Vitamin D deficiency has a causative role in the systemic inflammation that commonly accompanies it, with inflammation declining, reflected by reductions in elevated C-reactive protein (CRP), as vitamin D levels increase to normal levels, new research shows.
However, there is no reverse effect between the two: Changes in CRP levels did not appear to affect vitamin D levels.
first author Elina Hypponen, PhD, a professor in nutritional and genetic epidemiology and director of the Australian Centre for Precision Health, Adelaide, said in an interview.
“Given that the serum CRP level is a widely used biomarker for chronic inflammation, these results suggest that improving vitamin D status may reduce chronic inflammation, but only for people with vitamin D deficiency,” Dr. Hypponen and coauthors reported in their study, published in the International Journal of Epidemiology.
Vitamin D associated with CRP in ‘L-shaped’ manner
Nutritional factors are known to influence systemic inflammation in a variety of ways. However, there has been debate over the association between vitamin D – specifically, serum 25-hydroxyvitamin D (25[OH]D), an indicator of vitamin D status – and CRP, with some reports of observational associations between the two disputed in more robust randomized trials.
To further evaluate the relationship, the authors performed a bidirectional Mendelian randomization analysis, using a cohort of 294,970 unrelated participants of White/British ancestry in the UK Biobank, the largest cohort to date with measured serum 25(OH)D concentrations, they noted.
Overall, the average 25(OH)D concentration was 50.0 nmol/L (range, 10-340 nmol/L), with 11.7% (n = 34,403) of participants having concentrations of less than 25 nmol/L, considered deficient.
The analysis showed that genetically predicted serum 25(OH)D was associated with serum CRP in an L-shaped manner, with CRP levels, and hence inflammation, sharply decreasing in relation to increasing 25(OH)D concentration to normal levels.
However, the relationship was only significant among participants with 25(OH)D levels in the deficiency range (< 25 nmol/L), with the association leveling off at about 50 nmol/L of 25(OH)D, which is generally considered a normal level.
The association was supported in further stratified Mendelian randomization analyses, which confirmed an inverse association between serum 25(OH)D in the deficiency range and CRP, but not with higher concentrations of serum vitamin D.
Conversely, neither linear nor nonlinear Mendelian randomization analyses showed a causal effect of serum CRP level on 25(OH)D concentrations.
The findings suggest that “improving vitamin D status in the deficiency range could reduce systemic low-grade inflammation and potentially mitigate the risk or severity of chronic illnesses with an inflammatory component,” the authors noted.
Dr. Hypponen added that the greatest reductions in CRP are observed with correction of the most severe vitamin D deficiency.
“The strongest benefits of improving concentrations will be seen for people with severe deficiency,” Dr. Hypponen said in an interview.
“In our study, much of the benefit was achieved when people reached the National Academy of Sciences endorsed cutoff of 50 nmol/L [for vitamin D sufficiency].”