There is a high prevalence of hypovitaminosis D in patients with back pain regardless of whether or not they require surgical intervention. Furthermore, the risk of hypovitaminosis D is not limited to individuals with traditional clinical risk factors. Vitamin D plays an essential role in bone formation, maintenance, and remodeling, as well as muscle function. Published data indicate that hypovitaminosis D could adversely affect bone formation and muscle function in multiple ways. The literature contains numerous reports of myopathy and/or musculoskeletal pain associated with hypovitaminosis D. In terms of spinal fusion outcomes, a patient may have a significant decrease in pain and the presence of de novo bone on an X-ray, yet their functional ability may remain severely limited. Hypovitaminosis D may be a contributing factor to the persistent postoperative pain experienced by these patients. Indeed, hypovitaminosis D is not asymptomatic, and symptoms can manifest themselves independent of the musculoskeletal pathological changes associated with conditions like osteomalacia. It appears that vitamin D status is routinely overlooked, and there is a need to raise awareness about its importance among all healthcare practitioners who treat spine patients. 1. Introduction A large portion of the United States population experiences low back pain, and an increasing number undergo spinal fusion each year. While many patients achieve a satisfactory outcome, there is a subpopulation that fails to achieve acceptable outcomes. These patients may have obvious causes for their outcomes (e.g., pseudarthrosis); however, there are those that are deemed fused yet continue to experience low back pain and other symptoms. Although many factors may be considered when a patient experiences a suboptimal outcome following spinal fusion surgery, serum vitamin D concentration is rarely considered even though most physicians acknowledge its importance in maintaining musculoskeletal health. In this review, we discuss the role of vitamin D in musculoskeletal health especially in relation to low back pain and outcomes of spinal fusion surgery. Our discussion includes the risk factors and prevalence rates of hypovitaminosis D as well as the literature published on vitamin D and spinal surgery. A key concept is the fact that hypovitaminosis D is not asymptomatic, and we delineate the mechanisms by which hypovitaminosis D can adversely affect spinal fusion outcomes. 2. Vitamin D 2.1. What Is Vitamin D? The term vitamin D refers to a group of structurally related metabolites [1]. Vitamin
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