Vitamin D plays essential roles in your body, such as helping it absorb calcium, promoting bone health, and regulating immune function, inflammation, and mood. But as with many things in nutrition, more isn’t always better.
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.
As high-dose vitamin D supplements become more popular, cases of vitamin D toxicity have become more common and often stem from people taking extremely high doses of supplemental vitamin D for long periods.
Here’s what happens when you take too much vitamin D, plus ways to stay safe when supplementing with this nutrient.
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).
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.
“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.
Research shows that vitamin D toxicity can occur with prolonged daily intake above 10,000 IU, though the exact threshold can vary between individuals.
Vitamin D toxicity typically develops gradually, and symptoms can take months to develop. “Symptoms of vitamin D toxicity are usually driven by hypercalcemia, or too much calcium in the blood,” said Barlow. “The first signs of too much vitamin D often look like stomach trouble, including nausea, vomiting, and constipation.”
With time, symptoms like fatigue, dehydration, confusion, muscle weakness, and bone pain can develop. Vitamin D toxicity can also lead to kidney stones or even kidney damage.
Some of the most common signs of vitamin D toxicity:
- Nausea and vomiting
- Loss of appetite
- Constipation
- Excessive thirst and frequent urination
- Weakness or fatigue
- Bone pain
- Confusion or disorientation
Severe complications can include:
- Kidney damage or kidney stones
- Irregular heart rhythms (arrhythmias)
- Bone pain and calcium deposits in soft tissues
- Severe dehydration
- In rare cases, death
If you’re taking high-dose vitamin D supplements and experience these symptoms, it’s critical to seek medical help.
You can get vitamin D from food, supplements, or through sunlight. Here’s how each affects your vitamin D levels:
- Sunlight: Your body makes vitamin D from the sun by absorbing UV rays, creating pre-vitamin D, then converting it into its active form. Your body controls how much vitamin D it produces from sunlight, so sun exposure won’t cause toxicity.
- Food: The amounts found naturally in foods or added to foods are relatively small and not enough to reach harmful levels. Even vitamin D–rich foods like salmon or fortified cereals don’t contain enough to cause toxicity when eaten in normal amounts.
- Supplements: Daily use of very high doses of vitamin D can push blood levels beyond what the body can manage.
“Before getting processed by the liver, excess vitamin D is stored in fat and liver reserves,” Ryan Sultan, MD, psychiatrist at Integrative Psychiatry, told Health. “The process of breaking down vitamin D into its inactive components is slow, which is why taking in too much vitamin D too quickly, such as >10,000–40,000 IU per day for months, can be toxic.”
Even then, Sultan noted that it’s extremely difficult to reach toxic levels of vitamin D, even through supplementation. But it can happen if you’re taking much more than your body needs for a long time.
The good news is that vitamin D toxicity is rare and is usually caused by supplementation mismanagement, such as taking more than the recommended amount for a long period of time.
Fortunately, 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.
- Stick to the safe upper limit: Though 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.
- 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.
Vitamin D is vital for immunity, brain health, strong bones, and overall well-being, but taking in too much from supplements can be harmful.
To stay safe, it’s best to follow your healthcare provider’s guidance on dosing and check your levels before starting or adjusting a vitamin D supplement.
