Vitamins are important for your body to function properly, but too many can cause serious health problems. Vitamin D can be toxic when taken in high doses, but the exact amount of vitamin D that is dangerous is somewhat controversial. Talk to your doctor before taking any sort of vitamin supplement.
The Basics
To understand the risks of vitamin D, it is important to understand its physiology. Vitamin D can be found in some foods, such as liver, and it is also added to milk and other foods to increase their vitamin content. Your body also synthesizes vitamin D when your skin is exposed to the ultraviolet rays of the sun. Vitamin D is important for many functions, including maintaining the health of your bones and regulating your immune system.
Hypervitaminosis D
The main risk associated with consuming too much vitamin D is that it can cause your blood calcium levels to rise, as your intestines absorb more calcium when vitamin D is present. This can cause dehydration as your kidneys will excrete more urine to try to remove the excess calcium. Hypervitaminosis D can also cause weakness, constipation, fatigue, a lack of appetite and vomiting.
Maximum Vitamin D Dose
There is some controversy over how much vitamin D is safe. The current recommended maximum dose is 50 mcg per day, but a 2007 article in the "Journal of Bone and Mineral Research" notes that the human body can synthesize up to 250 mcg per day due to sunlight exposure, which suggests that the maximum recommended dose is too low, and that the maximum recommended amount should be 250 mcg per day. It's also possible that the amount of vitamin D that is toxic might vary from individual to individual.
Considerations
Although the maximum recommended dose might be unnecessarily low, it is safer to adhere to it than to risk a vitamin D overdose, especially because it is unlikely that any additional benefit can be obtained by consuming excess vitamin D. Before taking vitamin D supplements, talk to your doctor. If you plan on taking large amounts, your doctor might want to monitor your blood calcium levels to see if you are developing signs of a vitamin D overdose.
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