The Morning Habit That Changed My Afternoon Energy
For most of my adult life, I assumed the 3pm crash was just part of being a working woman. Coffee helped. So did sugar. Neither fixed it.
What actually fixed it was going outside within 30 minutes of waking up.
Not for a run. Not for a workout. Just outside. Five to ten minutes. Natural light on my face and into my eyes. Before coffee. Before breakfast. Before I looked at my phone.
Within two weeks of doing this, every morning, as part of the 90 Hard Women's Health Challenge, the 3pm crash I had written off as normal was gone. Here is why that happened, and why it will likely work for you too.
Your body runs on a 24-hour clock. Most of us are fighting it.
Inside your brain, in a region of the hypothalamus called the suprachiasmatic nucleus (SCN, your brain's master circadian clock), sits the timer that controls the timing of virtually every hormone in your body: cortisol, melatonin, insulin, growth hormone, leptin, and ghrelin.
The SCN is reset daily by one primary signal: light entering your eyes.
When bright light hits the specialised photoreceptors in your retina (called intrinsically photosensitive retinal ganglion cells, or ipRGCs) in the morning, it kicks off a sharp cortisol spike. This is called the cortisol awakening response (CAR). It is entirely healthy. It is your body's natural alarm system.
This morning cortisol spike does several things:
- Releases glucose and fatty acids for energy
- Sharpens your thinking and alertness
- Turns off melatonin production, keeping you awake
- Sets a timer for when melatonin will rise again, approximately 14 to 16 hours later
When the CAR happens at the right time, your cortisol follows its natural arc: peaking in the morning, falling gradually through the day, reaching its lowest point in the evening when melatonin rises and sleep becomes possible.
When the CAR is delayed (because you woke up and went straight to a dark room, looked at your phone, or worked under artificial light), the whole curve moves. It peaks later. It falls later. Your afternoon energy dip arrives earlier than it should. Your evening cortisol stays higher than it should be, which disturbs your sleep. And the next morning, the same pattern repeats.
What the research shows
A 2022 review published in Nature Neuroscience confirmed that morning light exposure within 30 minutes of waking noticeably strengthens the cortisol awakening response in healthy adults. Studies in women specifically found that irregular light exposure patterns were linked to a blunted CAR, higher evening cortisol, and disrupted sleep architecture (the internal structure of your sleep, including how much deep and REM sleep you actually get).
Disrupted sleep architecture matters beyond how tired you feel. It cuts into deep sleep, the stage where growth hormone is released, tissue repair happens, and memory consolidation occurs. It also reduces insulin sensitivity the following day, which contributes to the blood sugar instability behind cravings and energy dips.
One habit. Cascading effects.
How to do it properly
The light signal needs to reach your retina directly. This means:
Go outside. Even on overcast days, outdoor light delivers 10,000 to 50,000 lux. A bright indoor room delivers around 200 to 500 lux. That difference is large enough to matter.
No sunglasses for the first five minutes. You are not staring at the sun. You are just letting outdoor light reach your eyes normally. Sunglasses filter the wavelengths (particularly blue light in the 480nm range) that the ipRGCs respond to most strongly.
Within 30 minutes of waking. The CAR peaks in the first 20 to 30 minutes after waking. Getting light in during this window amplifies it. Getting it an hour later does not produce the same effect.
Consistency matters more than duration. Five minutes every morning beats 30 minutes twice a week.
What this has to do with perimenopause
If you are in perimenopause or approaching it, this habit matters more than it does for younger women.
Declining oestrogen disturbs circadian rhythm. Oestrogen adjusts how sensitive the SCN is to light signals. As oestrogen falls, the circadian system becomes less responsive, sleep becomes less robust, cortisol patterns become more erratic, and the whole hormonal cascade described above gets worse.
This means that the symptoms many women attribute to perimenopause (disrupted sleep, afternoon fatigue, brain fog, and that restless anxious feeling in the evenings) are partly the downstream result of a destabilised circadian system. Correcting the light signal at the start of the day is one of the most accessible, evidence-based things you can do. And it costs nothing.
Where to start
Tomorrow morning, before anything else:
- Wake up at a consistent time (this matters as much as the light)
- Go outside within 30 minutes
- Stay for at least five minutes
- No phone until you come back in
Do this for two weeks before you assess whether it is working. The circadian system responds to regularity over time, not to a single good morning.
If you want the full protocol, including how morning light fits alongside sleep consistency, protein timing, and cycle-aware exercise, the 90 Hard Women's Health Challenge walks you through 90 days of this, one day at a time.
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Debora Tentis is a Women's Health Pharmacist and Independent Prescriber Trainee based in Milton Keynes, UK. This article is for educational purposes and does not constitute medical advice. Please consult a qualified healthcare professional for personalised guidance on hormonal or sleep-related concerns.
