10% Happier with Dan Harris The Science of Supplements: What Works, What's Hype, and What Could Actually Harm You | Dr. Mahtab Jafari
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May 11, 2026 
Dr. Mahtab Jafari, a UC Irvine pharmaceutical scientist and healthspan researcher, breaks down supplement science with clarity. She tackles regulation and product quality. She covers vitamins and minerals, creatine and protein powders, sleep aids like melatonin, botanicals and herbs, probiotics and gut health, and the risks of contamination and blends.
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Grandmother's Garden Sparked A Career Testing Botanicals
- Mahtab Jafari's interest in botanicals began with her Iranian grandmother's garden remedies that often worked for minor ailments.
- Her lab later validated some effects, like cinnamon activating heat shock proteins, turning folklore into testable science.
Vitamin D Deficiency Threshold And Dosing
- Vitamin D deficiency definitions vary across groups, but <20 ng/mL is widely used as deficient.
- Supplement dosing depends on level; 2,000 IU/day for low levels and ~1,000 IU/day if sun exposure is limited.
Vitamin C Might Slightly Shorten Colds
- Vitamin C may shorten a cold by about 1.5 days if taken at 500–1,000 mg at symptom onset.
- Large daily megadoses (grams) are not recommended and dietary sources like kiwi or strawberries are effective.
