I live in Florida. Sunshine State. I get outside most days. I still supplement 5,000 IU of vitamin D3 every morning.
Then I tested my level: 58 ng/mL. Right in the sweet spot. I got there by supplementing — not by standing outside, and not by following the RDA.
The Data
42% of American adults are vitamin D deficient (Forrest & Stuhldreher, NHANES data, 2011). 82% of Black Americans. 69% of Hispanic Americans
The RDA (600-800 IU) was set to prevent rickets and maintain bone health. That's it. Not immune function, not cancer prevention, not longevity
Endocrine Society target: 40-60 ng/mL — double the lab "normal" cutoff of 20 ng/mL
70% reduction in respiratory infections in severely deficient individuals given daily D3 (Martineau, BMJ, 2017 — 25 RCTs, 11,000+ participants, Cochrane-level rigor)
25% reduction in cancer mortality when excluding early follow-up in the VITAL trial (Manson, NEJM, 2019 — 25,000+ participants)
D3 raises blood levels roughly 2x more effectively than D2 over 12 weeks (Tripkovic, AJCN, 2017). If your doctor prescribes D2, ask for D3
What To Do
Take 4,000-5,000 IU of D3 daily. Body weight matters: roughly 70-80 IU per kg. The Endocrine Society considers up to 10,000 IU/day safe.
Always pair with K2 (MK-7). Without K2, the calcium that vitamin D absorbs can deposit in arteries instead of bones. The Rotterdam Study found high K2 intake cut cardiovascular mortality by 50%.
Take with a fat-containing meal. A 2010 study found absorption increased ~50% when taken with food vs. empty stomach.
Fix magnesium first. The enzymes that activate vitamin D are magnesium-dependent. If you're mag-deficient (50% of Americans are), your D3 supplement is bottlenecked. Take magnesium glycinate alongside.
Product Pick
Thorne D3/K2 liquid — combines both in the right ratio. Two drops, done. No extra pills, no guessing about K2 dosing. It's been on my counter for eight months.
Quick Hit
Test twice a year. A home vitamin D test costs ~$40 and takes five minutes. It's the only way to know if your dose is actually working. Target: 40-60 ng/mL.
The standard recommendation of 600 IU was designed to prevent a disease largely eradicated in the 1930s. Your immune system, cardiovascular system, and brain didn't get the memo. When the Endocrine Society, multiple RCTs, and basic biology all point in the same direction, follow the evidence over the government's minimum.
Have you tested your vitamin D level? Hit reply and tell me where you landed.
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