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 recommended daily allowance (RDA) of 600 IU of vitamin D per day in the United States for most adults. According to the National Academy of Medicine, formerly known as the Institute of Medicine, 4,000 IU is the safe upper level of daily vitamin D intake. However, doses up to 10,000 IU have not been shown to cause toxicity in healthy people (11, 1).
The dose at which vitamin D supplements become toxic is unclear. However, it would have to be very high, well above the amount that most doctors usually prescribe. Research shows that taking 60,000 international units (IU) of vitamin D a day for several months can cause toxicity. Unlike water-soluble vitamins, the body doesn't have an easy way of getting rid of fat-soluble vitamins.
If you eat a well-balanced diet, which regularly includes good sources of vitamin D, you may not need any supplements. The main consequence of vitamin D toxicity is hypercalcemia, with symptoms including nausea, vomiting, weakness, and kidney failure. Overall, clinical trials show that vitamin D supplements don't reduce the risk of developing heart disease or dying from it, even if you have low blood levels of the vitamin. Vitamin D is very unlikely to cause serious symptoms of toxicity right away, and symptoms can take months or years to appear.
People with conditions such as inflammatory bowel disease, liver disease, or cystic fibrosis, among others, may have problems absorbing vitamin D, which can lead to deficiencies. In people who have multiple sclerosis, clinical trials show that taking vitamin D supplements doesn't prevent symptoms from worsening or returning. It is also available in dietary supplements that contain only vitamin D or vitamin D combined with some other nutrients. Vitamin D is stored in fat, so in people with obesity, less of the vitamin circulates in the blood, where it is available for use by the body.
As a result, the main symptom of vitamin D toxicity is hypercalcemia, or elevated levels of calcium in the blood (4,. However, clouds, smog, old age and having dark-colored skin reduce the amount of vitamin D your skin produces. Because vitamin D is fat-soluble, it's best absorbed when taken with a meal or snack that contains some fat. Foods with vitamin D contain small amounts of this vitamin, so it's unlikely that you'll get too much from your diet.
Recommended levels of vitamin D can be obtained from diet (such as wild mushrooms, oily fish), exposure to sunlight, and supplements. Most healthy people only need 400 to 800 IU of vitamin D a day, depending on their age and if they're breastfeeding or pregnant. Vitamin D toxicity can have devastating health effects, which may not manifest until months or even years after you start taking high doses.