Vitamin D axis and its role in skin carcinogenesis: a comprehensive review

The influence of vitamin D supplementation on IGF-1 levels in humans: A systematic review and meta-analysis

BACKGROUND

Inconsistencies exist with regard to influence of vitamin D supplementation on IGF-1 levels. The inconsistencies could be attributed to several factors, such as dosage and duration of intervention, among others. To address these inconsistencies, this study was conducted to determine the impact of vitamin D supplementation on IGF-1 levels through a systematic review and meta-analysis of randomized controlled trials (RCTs).

METHODS

A comprehensive systematic search was carried out in PubMed/MEDLINE, Web of Science, SCOPUS and Embase for RCTs that investigated the impact of vitamin D intake on circulating IGF-1 levels from inception until June 2019. Weighted mean difference (WMD) with the 95 % CI were applied for estimating combined effect size. Subgroup analysis was performed to specify the source of heterogeneity among studies.

RESULTS

Pooled results from eight studies demonstrated an overall non-significant increase in IGF-1 following vitamin D supplementation (WMD: 4 ng/ml, 95 % CI: -4 to 11). However, a significant degree of heterogeneity among studies was observed (I² = 66 %). The subgroup analyses showed that vitamin D dosage of ≤1000 IU/day (WMD: 10 ng/ml) significantly increased IGF-1 compared to the vitamin D dosage of <1000 IU/day (WMD: -1 ng/ml). Moreover, intervention duration ≤12 weeks (WMD: 11 ng/ml) significantly increased IGF-1 compared to intervention duration <12 weeks (WMD: -3 ng/ml). In the epidemiological cohort study, participants under 60 years of age with a higher dietary vitamin D intake had significantly higher IGF-1 levels when compared to those with lower dietary vitamin D intake in second categories.

CONCLUSION

The main results indicate a non-significant increase in IGF-1 following vitamin D supplementation. Additionally, vitamin D dosages of <1000 IU/day and intervention durations of <12 weeks significantly raised IGF-1 levels.

Immunohistochemical expression of vitamin D receptor in melanocytic naevi and cutaneous melanoma: a case-control study

BACKGROUND

Vitamin D deficiency is associated with higher risk of cancer, possibly due to its antiproliferative, antiangiogenic, proapoptotic, cell-differentiating and anti-invasive effects. The anticarcinogenic role of vitamin D in melanoma is still a matter of debate. Loss of nuclear and cytoplasmic vitamin D receptor (VDR) expression in melanoma cells has been reported.

OBJECTIVES

To analyse VDR immunohistochemical expression in benign dermal naevi (DN) and malignant melanoma (MM).

METHODS

A case-control study evaluated nuclear and cytoplasmic VDR immunohistochemical staining in 54 DN and 55 MM tissue samples.

RESULTS

There was significantly higher cytoplasmic VDR positivity in DN compared with MM (59% vs. 16%, P < 0·001). The mean VDR cytoplasmic expression was also higher in DN vs. MM (P < 0·001). No differences in nuclear VDR positivity were observed between groups, but mean nuclear VDR expression was significantly lower in DN vs. MM (P = 0·02). The loss of cytoplasmic VDR in MM was associated with Clark level, tumour staging and American Joint Committee on Cancer pTNM staging (P=0·004, 0·009 and 0·02, respectively).

CONCLUSIONS

Alterations in VDR expression and localization are found in MM compared with DN. Loss of cytoplasmic VDR was associated with melanoma tumour size, suggesting that loss of cytoplasmic VDR may be a prognostic factor.