Vitamin D plays essential roles in your body, such as regulating immune function, inflammation, and mood.1 But taking too much vitamin D in the form of supplements can cause toxic levels of vitamin D to build up in your body, leading to serious side effects.2

Symptoms and Complications

Vitamin D toxicity typically develops gradually, and symptoms can take months to develop.

Some of the most common signs of vitamin D toxicity are:32

• Nausea and vomiting
• Loss of appetite
• Constipation
• Excessive thirst and frequent urination
• Weakness or fatigue
• Bone pain
• Confusion or disorientation

“The first signs of too much vitamin D often look like stomach trouble, including nausea, vomiting, and constipation,” Benjamin Barlow, MD, chief medical officer of American Family Care, told Health.

“These are common symptoms for many illnesses, so it’s easy for vitamin D toxicity to stay undetected until it causes serious harm. That’s why it’s critical to stay up to date with your doctor on all vitamin supplements.” —Barlow

With time, symptoms can worsen.2

Severe complications can include:23

1. Kidney damage or kidney stones
2. Irregular heart rhythms (arrhythmias)
3. Bone pain and calcium deposits in soft tissues
4. Severe dehydration
5. In rare cases, death

Why It Happens

The medical term for vitamin D toxicity is hypervitaminosis D. This condition occurs when excessive vitamin D builds up in the body, causing dangerously high calcium levels (hypercalcemia).2

“While vitamin D is essential to maintain strong bones and muscles, there is such a thing as too much of a good thing. When there are elevated levels of calcium in our blood, it can cause damage to soft tissues, bones, kidneys, and arteries.” —Barlow

Vitamin D toxicity is rare and is almost always caused by taking excessively high doses of supplements, not from food or sun exposure. The body naturally regulates how much vitamin D it makes from the sun, and most food sources don’t contain enough vitamin D to become an issue, even if consumed in large portions.2

“There are rare genetic causes of vitamin D toxicity, but I have never seen a case of vitamin D toxicity linked to foods naturally rich in vitamin D. Vitamin D toxicity is almost always from consuming too many vitamin D supplements,” Neil Patel, MD, internal medicine specialist with Providence St. Joseph Hospital in Orange County, California, told Health.

The Safe Upper Limit

The National Institutes of Health (NIH) has set a tolerable upper intake level (the highest daily dose unlikely to cause adverse effects) for vitamin D at 4,000 IU (100 micrograms) per day.4

Research shows that vitamin D toxicity can occur with prolonged daily intake above 10,000 IU, though the exact threshold can vary between individuals.5

Prevention and Safety

Vitamin D toxicity is preventable and starts with smart supplement habits. Here’s how to stay safe:

• Know your vitamin D level: The only way to know if your vitamin D levels are high or low is to have your blood levels checked. “If you are taking a high dose of vitamin D, regular blood tests are a simple way to monitor your levels,” said Barlow. Recommendations for optimal blood levels of vitamin D vary, but usually fall between 40–70 ng/mL.1
• Stick to the safe upper limit: Although people with low vitamin D levels sometimes need higher doses, most healthy adults should keep supplemental vitamin D to 4,000 IU daily unless directed otherwise by a healthcare provider.4
• Check your labels: Patel recommended being careful when taking multiple supplements and noting how much vitamin D is in each. “It’s important that patients know what dosage of vitamin D they are getting from their multivitamin(s) or supplement(s),” he said.
• Work with a professional: If you need supplemental vitamin D, it’s best to work with a qualified healthcare provider and follow their recommendations for safe and appropriate dosing.