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Sleep, Light, and Glucose: How Your Night Routine Is Making You Metabolically Sick

InsulinJourney / 28 May 2025 /
Sleep, Light, and Glucose: How Your Night Routine Is Making You Metabolically Sick

Hi, I’m Alex, founder of InsulinJourney. A few years ago, I thought my diet was the problem. Then I realized I was doing everything right during the day… but completely sabotaging myself at night.

This is the part nobody talks about when it comes to blood sugar, insulin resistance, and prediabetes. Your body doesn’t just care what you eat — it cares WHEN you eat, sleep, and see light. And those late nights? That phone in your face at 11 PM? They might be slowly breaking your metabolism.

Here’s what I’ve learned (through personal experiments, science, and CGM testing):

How Circadian Rhythm Controls Glucose

Your body runs on a 24-hour biological clock — your circadian rhythm. It governs hormones, energy, sleep, and yes… blood sugar. At night, insulin sensitivity drops. Melatonin rises. Your body enters “repair mode,” not “digestion mode.”

Disrupt that cycle, and you start:

  • Storing more fat
  • Losing insulin sensitivity
  • Spiking glucose even from small meals
  • Sleeping poorly (which makes insulin resistance worse)
How I Found This Out (Real CGM Data)

One night, I stayed up late editing video. At 1:30 AM, I had a small snack. It was just Greek yogurt — normally very CGM-friendly. But that night? My glucose went from 5.5 mmol/L (99 mg/dL) to 8.4 mmol/L (151 mg/dL)… and stayed elevated until 5 AM.

Then I started wearing blue light blockers and going to bed at 22:30. My sleep improved. My glucose stabilized. Same meals, different timing — totally different result.

What Artificial Light Does

When you’re exposed to screens or bright lights after sunset:

  • Melatonin gets suppressed
  • Cortisol stays elevated
  • Sleep becomes shallow, fragmented
  • Glucose rises due to stress hormones

Even 30 minutes of bright screen time at night can shift your circadian rhythm and reduce insulin sensitivity the next day.

Shift Workers Have Higher Diabetes Risk

Studies show night shift workers are at significantly higher risk for:

  • Type 2 diabetes
  • Obesity
  • Cardiovascular disease

This isn’t just about sleep loss — it’s about circadian disruption. The same thing happens when we binge Netflix until 2 AM or doomscroll in bed.

What to Track

Use a CGM or glucose meter to track:

  • Glucose overnight (is it rising at 3 AM?)
  • Glucose after late meals or snacks
  • Post-sleep glucose (is your fasting number worse after poor sleep?)

My average glucose after 7.5h sleep: ~5.1 mmol/L (92 mg/dL) After <6h sleep: 5.8–6.2 mmol/L (104–112 mg/dL) — even with identical food.

Caffeine Before Bed: The Hidden Disruptor

I’ve always been sensitive to caffeine — and I know not everyone is. Many people truly believe that two or three cups of coffee a day have no impact on their sleep. I used to think the same. But when I started tracking glucose, HRV, and sleep quality, it became obvious: even a seemingly harmless cup in the afternoon was quietly messing with my system.

But when I started monitoring my recovery, glucose levels, and HRV, I saw the pattern. Even small doses of caffeine in the afternoon made my sleep lighter, raised my nighttime cortisol, and worsened my morning glucose.

Now? I stick with decaf in the second half of the day. A good black decaf coffee feels just as ritualistic and comforting — and my body thanks me for it.

Alcohol and the Illusion of Good Sleep

I tested this too. One glass of white wine at 8 PM and… boom. CGM shows a drop in glucose. I fall asleep quickly. Sounds great, right?

But then HRV tells a different story: stress patterns until 3 AM, shallow sleep, and a 0.5–0.8 mmol/L (9–14 mg/dL) increase in baseline glucose the next day.

It might feel like you’re relaxing. But your body is actually fighting — detoxifying, inflamed, restless. Multiply this by years or decades? That glass of wine becomes a slow metabolic wrecking ball.

Tips to Fix Your Night Routine:
  • Shut off all screens at least 60 min before bed
  • Use amber lighting or candles in the evening
  • Blue light blockers actually work — wear them 2–3 hours before bed
  • Get 10–20 minutes of morning sunlight daily
  • Don’t eat late: finish your last meal 2–3 hours before sleep
  • Cool bedroom (18–20 °C) helps glucose overnight
  • Switch to decaf in the afternoon
  • Watch out for alcohol’s hidden cost on glucose, sleep, and recovery
Don’t Skip This with Your Doctor

Most doctors don’t talk about sleep or light when it comes to blood sugar. But if you’re working on reversing insulin resistance, you NEED to:

  • Ask them to test fasting insulin (goal: <5 µIU/mL)
  • Do a Kraft Test if possible
  • Discuss sleep hygiene and light exposure as metabolic tools
  • Choose doctors who look metabolically healthy themselves
Final Thought

Your blood sugar doesn’t care just about carbs. It cares about rhythm, light, caffeine, alcohol, and sleep.

If you’ve been doing everything right during the day and still struggling — start with the night.

I share my personal experiments with CGM, sleep, and metabolism weekly in my newsletter IJ Pulse. Join here: https://insulinjourney.com/newsletter

Want deeper support with your glucose, insulin resistance, or energy? My coaching program IJ Method is designed to walk you step-by-step to reclaim metabolic health with data, food, habits, and lifestyle upgrades. https://insulinjourney.com/method

Also join me in real time Telegram Channel: https://t.me/insulinjourney

Alex Oleinik

I’m an entrepreneur, YouTuber, and creator of the Insulin Journey Method. My mission is to help people boost their energy, optimize their health, and build a sustainable lifestyle through science-backed strategies.

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