We Asked a Doctor If Vitamin D Can Really Support Your Immune System

Verywell Health • January 14, 2026 • health

Key Points:

Vitamin D acts as an immunomodulator hormone, activating immune cells and balancing the immune response to help fight infections and reduce excessive inflammation and autoimmunity.
Research on vitamin D supplements shows mixed results, with some studies indicating a modest reduction in infection risk and improved outcomes in autoimmune diseases, but benefits are generally marginal and require daily intake before illness.
Excessive vitamin D intake can lead to toxicity, affecting calcium levels, so it is important to monitor supplement use and blood levels, especially since vitamin D needs fluctuate with sun exposure.
Recommended vitamin D supplementation typically ranges from 400 to 5,000 IU daily, with most adults advised to start at 1,000 to 2,000 IU; consulting a physician