Although no effect on blood pressure was shown in these trials, a significant reduction in CRP (mean difference (MD) of -0.65 mg/L) was observed with vitamin D supplementation, including an MD of -0.91 mg/L in studies with a duration of 3 months or more, and an MD of -2.10 mg/L with doses of 1000 IU per day or less. This significant reduction in CRP is notable, in part because it is an apparent benefit of supplementation; potentially a more clinically relevant finding than the association between lower serum levels of CRP and a higher serum 25-OH vitamin D previously observed in several studies.
This is in line with many previous observational studies, such as a cross-sectional study that found that low 25-OH levels were associated with a nearly 3-fold increase in risk for cardiovascular events, magnified to nearly 5-fold when found in combination with elevated CRP levels. It is also consistent with several previously published meta-analyses of vitamin D supplementation, including a meta-analysis of 8 randomized trials that found vitamin D supplementation reduced CRP and improved glycemic control among participants with cardiovascular disease, and a meta-analysis of 33 trials that found vitamin D supplementation reduced CRP and malondialdehyde, and also improved multiple markers of antioxidant status (e.g., glutathione) among patients with diabetes.