Vitamin D inadequacy is pandemic in adults. Vitamin D deficiency causes osteopenia, precipitates and exacerbates osteoporosis, causes the painful bone disease osteomalacia, and increases muscle weakness, which worsens the risk of falls and fractures. Vitamin D deficiency can be prevented by sensible sun exposure and adequate supplementation. Monitoring serum 25-hydroxyvitamin D is the only way to determine vitamin D status. Recent recommendations suggest that in the absence of sun exposure, adults should ingest 1000 IU of vitamin D3 per day. The ideal healthy blood level of 25-hydroxyvitamin D should be 30 to 60 ng/mL. Vitamin D intoxication occurs when 25-hydroxyvitamin D levels are greater than 150 ng/mL. Three recent reports suggesting that vitamin D and calcium supplementation does not decrease the risk of fracture will be put into perspective in light of the vast literature supporting increasing vitamin D and calcium intake as an effective method for decreasing risk of vertebral and nonvertebral fractures.