Asthma is an airway condition associated with a chronic inflammatory response. Among adults, its prevalence is between 7% and 10%. Most patients self-report a history of asthma in childhood. Recent research indicates that vitamin D deficiencies and insufficiencies have been linked to the incidence of asthma in children.
Vitamin D is commonly known to support healthy bone mineralization and calcium homeostasis. It also has been shown to help support the inflammatory response and both innate and adaptive immune health. Vitamin D receptors (VDRs) are present throughout the body, which includes being located on some immune cells, such as lymphocytes and monocytes. Calcitriol (1,25[OH]2D) is a form of vitamin D that has been shown to help modulate T-cell differentiation, the secretion of interleukin (IL)-10 and the production of certain pro-inflammatory cytokines in monocytes and macrophages through VDR signaling. Vitamin D has also been shown to inhibit IL-1, IL-6, IL-8, and IL-12 and downregulate major histocompatibility complex class II molecules.
In a recently published review article by Salmanpour and colleagues, the potential connection between vitamin D status, immune health, and asthma are explored. The authors describe several biochemical mechanisms through which vitamin D may support airway health. For instance, calcitriol has been shown to help modulate matrix metalloproteinase-9 (MMP-9). MMP-9 is synthesized by certain inflammatory cells and may help promote airway health in the presence of the remodeling associated with asthma. MMP-9 activity is increased by tumor-necrosis factor-alpha (TNF-α) and it is attenuated by tissue inhibitors of matrix metalloproteinases (TIMP-1). VDRs and calcitriol have been shown to play a role in TNF-α levels and TIMP-1 to influence MMP-9 activity. Calcitriol may also help support extracellular matrix composition and immune cell infiltration.
Research indicates that vitamin D also influences the expression of disintegrin metalloprotease-33 and 24-hydroxylase (CYP24A1). Both of these are associated with airway smooth muscle health and the inflammatory response.
Eosinophil count and immunoglobulin E (IgE) are two biomarkers typically associated with asthma. Lowered vitamin D levels have been associated with increased eosinophils and total IgE. Some research suggests that vitamin D status may be considered a greater predictive factor for asthma than serum IgE levels or family history. However, more studies are needed before clinical conclusions can be made.
A clinical case-controlled study involving more than 900 children indicated a higher incidence of vitamin D deficiency in children with asthma. Among children with asthma, over 65% were reported to have vitamin D deficiencies and over 30% had insufficiencies. However, Salmanpour and colleagues report that more research is needed regarding the potential role of vitamin D supplementation in the presence of asthma.
Vitamin D may support many aspects of health, including bone mineralization, immune health, and a healthy inflammatory response. Although no clinical conclusions can be made at this time, further research may be warranted regarding vitamin D and its potential role in lung health in the presence of asthma.