pathways. Despite this, a clear understanding of the mechanisms by which these factors interact is unclear. This paper reviews the current understanding of the effects of vitamin D on DNA methylation. In light of current knowledge in the field, the potential mechanisms mediating vitamin D effects on DNA methylation are discussed, as are the limiting factors and future avenues for research into this exciting area.

Vitamin D and Rehabilitation after Stroke: Status of Art

Stroke is the first cause of disability in the population and post-stroke patients admitted to rehabilitation units often present a malnutrition status which can influence nutritional indices and then vitamin levels. Vitamin D deficiency seems implicated beyond stroke severity and stroke risk, and also affects post-stroke recovery. Some studies on vitamin D levels and outcome in stroke patients are available but very few data on vitamin D levels and outcome after rehabilitation treatment are reported. This literature review shows the possible relationship between vitamin D deficiency and recovery in post-stroke patients undergoing rehabilitation treatment. Moreover, because several studies have reported that single nucleotide polymorphisms and promoter methylation in genes are involved in vitamin D metabolism and might affect circulating vitamin D levels, these aspects are evaluated in the current paper. From the studies evaluated in this review, it emerges that vitamin D deficiency could not only have an important role in the recovery of patients undergoing rehabilitation after a stroke, but that genetic and epigenetic factors related to vitamin D levels could have a crucial role on the rehabilitation outcome of patients after stroke. Therefore, further studies are necessary on stroke patients undergoing rehabilitation treatment, including: (a) the measurement of the 25(OH) vitamin D serum concentrations at admission and post rehabilitation treatment; (b) the identification of the presence/absence of CYP2R1, CYP27B1, CYP24A1 and VDR polymorphisms, and (c) analysis of the methylation levels of these genes pre- and post-rehabilitation treatment.

Lifetime Ultraviolet Radiation Exposure and DNA Methylation in Blood Leukocytes: The Norwegian Women and Cancer Study

Ultraviolet radiation (UVR) exposure is a leading cause of skin cancers and an ubiquitous environmental exposure. However, the molecular mechanisms relating UVR exposure to melanoma is not fully understood. We aimed to investigate if lifetime UVR exposure could be robustly associated to DNA methylation (DNAm). We assessed DNAm in whole blood in three data sets (n = 183, 191, and 125) from the Norwegian Woman and Cancer cohort, using Illumina platforms. We studied genome-wide DNAm, targeted analyses of CpG sites indicated in the literature, global methylation, and accelerated aging. Lifetime history of UVR exposure (residential ambient UVR, sunburns, sunbathing vacations and indoor tanning) was collected by questionnaires. We used one data set for discovery and the other two for replication. One CpG site showed a genome-wide significant association to cumulative UVR exposure (cg01884057) (pnominal = 3.96e-08), but was not replicated in any of the two replication sets (pnominal ≥ 0.42). Two CpG sites (cg05860019, cg00033666) showed suggestive associations with the other UVR exposures. We performed extensive analyses of the association between long-term UVR exposure and DNAm. There was no indication of a robust effect of past UVR exposure on DNAm.

Solar Ultraviolet Radiation and Breast Cancer Risk: A Systematic Review and Meta-Analysis

BACKGROUND

A protective relationship has been hypothesized between exposure to solar ultraviolet radiation (UVR) and the development of breast cancer.

OBJECTIVE

The objective of this study was to conduct a systematic literature review and meta-analysis of studies examining the association of exposure to solar UVR and breast cancer risk.

METHODS

We searched Medline, EMBASE, and Web of Science for all studies investigating exposure to solar UVR and breast cancer risk. Separate analyses were performed using estimates of time spent in the sun, and ambient UVR. Associations were estimated using DerSimonian and Laird random-effect models. Heterogeneity was investigated through subgroup analyses and I2 statistics.

RESULTS

Fourteen studies were included in the review and 13 in the meta-analysis, with the majority (n=8) conducted in North America. We observed a decreased risk of breast cancer for individuals spending ≥1h/d in the sun during summer months over a lifetime or usual adulthood compared with <1h/d [pooled relative risk (RR)=0.84; 95% CI: 0.77, 0.91]. Spending ≥2h/d in the sun had a similar protective effect as 1 to <2h/d when compared with <1h/d (RR=0.83; 95% CI: 0.75, 0.93 vs. 0.83; 95% CI: 0.78, 0.89). Exposure during adolescence was suggestive of a lower risk of breast cancer than exposure later in life (≥45 years of age) (RR=0.83; 95% CI: 0.71, 0.98 vs. 0.97; 95% CI: 0.85, 1.11). Ambient UVR was not associated with the risk of breast cancer (RR=1.00; 95% CI: 0.93, 1.09).

