Dehydration, coffee and cortisol – what really happens in the body when you don't get enough fluids?
Have you ever said, or heard someone say, that "coffee goes straight through"? Many people find that they have to run to the bathroom shortly after their first cup of coffee of the day, and it's easy to think that coffee dehydrates us. But is that really true?
Coffee and dehydration – myth or truth?
Coffee contains caffeine, which has a mild diuretic effect, but the body still absorbs most of the fluid. This means that coffee actually counts towards your daily fluid intake, and that coffee alone does not lead to dehydration. What happens is that you add fluid to your body quickly, and combined with the effect of the caffeine, it can give the feeling that the coffee “goes right through.”
What many people don't know is that coffee can also help your body excrete a little more salts and minerals, especially sodium and potassium. For most people, this has little impact on their daily lives, but if you drink a lot of coffee or combine coffee drinking with exercise and sweating, the loss of electrolytes can be noticeable. This is one of the reasons why it's a good idea to think about how you can support both the fluid and mineral balance in your body.
What happens in your body when you are dehydrated?
Although coffee is not the only culprit, dehydration is a real problem that many of us underestimate. When the body loses fluid, blood volume decreases, the heart has to work harder, and body temperature rises more easily because the body loses the ability to regulate itself through sweat. Even with mild dehydration, you can notice symptoms such as headaches, dizziness, difficulty concentrating, and fatigue.
New research has shown that even mild dehydration makes the body more sensitive to stress. In a study published in the Journal of Applied Physiology in August 2025, people who drank less than 1.5 liters of fluid per day had more than 50% higher cortisol levels when stressed compared to those who drank the recommended amount. Dehydration also triggers the release of the hormone vasopressin, which helps the body retain water – but also increases the cortisol response.
Cortisol is useful in acute situations, but chronically elevated levels can lead to poor sleep, anxiety, a weakened immune system and an increased risk of heart and metabolic disease. High cortisol levels over time also contribute to low-grade inflammation in the body. This happens because stress hormones affect the immune system, increase the production of pro-inflammatory signaling substances and make the body more vulnerable to inflammation in joints, muscles and organs. Dehydration can therefore indirectly create a breeding ground for inflammatory conditions, precisely because the body is constantly in a "stress mode".
Fluid balance is also about electrolytes
It's not just water that counts when it comes to hydration. To maintain a good fluid balance, the body needs electrolytes such as sodium, potassium and magnesium. Without them, the cells are unable to utilize the fluid properly. So you can drink a lot of water and still feel thirsty if your salt balance is not in place. This is especially important during hard training, hot days or illness with fluid loss.
To support the body in a simple way, products such as Aarja's Mind Body Boost and the isotonic Sporty Boost can be useful, as they both contain salts and minerals that help maintain electrolyte balance. In addition, Magnesium Glycinate and Triple Magnesium can be important. This improves the body's ability to retain fluid, while also boosting energy levels and concentration.
How to avoid dehydration in everyday life
Avoiding dehydration is not about forcing yourself to drink gallons of water, but about maintaining a consistent fluid intake throughout the day. Drink before you feel very thirsty, and vary your fluid sources. Water is of course best, but herbal teas, smoothies, fruits and vegetables also contribute to hydration. Pay attention to your body's signals: dark urine, headaches and fatigue can be signs that you need more fluids. And remember: coffee can be a good part of your fluid balance, but it should not be your only source.
To further support the body, it can also be useful to supplement with nutrients that help it cope with stress and inflammation. Aarjas Curcumin + B12 + Ginger is a combination that both has anti-inflammatory properties and supports the nervous system, which can be especially important when the body is under stress – such as dehydration. Supplements such as OptiMSM + C and Omega 3 Krill with Astaxanthin can also help reduce inflammation and protect cells from oxidative stress, which is often exacerbated by both dehydration and high cortisol levels.
So the next time you feel like your coffee is “going straight through”, you can be sure that it is actually contributing to your fluid balance. But if you really want to take care of your body, you should combine fluids with electrolytes, listen to your body’s signals and make hydration a natural part of your everyday life. It’s a simple investment in better energy, a stronger immune system and lower stress levels – and here, selected supplements can also be a good support.