Chronic obstructive pulmonary disease (COPD) is a leading cause of morbidity and mortality worldwide. To synthesize data on the worldwide prevalence and severity of COPD by geographical region, age groups, and smoking status in a systematic review. A systematic search was performed following Meta-analysis of Observational Studies in Epidemiology (MOOSE) guidelines. International databases including PubMed, Scopus and Web of Science were searched for population- based studies published between January 2004 and May 2015 that reported the prevalence of COPD anywhere in the world. The prevalence of COPD was calculated based on World Health Organization (WHO) regions and sex and severity stages using metaprop. Meta-regression and subgroup analysis were applied to determine the sources of heterogeneity. Sixty papers were screened with a combined subject sample size of 127 598. The prevalence of post-bronchodilator COPD was 12.16% (10.91-13.40%). The pooled prevalence of COPD was 15.70% (13.80-18.59%) in men and 9.93% (8.73- 11.13%) in women. Among all WHO regions, the highest prevalence was recorded in the Region of the Americas (14.53%), and the lowest was recorded in the South-East Asia Region/Western Pacific Region (8.80%). Meta-regression model variables were: sample size, WHO region, study quality score, level of gathering data, publication year, and sampling methods that justified 29.82% of heterogeneity detected among COPD prevalence rates worldwide. Global prevalence of COPD among men is about 5% higher than among women. The most prevalent stage of COPD is stage 1.

Selenium is an essential mineral that plays a key role in plenty of major metabolic processes. A growing body of literature has shown that selenium deficiency leads to an increase in plasma TC and TG levels. This study explores the effect of selenium supplementation on serum level of lipid profile [total cholesterol (TC), triglyceride (TG), low-density lipoprotein (LDL), high-density lipoprotein (HDL), very low density lipoprotein (VLDL)]. We systematically searched PubMed/MEDLINE, ISI/WOS, and Scopus (from their commencements to Jan 2016) to identify the papers investigating the association between the intake of selenium and lipid profile. Data extracted from the relevant studies were screened. The pooled standardized mean difference was estimated using the random or fixed effects model. Heterogeneity among the studies was assessed using Q-test. Of the potentially relevant articles screened, 11 articles including 1221 participants were included in this meta-analysis. Results of meta-analysis showed that intake of selenium resulted in a statistically significant improvement in TC, [(SMD): –0.13, 95% CI: (–0.24, –0.02)], TG [(SMD): –0.19, 95% CI: (–0.38, –0.01)] and VLDL [(SMD): –0.34, 95% CI: (–0.63, –0.05)]. The selenium supplementation did not significantly improve lipid profile such as LDL [(SMD): –0.08, 95% CI: (–0.036, 0.19)], HDL [(SMD): 0.01, 95% CI: (–0.164, 0.18)], HDL/TC ratio [(SMD): 0.025, 95% CI: (–0.11, 0.16)], non-HDL-C [(SMD): 0.018, 95% CI: (–0.13, 0.16)]. This meta-analysis suggests that the effect of selenium supplementation on the serum levels of TG and VLDL is marginally significant. However, the supplementation has no effect on other serum lipids. Moreover, the study shows that the effect of selenium supplementation on lipid profile is negative.