What is the recommended treatment for an adult with a serum 25‑hydroxy‑vitamin D level of 28 ng/mL?

Treatment for Vitamin D Level of 28 ng/mL

For an adult with a serum 25-hydroxyvitamin D level of 28 ng/mL (classified as insufficiency), start oral vitamin D₃ (cholecalciferol) 1,000–2,000 IU daily and recheck levels in 3 months to confirm achievement of the target ≥30 ng/mL. 1

Understanding Your Current Status

Your level of 28 ng/mL falls into the "insufficiency" range (20–30 ng/mL), which is suboptimal but not critically deficient. 1, 2 While you are not severely deficient, this level is associated with:

• Increased risk of secondary hyperparathyroidism 2
• Reduced bone mineral density 1
• Higher fracture and fall risk compared to levels ≥30 ng/mL 1
• Suboptimal musculoskeletal health 3

The treatment goal is to achieve and maintain levels ≥30 ng/mL, which is the threshold for optimal bone health, fracture prevention, and overall health benefits. 1, 2, 3

Recommended Treatment Protocol

Initial Supplementation

Start with 1,000–2,000 IU of vitamin D₃ (cholecalciferol) daily. 1 This approach is appropriate because:

• Your level is only 2–8 ng/mL below target, so aggressive loading doses are unnecessary 1
• Daily supplementation of 1,000 IU raises serum 25(OH)D by approximately 10 ng/mL over 3 months 1
• Therefore, 1,000–2,000 IU daily should bring you from 28 ng/mL to 35–45 ng/mL within 3 months 1

Why Vitamin D₃ Over D₂

Cholecalciferol (D₃) is strongly preferred over ergocalciferol (D₂) because it maintains serum concentrations longer and has superior bioavailability, particularly when using daily dosing. 1, 4

Alternative High-Dose Option

If you prefer weekly dosing or need faster correction, an alternative is ergocalciferol 50,000 IU once weekly for 8 weeks, followed by maintenance dosing. 1, 4, 5 However, for insufficiency (versus frank deficiency <20 ng/mL), the daily approach is generally preferred and equally effective. 1

Essential Co-Interventions

Ensure adequate calcium intake of 1,000–1,500 mg daily from diet plus supplements if needed. 1, 4, 5 Vitamin D cannot exert its full bone-protective effects without sufficient calcium. 1

• If using calcium supplements, take them in divided doses of no more than 600 mg at once for optimal absorption 1
• Common dietary sources include dairy products, fortified foods, and leafy greens 1

Monitoring Protocol

Recheck your serum 25(OH)D level 3 months after starting supplementation. 1, 4, 5 This timing is critical because:

• Vitamin D has a long half-life and requires 3 months to reach steady-state levels 1
• Measuring earlier will not accurately reflect your true response to treatment 1
• Three months allows you to confirm achievement of the ≥30 ng/mL target before adjusting your regimen 1

Once your level is stable in the target range (30–44 ng/mL), annual monitoring is sufficient. 1, 4

Maintenance Phase

After reaching your target level, continue maintenance supplementation of 800–1,000 IU daily to sustain optimal levels. 1, 5 Do not stop supplementation once you reach target, as levels will gradually decline without ongoing intake. 1

Safety Considerations

Daily doses up to 4,000 IU are completely safe for adults. 1, 3, 6 Your recommended dose of 1,000–2,000 IU is well below this safety threshold. 1

• The upper safety limit for serum 25(OH)D is 100 ng/mL, far above what you will achieve with recommended dosing 1, 3
• Toxicity is rare and generally only occurs with prolonged daily doses >10,000 IU or serum levels >100 ng/mL 1, 3
• Symptoms of toxicity include hypercalcemia, nausea, weakness, and confusion 1

Common Pitfalls to Avoid

• Do not rely on standard multivitamins alone, which typically contain only 400 IU of vitamin D—insufficient to correct insufficiency 4
• Do not depend solely on sun exposure for vitamin D repletion, as this carries skin cancer risk and is often impractical 4
• Do not measure your level earlier than 3 months after starting supplementation, as it will not accurately reflect your steady-state response 1
• Do not stop supplementation once you reach target levels; continue maintenance dosing to prevent recurrence 1, 5

Expected Outcomes

With 1,000–2,000 IU daily supplementation, you should expect:

• Serum 25(OH)D to increase by approximately 10–20 ng/mL over 3 months 1
• Achievement of the optimal range of 30–44 ng/mL for overall health benefits 1, 2
• Reduced risk of fractures, falls, and secondary hyperparathyroidism 1, 2