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.
MATERIALS AND METHODS: TGBII was performed in male Wistar rats (3 to 5 months, 150 to 300 g) which underwent bilateral common carotid artery occlusion (BCCAO) for 20 minutes, then reperfused for 10 days (BCCAO group, n = 6). Two groups of BCCAO were treated with intraperitoneal injection of calcitriol 0.125 μg/kgBW (VD1 group) and 0.5 μg/kgBW (VD2 group). The spatial memory function was tested using a probe test with Morris water maze (MWM). mRNA expression of BAX and SOD2 were assessed by the RT-PCR method. Meanwhile, immunohistochemical staining was used for identification of SOD2 protein. Statistical analysis is tested using one-way ANOVA followed by post-hoc LSD.
RESULTS: MWM showed a shorter duration in target quadrant of BCCAO group than the SO group, which is associated with BAX upregulation and SOD2 downregulation. The VDtreated groups had longer duration probe test compared to BCCAO. Furthermore, VD-treated groups had a longer duration in probe test with lower mRNA expression of BAX and higher expression of SOD2. However, there was no significant difference in VD1 and VD2. Immunostaining showed a reduced SOD2 signal in pyramidal cell of CA1 area in BCCAO group and ameliorated in VD1 and VD2 groups.
CONCLUSION: Vitamin D ameliorates memory function and attenuates oxidative stress and apoptosis in the TGBII model.