Series: CentoViva learnings

Third piece of body-homework, and the one that changed my behavior fastest.

Sleep isn't downtime. It's the maintenance shift, the brain flushes metabolic waste (in mice, the spaces between brain cells expand about 60% during sleep and waste clearance roughly doubles), memories consolidate, growth hormone pulses for tissue repair.

But late nights add a second problem on top of short sleep: misaligned clocks. Light at night suppresses melatonin, one study found ordinary room light before bed cut melatonin duration by about 90 minutes. And eating late tells your liver and gut it's daytime while your brain disagrees. The clocks desync.

The measurable effects of short sleep stacked up fast when I read them. Hunger hormones tilt toward eating more, the "I'm full" signal down 18%, the "I'm hungry" signal up 28%, which makes any calorie target materially harder. Thinking dulls to roughly the level of mild intoxication: about 17 hours awake performs like a blood-alcohol level of 0.05%. And over years, short sleep roughly doubles the odds of developing hypertension in midlife.

The through-line across all three of these inquiries, alcohol, smoking, sleep, is the same: none of them breaks the body in one night. They each make the repair ledger run at a deficit, quietly, until it doesn't. Fixing my sleep is the highest-leverage item on my list right now.

Sources: Xie et al., "Sleep drives metabolite clearance from the adult brain," Science 2013, https://doi.org/10.1126/science.1241224 · Gooley et al., "Exposure to room light before bedtime suppresses melatonin onset and shortens melatonin duration in humans," JCEM 2011, https://pubmed.ncbi.nlm.nih.gov/21193540/ · Spiegel et al., "Sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite," Ann Intern Med 2004, https://pubmed.ncbi.nlm.nih.gov/15583226/ · Williamson and Feyer, "Moderate sleep deprivation produces impairments in cognitive and motor performance equivalent to legally prescribed levels of alcohol intoxication," Occup Environ Med 2000, https://pubmed.ncbi.nlm.nih.gov/10984335/ · Gangwisch et al., "Short sleep duration as a risk factor for hypertension," Hypertension 2006, https://www.cuimc.columbia.edu/news/lack-sleep-linked-increased-risk-high-blood-pressure

Note: the brain-clearance finding is disputed. A 2024 Nature Neuroscience study in mice found clearance reduced, not increased, during sleep. This post follows Xie et al. 2013, the mainstream citation. https://www.nature.com/articles/s41593-024-01638-y

Another one from my body-homework. Everyone knows smoking is bad. What I didn't know is how cruel the math is for occasional smoking.

A meta-analysis of 141 cohort studies found that one cigarette a day carries about half the excess heart-disease risk of twenty a day, 46% in men and 31% in women. Not five percent. Half. Going from zero to "just one when I go out" buys a wildly disproportionate share of the risk; going from a pack to two packs buys far less additional risk. The researchers' conclusion was blunt: no safe level of smoking exists for cardiovascular disease.

The mechanism surprised me too. The damage isn't mainly the nicotine. That's the hook. It's the combustion: thousands of chemicals, plus carbon monoxide, which grabs your hemoglobin about 200 times tighter than oxygen does. Every cigarette is a stretch of time your blood is carrying less oxygen, and delivering it worse.

One genuinely hopeful finding: the lungs' cleaning system recovers fast. Studies of quitters show airway clearance measurably improving within weeks… in one study it was back in the normal range by day 15. The body wants to repair. You just have to stop re-injuring it.

The pattern I'm noticing: the body is forgiving of a lot, but it keeps score honestly. “Occasional” is a story we tell ourselves. The ledger doesn't round down.

Sources: Hackshaw et al., "Low cigarette consumption and risk of coronary heart disease and stroke," BMJ 2018, https://doi.org/10.1136/bmj.j5855 · Ramos et al. 2011 on nasal mucociliary clearance returning to the normal range by day 15 after quitting, as reviewed in Int Arch Otorhinolaryngol, https://www.thieme-connect.com/products/ejournals/html/10.1055/s-0040-1702965

I drink occasionally. One small drink, socially, never more. I usually don't even finish it.

I've always known alcohol hurts. But it's also one of the most heavily marketed vices on the planet. Every ad sells the same story: fun, friends, freedom. Nobody advertises the bill.

Gen Z saw through it before the rest of us. They barely drink. Most health-focused generation I've seen… they looked at the deal and passed.

So I got curious about the actual mechanism. What does it do, and why does the damage look the way it does? Because one thing I've noticed just from watching people over the years: alcohol ages people fast. You can see it in the face first… the skin, the eyes, a puffiness that doesn't go away. I wanted to know why.

Here's what I found, plainly. The body doesn't treat alcohol like food. It treats it like a poison that happens to carry calories. The liver drops everything else to clear it first, so while it's busy, fat burning pauses. Seven calories a gram, zero nutrition.

The liver breaks it down in two passes. The stuff in the middle, acetaldehyde, is the nasty one… it's classified as carcinogenic to humans.

Then the brain. Alcohol makes you feel relaxed, but it breaks sleep apart. Less dreaming, and the second half of the night in pieces. You can watch it on any sleep tracker… deep early, shattered late. Knocked out is not slept.

This doesn't change what I do. One small drink, usually unfinished. But now I can see the bill clearly, and I understand what I've been seeing in people's faces all these years.

What I still don't know: how much of the aging is the alcohol itself, and how much is the bad sleep and late-night food that travel with it. That's my next question.

Sources: IARC Monographs on acetaldehyde associated with alcoholic beverage consumption, classified as carcinogenic to humans (Group 1), https://monographs.iarc.who.int/ · NIAAA on alcohol metabolism and sleep, https://www.niaaa.nih.gov/