Vitamin D Supplementation for a Level of 23 ng/mL
For an adult with a vitamin D level of 23 ng/mL (insufficiency), start with 50,000 IU of vitamin D3 (cholecalciferol) once weekly for 8 weeks, followed by maintenance therapy of 800-2,000 IU daily to achieve and maintain a target level of at least 30 ng/mL. 1
Understanding Your Current Vitamin D Status
Your level of 23 ng/mL falls into the "insufficiency" category (defined as 20-30 ng/mL), which is suboptimal but not severely deficient 1, 2. While you're above the deficiency threshold of 20 ng/mL, you're below the optimal target of 30 ng/mL needed for anti-fracture efficacy and maximal health benefits 1.
Initial Loading Phase Treatment
The standard regimen is 50,000 IU of vitamin D3 once weekly for 8 weeks, which will typically raise your level by approximately 16-28 ng/mL, bringing you into the optimal range of 30-40 ng/mL 1.
Vitamin D3 (cholecalciferol) is strongly preferred over vitamin D2 (ergocalciferol) because it maintains serum levels longer and has superior bioavailability, particularly important for weekly dosing schedules 1.
An alternative approach for mild insufficiency like yours is to add 1,000-2,000 IU of over-the-counter vitamin D3 daily and recheck levels in 3 months, though this slower approach takes longer to achieve optimal levels 1.
Why the Loading Dose Approach is Preferred
The weekly 50,000 IU regimen is recommended because standard daily doses would take many weeks to normalize your levels 1. Using the rule of thumb that 1,000 IU daily increases serum levels by approximately 10 ng/mL, you would need several months on daily supplementation alone to reach your target 1, 2, 3.
Maintenance Phase After Loading
After completing the 8-week loading phase, transition to 800-2,000 IU daily to maintain optimal levels 1, 4.
The specific maintenance dose depends on your individual factors: 800 IU daily is the baseline recommendation, but 1,000-2,000 IU daily is appropriate if you have risk factors such as obesity, dark skin pigmentation, limited sun exposure, or are over age 65 1, 2.
An alternative maintenance regimen is 50,000 IU monthly (equivalent to approximately 1,600 IU daily), which can improve compliance 1.
Essential Co-Interventions
Ensure adequate calcium intake of 1,000-1,500 mg daily from diet plus supplements if needed, as vitamin D works synergistically with calcium for bone health 1.
Take vitamin D supplements with your largest, fattiest meal of the day to maximize absorption, since vitamin D is fat-soluble 1.
If taking calcium supplements, divide them into doses of no more than 600 mg at once for optimal absorption 1.
Monitoring Protocol
Recheck your 25(OH)D level 3 months after completing the loading phase (i.e., at 5 months total from starting treatment) to confirm you've reached the target of at least 30 ng/mL 1, 2.
If using weekly dosing, measure levels just prior to your next scheduled dose 1.
Once stable in the optimal range, recheck levels annually 1.
Target Levels and Safety
Your goal is to achieve and maintain a level of at least 30 ng/mL, which provides anti-fracture efficacy and optimal health benefits 1, 5.
The optimal range is 30-80 ng/mL, with an upper safety limit of 100 ng/mL 1, 2.
Daily doses up to 4,000 IU are completely safe for adults, and the weekly 50,000 IU regimen (equivalent to about 7,000 IU daily) is well-established as safe with no significant adverse events 1, 2, 6.
Common Pitfalls to Avoid
Do not use single annual mega-doses (≥500,000 IU), as they have been associated with adverse outcomes including increased falls and fractures 1, 2, 6.
Avoid active vitamin D analogs (calcitriol, alfacalcidol, doxercalciferol, paricalcitol) for nutritional vitamin D insufficiency, as they bypass normal regulatory mechanisms and carry higher risk of hypercalcemia 1.
Don't assume you'll respond the same as others—individual responses vary due to genetic differences in vitamin D metabolism, body composition, and other factors 1, 2.
Special Considerations
If you have chronic kidney disease (CKD stages 3-4), the same loading regimen with cholecalciferol is appropriate, as CKD patients are at particularly high risk for deficiency due to reduced sun exposure, dietary restrictions, and urinary losses 1.
If you have malabsorption syndromes (inflammatory bowel disease, post-bariatric surgery, celiac disease, pancreatic insufficiency), you may require higher oral doses or intramuscular administration if oral supplementation fails to achieve target levels 1.
If you are obese, you may require higher maintenance doses (2,000-3,000 IU daily) as adipose tissue sequesters vitamin D 1, 2.
Expected Response
Based on the evidence, the 50,000 IU weekly regimen for 8 weeks should increase your level from 23 ng/mL to approximately 35-45 ng/mL, well within the optimal range 1, 3. If your level remains below 30 ng/mL after 3 months despite good compliance, consider increasing your maintenance dose or investigating for malabsorption 1.