DISCUSSION

To our knowledge, this was the first meta-analysis to estimate the risk of developing breast cancer associated with time spent in the sun. The results suggest that obtaining greater than an hour a day in the sun during the summer months could decrease the risk of developing breast cancer. https://doi.org/10.1289/EHP4861.

Vitamin D, DNA methylation, and breast cancer

BACKGROUND

Vitamin D has anticarcinogenic and immune-related properties and may protect against some diseases, including breast cancer. Vitamin D affects gene transcription and may influence DNA methylation.

METHODS

We studied the relationships between serum vitamin D, DNA methylation, and breast cancer using a case-cohort sample (1070 cases, 1277 in subcohort) of non-Hispanic white women. For our primary analysis, we used robust linear regression to examine the association between serum 25-hydroxyvitamin D (25(OH)D) and methylation within a random sample of the cohort ("subcohort"). We focused on 198 CpGs in or near seven vitamin D-related genes. For these 198 candidate CpG loci, we also examined how multiplicative interactions between methylation and 25(OH)D were associated with breast cancer risk. This was done using Cox proportional hazards models and the full case-cohort sample. We additionally conducted an exploratory epigenome-wide association study (EWAS) of the association between 25(OH)D and DNA methylation in the subcohort.

RESULTS

Of the CpGs in vitamin D-related genes, cg21201924 (RXRA) had the lowest p value for association with 25(OH)D (p = 0.0004). Twenty-two other candidate CpGs were associated with 25(OH)D (p < 0.05; RXRA, NADSYN1/DHCR7, GC, or CYP27B1). We observed an interaction between 25(OH)D and methylation at cg21201924 in relation to breast cancer risk (ratio of hazard ratios = 1.22, 95% confidence interval 1.10-1.34; p = 7 × 10-5), indicating a larger methylation-breast cancer hazard ratio in those with high serum 25(OH)D concentrations. We also observed statistically significant (p < 0.05) interactions for six other RXRA CpGs and CpGs in CYP24A1, CYP27B1, NADSYN1/DHCR7, and VDR. In the EWAS of the subcohort, 25(OH)D was associated (q < 0.05) with methylation at cg24350360 (EPHX1; p = 3.4 × 10-8), cg06177555 (SPN; p = 9.8 × 10-8), and cg13243168 (SMARCD2; p = 2.9 × 10-7).

CONCLUSIONS

25(OH)D concentrations were associated with DNA methylation of CpGs in several vitamin D-related genes, with potential links to immune function-related genes. Methylation of CpGs in vitamin D-related genes may interact with 25(OH)D to affect the risk of breast cancer.

Duration of Casual Sunlight Exposure Necessary for Adequate Vitamin D Status in Indian Men

OBJECTIVES

To investigate the duration of casual sunlight ultraviolet-B (UVB) exposure required to maintain optimal Vitamin D status (25-hydroxyvitamin-D [25(OH)D]) >50 nmol/L in urban Indian men, using polysulfone (PSU) dosimeters and a sunlight exposure questionnaire.

METHODS

In healthy men (aged 40-60 years) from Pune (18.52° N, 73.86° E), India, serum 25(OH)D was measured using enzyme-linked immunosorbent assay. Sunlight exposure was assessed using PSU dosimeter and by questionnaire.

RESULTS

Of 160 men (48.3 ± 5.6 years), 26.8% were deficient and 40.6% had insufficient Vitamin D concentrations. A hyperbolic function for the relationship between PSU measured sunlight exposure in standard erythema dose (SED) and serum 25(OH)D concentrations (r = 0.87, P < 0.01) revealed that daily exposure of 1 SED was sufficient to maintain serum 25(OH)D concentrations over 50 nmol/L. The curve plateaued around 5 SED (80 nmol/L) and extrapolation of the curve (>5 SED) did not increase 25(OH)D concentrations above 90 nmol/L. Receiver operating curve analysis confirmed that 1 SED-UV exposure was sufficient to maintain 25(OH)D concentrations over 50 nmol/L. Based on the questionnaire data, >1 h of midday casual sunlight exposure was required to maintain serum 25(OH)D concentrations above 50 nmol/L. Duration of sunlight exposure assessed by questionnaire and PSU dosimeter showed a significant correlation (r = 0.517, P < 0.01).

CONCLUSION

In urban Indian men, >1 h of casual midday sunlight exposure daily was required to maintain serum 25(OH)D concentrations above 50 nmol/L, and >2 h of casual sunlight exposure was needed to maintain 25(OH)D concentrations above 75 nmol/L. Excess sunlight did not increase 25(OH)D linearly. The sunlight exposure questionnaire was validated for use in clinical studies and surveys.

