What is already known on this topic? The effects of vitamin D on hypertension risk and blood pressure have been explored widely in cohort studies and randomized controlled trials (RCTs), but whether the association is causal still is unknown. What is added by this report? We performed an update meta-analysis of both cohort studies and RCTs in a generally heathy population and found that the dose-response relationship between circulating 25-hydroxyvitamin D level and hypertension risk was approximately L-shaped. However, pooled results of RCTs showed that there was still no significant reduction in systolic and diastolic blood pressure. What are the implications for public health practice? Vitamin D supplementation is ineffective to prevent hypertension.

Objective:The present study aimed to evaluate the validity and reproducibility of a thirteen-item FFQ regarding identification of dietary conditions in a rural population in China.Design:A reproducibility study repeated the first FFQ (FFQ1) approximately 4 weeks later (FFQ2). A validity study evaluated the mean of three consecutive 24 h diet recalls as the reference measure.Setting:Cross-sectional study.Participants:Residents of a rural area in Henan Province, which is located in the central region of China.Results:A total of 295 individuals participated in the reproducibility study. In addition, 123 people agreed to participate in the validity study. Spearman’s correlation coefficients between the two FFQ ranged from 0·06 (vegetables) to 0·58 (eggs). Spearman’s correlation coefficients between the two methods of collection ranged from 0·01 for cereal to 0·49 for staple foods. The mean of the intraclass correlation coefficients of the two FFQ (FFQ1 v. FFQ2) was 0·19. Bland–Altman analysis indicated good agreement for most food groups across the range of intake for the two studies.Conclusions:The study demonstrated that our FFQ design could be used as a representative tool to conduct a dietary evaluation of a rural population.

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Previous studies have suggested that vitamin D is associated with cardiovascular disease (CVD), however, the relationship between vitamin D levels and CVD risk is still unclear. The purpose of this study was to assess the relationship of serum concentration of 25-hydroxyvitamin D (25(OH)D) with CVD in rural residents of Henan province of China. Basic information and medical history were gathered through face-to-face surveys from July 2013 to August 2015, and biochemical indicators were gathered in a laboratory setting. Logistic and restricted cubic splines regression analyses were used to estimate odd ratios (ORs) and 95% confidence intervals (95%CI) of CVD. A total of 1078 participants were included, the mean serum 25(OH)D concentration was determined to be 25 ± 18 ng/ml, with 54.45% of the participants presenting vitamin D deficiency [25(OH)D < 20 ng/mL]. Moreover, the prevalence of CVD was 59.28% in the vitamin D deficient group, which was higher than in the insufficient (48.55%) and sufficient groups (52.78%). After adjusting for potential confounders, compared with the deficient group, the ORs (95%CI) of CVDs were 0.68 (0.50, 0.91) in the insufficient group and 0.81 (0.56, 1.16) in the sufficient group. A nonlinear (U-shaped) association was observed between the risk of CVD and 25(OH)D concentration. Further research suggested that the risk of CVD was higher in males than in females. In conclusion, a U-shape association between serum levels of 25(OH)D and the risk of CVD was identified in our study, suggesting a nonlinear relationship between vitamin D with the prevalence of CVD.

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