Vitamin D supplement 'overdosing' is possible and harmful, warn doctors

Stock image of supplements
Overdosing on the popular supplement is possible, and can be incredibly harmful. Photo credit: Getty Images

Researchers have issued a warning about consuming too much vitamin D after a man was hospitalised for his excessive intake, effectively overdosing on the supplement.

The condition, previously referred to as 'hypervitaminosis D', caused the middle-aged man, from the United Kingdom, to suffer repeated bouts of vomiting, nausea, abdominal pain, leg cramps, tinnitus, a dry mouth, increased thirst and diarrhoea, with the patient losing almost 13kg in weight. 

Doctors who treated the man discovered he had been taking a cocktail of vitamins, elevating his levels of calcium and magnesium. Most worryingly, the amount of vitamin D in his system was seven times higher than the normal level.

Stopping the vitamins didn't have an immediate curative effect, the researchers noted, as vitamin D has an approximate half-life of two months. With the numerous other issues that can arise from too much vitamin D, the authors are now urging people to follow the recommended dosage, warning that 'overdosing' on the supplement is both possible and harmful.

In the journal BMJ Case Reportsa repository of evidence regarding health and its social determinants, the doctors - from the University NHS Foundation Trust in Canterbury - noted that 'hypervitaminosis D' is on the rise and linked to a wide range of potentially serious health issues.

According to the report, the man - who was referred to hospital by his family doctor - had been suffering from the aforementioned symptoms for nearly three months. The symptoms started about one month after he began an intensive regimen of vitamins and supplements, on the advice of a nutritional therapist.

The man had suffered from a myriad of health issues, including tuberculosis, an inner ear tumour which led to deafness, a build-up of fluid in the brain, bacterial meningitis and chronic sinusitis.

He had been taking high doses of more than 20 over-the-counter supplements each day, a cocktail that contained vitamin D 50,000 mg (the recommended daily intake is between 400 and 800 IU); vitamin K2 100 mg (daily requirement 100-300 μg); vitamin C; vitamin B9 1000 mg (daily requirement 400 μg); vitamin B2; vitamin B6; omega 3 2000 mg twice daily (daily requirement 200–500 mg); plus several other vitamins, minerals and probiotic supplements.

Once his symptoms developed, the man stopped taking his daily cocktail, but the side effects persisted.

The results of blood tests ordered by his family doctor revealed he had very high levels of calcium and slightly raised levels of magnesium, but his vitamin D level was seven times the sufficient amount.

While the tests indicated his kidneys weren't working well - acute kidney injury - the results of various X-rays and scans to check for cancer were normal.

The man stayed in hospital for eight days, during which he was given intravenous fluids to flush out his system and treated with bisphosphonates: drugs that are normally used to strengthen bones or lower excessive levels of calcium in the blood.

Two months after being discharged from hospital, the man's calcium level had returned to normal, but his vitamin D level was still abnormally high.

"Globally, there is a growing trend of hypervitaminosis D, a clinical condition characterised by elevated serum vitamin D3 levels with women, children and surgical patients most likely to be affected," the authors wrote in their report.

The recommended intake of vitamin D can be obtained from foods such as wild mushrooms and oily fish, as well as exposure to sunlight and supplements.

"Given its slow turnover (half-life of approximately two months), during which vitamin D toxicity develops, symptoms can last for several weeks," warned the authors.

There are many, varied symptoms of hypervitaminosis D, the authors pointed out, which are mostly caused by excess calcium in the blood. Symptoms can include drowsiness, confusion, apathy, psychosis, depression, stupor, coma, anorexia, abdominal pain, vomiting, constipation, peptic ulcers, pancreatitis, high blood pressure, abnormal heart rhythm and kidney abnormalities, including renal failure.

Other associated features such as keratopathy (inflammatory eye disease), joint stiffness (arthralgia) and hearing loss or deafness have also been reported, they added.

While hypervitaminosis D is on the rise, it is still relatively uncommon, cautioned the authors.

Nevertheless, complementary therapy - including the use of dietary supplements - is popular, and people may not realise that it's possible to overdose on vitamin D, or the potential consequences of doing so, they said.

"This case report further highlights the potential toxicity of supplements that are largely considered safe until taken in unsafe amounts or in unsafe combinations."

This article was amended to correct the recommended daily intake of vitamin D.