Vitamin D insufficiency affects an estimated 35-40% of US adults, with higher rates in older adults, people with darker skin, and northern latitudes. Severe deficiency causes rickets in children (irreversible bone deformities if untreated) and osteomalacia in adults. Most cases are subclinical and detected by blood test.
Common symptoms
Bone pain or muscle aches
Muscle weakness, especially in the legs
Fatigue
Frequent illness or infections
Mood changes — depressive symptoms (in deficient populations)
Slow wound healing
Hair loss
Bone deformities in children (rickets) — bowed legs, delayed growth
Often asymptomatic until severe
At-risk groups
Adults aged 65+ (skin produces less vitamin D from sunlight)
People with darker skin (melanin reduces vitamin D synthesis)
People living above 37° latitude (limited UVB year-round)
Indoor lifestyle, office workers, night shift workers
People with obesity (vitamin D sequestered in fat tissue)
Exclusively breastfed infants without supplementation
People with malabsorption conditions (celiac, Crohn's, gastric bypass)
People taking corticosteroids, anticonvulsants, or weight-loss drugs
People who consistently use sunscreen or cover skin for cultural reasons
When to see a doctorPersistent bone or muscle pain, frequent infections, or unexplained fatigue in any at-risk group warrants a 25-hydroxyvitamin D blood test. Levels below 20 ng/mL indicate deficiency; 20-30 ng/mL is insufficient. Important: do not take high-dose vitamin D (>4,000 IU/day) without lab confirmation — toxicity causes hypercalcemia.