From the Guidelines
Taking vitamin D3 5000 IU daily for 8 weeks is generally considered safe for treating vitamin D deficiency, but you should get your levels checked soon. For most adults with deficiency, doses between 1000-5000 IU daily are commonly recommended for repletion, with higher doses often needed initially 1. After 8 weeks of supplementation, it's appropriate to have your vitamin D levels tested to ensure you're reaching adequate levels (typically 30-50 ng/mL) without overshooting into potentially harmful territory (above 100 ng/mL). Some key points to consider include:
- The goal of supplementation is to bring serum 25(OH) D levels to 30 ng/ml (75 nmol/L) or higher for bone health 1
- Vitamin D toxicity is uncommon but may occur with daily doses of more than 50,000 IU per day that produce 25(OH) D levels larger than 150 ng/mL 1
- Current expert opinion recommends 800 to 1000 IU of vitamin D daily for adults older than age 50, but many patients need more than the recommended amount and should be repleted based on serum 25(OH) D level 1 Once your levels normalize, you may need to reduce to a lower maintenance dose (typically 1000-2000 IU daily). Vitamin D is fat-soluble and can accumulate in the body over time, so monitoring is important for long-term supplementation. Factors like your initial deficiency severity, body weight, skin tone, sun exposure, and certain medical conditions can all affect how much supplementation you need. Taking vitamin D with a meal containing some fat can improve absorption.
From the Research
Vitamin D3 Supplementation
- The study 2 found that long-term supplementation with vitamin D3 in doses ranging from 5000 to 50,000 IUs/day appears to be safe, with no cases of vitamin D3-induced hypercalcemia or adverse events attributable to vitamin D3 supplementation.
- However, another study 3 found that long-term vitamin D supplementation resulted in increased risks of hypercalcemia and hypercalciuria, which were not dose-related.
Hypercalcemia Risk
- A study 4 found that hypervitaminosis D was found in 1.86% of samples, and 11.1% of these samples displayed hypercalcemia, with most cases occurring at 25-OH-vitamin D levels between 161 and 375 nmol/L.
- Another study 5 found that hypercalcemia occurs in up to 4% of the population in association with malignancy, primary hyperparathyroidism, ingestion of excessive calcium and/or vitamin D, and other causes.
- A case report 6 described a patient with multiple sclerosis who developed severe hypercalcemia attributed to the additive effect of 5500 IU of cholecalciferol and 2020 mg of calcium daily.
Monitoring Vitamin D Levels
- The study 2 found that analysis of 777 patients not on D3 revealed 28.7% with 25-hydroxyvitamin D3 (25OHD3) blood levels < 20 ng/ml, and 64.1% < 30 ng/ml, highlighting the importance of monitoring vitamin D levels.
- It is recommended to check vitamin D levels regularly, especially when taking high doses of vitamin D3, to avoid hypercalcemia and other adverse effects 3, 4, 5, 6.