The core argument here is simple: what you do in the first 90 minutes after waking sets the neurochemical trajectory for the rest of your day. Huberman has been making this case for years, and the research keeps reinforcing him. Light first. Delay caffeine. Move your body. Do hard things early. These aren't lifestyle tips. They're biological protocols.
When photons hit your retinal ganglion cells, they signal the suprachiasmatic nucleus — your brain's master clock. This triggers the cortisol awakening response, which peaks around 30 minutes after waking. This is the good cortisol. The morning kind. The kind that drives mental clarity, focus, and readiness. Miss the light, and you blunt that peak. You'll feel foggy until adenosine clears and your stimulants do the work cortisol should have done for free.
Our knowledge base has multiple articles covering the suprachiasmatic nucleus and circadian light signaling, and they all point to the same conclusion: the timing of your first light exposure is the most powerful lever you have for sleep quality and daytime alertness. Not supplementation. Not cold. Light first.
Here is what Huberman doesn't say explicitly but the data supports: cold exposure in the morning does something remarkably similar to morning light. The norepinephrine surge from cold water hits the same wakefulness circuitry that light is calibrating. They are complementary signals, not competing ones. Light anchors your circadian clock. Cold amplifies the alertness state on top of it. Together, they create a neurochemical readiness that caffeine only approximates — and without the adenosine rebound crash three hours later.
The 90-minute caffeine delay Huberman recommends is directly related. Adenosine — your sleep pressure chemical — is still circulating when you wake. Your morning cortisol pulse is designed to clear it naturally. Caffeine just blocks those receptors temporarily, which is why the afternoon crash comes: the adenosine floods back in. Wait, let cortisol do its work, then add caffeine on a already-cleared system. Cleaner, longer, no crash.
The morning workout timing is worth examining. Huberman trains early, and it works for him. But we have strong evidence across our database that afternoon training — when core body temperature is naturally elevated and motor neuron recruitment is optimal — produces better strength and performance outcomes. Morning exercise has real benefits: it builds adherence, front-loads the cortisol response, creates psychological momentum. But if you are optimizing for performance, the afternoon window is hard to argue against.
contrast therapy — hot to cold — compresses the same temperature oscillation your body runs naturally across 24 hours into a 20-minute session. Your core temperature drops before waking, rises through the morning, peaks in late afternoon, then falls again before sleep. That oscillation is the circadian signal. When you train your thermoregulatory system with contrast, you sharpen its sensitivity to that cycle. Better thermoregulation means more pronounced morning cortisol, sharper light response, and more consistent sleep onset at night. Your morning light ritual and your thermal practice are not two separate habits. They are two inputs into the same underlying system.