Prohormone effects?
The anti-inflammatory effects observed with serum vitamin D could be related to its role as a prohormone that can impact vitamin D receptor–expressing immune cells, such as monocytes, B cells, T cells, and antigen-presenting cells, the authors noted.
“Indeed, cell experiments have shown that active vitamin D can inhibit the production of proinflammatory cytokines, including [tumor necrosis factor]–alpha, interleukin-1b, IL-6, IL-8, and IL-12, and promote the production of IL-10, an anti-inflammatory cytokine,” they explained.
In that regard, adequate vitamin D concentrations could be important in preventing inflammation-related complications from obesity and reduce the risk or severity of chronic illnesses with an inflammatory component, such as cardiovascular diseases, diabetes, autoimmune diseases, neurodegenerative conditions, and others, the authors noted.
Previous studies unable to assess effect of deficiency
While the current findings contradict other studies that have used Mendelian randomization and showed no causal effect of 25(OH)D on CRP, those previous studies only used a standard linear Mendelian randomization method that could not rule out the possibility of a ‘threshold effect’ restricted to vitamin D deficiency, the authors noted.
“Indeed, it is logical to expect that improving vitamin D status would be relevant only in the presence of vitamin D deficiency, whereas any further additions may be redundant and, in the ... extreme of supplementation, might become toxic,” they wrote.
However, the nonlinear Mendelian randomization approach used in the current study allows for better detection of the association, and the authors point out that the method has also been recently used in research showing an adverse effect of vitamin D deficiency on cardiovascular disease risk and mortality, which would not be visible using the standard linear Mendelian randomization approach.
Meanwhile, the current findings add to broader research showing benefits of increases in vitamin D to be mainly limited to those who are deficient, with limited benefit of supplementation for those who are not, Dr. Hypponen emphasized.
“We have repeatedly seen evidence for health benefits for increasing vitamin D concentrations in individuals with very low levels, while for others, there appears to be little to no benefit,” Dr. Hypponen said in a press statement.
“These findings highlight the importance of avoiding clinical vitamin D deficiency and provide further evidence for the wide-ranging effects of hormonal vitamin D,” she added.
The study was financially supported by the National Health and Medical Research Council, Australia. The authors reported no relevant financial relationships.
A version of this article first appeared on Medscape.com.