Drinking Enough Water May Lower Cortisol Levels

About 50 to 60% of your body is made up of water, so it’s understandable that hydration is important for our health. According to recent statistics, most of us do not consume enough water, with the average US adult consuming just 44 fluid ounces of water per day. This is well below the recommended 15.5 cups per day for men and 11.5 cups per day for women (or 124 fluid ounces and 92 fluid ounces, respectively).

Water is involved in almost every process that occurs in your body. From regulating body temperature through sweat to transporting nutrients and oxygen to cells, hydration plays a key role in many of the body’s essential functions. This means that if you become dehydrated, your joints may have a hard time maintaining lubrication and you may even experience constipation.

Researchers from the United Kingdom wanted to know whether fluid status played a role in stress levels. They hypothesized that individuals with habitually low fluid intake and suboptimal fluid status would have greater cortisol reactivity (the body’s cortisol response to a stressor) to acute psychosocial stress. In other words, do chronically dehydrated people react more strongly to stress than well-hydrated people when exposed to the same stressful event? They published their results in the Journal of Applied Physiology. Let’s break down what they found.

How was this study conducted?

The researchers recruited healthy, recreationally active men and women between the ages of 18 and 35. Before the official study period began, all potential participants recorded seven days of fluid intake from all sources, including water, milk, juice, coffee, tea, soda, alcohol, and all other beverages. In addition, they were given containers to collect all urine produced between 4 and 8 p.m. on two different days, a weekday and a weekend day.

For this study, researchers only included people with low (less than 1.6 liters per day for men and less than 1.5 liters/day for women) and high (at least 2.9 liters/day for men and at least 2.5 liters/day for women) fluid intake. To be divided into either group, participants also had to meet criteria based on urine samples indicating suboptimal (low) and optimal (high) fluid status.

Once participants entered the study, they visited the laboratory and completed questionnaires about stress, anxiety, and sleep. They were also informed about the mental performance task that they had to complete in the laboratory at the end of the study period.

For the next seven days, participants were given a smart water bottle to ensure they met their recommended daily fluid intake, which was based on their baseline hydration levels. On days five and six, participants submitted all the urine they produced between 4 and 8 p.m. On days seven and eight, they fasted and answered questionnaires in the laboratory, where they also provided another urine and blood sample. Also on the eighth day, the participants completed their mental performance task, the so-called Trier Social Stress Test (TSST), which lasted about two hours. They were instructed not to eat, brush their teeth, or drink anything with caffeine or alcohol for two hours before their arrival.

The Trier social stress test included a 30-minute acclimatization period in a reception area in which participants were able to switch off from any stress before arriving in the laboratory. After acclimatization, participants underwent three elements while standing in front of two observers and a video camera: five minutes of preparation, a five-minute mock interview, and a five-minute mental arithmetic task.

Saliva samples were collected at different intervals – before the TSST and some after the TSST – to test cortisol levels. Participants’ heart rates were also continuously monitored throughout the TSST using a chest strap heart monitor.

What did this study show?

After collecting all the data and conducting statistical analysis, the researchers found that those in the low-hydration group consistently had higher stress markers in saliva, urine and blood. Special:

• Despite similar increases in anxiety and heart rate during the test, salivary cortisol increased significantly in the low-hydration group but not in the high-hydration group.
• Pretest hydration status was associated with the level of salivary cortisol reactivity, with salivary cortisol reactivity being greater in the low hydration group.
• Darker pretest urine (indicating low fluid status) was associated with greater salivary cortisol reactivity.

Researchers suggest that these findings may provide a possible explanation for why habitual low fluid intake and suboptimal fluid balance are linked to poor long-term health outcomes, as the body’s water regulation and stress response systems share overlapping physiological pathways.

A limitation of this study design is that it cannot draw conclusions about causality, only correlation. In other words, it can only be suggested that there is a connection between poor fluid status and cortisol levels. It is also not possible to draw conclusions about specific long-term health effects. Researchers suggest conducting larger, longer-term studies to examine the links between hydration, cortisol and health outcomes.

How does this translate to real life?

Cortisol is the body’s primary stress hormone. It is released in response to immediate and long-term threats, whether real or perceived – like a jump scare in a horror film. Cortisol is necessary when we need to take action against a perceived threat, but when continuously released due to long-term stress, it can cause problems – physically, mentally and emotionally. Finally, fight-or-flight mode can become quite tiring for you over time.

This study is interesting because it suggests that hydration status partially determines how well you handle stress. Who knew your water bottle could actually be a stress management tool?

If you are one of those who suffer from dehydration, it is time to step up your fluid intake. However, there are a few things you should consider before you get started. First, when you are chronically dehydrated and start to give your body the fluids it needs, you may initially experience bloating and a feeling of swelling. This will go away if you just persevere and keep hydrating – and yes, you will go to the bathroom more often. (Just think of it as an opportunity to get more physical activity.)

Additionally, if you’re not used to staying hydrated, drinking a lot more water every day can be overwhelming. As mentioned earlier, experts recommend about 15.5 cups of water for men and 11.5 cups for women every day. (In this study, men saw benefits when they drank about 12.25 cups of water daily, while women drank about 10.5 cups.)

If these numbers seem impossible, remember that it’s okay to break them down and start small. If you find that you can’t drink about 1 cup of water per waking hour, try increasing the amount. Even if you start with half a cup of water every hour, you can change your habits and slowly get used to drinking more fluids. You can also track your water intake for a few days, average your baseline, and start gradually increasing your water intake from there.

In addition to hydrating and maintaining adequate hydration, you can also combat stress by practicing deep (diaphragmatic) breathing and visualization, taking a trip to nature, going for a walk, and other activities you enjoy. It’s also important to get to the root of chronic stress and determine what actions you can take to resolve it. A therapist may be a good choice for you if you struggle with stress.

Our expert opinion

This study suggests that people with low fluid balance and low fluid intake may have higher levels of cortisol, the stress hormone, when exposed to stress-inducing events. Higher cortisol levels can lead to greater inflammation and an increased risk of disease, including heart disease, cancer, arthritis, diabetes and autoimmune diseases. While most liquids can contribute to your hydration levels, it’s important to make sure you drink enough plain water. If you don’t like plain water – or even if you do – consider replacing it with sparkling water or water flavored with fruits and herbs. You’ll love our lemon, cucumber and mint infused water and our watermelon basil agua fresca.