Why You Have No Energy in Autumn: Light, Cortisol, ATP

Every year, towards the end of October, I think the same thing: I have gone soft.

The alarm goes off and I lie there another twenty minutes. By eleven my head is running at half speed. By four in the afternoon I am in a state best described as cotton wool. And every year I spend a fortnight forgetting that exactly this happened last October, and the October before, and that in June, on the same schedule and the same workload, I got up on my own ten minutes before the alarm.

The difference between June and October is not character. It is the amount of light reaching my eyes, and everything that follows from it.

What follows is the mechanism. No autumn blues as a diagnosis, and no promise that one jar fixes everything.

What this is and why it matters

Autumn fatigue is not one condition. It is several shifts stacking on top of each other inside the same six weeks.

The first and largest is daylight. In temperate latitudes, from late September to late October, the day loses roughly four minutes of light every twenty-four hours. Over a month that adds up to about two hours. By early November the gap against the June maximum reaches five to six hours. This is not "it has got cloudier". It is a different lighting regime.

The second shift is intensity, and this is where the numbers surprise people most. Outdoor illuminance on a clear summer noon runs to 50,000–100,000 lux. Outdoors at a grey November noon: 1,000–5,000 lux. In a well-lit office: 300–500 lux. So even a dull day outside is several times brighter than your desk, and a summer noon is hundreds of times brighter. Anyone who walks the car park–office–car park route from October to March is living at an illuminance their biology reads as prolonged dusk.

The third is temperature and food. The body spends more on thermoregulation, and the diet drifts towards fast carbohydrates on its own: a light-starved brain asks insistently for serotonin, and the shortest route there is sugar.

Why this is worth understanding rather than simply enduring: fatigue of this origin does not respond to willpower. Blaming yourself for it is pointless. Adjusting the inputs, on the other hand, is entirely doable — the inputs specifically, because everything downstream is handled by physiology, and handled fairly predictably.

How it works: light, cortisol, adenosine, ATP

Let me walk the chain from the eye to the mitochondrion.

Light as a signal, not as illumination.

Besides rods and cones, the retina holds a third cell type: intrinsically photosensitive ganglion cells carrying the pigment melanopsin. They take no part in forming the image. Their job is to tell the brain what time of day it is. Melanopsin peaks in the blue part of the spectrum, around 480 nanometres, and the signal from these cells runs straight to the suprachiasmatic nucleus of the hypothalamus — the body's central clock.

That clock synchronises to light. Not to your alarm and not to your work schedule, but to how much bright light hit the retina and precisely when. Morning light shifts the phase earlier; evening light shifts it later.

Cortisol.

Cortisol follows a daily curve, and its key feature is the rise in the first 30–45 minutes after waking, the cortisol awakening response. This is a normal and necessary mechanism. Cortisol in that first hour is not the "stress hormone" — it is the signal to start metabolism, mobilise glucose and switch attention on.

The amplitude of that rise depends partly on light. Waking in the dark and sitting for an hour at 200 lux is not the same input as stepping outside into three thousand. The curve comes out flatter. A flat curve means a sluggish start in the morning and an insufficient drop by evening, and you go to bed tired but wide awake.

A separate word on melatonin. With a late bedtime and a pre-dawn alarm, melatonin secretion is still running while you are already on your way to work. Hence the familiar sense that the first two hours of the day happen without you.

Adenosine, and why coffee does not give you energy.

While you are awake, adenosine accumulates in the brain as a by-product of energy expenditure. The more adenosine sitting on receptors, the stronger the sleepiness. It is a fatigue counter, and it is an honest one.

Caffeine resembles adenosine closely enough to occupy the same receptors without activating them. It adds no energy. It hides the reading on the counter. Adenosine keeps piling up regardless — you simply stop feeling it. When the caffeine clears, everything accumulated takes the receptors at once, and you get what people call the crash.

Caffeine's half-life in an adult averages five to six hours, and considerably longer in some people. The practical conclusion is simple: a cup at four in the afternoon leaves roughly half the dose at ten in the evening and about a quarter at midnight. Then shallow sleep, a wrecked morning, and an urgent need for that first cup. The loop closes.

Mitochondria and ATP.

Below all these signals sits the level where fatigue stops being a sensation and becomes arithmetic.

The cell's energy currency is ATP, adenosine triphosphate. Mitochondria make it, and the crucial property of ATP is that it is essentially not stored. An adult body holds around 250 grams of it at any moment, while turning over an amount comparable to body weight across a day. The molecule is synthesised and spent, synthesised and spent, with no buffer.

So "no energy" at cell level is not an empty tank. It is reduced throughput: mitochondria producing more slowly than the cell spends. The reasons vary — missing substrates and cofactors, less oxygen, disrupted sleep, low-grade inflammation.

And here is the point. Caffeine has no effect on ATP production whatsoever. It works at the receptor, not at the power plant. Which sets the whole logic of an autumn protocol: repair the input and the production, not the perception.

What seasonal adjustment actually gives you

Let me be straight about what it will not give you: summer in November. The light is not coming back, and pretending October is May is pointless.

What does change.

