The principle of first do no harm is often attributed to the father of medicine Hippocrates, although, the evidence is sparse. As healthcare professionals how do we define harm or, for that matter, safety? Recently, many people were advised by the UK to take vitamin D supplements, particularly in the autumn and winter months with a recommended dose for adults of 400 IU a day. However, the recommendation to supplement was recently withdrawn as it is said to be no longer current. Therein lies the paradox of recommending supplements across populations as being safe and effective.

The US market for over the counter vitamins is over $30 billion a year, more than that for statins, which would indicate that many people believe in the efficacy of routine vitamin supplementation. However, a recent review of published data by the US Preventive Services Task Force (USPSTF) makes interesting reading; the USPSTF makes evidence-based recommendations about a wide variety of health interventions, from aspirin for primary prevention to screening for lung cancer.

The USPSTF tasked researchers with updating the data on vitamin supplementation with two important outcomes in mind: cancer and cardiovascular death. Why vitamins? Because the observational data is clear and compelling. People with vitamin deficiencies are at higher risk for these bad outcomes, yet the results were surprising. For only one of the outcome variables, cancer prevention, was there any evidence of an effect, and that was a marginal reduction in the incidence of cancer, around 0.2%. One could argue that a healthy diet could have a similar effect.

Let’s look at the safety issues. The vast majority of people taking a vitamin supplement will have few adverse effects. This assumes that this vast majority follow dosage recommendations: a recent case report from the British Medical Journal Case Reports describes a middle-aged man who was referred to hospital by his family doctor after complaining of recurrent vomiting, nausea, abdominal pain, leg cramps, tinnitus, dry mouth, increased thirst, diarrhoea, and weight loss. 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 over 20 high dose supplements including 150,000 IU of vitamin D daily, though the NHS recommended dose for winter supplementation was 400 IU daily. The man had evidence of acute renal injury and required hospitalisation for 8 days, during which time he was given intravenous fluids to flush out his system and treated with bisphosphonates. Two months after discharge from hospital, his calcium level had returned to normal, but his vitamin D level was still abnormally high.

This issue calls into question our concepts of safe and harmful as we attempt to follow the “first do no harm” principle; there is no absolutely safe intervention that has a pharmacological effect and there is nothing that we can do to prevent misuse of what most people think of as safe products.

Oh, and as for those $30 billions in supplements in the United States; as one eminent urologist noted, vitamins give you expensive pee unless you have a proven deficiency.