Not Drinking Enough Water Could Be Stressing You Out

Imagine standing in front of a room full of strangers, told to give a speech you didn’t prepare for, then asked to do maths on the spot.

Stressful, right?

In a recent study, the people who were even slightly dehydrated had way bigger stress hormone spikes than those who were well-hydrated.

That’s because hydration doesn’t just affect how your body feels, it can change how your body reacts to pressure. And when it comes to cortisol (your stress hormone), the difference between hydrated and under-hydrated could be the difference between calm under fire and complete overdrive.

Which begs the question:

What is cortisol and how does hydration turn its volume up or down?

Cortisol is often called your body’s “stress hormone,”but that doesn’t make it a villain. It’s more like your internal alarm system, designed to wake you up, give you energy, and help you handle pressure when you need it most.

In the right amounts, cortisol is incredibly useful. It rises in the morning to get you out of bed, gives you an edge during tough workouts, and sharpens your focus in high-stakes situations.

Think of it like a smoke alarm: when it goes off at the right time, it protects you.

But when cortisol spikes too high, too often, it stops being helpful. That constant “alarm” leaves you feeling restless, fatigued, or wired at the wrong times. Over the long run, exaggerated cortisol is linked with disrupted sleep, slower recovery, and increased risks for things like high blood pressure and metabolic issues.

So, the big question researchers are now asking is simple:

Stress shows up differently for everyone: racing thoughts, snapping at small things, poor sleep, dragging through a workout. What most people don’t realise is that hydration can shape how hard those stress signals hit. That’s not guesswork; it’s what recent studies have tested directly.

One trial looked at the body’s natural morning rhythm. Cortisol naturally spikes in the first hour after waking; it’s called the cortisol awakening response (CAR). Researchers tested whether fluid intake could blunt or change that spike (Kashi et al., 2025a). The result? It didn’t. Whether people drank more, less, or changed their intake, the morning cortisol rise stayed the same.

This matters because it clears up a misconception: drinking litres before bed won’t “switch off” your morning stress hormones. But that isn’t the full story, because mornings aren’t when stress derails most of us.

To test real-life pressure, researchers turned to the  Trier Social Stress Test, a scenario designed to make people uncomfortable: delivering a speech and solving maths under scrutiny. Here, hydration told a different story. Participants who drank less water and showed markers of dehydration had significantly greater cortisol spikes than those who were well hydrated (Kashi et al., 2025b). In fact, something as simple as morning urine colour predicted how intensely their body would react.

Other findings confirm this link between hydration status and cortisol dynamics across healthy adults (Zaplatosch et al., 2025).

The takeaway is simple: hydration doesn’t erase your natural morning rhythm, but it does decide how forcefully your stress system reacts when the stakes are high. It shows that hydration shifts from being just a ‘wellness habit’ to something that actively shapes how you experience stress in the moments that matter. And those moments aren’t confined to the lab; they show up at work, in training, and even when you’re trying to switch off at night.

Science in the lab is one thing. But what do those sharper cortisol spikes actually feel like day-to-day? They can show up in ways most people don’t even connect to hydration.

At work, it might look like losing patience faster than you should, or feeling your heart race during a tense meeting. Those bigger stress hormone surges make pressure feel heavier and recovery from it slower.

In training, dehydration doesn’t just leave you thirsty, it makes sessions feel tougher than they need to be. Higher cortisol reactivity means your body works harder under the same load, and winding down afterwards can take longer.

And at night, pairing low hydration with caffeine is like adding fuel to the fire. Your stress system is already primed to overreact, and instead of switching off, it stays switched on.

The point is simple: dehydration doesn’t only show up as thirst. It hides in everyday stress, making small challenges feel bigger, and recovery feel harder. And that’s exactly why consistent hydration matters.

Understanding the science is one thing. Putting it into action is where the benefits happen. Here are five simple steps to help you keep your stress system steady; with hydration as the foundation.

Step 1: Check yourself

The easiest way to gauge hydration isn’t fancy tech, it’s your urine colour. Pale yellow means you’re in a good place; darker shades are a sign your body may already be under pressure. Make it a morning habit to check in.

Step 2: Build hydration habits

Consistency matters more than last-minute litres. Sip across the day instead of playing catch-up at night. If you’re sweating through training or working outdoors, water alone may not cut it, that’s when electrolytes keep balance in check.

Step 3: Support recovery

Hydration isn’t only about fluids. Minerals like magnesium play a key role in calming the nervous system and supporting quality sleep, two areas cortisol can disrupt when stress runs high.

Step 4: Balance the stress response

Adaptogens are plant-based compounds shown to help the body adapt to stress. They won’t eliminate pressure, but they may help your system stay composed instead of tipping over.

Step 5: Add nutrient support

Nutrition also shapes how quickly cortisol settles. A mix of carbohydrate and vitamin C after training, for example, has been shown to help cortisol return to baseline faster, supporting both recovery and resilience.

Think of it as building your stress shield: one sip, one habit at a time.

Hydration won’t erase stress, life will always throw deadlines, tough sessions, and late nights your way. But the research is clear: staying consistently hydrated helps stop your body from overreacting when the pressure is on.

At ASN, we believe small daily habits make the biggest difference. That’s why our hydration and recovery range goes beyond the water bottle, offering science-backed options like electrolytes, magnesium, and adaptogens to support your body when it needs it most. And because no two stressors look the same, our team is here to help you find the right fit; whether that’s in-store with expert advice, or through the ease of shopping online and click & collect.

Deadlines won’t disappear, but dehydration doesn’t need to make them worse. With the right tools and knowledge, you can keep your stress system steady, your training on track, and your recovery where it should be.

Kashi, D. S., Hunter, M., Edwards, J. P., Zemdegs, J., Lourenço, J., Mille, A.-C., Perrier, E. T., Dolci, A., & Walsh, N. P. (2025). Habitual fluid intake and hydration status influence cortisol reactivity to acute psychosocial stress. Journal of Applied Physiology, 139. https://doi.org/10.1152/japplphysiol.00408.2025

Kashi, D. S., Hunter, M., Zemdegs, J., Lourenço, J., Quinquis, L., Mille, A. C., Perrier, E. T., Dolci, A., & Walsh, N. P. (2025). The influence of low and high daily fluid intake on the cortisol awakening response. Proceedings of the Nutrition Society, 84(OCE3). https://doi.org/10.1017/s0029665125100876

Zaplatosch, M. E., Wideman, L., McNeil, J., Sims, J. N. L., & Adams, W. M. (2025). Relationship between fluid intake, hydration status and cortisol dynamics in healthy, young adult males. Comprehensive Psychoneuroendocrinology, 21, 100281. https://doi.org/10.1016/j.cpnec.2024.100281