Vitamins Biomarker
Collection Type: Blood
Related System: Vitamins
25‑Hydroxyvitamin D (25‑OH D) is the main circulating form of vitamin D and the best indicator of overall vitamin D status. The blood test measures total 25‑OH D (both D2 and D3) to assess adequacy of vitamin D stores used for calcium and phosphorus balance, bone mineralization, and multiple cellular functions. Tests are ordered when bone pain, muscle weakness, recurrent fractures, delayed growth, or risk factors for deficiency (limited sun exposure, darker skin, obesity, malabsorption, older age) are present. Levels vary by age, skin pigmentation, season/geography, pregnancy, body mass index, and certain medications or chronic diseases.
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Symptom Checker30-100 ng/mL OR 75-250 nmol/L
Q: What if vitamin D-25 hydroxy is low?
A: If your 25‑hydroxy vitamin D is low, you may have higher risk of bone pain, muscle weakness and reduced bone density. Management typically includes clinician‑guided supplementation (often an initial higher dose then maintenance), sensible sun exposure and vitamin D–rich foods, and investigation for causes such as malabsorption or interacting medications. Levels are usually rechecked after 8 to 12 weeks and treatment adjusted by your healthcare professional.
Q: What is a dangerously low vitamin D level?
A: Vitamin D is measured as 25‑hydroxyvitamin D. Levels below about 12 ng/mL (30 nmol/L) are generally considered dangerously low and linked to osteomalacia in adults and rickets in children. Many guidelines classify <20 ng/mL (50 nmol/L) as deficient and 20–30 ng/mL (50–75 nmol/L) as insufficient. If low, seek medical evaluation and supervised supplementation.
Q: What is vitamin D 25-hydroxy normal range?
A: Vitamin D (25‑hydroxy) reference ranges are commonly: deficiency <50 nmol/L (<20 ng/mL); insufficiency 50–75 nmol/L (20–30 ng/mL); sufficiency 75–125 nmol/L (30–50 ng/mL). Some clinicians target ≥75 nmol/L for optimal bone health. Levels above about 125–150 nmol/L (50–60 ng/mL) may increase toxicity risk. Interpret results with clinical context and individual factors.
Q: Does low vitamin D 25 hydroxy cause weight gain?
A: Low 25‑hydroxyvitamin D is associated with higher body weight and obesity, but current evidence does not prove it causes weight gain. Low levels may result from fat sequestration and lifestyle factors (less sun, inactivity). Vitamin D supplementation alone generally doesn’t produce meaningful weight loss, though correcting deficiency can improve overall health. Any effect on weight is likely small and not firmly established.
Q: How can I increase my vitamin D 25 hydroxy?
A: Boost 25‑OH vitamin D with regular sensible sun exposure (short periods several times weekly, adjusted for skin tone/season), eat vitamin D‑rich foods (fatty fish, fortified milk/alternatives, egg yolks), and use vitamin D3 supplements if needed (take with a fat-containing meal). Check blood 25‑OH levels and follow your clinician’s recommended dose or prescription therapy if you’re deficient.
Q: Which disease is caused by vitamin D deficiency?
A: Vitamin D deficiency causes rickets in children—impaired bone mineralization leading to bowed legs, delayed growth and skeletal deformities—and osteomalacia in adults, characterized by bone pain, weakness and higher fracture risk. Chronic deficiency also contributes to secondary hyperparathyroidism, reduced bone density and muscle weakness, increasing fall and fracture risk. Prevention includes adequate sunlight, diet and supplementation when needed.