Using National Academies thresholds, NHANES 2011 to 2014 found about 18% of people in the US aged 1 and older at risk of inadequacy (25(OH)D 12 to 19.6 ng/mL) and 5% at risk of deficiency (below 12 ng/mL). Severe deficiency causes rickets in children and osteomalacia (soft bones) in adults. Most low levels cause no symptoms and are found only by a blood test.
Common symptoms
Often no symptoms until deficiency is severe
Bone pain or aching (osteomalacia)
Muscle weakness
In children: rickets, with bowed legs, delayed growth and soft bones
In infants with severe deficiency: poor growth, muscle spasms or seizures from low blood calcium
At-risk groups
Breastfed infants not given a vitamin D supplement
Older adults (the skin makes less vitamin D with age)
People who get little sun on their skin, including those who stay indoors or cover their skin
People with darker skin (melanin reduces vitamin D production)
People with conditions that limit fat absorption, such as celiac disease, Crohn's disease or cystic fibrosis
People with obesity or who have had gastric bypass surgery
People taking orlistat or long-term corticosteroids
When to see a doctorPersistent bone pain or muscle weakness, or a condition that affects vitamin D absorption, is a reason to ask a doctor about a 25-hydroxyvitamin D blood test; the Endocrine Society (2024) advises against routine testing of healthy people. The National Academies consider 20 ng/mL (50 nmol/L) or more sufficient for most people, with deficiency risk rising below 12 ng/mL (30 nmol/L). Do not take more than 4,000 IU a day without medical advice, because too much raises blood calcium.