The Relation Between Vitamin D and Traumatic Brain Injury: Possible Mechanisms and Effect on the Severity and Progression

Vitamin D is a fat-soluble, neuroactive secosteroid. It not only regulates calcium homeostasis but also plays an important role in other body functions such as neuronal function. The neuroprotective effect of vitamin D is not fully understood. However, several pathways were suggested. Vitamin D has an antioxidant effect through the upregulation of antioxidant enzymes and downregulation of the culprit cellular elements responsible for oxidative stress such as the M1 microglia. Vitamin D also plays a role in neuromodulation due to the expression of alpha 1 hydroxylase enzyme in multiple immune cells such as B cells, T cells, dendritic cells, monocytes, and macrophages. Moreover, its interaction with nerve growth factors and calcium regulation plays an important role in preserving neuronal function and preventing apoptosis. The relation between vitamin D and traumatic brain injury is complicated and not fully understood. It was hypothesized that they have a bidirectional relationship, meaning that traumatic brain injury may lead to exhaustion of the body’s vitamin D storage. Moreover, the level of vitamin D correlates with the severity of traumatic brain injury, with a worse prognosis associated with vitamin D deficiency. Several studies found that patients with TBI had either vitamin D insufficiency or deficiency. Additionally, previous studies reported that TBI patients who had vitamin D supplementation eventually had better prognosis and better management of the long-term sequelae. In this chapter, we aim to summarize the possible mechanisms of vitamin D neuroprotection, the possible role of vitamin D in TBI, and describe the relationship between vitamin D and the severity and progression of TBI.