Vitamin D is essential for healthy bones, calcium absorption, muscle function, and normal immune activity. Although deficiency can cause health problems, taking excessive amounts of vitamin D supplements can also be dangerous.
Vitamin D toxicity is uncommon and is usually caused by taking very high doses of supplements over time rather than from normal sunlight exposure or food. Excess vitamin D can raise calcium levels in the blood, a condition called hypercalcemia, which can affect the kidneys and other organs.
Possible warning signs include persistent thirst, frequent urination, nausea, vomiting, poor appetite, constipation, dehydration, weakness, and confusion. In more serious cases, excessive calcium can contribute to kidney stones, kidney damage, abnormal heart rhythms, and other complications.
However, these symptoms are not specific to vitamin D toxicity. They can have many other causes, so experiencing one of them does not automatically mean that vitamin D is the problem.
For most adults, the recommended daily intake is around 600 IU (15 mcg), increasing to 800 IU (20 mcg) for adults over 70. The usual tolerable upper intake level for adults is 4,000 IU (100 mcg) per day from all sources. Higher doses are sometimes prescribed for people with vitamin D deficiency, but these should generally be taken under medical supervision.
People can also unknowingly consume vitamin D from multiple products, including multivitamins, calcium supplements, fortified foods, and dedicated vitamin D supplements.
If you are taking high-dose vitamin D and develop concerning symptoms, don’t assume the cause or abruptly change a medically prescribed treatment without speaking with a healthcare professional. A clinician can evaluate your symptoms and, when appropriate, check calcium and vitamin D levels.
Vitamin D can be an important part of maintaining good health, but more is not necessarily better. Appropriate dosing, awareness of total intake, and medical guidance when high doses are needed are the safest approach.
