Vitamin D: 40-60 ng/mL, Dr. Holick, taking 6,000 IU daily, is at 80ng - video & summary Feb 2025
Dr. Michael Holick interview — Modern Healthspan (Richard)
Vitamin D: The Hormone That Can Save Your Life
(02:23–07:09) How he got into the field: Assigned to DeLuca's lab at Wisconsin against his wishes. Identified 25(OH)D as the major circulating form (3 months' work), then identified 1,25(OH)₂D₃ as the kidney-produced active form and was first to chemically synthesize it — used to get renal-failure patients out of wheelchairs. Later found the VDR in epidermal cells, which led to activated vitamin D as the still-standard first-line topical treatment for mild psoriasis.
(07:54–09:57) Vitamin vs. hormone: Not a true vitamin — skin makes it, and it requires two hydroxylations (liver, then kidney) before biologic activity. Kinetics from 1970s radiolabeled work: oral 25(OH)D takes ~12 hr for max calcium-absorption response vs. ~3–4 hr for 1,25(OH)₂D; 1,25(OH)₂D appears in circulation within 1–2 hr.
(10:42–12:42) Skin synthesis: 7-dehydrocholesterol absorbs UVB (290–315 nm) → previtamin D₃ → thermal isomerization to D₃ over a couple of hours. Says the common advice to sun early morning/late afternoon is the worst — all UVA, no UVB; production runs roughly 9–10 AM to 3–4 PM even in Panama. Statins don't affect it (epidermis makes its own cholesterol, avascular tissue).
(14:04–15:21) Sun dose vs. oral dose: 1 MED (slight pinkness at 24 hr) over a bathing-suit-exposed body ≈ 15,000–20,000 IU. A single oral dose peaks and falls within 72 hr; sun-derived peaks at ~24 hr and is sustained several days — lasts 2–3× longer. Plugs the free dminder app [dminder] for location/time-specific synthesis windows.
(17:20–19:37) UV lamps and formulation: Sperti lamp history (1940s, rickets prevention); LED narrow-band UVB shown efficient for previtamin D production; useful for malabsorption patients. Oil, capsule, or liquid — all essentially equally bioavailable via chylomicron/lymphatic uptake.
(19:37–22:48) Dosing and targets: 2011 Endocrine Society (he chaired): infants 400–1,000 IU, children 600–1,000, adults 1,500–2,000; obese need 2–3×. Maasai/Hadza reference levels 40–60 ng/mL (100–150 nmol/L), implying ≥4,000 IU/day intake equivalent. Target minimum 30 ng/mL, ideal 40–60, safe upper 100 ng/mL; toxicity concern only above ~150 ng/mL (375 nmol/L).
(25:47–29:32) Loading and D2: His 1998 Lancet protocol — 50,000 IU weekly × 8 weeks (~6,600 IU/day equivalent), then 50,000 IU every 2 weeks (~3,300 IU/day), holding 40–60 ng/mL out to 5 years. Argues the anti-D2 position is wrong: D2 and D3 raise levels essentially identically at physiologic doses and D2 is activated the same way. Attributes the 1950s European fortification ban to misdiagnosed Williams syndrome, not D toxicity.
(30:16–31:50) K2 — he disagrees with the consensus: Flatly says vitamin D is not influenced by vitamin K, and no study shows K2 helps vitamin D work. Dismisses the "K2 directs calcium to bone" claim, while acknowledging the Dutch association data on low K intake and vascular calcification. (Worth flagging — this cuts against a lot of what's circulating.)
(31:50–34:29) Aging: Calls the 2024 guideline (600 IU, 900 IU if 75+) illogical. 7-DHC declines with age — a 70-year-old makes <50% of a 20-year-old's — but absorption is equally efficient at 80 as at 20, so no higher oral dose needed; everyone at 1,500–2,000 IU minimum. He personally takes 6,000 IU/day and runs ~80 ng/mL (200 nmol/L). Sun still worthwhile for elders (β-endorphin, nitric oxide, BP).
(35:23–36:05) Breast milk argument: Human milk has essentially no vitamin D — evolutionarily nonsensical — but Hollis and Wagner showed 6,400 IU/day in lactating women supplies the infant fully, implying ancestral synthesis of 4,000–6,000 IU/day.
(36:56–48:56) Bone — the careful distinction: Vitamin D cannot treat osteoporosis. Deficiency → low ionized Ca → PTH ↑ → renal Ca reabsorption, more activation, and osteoclastic resorption ("holes"), plus phosphate wasting → mineralization defect (osteomalacia/rickets). The unmineralized, hydrated osteoid explains the throbbing bone pain misdiagnosed as fibromyalgia/CFS. Correcting deficiency mineralizes existing matrix (BMD gains of 5–15% in 1–2 years in his Black patients; ~50% in one tumor-induced osteomalacia case) but cannot refill resorbed matrix. Recommends 1,000 mg elemental calcium/day, preferably dietary, split twice daily, with meals; calcium citrate for stone-formers (binds oxalate, and higher calcium intake lowers stone risk).
(48:56–53:31) Immune function: Local activation in macrophages, colon, skin; ~2,000 genes up/downregulated. VITAL trial: 2,000 IU/day cut autoimmune disease incidence 22%. His own 190,000-sample COVID analysis: ≥34 ng/mL associated with 54% lower infection risk; 40–50% lower hospitalization/mortality. Says extraskeletal benefits need 40–60 (up to 80) ng/mL — higher than the bone-only threshold.
(54:27–57:19) Fat storage — unresolved: Obese (BMI >30) need ~2.5× the dose for the same blood level; adipose stores are not reflected in serum 25(OH)D. After gastric bypass with 50 kg fat loss over a year, blood levels did not rise despite large adipose stores — but he thinks slower ancestral fat utilization did release it. Actively researching the equilibration mechanism.
Note: The transcript garbles several names — DeLuca, Slominski, Maasai/Hadza, Sperti lamp, dminder — and the "45,000 units a day" at 34:29 is a mis-transcription of 4,000. Also, his 11:24 remark about "greater than 35 degrees" is stated confusingly; he means the zenith angle at high latitudes in winter, not a flat latitude cutoff.
His papers: [drmichaelholick.org].
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