Allostatic Load

We’ve all had times in our lives when the fight-or-flight response has kicked in — when our body gets primed to take action, when your rational, deliberate thinking steps back and survival instinct takes the lead, when panic grips you, when the colour drains from your face, when your heart starts to beat faster, and when the rest of the world slows down around you.

Yet you don’t need to be in a war zone, being mugged, or hanging off a cliff for this to happen. For most people, the fight-or-flight reaction happens when they’re doing something far more mundane. For some, all it takes for our body to trip into survival mode is to turn the corner and see our workplace, or it could be a brown envelope containing a bill, the ring of a doorbell, or even just the thought of leaving the house.

The Fight or Flight Response

The fight-or-flight response is a survival mechanism. For thousands of years, it’s helped humanity survive: physically ready in times of danger, focused on staying alive. It’s meant to be a short-term response to a dangerous stimulus, a source of strength we could tap into when needed, and a reservoir of stress hormones that would rev up our body’s systems to make us ready for an emergency and then be switched off again as our body recovers.

The trouble is, for some people, the fight-or-flight response stays on. It doesn’t switch off. In stressful jobs, we can end up in fight-or-flight mode most of the time. And even when we should be relaxing, switching off, our minds get preoccupied with work, with deadlines, with past events, and we stress about what-ifs and what may or may not happen.

Our mind perceives our worries as being dangerous, as being real. And even though there’s no imminent danger to our lives, it doesn’t matter. The fight-or-flight response still switches on.

When Stress Becomes Chronic

You wouldn’t be surprised that if your body is exposed to this type of stress for a long period of time, things go wrong. There are biological consequences of prolonged heightened stress. The wear and tear on your body from chronic stress is called allostatic load.

Although the fight-or-flight response is essential for managing acute, life-threatening threats, it can be very damaging to your body in the long run.

As your stress level increases, so does your allostatic load. Stress hormones in your body are released, namely cortisol and adrenaline. Your heart’s workload increases. The smooth muscle tone in your gut changes. Your blood becomes more able to coagulate. Your blood sugar levels increase. Your blood pressure spikes.

Research on chronic stress shows these physiological changes aren’t just temporary responses. When maintained over weeks, months, or years, they become pathological. Your body wasn’t designed to run in emergency mode constantly. It’s like redlining your car’s engine continuously. Eventually, something breaks.

The Medical Consequences

The effects of increased allostatic load are well known. We know it can contribute to cardiovascular disease and hypertension. It’s no coincidence that the peak time for having a heart attack is in the first three hours after waking. Cortisol and adrenaline surge naturally as you wake, blood pressure rises, and vascular tone and clotting activity shift — this happens to everyone, by design, whether or not you’re dreading the day ahead. If you’re already operating with high allostatic load, that natural morning surge is riding on top of an already-elevated baseline, which is exactly why it matters.

Chronic stress is a genuine, independent contributor to cardiovascular risk, consistently demonstrated across large studies — but it’s a smaller contributor than smoking or high cholesterol, not a comparable one, and it works partly by making those conventional risk factors worse rather than by overriding them. Eating well, exercising, and maintaining a healthy weight all still matter enormously, alongside managing your allostatic load, rather than being made redundant by it.

The more subtle changes of increased allostatic load are gradually becoming better understood: a weakened immune system, disruption in diurnal rhythms and sleep, increased neuromuscular tension, overstimulation of compensatory mechanisms in your body, and changes to the structure and function of your brain itself.

Research using brain imaging shows chronic stress is associated with reduced hippocampal volume — the hippocampus being the part of your brain most involved in memory and learning — and, in some studies, a more reactive amygdala, the brain’s fear centre. The direction of cause and effect here is genuinely debated in the research, and some of these changes appear at least partly reversible with treatment and stress reduction, which is worth holding onto alongside the concerning part.

What I See Every Day

I see the subtle signs of increased allostatic load in my practice every day: migraines, tension headaches, neck aches, panic attacks, insomnia, irritable bowel, tiredness, fatigue, stress, anxiety, and depression.

It takes seconds to see that someone’s looking tense. Maybe their breathing is higher in the chest and more rapid. Perhaps they can’t sit still. Maybe it’s the pallor in the face, the tone of the voice, the irritability in their manner. Or it’s just the feeling that follows them into the consultation room.

Some people spend much of their lives in a state of high allostatic load. They’re permanently ready for flight or fight, ready to snap at the least thing, their body constantly running emergency protocols for emergencies that don’t exist.

I think of a patient, a composite drawn from several people I’ve seen, who came to see me about insomnia. He hadn’t slept properly in two years, not since his promotion to senior management. He’d tried everything: sleep hygiene, supplements, different mattresses, white noise machines. Nothing worked.

When I examined him, his resting heart rate and blood pressure were both raised. He had a constant scowl, his jaw muscles were tight, and his dentist had him wearing a guard at night because he was grinding his teeth. His body was running in emergency mode around the clock, so of course he couldn’t sleep. You can’t sleep when your body thinks you’re being chased by a tiger.

The Training Effect

There’s a saying among soldiers: in the thick of battle, you won’t rise to the level of your expectations, but fall to the level of your training.

