Vitamin D
Product
Immune modulation during cold and flu season; optimizing levels to 45-70 ng/mL
"Vitamin D is probably the single most important immune modulating nutrient that you can take and probably sixty to eighty percent are insufficient or deficient in vitamin D. So it's an easy hack and it's cheap, it's pennies a day."
More source quotes
General health supplementation with strong evidence base and low risk profile
"I will happily take vitamin D. I know there's no real downside risk unless I overdose. I know it has a lot of benefit. I know there's evidence to it."
Hormone health, immune function, general health optimization
"Vitamin D, 5,000 to 10,000 IUs per day. Most people are underdosing vitamin D. I can see my bloods getting better when I take 5,000 as opposed to 3,000 IU of vitamin D and I'm not changing anything else. So vitamin D — and I get sunlight."