What is the appropriate treatment for an adult with a serum 25‑hydroxy‑vitamin D (25‑OH‑vitamin D) level of 28 ng/mL and no contraindications such as hypercalcemia, severe renal impairment, or granulomatous disease?

Treatment for Vitamin D Level of 28 ng/mL

For an adult with a serum 25-hydroxyvitamin D level of 28 ng/mL, add 1,000 IU of vitamin D3 (cholecalciferol) daily to current intake and recheck the level in 3 months, with the goal of achieving at least 30 ng/mL for optimal bone health and fracture prevention. 1

Understanding Your Vitamin D Status

Your level of 28 ng/mL falls into the "insufficiency" range (20–30 ng/mL), meaning it is suboptimal but not critically deficient. 1, 2 This level is just below the 30 ng/mL threshold required for:

• Anti-fracture efficacy – levels ≥30 ng/mL reduce non-vertebral fractures by 20% and hip fractures by 18% 1
• Fall prevention – anti-fall benefits begin at ≥24 ng/mL, but optimal protection requires ≥30 ng/mL 1
• Suppression of secondary hyperparathyroidism – PTH stabilizes when 25(OH)D reaches 28–30 ng/mL 3, 4

Recommended Treatment Approach

Initial Supplementation Strategy

Start with 1,000 IU vitamin D3 daily added to your current intake (diet + any existing supplements). 1 This conservative approach is appropriate for insufficiency (20–30 ng/mL) rather than frank deficiency (<20 ng/mL). 1, 2

• Why vitamin D3 (cholecalciferol) over D2 (ergocalciferol)? Vitamin D3 maintains serum concentrations longer and has superior bioavailability, particularly with intermittent dosing schedules. 5, 1
• Expected response: Approximately 1,000 IU daily raises serum 25(OH)D by ~10 ng/mL over 3 months, which should bring your level from 28 to ~38 ng/mL. 1

Alternative High-Dose Loading Regimen (If Faster Correction Desired)

If more rapid correction is preferred, you may use ergocalciferol 50,000 IU once weekly for 8 weeks, followed by maintenance dosing. 5, 1 However, this aggressive regimen is typically reserved for levels <20 ng/mL. 1, 6 For your level of 28 ng/mL, the daily 1,000 IU approach is more physiologic and equally effective. 1

Monitoring Protocol

• Recheck serum 25(OH)D in 3 months after starting supplementation to verify you have reached ≥30 ng/mL. 1, 2 Measuring earlier will not reflect steady-state levels and may lead to inappropriate dose adjustments. 1
• Once target levels are achieved (≥30 ng/mL), transition to maintenance dosing of 800–1,000 IU daily. 5, 1
• Annual monitoring is sufficient once levels are stable in the optimal range (30–50 ng/mL). 1

Essential Co-Interventions

Ensure adequate calcium intake of 1,000–1,200 mg daily from diet plus supplements if needed. 5, 1 Vitamin D cannot exert its full bone-protective effect without sufficient calcium. 1

• Take calcium supplements in divided doses of ≤600 mg at a time for optimal absorption. 1
• Separate calcium from iron-containing supplements by at least 2 hours to prevent absorption interference. 1

Safety Considerations

• Daily doses up to 4,000 IU are completely safe for adults; toxicity is rare below 10,000 IU/day or serum levels <100 ng/mL. 1, 7
• The upper safety limit for serum 25(OH)D is 100 ng/mL, far above the target range of 30–50 ng/mL. 1
• Avoid single mega-doses ≥300,000 IU, which paradoxically increase fall and fracture risk. 1

Common Pitfalls to Avoid

• Standard multivitamins contain only ~400 IU of vitamin D, which is insufficient to correct insufficiency or maintain optimal levels. 2
• Do not rely on sun exposure alone for vitamin D repletion due to skin cancer risk and impracticality. 1, 2
• Do not use active vitamin D analogs (calcitriol, alfacalcidol) to treat nutritional vitamin D insufficiency, as they bypass normal regulation and increase hypercalcemia risk. 1, 8

Special Populations Requiring Modified Approach

• Elderly (≥65 years): Start with at least 800 IU daily, as higher doses (700–1,000 IU) more effectively reduce falls and fractures in this age group. 1
• Obesity: Higher doses may be required because vitamin D is sequestered in adipose tissue. 1
• Malabsorption syndromes (post-bariatric surgery, inflammatory bowel disease, celiac disease): Intramuscular vitamin D 50,000 IU is preferred if oral supplementation fails. 1
• Chronic kidney disease (CKD stages 3–4): Use standard nutritional vitamin D (cholecalciferol or ergocalciferol), not active analogs, with the same target of ≥30 ng/mL. 8

Expected Clinical Benefits

Achieving and maintaining 25(OH)D ≥30 ng/mL provides:

• 20% reduction in non-vertebral fractures 1
• 18% reduction in hip fractures 1
• 19% reduction in fall risk (with doses of 700–1,000 IU/day) 1
• Suppression of secondary hyperparathyroidism and improved bone mineral density 3, 4