What are the implications of low Vitamin D3 (Cholecalciferol) levels with normal Vitamin D2 (Ergocalciferol) levels?

From the Guidelines

Having low vitamin D3 but normal vitamin D2 levels indicates a need to specifically increase vitamin D3 intake to improve overall vitamin D status and reduce the risk of related morbidities. To address this, consider taking a vitamin D3 supplement, as it is the form that the body naturally produces in response to sunlight exposure and is more effective at raising total vitamin D levels than D2 1. The recommended dose can vary depending on the severity of the deficiency, but a common range is 1,000-2,000 IU daily with food containing some fat to enhance absorption. Some key points to consider:

• Vitamin D3 supplementation is preferred over D2 for raising vitamin D levels in the body.
• Spending time in direct sunlight without sunscreen on arms and legs can help naturally boost vitamin D3 levels, but caution is advised due to the risk of skin cancer.
• Monitoring vitamin D levels through regular blood tests is crucial to ensure optimal levels (30-50 ng/mL) are reached without exceeding safe limits.
• Adequate vitamin D is vital for calcium absorption, bone health, immune function, and may play a role in preventing various chronic diseases. Given the potential for variability in assay methods and laboratory results, as well as the impact of inflammation on vitamin D levels, it's essential to work closely with a healthcare provider to determine the best course of action for addressing low vitamin D3 levels 1.

From the Research

Vitamin D3 and D2 Supplementation

• The provided studies focus on vitamin D3 supplementation, with one study comparing the effects of vitamin D2 and D3 supplementation 2.
• A study on healthy young adults found that supplementing with 2,000 IU/day of vitamin D3 maintained vitamin D levels within the recommended range, even after a 30-day break 3.
• Another study on adults with cystic fibrosis found that high-dose vitamin D3 therapy (50,000 IU/week) significantly increased serum 25-OHD levels 4.
• A study on elderly patients with severe vitamin D deficiency found that a single oral dose of 300,000 IU vitamin D3 raised mean 25-OH)D serum concentrations to the target mean of above 75 nmol/l at 3 months 5.

Comparison of Vitamin D2 and D3

• A study comparing the effects of high-dose bolus vitamin D2 and D3 supplementation found that vitamin D3 had greater potency than equimolar vitamin D2, with a higher, sustained serum 25-OH)D response and efficacious PTH suppression 2.
• The study suggests that vitamin D3 may be more effective than vitamin D2 in treating vitamin D insufficiency.

Calcium and Vitamin D Supplementation

• A study on healthy male volunteers found that twice-daily administration of 500 mg calcium and 400 IU vitamin D3 at 6-hour intervals provided a more prolonged decrease in serum parathyroid hormone levels than the administration of the same total amount of calcium and vitamin D, as a single morning dose 6.
• The study suggests that the timing and frequency of calcium and vitamin D supplementation may affect its efficacy in reducing secondary hyperparathyroidism.

Low Vitamin D3 but Normal D2

• There is limited information in the provided studies on the specific scenario of low vitamin D3 but normal D2 levels.
• However, the studies suggest that vitamin D3 supplementation can be effective in increasing serum 25-OH)D levels, regardless of the initial level of vitamin D2 3, 4, 5, 2.