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Open access

Zhen-yu Song, Qiuming Yao, Zhiyuan Zhuo, Zhe Ma and Gang Chen

Previous studies investigating the association of circulating 25-hydroxyvitamin D level with prognosis of prostate cancer yielded controversial results. We conducted a dose–response meta-analysis to elucidate the relationship. PubMed and EMBASE were searched for eligible studies up to July 15, 2018. We performed a dose–response meta-analysis using random-effect model to calculate the summary hazard ratio (HR) and 95% CI of mortality in patients with prostate cancer. Seven eligible cohort studies with 7808 participants were included. The results indicated that higher vitamin D level could reduce the risk of death among prostate cancer patients. The summary HR of prostate cancer-specific mortality correlated with an increment of every 20 nmol/L in circulating vitamin D level was 0.91, with 95% CI 0.87–0.97, P = 0.002. The HR for all-cause mortality with the increase of 20 nmol/L vitamin D was 0.91 (95% CI: 0.84–0.98, P = 0.01). Sensitivity analysis suggested the pooled HRs were stable and not obviously changed by any single study. No evidence of publications bias was observed. This meta-analysis suggested that higher 25-hydroxyvitamin D level was associated with a reduction of mortality in prostate cancer patients and vitamin D is an important protective factor in the progression and prognosis of prostate cancer.

Open access

Qiu-ming Yao, Bin Wang, Xiao-fei An, Jin-an Zhang and Liumei Ding

Background

Type 2 diabetes is a risk factor for testosterone deficiency and impaired sex steroid status. Some studies also investigated the association of testosterone level with diabetes risk in men, but reported controversial findings. To clarify this issue, we conducted a systematic review and meta-analysis.

Methods

PubMed, EMBASE and Web of Science were searched for eligible cohort or nested case–control studies published up to August 15, 2017. Meta-analysis was used to calculate the pooled relative risk (RR) of type 2 diabetes associated with higher testosterone level.

Results

Thirteen cohort or nested case–control studies with 16,709 participants were included. Meta-analysis showed that higher total testosterone level could significantly decrease the risk of type 2 diabetes in men (RR = 0.65; 95% CI 0.50–0.84; P = 0.001), and higher free testosterone level could also decrease the risk of type 2 diabetes in men (RR = 0.94; 95% CI 0.90–0.99; P = 0.014). After excluding two studies that did not calculate RRs by quartiles of testosterone levels, both higher total testosterone and free testosterone levels could decrease the risk of type 2 diabetes in men, and the pooled RRs were 0.62 (95% CI 0.51–0.76; P < 0.001) and 0.77 (95% CI 0.61–0.98; P = 0.03), respectively.

Conclusion

This meta-analysis suggests that higher testosterone level can significantly decrease the risk of type 2 diabetes in men. Therefore, combined with previous researches, the findings above suggest a reverse-causality scenario in the relation between testosterone deficiency and risk of type 2 diabetes in men.