The body can absorb as much vitamin D3 as you can consume in supplement form. Moreover, you can absorb too much and may not be able to use it all. If you take too much, toxicity will result. Your liver changes vitamin D, regardless of the source, into calcitriol, a prehormone, which is then stored in the liver and body fat until needed. When you run out of storage space, the excess is released into the blood and overloads your system.
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Many of the water-soluble vitamins, such as vitamin C, are quickly released by the body when you have absorbed all you can. The excess is excreted in the urine and feces. Of course, it is possible to overdose, but real toxicity is rare with the water-soluble vitamins. Vitamins A and D are fat soluble and can build up to toxic levels when taken in excessive amounts, especially over time.
Symptoms of Toxicity
The first sign of vitamin D toxicity is an increase in the level of calcium in your blood and urine. MayoClinic.com states that this excess blood calcium can cause the following symptoms: “Nausea, vomiting, poor appetite, constipation, weakness, confusion, heart rhythm abnormalities, and kidney stones.” These are severe consequences and you should not risk them by experimenting with megadoses of vitamin D3 supplements.
Storage of Vitamin D3
Toxicity does not occur when the vitamin is synthesized on the skin from exposure to sunlight. The body has a feedback system for increasing and decreasing vitamin D production on the skin as needed. Since the natural system is through the skin and sun exposure varies, your body is designed to store vitamin D and can do so safely in reasonable amounts. Nevertheless, vitamin D deficiency is common and has serious consequences.
Safe Doses of Vitamin D3
The recommended amount of vitamin D3 as a supplement is up to 1,000 international units per day. You can take it daily or as a larger weekly dose of up to 7,000 IU or a monthly dose of 28,000 IU. The vitamin will be absorbed and used. If you are concerned about having an optimal level, ask your doctor to check a vitamin D level. Your goal for best health is to be in the high-normal range. If you are deficient, your doctor can help you to adjust your dose to attain and maintain an optimal level of this critical vitamin.