Are You Vitamin D Deficient? If you live below the line drawn from Los Angeles to Atlanta, your skin can convert the inactive form of vitamin D to the active form. Otherwise, you need a supplement—the active form is vitamin D3. A tanning booth? Only if you think you can beat skin cancer.
To learn your level before supplementing, ask your doctor for a serum 25-hydroxyvitamin D concentration. The standard test uses a scale of 8 to 40 ng/mL. Low vitamin D levels are common and often underlooked in those with chronic back pain, and osteoarthritis.