The main consequence of vitamin D toxicity is a buildup of calcium in your blood (hypercalcemia), which can cause nausea and vomiting, weakness, and frequent urination. Vitamin D toxicity might progress to bone pain and kidney problems, such as the formation of calcium stones.
Taking 60,000 international units (IU) a day of vitamin D for several months has been shown to cause toxicity. This level is many times higher than the U.S. Recommended Dietary Allowance (RDA) for most adults of 600 IU of vitamin D a day.
Why too much vitamin D can be bad for you
Doses higher than the RDA are sometimes used to treat medical problems such as vitamin D deficiency, but these are given only under the care of a doctor for a specified time frame. Blood levels should be monitored while someone is taking high doses of vitamin D.
Vitamin D deficiency is extremely common. In fact, up to 40% of U.S. adults are considered to have insufficient levels (not enough) of vitamin D, while around 6% are considered deficient in vitamin D. Worldwide, vitamin D deficiency affects around 1 billion people (1, 2, 3).
Vitamin D supplements are considered very safe, and toxicity is uncommon. This is because a healthy person would need to take extremely large doses of vitamin D over time in order to reach toxic or dangerous levels in the body (5).
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 in hopes of improving symptoms of multiple sclerosis was hospitalized for symptoms including nausea, vomiting, and muscle weakness.
Even though toxicity is unlikely if you keep your daily intake levels below 10,000 IU per day and avoid excessively high intakes of vitamin D supplements, experts recommend that people with typical vitamin D levels do not exceed 4,000 IU of vitamin D per day (12).
Keep in mind that people who are low or deficient in vitamin D typically need to take much higher levels than the current Tolerable Upper Intake Level (UL) of 4,000 IU per day to reach and maintain optimal vitamin D levels.
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 (very high doses) of vitamin D supplements for extended periods of time.
For example, 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 (16).
In one case study, a boy developed stomach pain and constipation after taking improperly labeled vitamin D supplements, whereas his brother experienced elevated blood levels without any other symptoms (18).
In another case study, an 18-month-old child who was given 50,000 IU of vitamin D3 for 3 months experienced diarrhea, stomach pain, and other symptoms. These symptoms resolved after the child stopped taking the supplements (19).
Taking vitamin D can increase levels of calcium in the blood, and too much calcium can cause side effects. 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.
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.
So, deficiency is very common. In fact, estimates suggest that about 1 billion people worldwide are deficient in vitamin D, while 50% of people may have levels insufficient to maintain optimal health (2, 3).
Healthcare professionals may recommend people who are very low in vitamin D take very high weekly doses of 50,000 IU for 8 weeks, followed by a maintenance dose of 2,000 IU per day after their levels reach 30 ng/mL (3).
Healthcare professionals may prescribe vitamin D supplements for people with vitamin D insufficiency or deficiency. They will monitor your blood levels to ensure your safety and will reduce your dose or discontinue the supplement once you reach optimal levels.
Vitamin D is having its day in the sun. In recent years, research has associated low blood levels of the vitamin with higher risks of everything from heart disease, diabetes, and cancer to mood disorders and dementia. The findings have not gone unnoticed. Vitamin D supplements and screening tests have surged in popularity.
Vitamin D, nicknamed "the sunshine vitamin" because your body produces it after sun exposure, has long been known to help build strong bones by increasing the body's absorption of calcium and phosphorous. But beginning in 2000, research into vitamin D's role in other health conditions began to expand rapidly.
While there is strong support for vitamin D's role in bone health, the evidence that it prevents other health conditions is not yet conclusive, says Dr. Manson. "Research on vitamin D and calcium supplementation has been mixed and, especially when it comes to randomized clinical trials, has been generally disappointing to date," she says.
Dr. Manson was a principal investigator of the recently published Vitamin D and Omega-3 Trial (VITAL), a large study (more than 25,000 participants nationwide). The study found that those taking a vitamin D supplement did not lower rates of heart attack, stroke, or cancer. However, among people who later developed cancer, those who took vitamin D supplements for at least two years had a 25% lower chance of dying from their cancer compared with those who received a placebo.
Where you live. If you live in the northern states (latitudes north of 37), you are at higher risk for a vitamin D deficiency because your skin may not be able to produce any vitamin D from sun exposure during the winter months.
Your skin color. People with darker skin typically have lower levels of vitamin D than lighter-skinned individuals. African Americans have, on average, about half as much vitamin D in their blood compared with white Americans.
Your weight. If you have a body mass index above 30, you may have low blood levels of vitamin D. Vitamin D is stored in fat, so in people with obesity, less of the vitamin circulates in the blood, where it's available for use by the body.
The foods you eat. Very few foods naturally contain vitamin D. The U.S. government started a vitamin D milk fortification program in the 1930s to combat rickets, a bone-weakening disease caused by vitamin D deficiency, which was a major public health problem at the time. Breakfast cereals and some types of orange juice may also be fortified, but this varies by brand. So, the amount of vitamin D you get from food depends on the food you eat and how much milk you drink.
Certain health conditions. People with conditions such as inflammatory bowel disease, liver disease, or cystic fibrosis, among others, may have trouble absorbing vitamin D, which can lead to deficiencies.
Despite the fact that some studies have found an association between low blood levels of vitamin D and various diseases, it hasn't been proven conclusively that a vitamin D deficiency actually causes disease, says Dr. Manson.
For example, a person with a serious illness may have a vitamin D deficiency. But that may have developed because she or he spends little time outdoors being physically active or because the person has a poor diet, both of which are risk factors for many diseases, as well as for deficiency, says Dr. Manson. Another issue is that diseases can cause inflammation, which can reduce vitamin D levels in the blood. Obesity, which has its own links to many conditions, can also reduce the amount of vitamin D in the blood because your body stores the vitamin in fat tissue, removing it from the bloodstream, where it would show up on tests. "Thus, a low vitamin D level may be a marker for other conditions, but not necessarily a direct cause of disease," says Dr. Manson.
Although the research is still hazy, some people will benefit from taking vitamin D supplements, along with sufficient calcium intake, to promote their bone health. But they don't require large amounts of vitamin D to get the benefit. "More is not necessarily better. In fact, more can be worse," says Dr. Manson. For example, a 2010 study published in JAMA showed that intake of very high doses of vitamin D in older women was associated with more falls and fractures.
In addition, taking a supplement that contains too much vitamin D can be toxic in rare cases. It can lead to hypercalcemia, a condition in which too much calcium builds up in the blood, potentially forming deposits in the arteries or soft tissues. It may also predispose people to painful kidney stones.
Watch your numbers. If you're taking a vitamin D supplement, you probably don't need more than 600 to 800 IU per day, which is adequate for most people. Some people may need a higher dose, however, including those with a bone health disorder and those with a condition that interferes with the absorption of vitamin D or calcium, says Dr. Manson. Unless your doctor recommends it, avoid taking more than 4,000 IU per day, which is considered the safe upper limit.
Choose food over pills. If possible, it's better to get your vitamin D from food sources rather than supplements (see "Selected food sources of vitamin D.") Choose fortified dairy products (which have the nutrient added to the food), fatty fish, and sun-dried mushrooms, which are all high in vitamin D. The FDA has made it easier for you to see how much you're getting, thanks to new nutrition labels that list the vitamin D content of foods.
Let your doctor know. "Many people are taking high-dose supplements on their own and their doctors may not even be aware of it," says Dr. Manson. Discuss supplement use with your doctor to ensure that the amount you're taking is appropriate for your needs. If you have a well-balanced diet, which regularly includes good sources of vitamin D, you may not need a supplement at all. 2ff7e9595c
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