Podbit · The Diary Of A CEO with Steven Bartlett
Vitamin D is synthesized on the skin exactly like a hormone, acts on DNA receptors inside cells, and should be managed like estrogen or testosterone with blood-level monitoring. Calling it a vitamin was a historical error that sent it to the over-the-counter shelf.
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At 40:40 · chapter starts 40:36
This chapter delivers the episode's sharpest reframe. Dr. Gominak explains that vitamin D is not a dietary nutrient for humans in any meaningful biological sense — it is made on bald human skin exactly as it is on animal fur, where animals lick it off and absorb it orally. Humans can't lick their skin, so we absorb it directly through the skin. Eating salmon for vitamin D, she says, is like eating salmon to get a normal menstrual cycle from salmon oestrogen: it is that foreign. The classification error happened in the early twentieth century before the distinction between vitamins and hormones was well understood, and medicine doubled down on it in the 1980s when it decided vitamins were for 'lesser humans' and pushed vitamin D onto pharmacy shelves over the counter. She explains how this compares to oestrogen, testosterone, and thyroid — all managed via blood-level monitoring in tight bands because too much and too little are both harmful. She rejects the flat-dose approach used in virtually all vitamin D research (e.g. 4,000 IUs regardless of blood level) as fundamentally wrong for a hormone, which is exactly why that research keeps producing null or contradictory results. The Endocrine Society, she notes, acknowledged this flaw in 2004 but still chose to walk away from the question rather than fund better studies.
Vitamin D is synthesized on the skin like a hormone and acts on DNA receptors — calling it a vitamin was a historical mistake that shaped decades of bad medical guidance.
Spike your cortisol in the first 1–3 hours of your day — with sunlight, hydration, exercise, or caffeine — and you set up elevated mood, focus, and stress resilience for the rest of the day. Miss that spike and you get a flat cortisol curve: brain fog, poor learning, and bad sleep. The bookend is equally important: dim lights, no caffeine, and wind down the final hour.
Bottom-up impulses — just eat the cookie, keep scrolling — are driven by deep brain structures. Top-down prefrontal control is the thing that lets you wait, learn, and grow. Every small act of choosing the harder thing, from picking up trash to doing the workout you dread, greases that top-down circuit — and it transfers to everything else.
A Washington University in St. Louis study found that the attention-improvement effects of Ritalin are effectively equal to a great night's sleep. Stimulants also stunt growth and reduce sleep quality. The new direction is combining lower medication doses with genuinely better sleep — not replacing sleep with pharmacology.
Two big inhales through the nose, then a full exhale to empty — that's the physiological sigh. It fires a specific vagal pathway to slow your heart rate, offload CO2, and tip the autonomic nervous system toward calm instantly. Doing just 10 deliberate exhales throughout the day measurably elevates HRV by nighttime.
Presence isn't a state you fall into — it's something you actively produce by anchoring perception to the immediate environment. Ask 2–3 trivially specific questions about your surroundings (how many cans, what does it smell like) to pull your brain out of past/future mode. Then deliberately choose what to think or say next. That's it.
Acknowledge the thing, feel all of it, uncouple the emotion from the memory, then transmute the experience into something meaningful. Most people stall at step 2 — feeling the feelings — and never reach uncoupling. An entire generation is stuck there, confusing emotional processing for healing. Moving through all four is the actual path out.
Nicotine creates a uniquely alert-and-calm state ideal for learning — but only at low doses used occasionally. If you're using 3–6 mg pouches multiple times a day, you're not getting a cognitive enhancement, you're just rescuing yourself from withdrawal. For a genuine performance effect, use it once or twice per week at most.
Two injections of BPC-157 (100–200 mcg) eliminated shoulder pain Huberman couldn't shift for months. The peptide pinealon gave him 2.5–3 hours of REM sleep inside 6 hours — an effect that persisted into subsequent nights and scaled down to just once per week. Neither is in the book because the human data aren't there yet, but the animal evidence is strong.
Long, slow cardio builds capillary networks and mitochondrial richness; high-intensity intervals push VO2 max. You don't need huge volumes of either. Huberman's protocol: one 45–60 minute long slow session, one near-maximal effort HIIT session (Airdyne 20-on/10-off for 6–8 rounds), and one medium 30-minute effort per week. That's the complete cardio picture.
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