Diagnosis n treatment of vitamin D deficiency.
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Vitamin D deficiency: diagnosis and treatment
Diagnosis
Best initial test: serum 25-hydroxyvitamin D [25(OH)D]. It reflects body vitamin D stores. Do not use 1,25-dihydroxyvitamin D for routine deficiency assessment.
Commonly used interpretation:
| Serum 25(OH)D | Interpretation |
|---|---|
| <12 ng/mL (<30 nmol/L) | Deficiency, often severe |
| 12-20 ng/mL (30-50 nmol/L) | Inadequate / insufficient |
| ≥20 ng/mL (≥50 nmol/L) | Adequate for most people |
| >50-60 ng/mL | Usually unnecessary; review supplementation |
| >150 ng/mL | Possible toxicity |
Clinical features
- Often asymptomatic
- Bone pain or tenderness
- Proximal muscle weakness, myalgia, fatigue
- Falls or fragility fractures
- In children: rickets, delayed growth, bowed legs
- In adults with marked prolonged deficiency: osteomalacia
Useful accompanying tests, especially if deficiency is severe, symptomatic, recurrent, or unexplained:
- Serum calcium, phosphate, alkaline phosphatase
- Parathyroid hormone (PTH), often elevated due to secondary hyperparathyroidism
- Creatinine/eGFR
- Magnesium if hypocalcemia or poor response to therapy
- Consider coeliac disease or other malabsorption evaluation when appropriate
Who should be tested?
Testing is most useful in people at risk, such as those with:
- Little sun exposure, darker skin, covering clothing, institutionalization
- Older age
- Obesity
- Malabsorption: coeliac disease, inflammatory bowel disease, bariatric surgery, pancreatic disease
- Chronic kidney or liver disease
- Osteoporosis, fragility fracture, rickets/osteomalacia, unexplained high alkaline phosphatase
- Medicines affecting vitamin D metabolism, such as enzyme-inducing antiseizure drugs, rifampicin, or long-term glucocorticoids
Routine testing of every healthy adult is generally not necessary.
Treatment
1. Typical adult deficiency
Vitamin D3 (cholecalciferol) is generally preferred.
A common repletion regimen is either:
- 50,000 IU orally once weekly for 6-8 weeks, or
- 6,000 IU orally daily for 6-8 weeks
Then switch to maintenance 1,500-2,000 IU daily.
A practical alternative for mild deficiency or insufficiency is:
- 1,000-2,000 IU daily for about 3 months, then maintenance dosing based on risk and follow-up level.
Take it with a meal containing some fat to improve absorption.
2. Severe deficiency, obesity, malabsorption, or drugs that accelerate vitamin D breakdown
These patients may need higher doses, for example:
- 6,000-10,000 IU/day during repletion, followed by
- 3,000-6,000 IU/day maintenance
This should be individualized and monitored by a clinician, especially in malabsorption, kidney disease, liver disease, or with recurrent low levels.
3. Calcium intake
Ensure adequate calcium through food first. Many adults need roughly 1,000-1,200 mg/day total calcium from diet plus supplements if dietary intake is inadequate. Do not automatically prescribe high-dose calcium to everyone, particularly if there is a history of kidney stones or hypercalcemia.
4. Follow-up
Recheck 25(OH)D after about 8-12 weeks if the patient had a low baseline value, symptoms, major risk factors, malabsorption, or high-dose treatment. Also recheck calcium when clinically indicated.
The goal is usually at least 20 ng/mL (50 nmol/L) for most people. Some bone/metabolic specialists target higher levels in selected patients with osteoporosis, osteomalacia, or malabsorption, but excessive levels provide no routine benefit.
Special situations
- Chronic kidney disease: Management can be different because impaired kidneys may not activate vitamin D normally. Check calcium, phosphate, PTH, and renal function. Active vitamin D analogues such as calcitriol are not routine treatment for ordinary nutritional deficiency and should be used only under appropriate supervision.
- Children, pregnancy, breastfeeding: Dosing depends on age, weight, baseline level, and local guidance. Avoid applying adult high-dose schedules without medical advice.
- Hypercalcemia, sarcoidosis, tuberculosis, lymphoma, primary hyperparathyroidism, recurrent kidney stones: use vitamin D cautiously and with clinician-led calcium monitoring.
Toxicity and safety
Vitamin D toxicity is uncommon but can occur from prolonged excessive supplementation. It causes hypercalcemia, with nausea, vomiting, constipation, thirst, frequent urination, confusion, weakness, and kidney stones or kidney injury.
Without medical supervision, avoid long-term doses above 4,000 IU/day in adults. Short-term higher repletion doses are commonly used when deficiency is confirmed.
When urgent assessment is needed
Seek prompt medical care for confusion, severe vomiting, marked weakness, dehydration, severe thirst/polyuria, or symptoms of high calcium, especially if taking high-dose vitamin D or calcium supplements.
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