Heatwave: fluid balance, electrolytes, supplements

Heatwave: what happens in the body and how to support fluid balance?

When temperatures rise for several days in a row, the body is affected more than many people realize. A heatwave isn’t just uncomfortably hot. The body has to work harder to keep a stable core temperature and this can affect fluid balance, electrolytes, circulation, muscles, energy, sleep and recovery. In heat, sweating increases. When we sweat, we lose not only water but also important electrolytes such as sodium, potassium, magnesium and chloride. If the losses are large, or if you drink a lot of water without replacing salts and minerals, you may feel tired, weak, dizzy, get headaches, muscle cramps or reduced stamina. That’s why it’s important to think about more than just water during a heatwave. Fluids, electrolytes, minerals, rest, cooling and the right food together play an important role in how the body handles high temperatures.

What is a heatwave?

A heatwave is a period of unusually high temperatures, often for several days in a row. The exact definition can vary, but from the body’s perspective it’s mainly the combination of high temperature, strong sun, high humidity, poor sleep at night and insufficient recovery that makes the heat taxing. When the body is exposed to heat it tries to cool itself by:

increasing sweating
dilating blood vessels in the skin
increasing blood flow to the skin
increasing the heart’s workload
reducing performance during physical activity

These are normal protective mechanisms. Problems arise when fluid loss exceeds intake, when electrolytes aren’t replaced, or when the body doesn’t get a chance to cool down and recover.

Common symptoms in heat, dehydration and electrolyte deficiency

During a heatwave the body can signal imbalance in several ways. Common symptoms include:

fatigue and lack of energy
headache
dizziness or feeling unsteady
dry mouth
dark urine or decreased urine output
muscle cramps
nausea
palpitations
difficulty concentrating
poorer sleep

It’s important to understand that dehydration and electrolyte deficiency aren’t always the same thing. You can drink a lot of water and still feel “drained” if you’re simultaneously losing a lot of salts through sweating.

Why electrolytes matter during a heatwave

Electrolytes are minerals that carry an electric charge in the body. They’re needed for nerve signals, muscle function, fluid balance, blood pressure regulation and normal heart function. The most important electrolytes during heat and sweating are:

Sodium – helps the body retain fluid and is the electrolyte we lose the most of in sweat.
Potassium – important for muscles, the nervous system and fluid balance inside cells.
Magnesium – needed for muscles, the nervous system, energy metabolism and electrolyte balance.
Chloride – works with sodium and is important for fluid balance and stomach acid.

During a heatwave, sodium is especially important because sweat contains significant amounts of salt. People who eat a lot of clean, unprocessed food often consume less salt than those who eat a lot of ultra-processed food. That can be positive in many contexts, but with heavy sweating the need for salt and electrolytes can increase.

Should you just drink more water when it’s hot?

Water is essential, but it isn’t always enough. In mild heat and with low physical activity, it’s often sufficient to drink regularly and eat mineral-rich food. But with heavy sweating, exercise, sauna, outdoor work or prolonged heat, the body may need both fluids and electrolytes. A common mistake is to drink large amounts of plain water without getting enough salts. That can dilute electrolytes in the body and leave you feeling weak, tired or dizzy even though you’re drinking a lot.

A simple rule of thumb is:

Drink regularly throughout the day.
Salt your food as needed.
Use electrolytes with heavy sweating or prolonged heat.
Avoid large amounts of alcohol, as it can impair fluid balance.
Be extra careful with intense training in the middle of the day.

Who is especially sensitive to heatwaves?

Some people are more affected by heat than others. Extra caution is needed for:

older adults
young children
pregnant individuals
people with cardiovascular disease
people with kidney problems
people with diabetes
people with high blood pressure
people using diuretics
people using medications that affect blood pressure, kidneys or electrolytes

For these groups it’s especially important to consult a healthcare provider if unsure, particularly before using electrolyte supplements or minerals in higher doses.

Diet during a heatwave

When it’s very hot, many people experience reduced appetite. Then it’s wise to focus on easy-to-digest, nutrient-dense foods that provide protein, minerals and energy without overburdening digestion. We recommend prioritizing:

eggs
fish and seafood
high-quality meat
yogurt, kefir or cheese if dairy is tolerated
fruit and berries
honey as an easily accessible carbohydrate source if needed
mineral-rich salt on food
natural fats like butter and tallow in reasonable amounts

Try to avoid large amounts of ultra-processed food, seed oils, alcohol and lots of sugar. These can contribute to poorer fluid balance, more oxidative stress and worse recovery.

Supplements that may help during a heatwave

Supplements should not replace fluids, food, cooling or medical care. However, certain supplements can be valuable to support fluid balance, electrolytes, muscles, the nervous system and recovery during hot periods.

1. Electrolytes Plus+ – first choice for sweating and heat

During a heatwave, electrolytes are often the most relevant supplement. When we sweat, we lose primarily sodium, but also other minerals. Electrolytes Plus+ is therefore our first choice in heat, sweating, training, sauna or when you feel weak and “drained” despite drinking water. Electrolytes help the body keep fluid in the right place, support normal muscle function and maintain nerve signaling.