Answer: Vitamin D apparently from Vitamin D Council 2005

Yes, cholecalciferol is a rat poison.

If it's a rat poison, why did Professor Heaney just recommend up to 4,000 units every day? J Steroid Biochem Mol Biol. 2005 Jul 15; Epub ahead of print
The answer is dosage. To demonstrate the point, I recently swallowed an entire bottle (100 capsules) of vitamin D (40,000 units) in front of a skeptical audience to convince them that vitamin D is safer than water. Here's why. Eight glasses of water a day is fine for healthy adults. Ten times that amount, eighty glasses of water, will make you sick from water intoxication.

Humans need about 4,000 units of vitamin D a day (from all sources). Ten times that amount, 40,000 units, is very safe in a single dose, as I demonstrated to the audience. Therefore, vitamin D has a safer therapeutic index than water.

(Taking the entire bottle certainly got the audience's attention. I think they were paying close attention to see if I would drop dead. By the way, if you were to take 40,000 units every day for months you would get vitamin D toxicity, after years of such doses you would probably die. After taking 40,000 units at one time - equivalent to two days at the beach - I simply stayed out of the sun for several days.)

A rat poison safer than water – but why do we need vitamin D? Within the last several months, scientists published impressive new evidence that vitamin D is involved in a staggering array of diseases: age related cognitive decline, heart disease, breast cancer, tuberculosis, Parkinson's disease, prostate cancer, chronic pain, fractured hips, premenstrual syndrome and diabetes.
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Vitamin D Council Glossary

Vitamin D hypersensitivity
Rare syndrome that occurs when abnormal tissue subvert the kidney's normal regulation of endocrine calcitriol production, causing high blood calcium (hypercalcaemia).
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WikiPedia Sarcoidosis approximately 1 in 5000 people

Sarcoidosis frequently causes an increase in vitamin D production outside the kidney.
(So the person probably already has too high a level of vitamin D in their blood. One of the rare cases that a vitamin D test would prove useful before supplementation)

Sarcoidosis occurs throughout the world in all races with an average incidence of 16.5/100,000 in men and 19/100,000 in women.
The disease is most prevalent in Northern European countries, and the highest annual incidence of 60/100,000 is found in Sweden and Iceland.
In the United States, sarcoidosis is more common in people of African descent than Caucasians, with annual incidence reported as 35.5 and 10.9/100,000, respectively.51 Sarcoidosis is less commonly reported in South America, Spain, India, Canada, and the Philippines.
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