This applies to stress as well. Your body learns. If you consistently operate with high allostatic load, that becomes your new baseline. Your nervous system recalibrates. What would have been an emergency response for someone else becomes your normal. You’ve trained your body to exist in a state of chronic stress.

Research on stress adaptation shows this pattern clearly. People in chronically stressful environments develop what looks like tolerance — they function despite high stress levels. But this isn’t a healthy adaptation. It’s pathological recalibration. Their body has given up trying to return to normal and accepted crisis mode as baseline.

The consequence is that when additional stress occurs, and it will, these people have no reserve capacity. They’re already running at maximum. Any additional demand can push them into a complete breakdown — panic attacks, cardiac events, psychological collapse.

Recognising High Allostatic Load

So how do you know if you’re operating with high allostatic load? Ask yourself: do you wake up tired? Do you struggle to fall asleep or stay asleep? Are you always frowning? Do you grind your teeth? Do you get frequent headaches? Does your neck and shoulder area feel constantly tense? Are you irritable with people? Do you get sick frequently? Do minor setbacks feel overwhelming?

If you’re answering yes to most of these, your allostatic load is probably elevated. There isn’t a single blood test your GP can order that measures it directly — it’s a research index built from a combination of markers, not a routine clinical test — but the pattern above is a reasonable guide, and it’s worth acting on rather than waiting for a number to confirm it.

Studies on workplace stress show that people consistently underestimate their own stress levels. They’ve adapted to it so completely that crisis mode feels normal. They don’t recognise they’re operating with high allostatic load until something forces them to confront it, which in my line of work is often a medical crisis.

Turning Down the Load

The good news is that allostatic load can be reduced. Your body can recalibrate back to a healthier baseline. But it requires deliberate effort and sustained changes.

The treatment for the patient above wasn’t primarily about sleep. It was about reducing his allostatic load, and most importantly, he engaged with the process. He addressed his catastrophic thinking patterns through CBT, and he implemented a daily mindfulness practice to reduce his overactive Default Mode Network. We established strict work boundaries: no emails after 6pm, no work on weekends. He took time to decompress away from work, and he added regular exercise to metabolise stress hormones.

Within three months, he’d distanced himself from work, kept to the boundaries agreed, and his blood pressure had normalised. He was sleeping six to seven hours nightly. His allostatic load had decreased because we’d systematically removed the factors that had kept it elevated.

Research on stress-reduction interventions consistently shows this pattern: allostatic load responds to sustained changes in lifestyle, thought patterns, and stress management practices. But it takes time. Your body didn’t develop high allostatic load overnight. It won’t resolve overnight either.

The Connection to Everything Else

This exists within a larger context. Negative thoughts, anxiety, overactive Default Mode Networks, and various cognitive patterns that keep you stuck all contribute to allostatic load. Your psychological patterns have physiological consequences.

When your Default Mode Network catastrophises constantly, your body responds with stress hormones. When you ruminate about past failures or future disasters, your allostatic load increases. When you operate with persistent anxiety, your cardiovascular system pays some of the price.

This is why the tools discussed elsewhere in this hub aren’t just about feeling better emotionally. They’re about preventing your body from running itself into the ground with sustained emergency responses to threats that don’t exist.

What You Need to Do

In addition to the specific changes to your thought patterns and emotions possible through the other tools in this hub, you must also learn to reduce your overall allostatic load.

This means proper sleep, not negotiable: seven to eight hours nightly, and regular exercise, not optional. You need boundaries around work; your body can’t recover if you’re constantly accessible. You need time to unwind and decompress, and to do the things you enjoy regularly.

This means recognising when you’re running in emergency mode for non-emergencies: when you’re treating every deadline like life or death, when you’re responding to every email like it’s urgent, when you’re operating as if you’re constantly under threat.

Your body is trying to save your life. That’s what the fight-or-flight response is for. But often it’s responding to threats that don’t exist, and in the process, it’s wearing you down through sustained high allostatic load.

The tools work. The changes work. But you have to actually implement them. Because right now, whether you feel it or not, your body’s paying some of the price for your mind’s patterns, and eventually, that bill comes due.

Further reading

1. McEwen, B. S., & Stellar, E. (1993). Stress and the individual: Mechanisms leading to disease. Archives of Internal Medicine, 153(18), 2093–2101.
2. Seeman, T. E., Singer, B. H., Rowe, J. W., Horwitz, R. I., & McEwen, B. S. (1997). Price of adaptation: Allostatic load and its health consequences. Archives of Internal Medicine, 157(19), 2259–2268.
3. Juster, R. P., McEwen, B. S., & Lupien, S. J. (2010). Allostatic load biomarkers of chronic stress and impact on health and cognition. Neuroscience & Biobehavioral Reviews, 35(1), 2–16.
4. Kivimaki, M., & Steptoe, A. (2018). Effects of stress on the development and progression of cardiovascular disease. Nature Reviews Cardiology, 15(4), 215–229.
5. Lupien, S. J., McEwen, B. S., Gunnar, M. R., & Heim, C. (2009). Effects of stress throughout the lifespan on the brain, behaviour and cognition. Nature Reviews Neuroscience, 10(6), 434–445.