From the Guidelines
For a vitamin D level of 18 ng/mL, the recommended supplementation is typically 50,000 IU of vitamin D2 or D3 once weekly for 8 weeks, followed by maintenance therapy of 1,000-2,000 IU daily. This recommendation is based on the guidelines provided by the NCCN task force report on bone health in cancer care 1. The goal of supplementation is to bring serum 25(OH)D levels to 30 ng/mL or higher, which is considered adequate for bone health.
Key Considerations
- The initial high-dose weekly regimen is necessary to quickly increase vitamin D levels, as vitamin D is fat-soluble and takes time to build up in the body's tissues.
- After the initial treatment period, a repeat blood test should be done to ensure the level has increased to the target range of 30-50 ng/mL.
- If levels remain low, the high-dose weekly regimen may need to be continued longer.
- Vitamin D is crucial for calcium absorption, bone health, immune function, and may have other health benefits.
- Taking vitamin D supplements with food containing some fat can improve absorption.
- Some patients may also need concurrent calcium supplementation, typically 1,000-1,200 mg daily, to optimize bone health while correcting the vitamin D deficiency.
Choosing Between Vitamin D2 and D3
- Both vitamin D2 and D3 can be used for supplementation, but vitamin D3 may be more effective in raising 25(OH)D concentrations and maintaining those levels for a longer time when longer dosing intervals are employed 1.
- However, when given as daily doses, vitamin D2 and D3 seem to have similar effects on 25(OH)D levels 1.
- The choice between vitamin D2 and D3 may depend on patient preference, dietary restrictions, and availability of the supplements.
From the Research
Vitamin D Supplementation Dose
The recommended supplementation dose of vitamin D for a vitamin D level of 18 ng/mL is not explicitly stated in the provided studies. However, based on the available evidence, the following points can be considered:
- A study published in 2018 2 found that a maintenance dose of 2,000 IU of vitamin D3 was not enough to keep 25(OH)D levels above 30 ng/mL in patients who were initially vitamin D deficient.
- Another study published in 2020 3 noted that government and scientific societies have published recommendations for vitamin D intake, which vary from 400-1000 IU/d (10-25 μg/d) for an average adult.
- A 2021 study 4 suggested that testing of serum 25-hydroxy-vitamin D (25OH-D) levels should be performed before prescribing vitamin D supplementation, and proposed an algorithm for vitamin D dosing principles when baseline 25OH-D levels are known.
- A 2025 study 5 found that supplementing with 2,000 IU/day of vitamin D3 maintained vitamin D levels within the recommended range in healthy young adults, while a dose of 4,000 IU/day was more effective for maintaining levels above 100 nmol/l.
Key Considerations
Some key considerations when determining the recommended supplementation dose of vitamin D include:
- Baseline 25(OH)D level: The initial level of 25(OH)D can affect the response to vitamin D supplementation.
- Body mass index (BMI): BMI can influence the response to vitamin D supplementation, with higher BMIs potentially requiring higher doses.
- Type of vitamin D: The type of vitamin D used (D2 or D3) can affect the increase in 25(OH)D levels, with D3 potentially being more effective than D2 6.
- Individual variability: There can be significant individual variability in response to vitamin D supplementation, making it important to monitor 25(OH)D levels and adjust the dose as needed.