According to a study that was published in the International Journal of Epidemiology, vitamin D insufficiency may be the root cause of systemic inflammation.

In a bidirectional Mendelian randomization procedure, serum 25(OH)D concentrations were evaluated using a cohort of 294,970 people. Of them, 11.7% (n = 34,403) of subjects had values below the deficiency threshold (25 nmol/L). The research revealed an L-shaped relationship between genetically predicted blood 25(OH)D and serum CRP, with CRP levels and inflammation abruptly dropping with rising 25(OH)D concentration to normal levels.

Further, several pleiotropy-robust approaches using stratified MR analyses consistently produced data that confirmed the inverse relationship between 25(OH)D and CRP in the deficient range (P = 1.10E-05) but not at higher concentrations.

Thus, it seems likely that poor vitamin D levels in the body are causing the observed correlation between 25(OH)D and CRP. These findings imply that elevating vitamin D levels may lessen chronic inflammation, but only in vitamin D deficient individuals.  (Medscape - Aug 19, 2022.)

https://www.medscape.com/viewarticle/979452?src=#vp_2