What Sleep Does to Your Immune System
The link between short sleep and getting sick is one of the better-evidenced findings in the field, including a study that deliberately infected people to prove it.
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Day
Where your output comes from, and what it quietly borrows against tonight. Caffeine timing, training windows, the afternoon dip, naps, and focus that does not need to be forced.
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Articles in Day
Social Jetlag: What the Weekend Lie-In Costs You
Shifting your sleep by three hours on Saturday is the same signal as flying to Denver and back, twice a month, every month.
Can You Catch Up on Sleep?
Partly. Some things recover in one night, some take several, and at least one measure does not fully return at all.
Drowsy Driving: Why You Cannot Tell How Impaired You Are
The defining feature of sleep deprivation is that it degrades the faculty you would use to assess it. That is not a metaphor — it is the finding.
Does Exercise Actually Help You Sleep?
Yes, and the effect is more reliable than most sleep interventions — but it is smaller per night and slower to arrive than the internet implies.
How Much Daylight Do You Actually Need?
The honest answer is a lot more than you are getting, and the numbers explain why an office by a window does not count.
Ten Questions to Ask Before Buying Any Sleep Gadget
The sleep tech market runs on a reliable trick: sell you a measurement and let you assume measurement is treatment. Ten questions that separate a device that changes something from one that just tells you a number.
Mouth Tape for Shift Workers and Daytime Sleepers
Daytime sleep is lighter, shorter and more fragmented — which makes protecting its quality worth more, and makes one specific mistake more tempting.
Ten Ways to Get Your Energy Back Without More Caffeine
Caffeine does not create energy — it blocks your ability to feel tiredness that is still there. Ten things that actually change how much energy you have, roughly ordered by how much they return per unit of effort.
When to Stop Drinking Caffeine (Work Backward From Your Bedtime)
The advice is usually "no caffeine after 2pm." That number is made up. The real cutoff depends on one thing you can calculate in about ten seconds — and for most people it lands earlier than they'd like.
How Long to Nap: A Decision Tree, Not a Rule
Twenty minutes and ninety minutes are both correct answers. Forty-five is the one that ruins your afternoon. Which one you want depends on what you are trying to buy.
The 3pm Crash Is Not a Caffeine Problem
The afternoon dip is a real circadian event, not a character flaw or a caffeine deficiency. Treating it with more coffee fixes two hours and bills tonight for it. Here is what actually works.
Why Coffee Stopped Working, and How to Reset It
You went from one cup to four and now none of them do anything. That is not you needing more coffee — it is your brain growing extra receptors to cancel it out. Here is the mechanism, and how to get the effect back.
Why a Bad Night Makes You Hungry All Day
Two nights of short sleep moves your hunger hormones roughly 18% down on satiety and 28% up on hunger — and steers the craving specifically toward carbohydrate. It is not weak willpower. It is endocrinology.
The Best Time of Day to Train, According to Your Body Temperature
Strength and power peak in the late afternoon, tracking core temperature. But the session you actually do beats the physiologically optimal one you skip — and evening training wrecks sleep far less than people claim.