Magnesium supplements most likely to cause diarrhoea: Causes, risk factors, and management tips |
Magnesium is an essential mineral that plays a key role in muscle function, nerve signalling, and energy production. While it is vital for health, taking too much, especially through supplements, can lead to uncomfortable side effects. One of the most common is diarrhoea, which happens when excess magnesium remains unabsorbed in the intestines and draws water into the bowel. This effect is particularly linked to certain supplement types, such as citrate and oxide. Understanding why magnesium can cause diarrhoea, recognising the risks, and knowing how to manage intake can help you maintain balance and enjoy its benefits safely.
Why magnesium can cause diarrhoea
Most magnesium supplements are salts, which means they are bound to another compound to aid absorption. When the body cannot absorb all of the magnesium, it stays in the intestines, where it pulls water into the bowel. This speeds up movement through the digestive tract, often leading to diarrhoea.Magnesium is mainly absorbed in the small intestine, though some absorption happens in the colon. Smaller doses are usually absorbed more effectively, while larger amounts are more likely to remain unabsorbed. This unabsorbed magnesium causes cramping, watery stools, and frequent bowel movements.NHS states that the tolerable upper intake level (UL) for supplemental magnesium is 350 mg/day for healthy adults. It affirms that high-dose supplements can lead to adverse effects like diarrhea.This does not include magnesium from food, which rarely causes problems.
Types of magnesium more likely to cause diarrhoea
Not all forms of magnesium affect the body in the same way. Some are absorbed less efficiently and are more likely to lead to digestive upset:
- Magnesium citrate – Commonly used as a laxative, it draws water into the stool and works quickly.
- Magnesium oxide – Poorly absorbed and often linked to loose stools.
- Magnesium hydroxide (“milk of magnesia”) – Acts as a saline laxative, triggering bowel movements within hours.
- Magnesium carbonate – Less commonly used but still capable of causing diarrhoea.
- Magnesium sulfate (Epsom salts) – Works as an osmotic laxative and often results in watery stools.
- Magnesium chloride – Can cause diarrhoea in supplement form, though it is also available topically.
Despite these side effects, magnesium citrate and magnesium oxide are still widely used because they are effective for constipation relief.
Signs of too much magnesium
Excess magnesium from food is rare, but supplements can easily cause an overload. Early signs include:
- Abdominal cramping
- Diarrhoea
- Nausea and vomiting
- Fatigue and weakness
- Low blood pressure
- Facial flushing
In severe cases, especially in people with kidney issues, hypermagnesaemia can occur. This is a dangerous condition that may cause irregular heartbeat, breathing difficulties, extreme low blood pressure, and even cardiac arrest. Seek medical help immediately if you experience these symptoms.
How much magnesium do you need daily?
The recommended dietary allowance (RDA) for magnesium depends on age and gender. According to the National Institutes of Health (NIH), adult men need between 400 and 420 mg of magnesium per day, while women require 310 to 320 mg depending on age.Women between 19 and 30 years need about 310 mg per day, while women aged 31 years and older require around 320 mg. For men, the requirement is slightly higher, with 400 mg per day for those aged 19 to 30 years and 420 mg for men over 31. Many people do not meet these daily needs through diet alone, which is why supplements are often used. However, getting magnesium from natural food sources remains the safest and most effective way to maintain healthy levels.
Foods rich in magnesium
Eating a magnesium-rich diet lowers your risk of deficiency without the side effects linked to supplements. Top sources include:
- Pumpkin seeds – ~500 mg per 100 g
- Almonds – ~260 mg per 100 g
- Cashews – ~250 mg per 100 g
- Spinach – 160 mg per cup (cooked)
- Edamame – 100 mg per ½ cup
- Milk – 30 mg per cup
Incorporating these foods into your daily diet helps balance magnesium naturally.
How to prevent or manage diarrhoea from magnesium
If magnesium supplements are causing digestive upset, you can take steps to minimise the problem:
- Start with a low dose and increase slowly.
- Split the daily dose into smaller portions throughout the day.
- Take magnesium with food to ease digestion.
- Switch to a gentler form, such as magnesium glycinate, which is easier on the stomach.
- Stay hydrated and replace lost electrolytes if diarrhoea occurs.
Magnesium is vital for overall health, but in supplement form it can sometimes cause diarrhoea—especially when taken in high doses or in poorly absorbed forms like citrate or oxide. By understanding which types of magnesium are most likely to trigger digestive upset, sticking to recommended doses, and prioritising food sources, you can enjoy the benefits without unwanted side effects. If diarrhoea or other symptoms persist, consult a healthcare professional for personalised guidance.Disclaimer: This article is for general informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider regarding any medical condition or lifestyle change.Also Read: Why men face a higher risk of blood cancer than women: Lymphoma risk factors, hormones, and immunity
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