A man was left in hospital for over a week after taking 80 times the recommended daily dose of vitamin D as part of a health drive.
The case study, published in the British Medical Journal, has led to an NHS doctor issuing a warning to those taking supplements.
The man began taking the vitamins after visiting a private nutritionist and was taking 20 different supplements per day.
The report says the man’s kidneys “stopped working” and he subsequently spent eight days in hospital.
The daily recommended dose is 600mg, but the report says the man was taking 50,000mg.
The health service also says that taking more than 100mcg of vitamin D per day could be “harmful”.
It added: “Taking too many vitamin D supplements over a long period of time can cause too much calcium to build up in the body (hypercalcaemia). This can weaken the bones and damage the kidneys and the heart.”
The man’s hospital admission came four months after he began taking the supplements, which included omega 3, magnesium, and vitamin C.
In that time he has lost nearly two stone, but was suffering from leg cramps, stomach ache, vomiting, nausea, and tinnitus.
Doctors who reviewed his case said there was “too much calcium” in his blood. Having too much calcium in your blood can lead to a coma.
NHS doctor Dr Alamin Alkundi, who looked at the man’s case, said that cases of “hypervitaminosis D” were rising around the world.
He added: “This case report further highlights the potential toxicity of supplements that are largely considered safe until taken in unsafe amounts or in unsafe combinations.”
The man’s vitamin D levels will still be abnormally high two months after leaving hospital, as the supplement can take “several weeks” to leave the body.
When taken correctly vitamin D can “help regulate the amount of calcium and phosphate in the body”, the NHS says.
It adds that it is important to take vitamin D daily during the autumn and winter, as this is when there is less sunshine, which is a natural source of vitamin D.