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Vitamin D Side Effects and Toxicity Symptoms

Vitamin D is vital for your health, but excessive intake can cause side effects. This article explores 6 signs and symptoms of vitamin D toxicity and how to avoid taking too much.

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Vitamin D Side Effects: 6 Signs of Toxicity
Last updated on February 3, 2026, and last reviewed by an expert on February 1, 2026.

Vitamin D plays an important role in maintaining your overall health.

Vitamin D Side Effects: 6 Signs of Toxicity

It’s necessary for the growth and development of your muscle cells, proper functioning of the innate and adaptive immune system, maintenance of your skeletal health, and more.

Insufficient or deficient levels of vitamin D may increase your risk of disease and infection, bone demineralization, and other negative health outcomes.

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Vitamin D deficiency is extremely common. Research shows that around 40% of U.S. adults have insufficient vitamin D levels, while approximately 6% are considered deficient.1 Worldwide, vitamin D deficiency affects roughly 1 billion people.

Factors that increase the risk of vitamin D deficiency include:

Because vitamin D insufficiency and deficiency are so common, many people use supplements to maintain healthy levels. But unlike water-soluble vitamins, vitamin D is fat-soluble, which means your body stores it rather than flushing out excess amounts.

Vitamin D supplements are generally safe, and toxicity is uncommon. A healthy person would need to take extremely large doses over time to reach toxic or dangerous levels. However, vitamin D toxicity is more common in people with certain medical conditions, including:

Though uncommon, vitamin D toxicity can occur in cases of:

Vitamin D toxicity goes by a few other names, including hypervitaminosis D and vitamin D intoxication.

This article explores 6 signs and side effects related to vitamin D toxicity.

1. Elevated blood vitamin D levels

For vitamin D to reach toxic or dangerous levels in the body, it needs to exceed 100 nanograms (ng) per mL.

Hypervitaminosis D is defined as blood vitamin D levels over 100 ng/mL, while vitamin D intoxication is defined as serum levels over 150 ng/mL.2

Recommendations on optimal vitamin D levels vary, but research suggests that levels between 30–60 ng/mL are likely optimal and may help protect against illness and disease.

How Much Vitamin D Is Too Much? Vitamin D Toxicity Explained
Suggested read: How Much Vitamin D Is Too Much? Vitamin D Toxicity Explained

Even when taking high-dose vitamin D supplements, it’s unlikely that a healthy person’s blood vitamin D levels would come close to toxic territory.

Most cases of vitamin D toxicity result from inappropriate supplement dosing and prescription errors. For example, a 2020 case report described a 73-year-old man who developed vitamin D toxicity after taking 10,000 IU daily for years.

In another 2020 case report, a 56-year-old woman who took an average of 130,000 IU of vitamin D per day for 20 months was hospitalized for symptoms including nausea, vomiting, and muscle weakness. Her vitamin D levels were 265 ng/mL — and 130,000 IU is over 30 times the generally recommended safe upper limit of 4,000 IU per day.

Experts recommend that people with typical vitamin D levels don’t exceed 4,000 IU of vitamin D per day. Those who are low or deficient may need higher doses to reach optimal levels, but this should be done under medical supervision.

Summary: Vitamin D levels greater than 100 ng/mL may be harmful. Toxicity symptoms have been reported at extremely high blood levels in cases where people took megadoses for extended periods.

2. Elevated blood calcium levels

Vitamin D helps your body absorb calcium from the food you eat. This is one of its most important functions.

However, excessive vitamin D intake can raise blood calcium to levels that cause unpleasant and potentially dangerous symptoms. The symptoms of vitamin D toxicity are primarily related to hypercalcemia (excessively high blood calcium).3

Symptoms of hypercalcemia include:

The normal range of blood calcium is 8.5–10.8 mg/dL. Hypercalcemia typically develops after people take megadoses of vitamin D for a prolonged period.

Suggested read: Magnesium Dosage: How Much Should You Take Per Day?

A 2015 case study reported that an older man with dementia who received 50,000 IU of vitamin D daily for 6 months was repeatedly hospitalized with symptoms related to high calcium levels.

Hypercalcemia can be life-threatening and requires immediate medical attention.

Summary: Taking too much vitamin D may result in excessive calcium absorption, which can cause several potentially dangerous symptoms.

3. Gastrointestinal symptoms

The main side effects of excessive vitamin D levels are related to elevated calcium in the blood. Some of the main gastrointestinal symptoms of hypercalcemia include:

Not everyone with hypercalcemia experiences the same symptoms. One woman experienced nausea and weight loss after taking a supplement that was later found to contain 78 times more vitamin D than stated on the label.

These symptoms occurred in response to extremely high doses of vitamin D3, which led to calcium levels greater than 12 mg/dL.

In one case study, a boy developed stomach pain and constipation after taking improperly labeled vitamin D supplements, while his brother experienced elevated blood levels without other symptoms.

If you’re looking to support your digestive health, consider focusing on foods that improve digestion rather than relying solely on supplements.

Summary: If you take large doses of vitamin D, you may experience stomach pain, loss of appetite, constipation, or diarrhea as a result of elevated calcium levels.

4. Altered mental status

Hypercalcemia can affect mental status in people with vitamin D toxicity. People with vitamin D toxicity–induced hypercalcemia commonly experience confusion, depression, and psychosis. In extreme cases, coma has been reported.

