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Place · Level 3
世界最普及精神物质 + 茶叶独有氨基酸 · 1:2 协同最有 RCT 证据的认知组合· 但个体差异极大
synergy · 1
Among the nootropic shelf, one of the few combinations with real synergy evidence is caffeine plus L-theanine — not stacking cholines on top. Before combining, ask what you are actually short of: attention suppressed by adenosine, or acetylcholine.
antagonism · 3
↮Sleep Architecture & Sleep Debt
Process S in the two-process model is homeostatic sleep pressure: the longer you are awake the higher it climbs, and accumulating adenosine is one of its molecular signals. Caffeine blocks the adenosine receptor — it does not remove the tiredness, it hides the gauge.
↮Iron
What blocks non-heme iron is the polyphenols in tea and coffee, not caffeine itself — a strong cup with a meal can wipe out most of that meal's non-heme iron absorption. Moving tea and coffee between meals is enough.
The sleep-hygiene list is not wrong — it removes obvious obstacles, and with a 5-6 hour caffeine half-life an afternoon cut-off makes sense. But note what it is in most CBT-I trials: the control arm. Hygiene alone does not treat chronic insomnia.
depletes · 1
Caffeine does depress intestinal calcium absorption — but only very slightly, and it has no effect on total 24-hour urinary calcium (Heaney 2002). How slight? One to two tablespoons of milk fully offsets it. In people meeting their calcium RDA there is no evidence caffeine harms bone. The teaching value of this edge is precisely how small it is: a real interaction that marketing inflated into a big one.
regulates · 4
Caffeine is shaped like adenosine: it parks in the neuron's adenosine receptors without pressing the button, locking the 'time to sleep' signal outside the door. It doesn't give you energy — it mutes the fatigue signal for a while.
Caffeine's half-life is 5-7 hours — half of your 3pm cup is still in you when you lie down. It doesn't have to keep you awake to count: it cuts deep sleep even when you do fall asleep. So 'I sleep fine after coffee' and 'that cup had no effect on me' are two different statements.
Caffeine with L-theanine (roughly 100 : 200 mg) softens the jitter and smooths the curve, but smoothing is not raising: on an all-nighter it improves how the hours feel, not the ceiling on alertness.
Caffeine is a timing input too: it does more than keep you awake, it signals the SCN. For shift workers the hour matters more than the dose — keep it to the front of the shift so it does not push an already-shifted clock further.