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

'Overdosing' on vitamin D supplements is both possible and harmful, warn doctors in the journal BMJ Case Reports after they treated a man who needed hospital admission for his excessive vitamin D intake.

The case concerns a middle-aged man who was referred to hospital by his family doctor after complaining of recurrent vomiting, nausea, abdominal pain, leg cramps, tinnitus (ringing in the ear), dry mouth, increased thirst, diarrhoea, and weight loss (28 lbs or 12.7 kg). These symptoms had been going on for nearly 3 months, and had started around 1 month after he began an intensive vitamin supplement regimen on the advice of a nutritional therapist.

He had been taking high doses of more than 20 over the counter supplements every day containing: vitamin D 50000 mg-the daily requirement is 600 mg or 400 IU; vitamin K2 100 mg (daily requirement 100–300 μg); vitamin C, vitamin B9 (folate) 1000 mg (daily requirement 400 μg); vitamin B2 (riboflavin), vitamin B6, omega-3 2000 mg twice daily (daily requirement 200–500 mg), plus several other vitamin, mineral, nutrient, and probiotic supplements.

The results of blood tests ordered by his family doctor revealed that he had very high levels of calcium and slightly raised levels of magnesium. And his vitamin D level was 7 times over the level required for sufficiency. The man stayed in hospital for 8 days, during which time 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 discharge from hospital, his calcium level had returned to normal, but his vitamin D level was still abnormally high.

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

Reference: Vitamin D intoxication and severe hypercalcaemia complicating nutritional supplements misuse doi 10.1136/bcr-2022-250553; BMJ Case Reports.