Night leg cramps: why at night, and what actually helps?
by AUA Hydrate
It is three in the morning. The calf hardens in an instant, the foot twists, and you have to jump out of bed to stretch the leg. The pain fades within a minute — sleep takes far longer to return. Night leg cramps affect athletes and non-athletes alike, and become more common with age. Why do they strike at night in particular — and what can be changed?
⏱ The essentials in 20 seconds
- At night the foot stays pointed and circulation slows: a shortened muscle contracts more easily.
- What happens at night is set up during the day: sweating, coffee, late training, a potassium-poor diet.
- Magnesium and potassium contribute to normal muscle function — provided you take them in regularly.
- Frequent or severely painful cramps deserve medical advice: hydration is not always the culprit.
Why at night rather than during the day?
A cramp is an involuntary, sudden and sustained muscle contraction. Three conditions line up particularly well during sleep.
1. The muscle sleeps in a shortened position
Lying on your back or your front, the foot naturally extends, toes pointing away. The calf then sits in its shortest position — exactly where it fires most easily. A single turn in bed is sometimes enough.
2. Circulation slows right down
At night, heart rate and blood flow drop. Leg muscles, motionless for hours, receive less blood: the day's metabolic waste clears more slowly, and minerals reach the fibres less easily.
3. The nerve is more excitable
This is the most important point, and the least known. A cramp does not start in the muscle but in the nerve that commands it. That nerve's excitability depends directly on the balance of sodium, potassium, calcium and magnesium on either side of the cell membrane. When that balance drifts, the firing threshold drops: the nerve goes off on its own.
What happens at night was decided during the day
A night cramp is rarely about one night. More often it is the closing balance of a day that was never topped up:
- 🥵 You sweated — sport, heat, physical work. Sweat carries away sodium above all.
- ☕ You lined up the coffees without drinking water alongside. We cover that effect in coffee, tea, alcohol: what really dehydrates.
- 🏃 You trained late in the day, leaving little recovery time before bed.
- 🥗 You eat « healthy » but low in salt, and light on potassium-rich vegetables.
- 🍷 You had a glass or two: alcohol increases the urinary loss of water and minerals.
The common thread: the body ends the day with its mineral stores drawn down, and night falls at the worst moment.
So why not just drink more water in the evening?
That is the natural reflex, and often a false good idea. A large glass of plain water at bedtime dilutes the minerals you have left without adding any — and wakes you at four for another reason. Better to spread out, across the day, water that also brings minerals: that is the whole subject of why water alone is no longer enough.
Magnesium, potassium, sodium: who does what
Three minerals keep coming up in this story, and their roles complement each other.
- Magnesium — contributes to normal muscle function and to the normal functioning of the nervous system. The mineral of release: it helps the muscle let go of its contraction.
- Potassium — also contributes to normal muscle function. It works in tandem with sodium to hold the cell's electrical balance.
- Sodium — the forgotten one of modern diets. Yet it is what you lose most when sweating, and without it the water you drink does not stay where it is needed.
The eight other actives in a complete formula (calcium, chloride, phosphorus, zinc, chromium, vitamins C and B12) each play their part: we take them one by one in the 10 essential minerals and vitamins.
Evening habits that make a difference
- 🧘 Stretch the calf for 30 seconds before bed — leg straight, heel down, toes pulled towards you. The most commonly recommended measure.
- 💧 Spread mineralised hydration across the day, rather than drinking it all at the last minute.
- 🍌 Put potassium on the evening plate: banana, avocado, potato, green vegetables.
- 🛏 Loosen the sheets at the foot of the bed: a tightly tucked blanket holds the foot extended all night.
- 🚶 Walk for five minutes after dinner to get the legs circulating again.
💡 The AUA tip: if your cramps mostly follow training or hot weather, timing matters as much as dose — see our guide to the 5 key moments and cramps and headaches: the role of electrolytes.
When it is not about hydration
To be clear: not every night cramp comes from a lack of minerals. Other causes are common, and some call for medical advice.
- 💊 Certain medications — diuretics, statins, some blood pressure treatments.
- 🩺 Circulatory or venous problems in the legs.
- 🤰 Pregnancy, particularly in the third trimester.
- 🦶 Nerve damage (neuropathy), notably with diabetes.
- 🧪 Confirmed deficiencies — shown by a blood test, not by guesswork.
Very frequent or very painful cramps, cramps in muscles other than the legs, or cramps with swelling, numbness or weakness: speak to your doctor or pharmacist. Well-managed hydration is a first step, not a treatment.
Where AUA Hydrate fits in
One stick of AUA Hydrate dissolved in 500 ml of water delivers 10 actives — six electrolytes including sodium, potassium and magnesium, two trace elements and two vitamins — for 2 kcal and no sugar. Formulated in Switzerland by nutritionists.
It is not a medicine, and we promise no end to cramps. It is a simple way not to finish the day in mineral deficit — the ground on which night cramps thrive.
An evening ritual, not a chore
Pick your flavour from our three tastes — strawberry, peach, lemon — and keep a stick on the bedside table.
