Vitamin C intake and multiple health outcomes: an umbrella review of systematic reviews and meta-analyses.

The purpose of this article was to assess the existing systematic reviews and meta-analyses for the association between vitamin C intake and multiple health outcomes. A total of 76 meta-analyses (51 papers) of randomised controlled trials and observational studies with 63 unique health outcomes were identified. Dose-response analysis showed that vitamin C intake was associated with reduced risk of all-cause mortality, cardiovascular disease (CVD), oesophageal cancer, gastric cancer, cervical cancer and lung cancer with an increment of 50-100 mg per day. Beneficial associations were also identified for respiratory, neurological, ophthalmologic, musculoskeletal, renal and dental outcomes. Harmful associations were found for breast cancer and kidney stones for vitamin C supplement intake. The benefits of vitamin C intake outweigh the disadvantages for a range of health outcomes. However, the recommendation of vitamin C supplements needs to be cautious. More prospective studies and well-designed randomised controlled trials (RCTs) are needed.

A dose-response meta-analysis of green tea consumption and breast cancer risk.

Whether drinking green tea (GT) could reduce the risk of breast cancer (BC) is still controversial. The search was performed using PubMed, Embase and Web of Science databases. The generalised least square method and constrained cubic spline model were performed to assess the dose-response trends between GT consumption and BC risk. The attributable risk proportion (ARP) was also calculated. A total of 16 studies were included and the pooled relative risks was 0.86 (95%CI: 0.75-0.99) for BC risk at the highest vs. lowest levels of GT consumption. GT consumption (pnonlinearity = .110), drinking GT years (pnonlinearity = .393) and BC risk were both negatively linearly correlated. Moreover, The ARP results demonstrated in China, people who drink GT do not suffer from BC, 23.5% of which may be attributed to drinking GT. In conclusion, drinking GT may have a positive effect on reducing BC risk, especially in long-term, high doses.