What is the appropriate vitamin D repletion regimen for an adult with a serum 25‑hydroxyvitamin D level of 17.1 ng/mL and no history of hypercalcemia, granulomatous disease, severe renal impairment, or sarcoidosis?

Vitamin D Replacement for Level of 17.1 ng/mL

For an adult with a vitamin D level of 17.1 ng/mL, initiate cholecalciferol (vitamin D3) 50,000 IU once weekly for 8–12 weeks, followed by maintenance therapy with 800–2,000 IU daily to achieve and sustain a target level of at least 30 ng/mL. 1

Understanding Your Deficiency Status

Your level of 17.1 ng/mL falls below the 20 ng/mL threshold that defines vitamin D deficiency, placing you at increased risk for secondary hyperparathyroidism, reduced bone mineral density, and elevated fracture risk. 1, 2 This degree of deficiency requires active treatment rather than simple maintenance supplementation. 1

Loading Phase Protocol

• Administer cholecalciferol (vitamin D3) 50,000 IU once weekly for 8 weeks if your deficiency is moderate (10–20 ng/mL), or extend to 12 weeks if your level is below 10 ng/mL or if you have symptoms such as bone pain or muscle weakness. 1, 2

• Cholecalciferol (D3) is strongly preferred over ergocalciferol (D2) because D3 maintains serum levels longer, has superior bioavailability, and is more effective when using intermittent (weekly) dosing schedules. 1, 2

• The 50,000 IU weekly regimen typically raises your 25-hydroxyvitamin D level by approximately 40–70 nmol/L (16–28 ng/mL), which should bring your level into the target range of at least 30 ng/mL. 1

Essential Co-Intervention: Calcium

• Ensure total calcium intake of 1,000–1,500 mg daily from diet plus supplements if needed, because vitamin D therapy requires adequate dietary calcium for optimal bone response and to suppress parathyroid hormone. 1, 2

• If you use calcium supplements, take them in divided doses of no more than 600 mg at a time to maximize intestinal absorption. 1

Maintenance Phase After Loading

• Transition to a maintenance dose of 800–2,000 IU daily after completing the 8–12 week loading phase to sustain your level above 30 ng/mL. 1

• An alternative maintenance regimen is 50,000 IU once monthly (equivalent to approximately 1,600 IU daily), which can be more convenient while achieving similar steady-state concentrations. 1

Monitoring Protocol

• Recheck your 25-hydroxyvitamin D level 3 months after starting supplementation to confirm that you have reached the target of at least 30 ng/mL, as vitamin D has a long half-life and levels need adequate time to plateau before measurement accurately reflects your response. 1, 3, 2

• Monitor serum calcium and phosphorus every 3 months during high-dose therapy to detect hypercalcemia early. 1, 2

• Once your level is stable in the target range, annual reassessment of vitamin D status is sufficient. 1, 3

Target Levels and Expected Benefits

• The minimum target is 30 ng/mL for anti-fracture efficacy, with some experts recommending 30–40 ng/mL for optimal musculoskeletal health, cardiovascular protection, and fall prevention. 1, 2

• Anti-fall efficacy begins at achieved levels of at least 24 ng/mL, while anti-fracture efficacy requires at least 30 ng/mL. 1

• The upper safety limit is 100 ng/mL, well above the levels expected with standard repletion regimens. 1

Safety Considerations and Contraindications

• Daily doses up to 4,000 IU are completely safe for adults, with some evidence supporting up to 10,000 IU daily for several months without adverse effects. 1

• Immediately discontinue all vitamin D supplementation if your serum calcium rises above 10.2 mg/dL (2.54 mmol/L), as this indicates a risk of hypercalcemia. 1, 2

• Do not use active vitamin D analogs (calcitriol, alfacalcidol, doxercalciferol, paricalcitol) to treat nutritional vitamin D deficiency, as they bypass normal regulatory mechanisms and dramatically increase the risk of hypercalcemia. 1, 2

• Vitamin D toxicity is rare and typically occurs only with prolonged daily doses exceeding 10,000 IU or serum levels above 100 ng/mL. 1

Common Pitfalls to Avoid

• Standard multivitamin preparations containing only 400 IU are grossly inadequate for correcting deficiency and should not be relied upon as your sole source of vitamin D. 1, 3

• Avoid single ultra-high loading doses exceeding 300,000 IU, as they have been shown to be inefficient or potentially harmful, particularly for fall and fracture prevention. 1

• Do not rely on sun exposure alone for vitamin D repletion, as it carries skin cancer risk and is often impractical for achieving adequate levels. 3

• Ensure compliance with the weekly regimen, as poor adherence is a common reason for inadequate response; monitoring can actually improve compliance by demonstrating treatment effectiveness. 1

Special Populations Requiring Modified Approach

• If you have chronic kidney disease (CKD) with an estimated GFR of 20–60 mL/min/1.73 m², use the same standard nutritional vitamin D replacement with cholecalciferol or ergocalciferol; do not use active vitamin D analogs. 1, 2

• If you have malabsorption syndromes (inflammatory bowel disease, post-bariatric surgery, celiac disease, pancreatic insufficiency), intramuscular vitamin D 50,000 IU may be preferred, as IM administration results in significantly higher levels and lower rates of persistent deficiency compared to oral supplementation. 1

• If you are elderly (≥65 years), a minimum of 800 IU daily is recommended for maintenance, though higher doses of 700–1,000 IU daily more effectively reduce fall and fracture risk. 1