An earlier, cleaner start. When bright light reaches the retina within the first hour of waking, the cortisol curve steepens and the sleep phase gradually drifts earlier. For me that takes about ten days — not one morning.

Level energy instead of a sawtooth. Drop the third cup and the three-to-four-o'clock trough goes with it. The curve sits below the caffeine peak, but there are no holes in it.

Deeper sleep. Removing evening caffeine is the cheapest sleep improvement in existence. It costs nothing and works from the first week.

Less sugar craving in the afternoon. Not through willpower, but because part of that craving is an attempt to top up fast glucose against a sleep debt.

All of it is about regularity rather than a one-off push. That is the dull part, and there is no way around it.

Who needs this most — and who needs more than this

Most relevant to the following.

Anyone living above the fiftieth parallel: the higher the latitude, the sharper the seasonal swing. London gets under eight hours of daylight in late December; go far enough north and the sun does not clear the horizon at all.

Office workers on the dark-to-dark route. Even twenty minutes outside at lunch changes the daily light dose dramatically.

Anyone drinking more than two coffees a day with the last one after three in the afternoon.

People past 45, whose circadian amplitude declines physiologically while sensitivity to shifts goes up.

Women in perimenopause, where the seasonal shift lands on top of a hormonal one and "no energy" gets louder.

Now, honestly, about who needs more than this.

If the fatigue lasts longer than two or three months and has no seasonal pattern; if it comes with breathlessness, hair loss, feeling cold, weight change; if the morning improves from nothing at all — this is not a matter for light and adaptogens. Iron deficiency, thyroid dysfunction, sleep apnoea, anaemia, depressive disorder are conditions with specific diagnosis and specific treatment. A full blood count, ferritin, TSH and a conversation with a doctor will do more here than any protocol from a blog.

And a category of its own: if you sleep five hours, no adaptogen turns them into eight. There is nothing to discuss there.

How to apply it: a four-week autumn protocol

The order is not arbitrary — free and powerful first, everything else after.

One: light in the first hour after waking. Twenty to thirty minutes outdoors, no sunglasses, overcast weather included. If that is genuinely impossible, a 10,000-lux lamp for twenty minutes over breakfast. This is the single item worth doing even if you ignore all the others.

Two: light at midday. Fifteen minutes outside in the middle of the day. This is not about vitamin D — autumn sun angles in temperate latitudes make that difficult anyway. It is about confirming the "it is daytime" signal.

Three: the caffeine window. First cup no sooner than 60–90 minutes after waking, so you do not blunt the natural cortisol rise. Last cup no later than 2 p.m. Anything after that is subtracted from the night.

Four: that third cup. Mine sat at around four in the afternoon, and it was never about taste — it was about dragging the day to the finish. I replaced it with a cordyceps coffee drink. Cordyceps is an adaptogenic fungus from TCM; its components include cordycepin, adenosine and polysaccharides, and with regular use it supports the body's adaptation to load rather than muting the sensation of fatigue. One detail people forget: there is coffee in that drink too, so the timing rule still stands — this cup must not drift into the evening.

Five: warm food. In TCM logic, autumn belongs to the season of dryness, and cold food at this time is treated as an extra load on digestion. Testing this on yourself is easy: a warm breakfast instead of a cold one changes how the first hour feels faster than any supplement.

Six: movement before noon. Twenty minutes of walking is not sport, it is a signal to the clock. Intense training after eight in the evening, meanwhile, winds some people up rather than down.

Seven: evening light downwards. Two hours before bed, kill the overhead light and keep warm lamps at eye level and below. Melanopsin cells are more sensitive to light arriving from above — evolutionarily sensible, since the sky is up there. More on the mechanics of night-time recovery in the piece on sleep quality.

Eight: a support course, if you run one at all. Adaptogens work cumulatively and the horizon for judging them is weeks, not days. Cordyceps and lingzhi are the usual choices here — I have a separate piece on the latter — while spirulina covers the protein and mineral base of the diet. The measure is four weeks minimum; below that there is nothing to assess.

And an honest note on who should skip all of it. Caffeinated drinks are not an option with arrhythmias, uncontrolled hypertension, anxiety disorders, or during pregnancy and breastfeeding. Cordyceps and other fungal extracts call for a conversation with your doctor in autoimmune conditions and when taking immunosuppressants or anticoagulants. Spirulina is unsuitable in phenylketonuria and warrants caution in autoimmune thyroiditis. If you are on prescribed treatment: doctor first, blog second.

Conclusion

There really is no energy in autumn, and that is neither a metaphor nor a weakness of character.

The day is several hours shorter. Indoor illuminance runs tens of times below outdoor. The cortisol curve flattens, melatonin drifts, and we mute the adenosine counter with caffeine instead of resetting it with sleep.

In that arrangement, the third coffee is not a solution but a loan. At a high rate, too: repayment falls due at night, on the same card.

What can actually be done: get light back into the first hour of the morning, close the caffeine window by two in the afternoon, swap the evening stimulant for something that works cumulatively, and give yourself four weeks instead of four days. My own benchmark is ten days to the first noticeable shift and a month to the state where October stops feeling like a punishment.

And yes, next autumn I will again decide I have gone soft. Except now I know how many minutes of light I have lost since September — and what to do about it.