Genetic and epigenetic factors influencing vitamin D status

The global prevalence of vitamin D deficiency appears to be increasing, and the impact of this on human health is important because of the association of vitamin D insufficiency with increased risk of osteoporosis, cardiovascular disease and some cancers. There are few studies on the genetic factors that can influence vitamin D levels. In particular, the data from twin and family-based studies have reported that circulating vitamin D concentrations are partially determined by genetic factors. Moreover, it has been shown that genetic variants (e.g., mutation) and alteration (e.g., deletion, amplification, inversion) in genes involved in the metabolism, catabolism, transport, or binding of vitamin D to it receptor, might affect vitamin D level. However, the underlying genetic determinants of plasma 25-hydroxyvitamin D3 [25(OH)D] concentrations remain to be elucidated. Furthermore, the association between epigenetic modifications such as DNA methylation and vitamin D level has now been reported in several studies. The aim of current review was to provide an overview of the possible value of loci associated to vitamin D metabolism, catabolism, and transport as well epigenetic modification and environmental factors influencing vitamin D status.

Epigenetic Regulation of Centromere Chromatin Stability by Dietary and Environmental Factors

The centromere is a genomic locus required for the segregation of the chromosomes during cell division. This chromosomal region together with pericentromeres has been found to be susceptible to damage, and thus the perturbation of the centromere could lead to the development of aneuploidic events. Metabolic abnormalities that underlie the generation of cancer include inflammation, oxidative stress, cell cycle deregulation, and numerous others. The micronucleus assay, an early clinical marker of cancer, has been shown to provide a reliable measure of genotoxic damage that may signal cancer initiation. In the current review, we will discuss the events that lead to micronucleus formation and centromeric and pericentromeric chromatin instability, as well transcripts emanating from these regions, which were previously thought to be inactive. Studies were selected in PubMed if they reported the effects of nutritional status (macro- and micronutrients) or environmental toxicant exposure on micronucleus frequency or any other chromosomal abnormality in humans, animals, or cell models. Mounting evidence from epidemiologic, environmental, and nutritional studies provides a novel perspective on the origination of aneuploidic events. Although substantial evidence exists describing the role that nutritional status and environmental toxicants have on the generation of micronuclei and other nuclear aberrations, limited information is available to describe the importance of macro- and micronutrients on centromeric and pericentromeric chromatin stability. Moving forward, studies that specifically address the direct link between nutritional status, excess, or deficiency and the epigenetic regulation of the centromere will provide much needed insight into the nutritional and environmental regulation of this chromosomal region and the initiation of aneuploidy.

Global DNA hypomethylation in leukocytes associated with glioma risk

Global DNA hypomethylation in leukocytes has been associated with increased risk for a variety of cancers. However, the role of leukocyte global DNA hypomethylation in glioma development, if any, is largely unknown. To define this role, we performed a case-control study with 390 glioma patients and 390 controls with no known cancer. Levels of 5-methylcytosine (5-mC%), a marker for global DNA methylation, were measured in leukocyte DNA. Overall, median levels of 5-mC% were significantly lower in glioma cases than in controls (3.45 vs 3.82, P=0.001). Levels of 5-mC% differed significantly by age and sex among controls and by tumor subtype and grade among glioma cases. In multivariate analysis, lower levels of 5-mC% were associated with a 1.31-fold increased risk of glioma (odds ratio = 1.31, 95% confidence interval = 1.10-1.41). A significant dose-response trend was observed in quartile analysis (P=0.001). In an analysis further stratified by clinical characteristics at baseline, the association between lower levels of 5-mC% and glioma risk was evident only among younger participants (age <52 years), women, and those with aggressive tumor characteristics, such as glioblastoma subtype, high tumor grade (grade III or IV), and absence of IDH1 mutation. Our findings indicate that global DNA hypomethylation in leukocytes may contribute to the development of glioma and that the association is affected by age, sex, and tumor aggressiveness.

