Vitamin D is important for your bones, muscles, nerves, immune system, and more.

But if you get too much, it could lead to a rare and possibly serious condition called vitamin D toxicity. You may hear your doctor call it hypervitaminosis D.

The condition can bring symptoms like weakness and vomiting. It can also affect your kidneys or heart rhythm.

Here’s why it happens, what the possible warning signs are, how it’s treated, and what you can do to prevent it.

Taking large doses of vitamin D supplements is usually what causes the condition.

Foods with vitamin D have small amounts of it, so it’s very unlikely that you’d get too much from your diet. Your skin also makes D when you get sunshine, but that doesn’t cause toxicity.

The dose at which vitamin D supplements become toxic isn’t clear. But it would need to be very high -- way above the amount most doctors usually prescribe. Research shows that taking 60,000 international units (IU) of vitamin D a day for several months can cause toxicity.

Your chances of getting this condition could go up if you’re on a fad diet that has you take megadoses of a D supplement.

It’s also possible to get the condition if you take the wrong amounts of high-dose vitamin D supplements that your doctor has prescribed for health issues like:

Some reports have described cases of vitamin D toxicity that were due to mistakes in the way vitamin D products were made or prescribed, including milk that was accidentally fortified with too much D.

If your doctor has you take a vitamin D supplement, make sure you know the right dose to take and how often to take it. If you’re on a high dose, the doctor will probably keep an eye on the level of vitamin D in your body by giving you blood tests.

Most healthy people only need 400 to 800 IU of vitamin D a day, depending on your age and whether you’re breastfeeding or pregnant.

Getting too much vitamin D can cause calcium to build up in your blood and body. That can bring on symptoms like:

Extremely high levels of vitamin D can lead to:

Your doctor will give you a physical exam and ask you about your symptoms.

They might have you take tests that check your:

The doctor may also check your bones with an X-ray.

You’ll probably stop taking vitamin D supplements under your doctor’s care. They’ll also limit how much calcium you get from food.

The doctor might need to give you fluids through a vein (IV) and have you take medications like steroids and bisphosphonates, too.

If you have kidney failure, you may need a treatment called hemodialysis. This takes over your kidneys’ job of filtering water and waste from your blood.

Most people with vitamin D toxicity recover without serious health complications, and they usually don’t get it again.

If your doctor tells you to take a vitamin D supplement, make sure you take the dose they prescribed. And only buy supplements from a reliable, licensed source. Ask your doctor or pharmacist, or check the NSF’s List of Certified Dietary Supplements. 

Lots of supplements that are a combination of vitamins have vitamin D in them. If you take one of these combo supplements, check the label to see how much D you’re getting.

National Institutes of Health: “Vitamin D.”

Mayo Clinic: “What is vitamin D toxicity? Should I be worried about taking supplements?”

Up to Date: “Overview of vitamin D.”

Medline Plus: “Phosphate in Blood.”

Johns Hopkins: “Phosphate in Blood.”

The New England Journal of Medicine: “Renal Osteodystrophy.”

National Institute of Diabetes and Digestive and Kidney Disease: “Hemodialysis.”

Stat Pearls: “Vitamin D Toxicity.”

NSF: “Search for NSF Certified Dietary Supplements."  

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