In a 2021 case report, a 64-year-old man accidentally took 200,000 IU of vitamin D per day because he misunderstood medication instructions. He showed altered mental status and other serious symptoms related to hypercalcemia.

He remained agitated and confused for the first 10 days of his hospital stay, but symptoms gradually improved as his calcium levels dropped. It took about 18 days for his calcium to return to expected levels.

Summary: Vitamin D toxicity can cause symptoms like confusion, agitation, and unresponsiveness. This appears to result from elevated calcium levels caused by high doses of vitamin D.

5. Kidney complications

In some cases, vitamin D toxicity can result in kidney injury and even kidney failure.

Too much vitamin D leads to high calcium levels, which can cause water loss through excessive urination and calcification of the kidneys. Hypercalcemia can also cause the blood vessels of the kidneys to constrict, leading to decreased kidney function.

Research shows moderate-to-severe kidney injury in people who develop vitamin D toxicity. A 2023 meta-analysis found that high-dose vitamin D supplementation (3,200–4,000 IU daily) increased the risk of hypercalcemia and hospitalization in a small proportion of individuals.4

Interestingly, vitamin D deficiency can also harm the kidneys and lead to severe complications in those with kidney disease. This is why maintaining optimal blood levels of vitamin D is critical — not too low, not too high.

Staying hydrated and getting enough potassium can support healthy kidney function alongside appropriate vitamin D levels.

Summary: Too much vitamin D may lead to kidney injury and can even lead to kidney failure in some cases.

6. Bone loss

While vitamin D is essential for calcium absorption and bone health, too much can actually have the opposite effect.

Some research suggests that very high blood levels of vitamin D may interfere with vitamin K2, which helps keep calcium in bones rather than in blood vessels and soft tissues. Without adequate vitamin K2 activity, calcium may be deposited in the wrong places.

Suggested read: Vitamin D Deficiency: Symptoms, Treatments, Causes & More

Additionally, chronic hypercalcemia from vitamin D toxicity can lead to increased bone resorption — the process where bone is broken down and its minerals released into the bloodstream.

Maintaining balanced levels of all bone-supporting nutrients is more effective than taking excessive amounts of any single vitamin.

Deficiency vs. toxicity

Vitamin D is involved in calcium absorption, immune function, and protecting bone, muscle, and heart health. Your body produces it when your skin is exposed to sunlight, and you can get it from certain foods.

Aside from fatty fish and fortified products, few foods are rich in vitamin D. Most people don’t get enough sun exposure to produce adequate amounts either.

Deficiency is common. Estimates suggest about 1 billion people worldwide are deficient, while 50% may have insufficient levels.

The only way to know your vitamin D status is through a blood test. Vitamin D deficiency is generally recognized as levels below 20 ng/mL. Levels between 21–29 ng/mL are considered insufficient.

If your healthcare provider finds you’re deficient, they may recommend supplements or vitamin D injections. For those who are very low, doctors sometimes prescribe 50,000 IU weekly for 8 weeks, followed by a maintenance dose of 2,000 IU daily.

Your doctor will determine the most appropriate dose based on your levels and overall health. If you’re taking high-dose supplements, your provider should monitor your vitamin D levels to ensure they don’t reach dangerous territory.

Summary: Vitamin D deficiency is common, and many people need supplements. However, avoid high-dose supplements without medical guidance.

Summary

Vitamin D is extremely important for your overall health. Even with a healthy diet, you may need supplements to reach optimal blood levels.

But it’s possible to get too much of a good thing.

Suggested read: How Much Vitamin D Should You Take for Optimal Health?

For people with adequate vitamin D levels, supplements of 4,000 IU or fewer per day are generally considered safe. Healthcare providers may prescribe higher doses for those who are deficient, but they should monitor your blood levels and adjust the dose once you reach optimal levels.

Avoid high-dose vitamin D supplements unless you’re being monitored by a healthcare professional.

It’s also worth noting that some cases of vitamin D toxicity occurred because people took improperly labeled supplements. Buy from reputable manufacturers to reduce the risk of accidental overdose.

If you’ve been taking vitamin D supplements and are experiencing any of the symptoms listed above, consult a healthcare provider as soon as possible.

Quick tip

If you want to know your vitamin D status, ask your healthcare provider about a blood test. Deficiency is common, and most people have no idea they’re low. Once you know your levels, your provider can recommend an appropriate daily dose.

  1. Liu X, Baylin A, Levy PD. Vitamin D deficiency and insufficiency among US adults: prevalence, predictors and clinical implications. Br J Nutr. 2018;119(8):928-936. PubMed ↩︎

  2. Vitamin D Toxicity. StatPearls. 2025. NCBI Bookshelf ↩︎

  3. Tebben PJ, Singh RJ, Kumar R. Vitamin D-Mediated Hypercalcemia: Mechanisms, Diagnosis, and Treatment. Endocr Rev. 2016;37(5):521-547. PubMed ↩︎

  4. Zittermann A, Trummer C, Theiler-Schwetz V, Pilz S. Long-term supplementation with 3200 to 4000 IU of vitamin D daily and adverse events: a systematic review and meta-analysis of randomized controlled trials. Eur J Nutr. 2023;62(4):1833-1844. PubMed ↩︎

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