Global methylation of blood leukocyte DNA and risk of melanoma

Global DNA methylation, possibly influenced by lifestyle and environmental factors, has been suggested to play an active role in carcinogenesis. However, its role in melanoma has rarely been explored. The aims of this study were to evaluate the relationship between melanoma risk and levels of 5-methylcytosine (5-mC), a marker for global DNA methylation, in blood leukocyte DNA, and to determine whether this 5-mC level is influenced by pigmentation and sun exposure. This case-control study included 540 melanoma cases and 540 healthy controls. Overall, melanoma cases had significantly lower levels of 5-mC% than healthy controls (median: 3.24 vs. 3.91, p < 0.001). The significant difference between two groups did not differ by pigmentation or sun exposure. Among healthy controls, however, those who had fair skin color (p = 0.041) or light or no tanning after prolonged sun exposure (p = 0.031) or used a sunlamp (p = 0.028) had lower levels of 5-mC% than their counterparts. In addition, those with an intermediate or high phenotypic index, an indicator of cutaneous cancer susceptibility, had 2.58-fold greater likelihood of having a low level of 5-mC% [odds ratio (OR): 2.58; 95% confidence interval (CI): 1.72, 3.96] than those with a low phenotypic index. Lower levels of 5-mC% were associated with a 1.25-fold greater risk of melanoma (OR: 1.25; 95% CI: 1.08, 1.37). A significant dose-response relationship was observed in quartile analysis (p = 0.001). Our results suggest that global hypomethylation in blood leukocyte DNA is associated with increased risk of melanoma and that the level of methylation is influenced by pigmentation and sun exposure.

Race/Ethnicity-Specific Association of Vitamin D and Global DNA Methylation: Cross-Sectional and Interventional Findings

Objectives

Understanding of the influence of vitamin D deficiency on epigenome will provide novel insights into the chronic disease risk. We tested our hypotheses that 1) vitamin D deficiency is associated with global hypomethylation and this association may be race/ethnicity dependent; and 2) vitamin D supplementation will increase global DNA methylation level.

Methods

A two-stage design, cross-sectional observation followed by a 16 week randomized, double- blinded, placebo-controlled trial (RCT) of vitamin D3 supplementation, was undertaken. Global DNA methylation level (percentage of 5-methylcytosine, %5-mC) was quantified using leukocyte DNA with the MethylFlash^TM Methylated DNA Quantification kit (Epigentek). Global methylation data was obtained from 454 Caucasians and African Americans (42%) in the observation cohort and 58 African Americans with vitamin D deficiency in the dose responsive RCT.

Results

In the cross-sectional study, African Americans had lower %5-mC than Caucasians (P = 0.04). A significant interaction was detected between plasma 25(OH)D and race on %5-mC (P = 0.05), as a positive association was observed between plasma 25(OH)D and %5-mC in African Americans (β = 0.20, p<0.01), but not in Caucasians (β = 0.03, p = 0.62). In the 16-week RCT, a dose-response benefit of vitamin D₃ supplementation was observed for %5-mC, as indicated by a significant linear upward trend (-0.01 ± 0.01%, placebo; 0.11 ± 0.01%, ~600 IU/day; 0.30 ± 0.01%, ~2,000 IU/day; and 0.65 ± 0.01%, ~4,000 IU/day group; P-trend = 0.04).

Conclusions

Vitamin D deficiency is associated with global hypomethylation in African Americans. Vitamin D3 supplementation increases global DNA methylation in a dose-response manner in African Americans with vitamin D deficiency.

Response of transposable elements to environmental stressors

Transposable elements (TEs) comprise a group of repetitive sequences that bring positive, negative, as well as neutral effects to the host organism. Earlier considered as "junk DNA," TEs are now well-accepted driving forces of evolution and critical regulators of the expression of genetic information. Their activity is regulated by epigenetic mechanisms, including methylation of DNA and histone modifications. The loss of epigenetic control over TEs, exhibited as loss of DNA methylation and decondensation of the chromatin structure, may result in TEs reactivation, initiation of their insertional mutagenesis (retrotransposition) and has been reported in numerous human diseases, including cancer. Accumulating evidence suggests that these alterations are not the simple consequences of the disease, but often may drive the pathogenesis, as they can be detected early during disease development. Knowledge derived from the in vitro, in vivo, and epidemiological studies, clearly demonstrates that exposure to ubiquitous environmental stressors, many of which are carcinogens or suspected carcinogens, are capable of causing alterations in methylation and expression of TEs and initiate retrotransposition events. Evidence summarized in this review suggests that TEs are the sensitive endpoints for detection of effects caused by such environmental stressors, as ionizing radiation (terrestrial, space, and UV-radiation), air pollution (including particulate matter [PM]-derived and gaseous), persistent organic pollutants, and metals. Furthermore, the significance of these effects is characterized by their early appearance, persistence and presence in both, target organs and peripheral blood. Altogether, these findings suggest that TEs may potentially be introduced into safety and risk assessment and serve as biomarkers of exposure to environmental stressors. Furthermore, TEs also show significant potential to become invaluable surrogate biomarkers in clinic and possible targets for therapeutic modalities for disease treatment and prevention.