Worried about getting too much vitamin D?

Unless you have access to pharmaceutical doses of vitamin D, it is very difficult to get too much vitamin D in your diet. Since vitamin D from the sun comes in a slightly different form, it is completely self-regulating. This articles gives you the facts about vitamin D overdose, mainly so you can be more comfortable with your supplement intake.

Examples of too much vitamin D: Medical accidents
Reports in the literature on vitamin D toxicity come from examples where enormous quantities of vitamin D were injested by accident (1). In that case, vitamin D concentrate was accidentally used as a cooking oil. When vitamin D overdose does occur, the patients developed calcemia, where high levels of calcium were in the blood.

According to the Merck Manual, symptoms of vitamin D toxicity are high blood pressure, nausea, and vomitting (2). Later symptoms include kidney malfunction in the form of excessive urine production and excessive thirst. Nervousness, weakness, and itch have also been reported. In case of a vitamin D overdose, the first things to do are to stop vitamin D consumption and reduce calcium intake. Treatment options are IV rehydration along with corticosteroids and biphosphonates.

What, exactly, is too much vitamin D?
Unfortunately, studies on prolonged high doses of vitamin D are very rare in the literature, primarily for ethical reasons. So, the 5000 IU vitamin D3 pills you can buy on the internet really haven't been evaluated anywhere. Single dose exposure to 100,000 IU of vitamin D3 has been reported without substantial side effects (3). Speculation in the literature indicates that it would probably take sustained intake of 50,000 IU per day over several months to see chronic toxicity, although substantiation is difficult to track down (2).

What is a safe intake of vitamin D?
The National Institute of Medicine sets the upper limit for vitamin D3 consumption to 2000 IU/day. This is the quantity where you can safely assume you will avoid vitamin D overdose. But a number of experts have argued vigorously that the currently recommended upper limit is actually a reasonable daily dose (4).

how to figure out not enough vs. too much vitamin D

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1. Pettifor, JM, Bikle, DD, Cavaleros, M, et al. "Serum levels of free 1,25-dihydroxyvitamin D in vitamin D toxicity." Ann Intern Med. 122 (1995) 511-3.
2. "Vitamin D" at Merck Manual of Diagnosis and Therapym Professional Edition. LINK
3. Trivedi, DP, Doll, R, Khaw, KT. "Effect of four monthly oral vitamin D3 supplementation on fractures and mortality in men and women living in the community: randomised double blind controlled trial." BMJ 326 (2003) 469.
4. Vieth, R. "What is the optimal vitamin D status for health?" Prog Biophys. Mol. Biol. 92 (2006) 26-32.