It is called "bottled sunshine" and claimed to be one of the most effective health supplements on the market. Scores of studies have suggested that it protects against heart disease, cancer, diabetes, high blood pressure, schizophrenia and multiple sclerosis, and a growing number of doctors have recommended it to their patients.
But vitamin D, it turns out, has been oversold. After reviewing more than 1,000 research papers, the authoritative Institute of Medicine in the US has concluded that the high levels often recommended are unnecessary and could even be harmful.
Over recent years the idea that everyone needs extra vitamin D has swept countries on both sides of the Atlantic as scientists and doctors, convinced by the growing body of evidence of the nutrient's role in a range of diseases, have advocated supplements.