Vitamin D3 (25 Hydroxy)

Vitamin D3 25-hydroxy (25(OH)D, calcifediol) is the main circulating form of vitamin D produced in the liver from cholecalciferol. It’s the standard blood marker for vitamin D status. Converted in the kidney to the active hormone calcitriol, it helps regulate calcium and phosphate balance, supporting bone health and immune function. Results are reported in ng/mL or nmol/L.

A low 25‑hydroxyvitamin D level indicates vitamin D insufficiency or deficiency, which can impair calcium absorption and bone health. Consequences include bone pain, muscle weakness, rickets in children, and osteomalacia or higher fracture risk in adults. Causes include inadequate sun exposure, poor dietary intake, malabsorption, obesity, liver or kidney disease, or certain medications. Treatment usually involves lifestyle changes and vitamin D supplementation under medical guidance.

Low vitamin D3 impairs calcium absorption, causing bone pain, muscle weakness and increased fracture risk; in children it can cause rickets and in adults osteomalacia. Deficiency is linked to fatigue, mood changes (including depression), weakened immunity with higher infection risk, and may worsen some chronic conditions. Severe or prolonged deficiency needs medical assessment and supplementation.

A vitamin D 25‑hydroxy blood test measures the circulating form of vitamin D to assess overall vitamin D status from sun exposure, diet, and supplements. It detects deficiency, insufficiency, or adequacy, guides treatment and monitoring, and helps evaluate causes of bone pain, muscle weakness, rickets or osteomalacia. Results are reported in ng/mL or nmol/L and can be affected by season, age and medical conditions.

If 25‑hydroxy vitamin D is high, it often reflects excessive supplementation and can cause hypercalcemia with symptoms like nausea, vomiting, weakness, increased thirst/urination, confusion, kidney stones and calcification. Stop supplements and contact a healthcare provider promptly for repeat testing, serum calcium and kidney function checks. Severe cases may need IV fluids, medications to lower calcium and specialist care.

Vitamin D deficiency has been linked to poorer sleep quality, shorter duration, and greater daytime sleepiness. Vitamin D receptors in brain regions that regulate sleep suggest a biological role; low levels are associated with higher risk of insomnia and sleep-disordered breathing. Correcting deficiency may improve sleep for some people, but evidence is mixed—get blood testing and discuss supplementation and dosing with your healthcare provider.