Can Vitamin D Cause Diarrhoea

Vitamin D is often celebrated as one of the most important nutrients for bone health, immunity, and overall wellbeing. Known as the sunshine vitamin, it is produced in the skin when exposed to sunlight and can also be obtained through diet and supplements. While it is essential for keeping the body healthy, too much of any nutrient can cause side effects. One question that often comes up is whether vitamin D can cause diarrhoea. The answer depends on how much you are taking, how your body processes the vitamin, and whether there are other factors at play.

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Why Vitamin D is Important

Vitamin D helps regulate the amount of calcium and phosphate in the body, both of which are vital for maintaining strong bones, teeth, and muscles. Without enough vitamin D, bones can become weak and brittle, leading to conditions such as rickets in children and osteomalacia in adults. Beyond bone health, vitamin D supports immune function and may influence mood and energy. Because it is not found in many foods naturally, many people in the UK rely on supplements, especially during the autumn and winter months when sunlight is limited.

Can Vitamin D Really Cause Diarrhoea

In normal amounts, vitamin D does not usually cause stomach problems. The nutrient is well tolerated when taken at recommended daily levels, which in the UK is 10 micrograms (400 IU) per day for most adults. Diarrhoea is not a common side effect of regular vitamin D use, but it can occur if intake is very high over a long period of time. This is because excessive vitamin D can cause calcium levels in the blood to rise too much, a condition known as hypercalcaemia. High calcium can upset the digestive system and may lead to nausea, abdominal pain, and diarrhoea.

How Much is Too Much

The NHS advises that adults should not take more than 100 micrograms (4,000 IU) of vitamin D per day unless advised by a doctor. Consistently taking more than this amount can increase the risk of side effects, including diarrhoea. Some people may also be more sensitive to supplements and experience digestive discomfort even at moderate levels, particularly if taken on an empty stomach or alongside other medications. It is always best to follow dosage guidance and consult with a healthcare professional before taking high-strength supplements.

Other Reasons Vitamin D May Upset the Stomach

It is also worth noting that not all cases of diarrhoea linked to vitamin D are caused by the vitamin itself. Some supplements contain added ingredients, fillers, or flavourings that may not agree with everyone. Liquid drops or chewable forms can sometimes contain sugar alcohols, which are known to cause loose stools in sensitive people. Taking vitamin D alongside a very high-fat meal may also affect digestion in some individuals, although this varies from person to person.

Who is More at Risk of Side Effects

Certain groups may be more prone to experiencing problems with vitamin D supplementation. People with conditions that affect calcium balance, such as kidney disease or parathyroid disorders, may need to be more cautious. Those taking calcium supplements at the same time may also be more likely to experience digestive symptoms if their combined intake is too high. Pregnant women and older adults should take extra care to stick within recommended limits to avoid unnecessary side effects.

How to Take Vitamin D Safely

For most people, vitamin D supplements are safe, effective, and beneficial when taken in the correct amounts. Taking them with food can help improve absorption and reduce the chance of digestive discomfort. If you notice diarrhoea or other symptoms after starting a supplement, it is sensible to stop taking it and speak with your GP for advice. Blood tests can check whether your vitamin D levels are too high or too low, which helps guide the safest approach for you.

Conclusion

Vitamin D is essential for health, but too much can cause digestive side effects, including diarrhoea. The problem usually occurs with very high doses taken over long periods rather than from normal daily use. Sticking to recommended amounts, choosing good-quality supplements, and being aware of your overall calcium intake can help you avoid issues while still reaping the benefits of the sunshine vitamin.

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