Vitamin D toxicity: How excess Vitamin D can harm your kidneys and heart

Vitamin D is widely touted for bone and overall health, but taking too much can backfire.

Vitamin D is widely touted for bone and overall health, but taking too much can backfire. In fact, recent reports have linked extreme vitamin D supplementation to serious organ damage.

In 2024, a UK man died due to complications related to excess vitamin D and calcium. The coroner ruled that an 89-year-old man’s heart failure and kidney failure were caused by excessive vitamin D intake. As the coroner warned, “Vitamin supplements can have potentially very serious risks and side effects when taken in excess.”

Cases like these underscore that “more” is not always better, and chronic overuse of vitamin D can trigger hypercalcemia (high blood calcium), which harms both the kidneys and the heart.

Health authorities generally recommend 600–800 IU (15–20 µg) of vitamin D daily for most adults. The Institute of Medicine (now NASEM) agrees: it sets the RDA at 600 IU for ages 19–70 and 800 IU for older adults.

Anything above these levels should be monitored. In fact, the Tolerable Upper Intake Level for adults is 4,000 IU/day. Staying under this limit is generally safe; beyond it, the risk of toxicity rises. As one review notes, chronic doses above 250 µg (10,000 IU) are classically associated with toxicity.

When it comes to blood tests, most experts agree that 25-hydroxyvitamin D levels above 50 ng/mL (125 nmol/L) can be risky, and levels over 150 ng/mL (375 nmol/L) are usually toxic. Some people are more sensitive, the Cleveland Clinic says symptoms of high calcium can appear in certain individuals taking as little as 2,000 IU per day.

Vitamin D toxicity (hypervitaminosis D) manifests through the effects of hypercalcemia. Early signs can be subtle, but generally include:

Gastrointestinal: nausea, vomiting, constipation, poor appetite, abdominal pain.

Neurologic: confusion, lethargy, weakness, headaches or even stupor/coma in severe cases.

Renal: excessive thirst, increased urination (polyuria), dehydration; kidney stones or nephrocalcinosis (calcium deposits in the kidney) may develop.

Musculoskeletal: bone pain, muscle weakness and fractures (from calcium leaching).

Cardiac: abnormal heart rhythms (arrhythmias), high blood pressure and palpitations.

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