When I first arrived in Tokyo from London with my young children, it was midwinter. The school that I had enrolled my son at had many children off with seasonal coughs and colds, and although I had moved thousands of miles away from home, the sight was a familiar one: tired and strained parents who had been up all night with their unwell children.

As a doctor and mother, I was asked by many an exhausted parent at the school gates what they could do to prevent their child succumbing to repeated infections. I was also often asked if supplements would help.

We know that vitamins and minerals that are sourced from food (and, in the case of vitamin D, from the sun) are essential for good health. There are some supplements that are well documented to be beneficial: folic acid for expectant mothers, for instance, and antioxidant supplements for people who have, or who are at risk of, certain eye conditions, such as age-related macular degeneration. As doctors, we regularly diagnose and treat people with vitamin and/or mineral deficiencies, and the effectiveness of treating them with specific supplements is well known. But what about their role in healthy individuals — in those who are well nourished and without any known deficiency? Vitamin and mineral supplements are big business in Japan, but are they really any use?