Vitamin D is unique because it functions as a vitamin, a hormone, and even a steroid, influencing countless bodily processes. Dr. Jason Schuster emphasizes that without optimal levels, immune function and overall health suffer.
Vitamin D – a vitamin, hormone, and steroid
According to Dr. Schuster, vitamin D is more than a simple nutrient; it acts as a vitamin, a hormone, and a steroid, participating in many physiological pathways, especially immune function. He notes that about 95 % of the U.S. population is deficient, making optimal levels essential for health.
- Acts as a vitamin (nutrient) and hormone (signaling molecule).
- Functions as a steroid‑like compound in the body.
- Critical for proper immune response and overall health.
From Sunlight to Bioavailable Form
Dr. Schuster explains that UVB radiation (290‑320 nm) converts 7‑dehydrocholesterol in the skin to previtamin D, which quickly rearranges into vitamin D. The liver then transforms it into 25‑hydroxy vitamin D, and the kidneys finalize activation to 1,25‑dihydroxy vitamin D (calcitriol), the most bioavailable form.
- UVB (290‑320 nm) + 7‑dehydrocholesterol → previtamin D → vitamin D.
- Liver conversion → 25‑hydroxy vitamin D (25‑OH D).
- Kidney conversion → 1,25‑dihydroxy vitamin D (calcitriol).
- Methylated supplements skip conversion steps, providing ready‑to‑use vitamin D.
Why Adequate Levels Pay Off
Dr. Schuster links sufficient vitamin D to reduced risk of severe COVID‑19, better immune function, and anti‑cancer/antiviral effects when blood levels exceed 40 ng/mL. He argues that the standard “normal” range (30‑50 ng/mL) is too low for optimal health.
- Improves immune response and lowers severe COVID‑19 risk.
- Anti‑cancer and antiviral benefits appear above ~40 ng/mL.
- Supports overall metabolic health and may mitigate obesity‑related deficits.
Optimal Supplementation
The FDA’s tolerable upper intake level of 4,000 IU is called “completely false” by Dr. Schuster. He recommends most people take 5,000‑10,000 IU daily, with 5,000 IU in summer and 10,000 IU in winter when UVB exposure is limited. Toxicity only emerges at extreme intakes (60‑100k IU/day) or accidental overdoses.
- Typical adult dose: 5,000‑10,000 IU per day (5k IU summer, 10k IU winter).
- The 4,000 IU UL is considered inaccurate by the speaker.
- Toxicity reported only above ~60,000 IU/day; mis‑reading dosage can cause issues.
- Body can process up to ~20,000 IU/day; excess is excreted.
- Desired blood level: 75‑85 ng/mL (standard “normal” 30‑50 ng/mL is inadequate).
“The tolerable upper intake level of 4,000 IU is completely false – most people need 5,000 to 10,000 IU per day.”— Dr. Jason Schuster
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