You’re depressed
Having the blues may be linked to an insufficient amount of vitamin D. According to the Vitamin D Council, vitamin D receptors have been found in many parts of the brain, including in areas linked to depression. Results from studies have been mixed—some researchers have found significant improvements in mood after supplementing with D, while others have not—but that could depend on the severity of the depression as well as the vitamin D deficiency. For example, researchers from Columbia University found that taking vitamin D supplements was effective for those who sufferred from clinically significant depression.