Experts are warning of the dangers of misusing vitamin D supplements, after a man needed hospital treatment for vitamin D intoxication and resulting severe hypercalcaemia.

Writing in BMJ Case Reports, UK researchers said there was a growing global trend of hypervitaminosis D, a clinical condition characterised by elevated serum vitamin D3 levels, with women, children, and surgical populations, most at risk.

'Patients often pursue unconventional or alterative therapy, the health outcomes of which remain uncertain. An example is the use of over-the-counter nutritional supplements,' the researchers wrote.

'Vitamin D is a fat-soluble vitamin in the body, along with vitamins A, E, and K. As a result, it undergoes widespread adipose tissue distribution. Given its slow turnover (half-life of approximately 2 months), during which vitamin D toxicity develops, symptoms can last for several weeks.'

Manifestations of vitamin D intoxication, which were largely caused by the resulting hypercalcaemia, included neuropsychiatric, renal, and gastrointestinal features as well as cardiovascular signs such as hypertension and arrythmias, the researchers said.

In this case, a GP referred a middle-aged man to hospital after he complained of recurrent vomiting, nausea, abdominal pain, leg cramps, tinnitus, dry mouth, increased thirst, diarrhoea, and weight loss (28 lbs).

He had been unwell for three months and noticed the symptoms started a month after starting a vitamin regimen therapy advised by a private nutritionist.

He had been taking more than 20 nutritional supplements daily, including vitamin D 150,000 IU daily; the daily requirement is 10mcg or 400IU.

The patient, whose medical history included bovine spinal tuberculosis, hydrocephalus, bacterial meningitis, and chronic rhinosinusitis, had discontinued the supplements but his symptoms persisted.

Initial blood tests found a range of elevated serum levels, including serum calcium (3.9 mmol/L; reference: 2.2-2.6 mmol/L) and serum vitamin D of >400 nmol/L (reference: >50 nmol/L equates to vitamin D sufficiency).

The tests also indicated acute kidney injury with serum creatinine 166 µmol/L (reference: 64-106 µmol/L and urea of 13.4 mmol/L (reference: 2.5-7.8 mmol/L).

The patient spent eight days in hospital where he was rehydrated using intravenous fluid therapy and started on oral bisphosphonate therapy, which was continued on discharge.

Two months after leaving hospital, his corrected serum calcium levels had dropped to 2.6mmol/L while his serum vitamin D level remained elevated at >400 nmol/L.

'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 study authors wrote.

'Further regulatory measures and education of the populace can help kerb the misuse of nutritional supplements to avoid untoward complications.'

The Government advises that everyone should consider taking a daily vitamin D supplement during the autumn and winter.

This comes after a study in May found that daily vitamin D supplements do not stop people with pre-diabetes from developing type 2 diabetes.