How could we have forgotten about vitamin D? Suddenly newspapers are reporting that one in four toddlers do not get enough and rickets is emerging again. The chief medical officer in England, Dame Sally Davies, has reminded doctors that children under five are one of a number of groups who need supplements. A recent survey of health professionals found most didn't know this.

Without vitamin D, bones become soft and bend in the middle, giving the typical rickets appearance of bow legs. A deficiency can cause muscle weakness, fatigue and an increased risk of infections because of damage to cells in the immune system, in particular TB.

But why should a healthy child, eating a varied diet, need supplements? Since some of the noise about vitamin D comes from Feeding for Life – sponsored by Cow & Gate, which happens to make milk products with vitamin D in them – isn't this just a push from the industry?

The solution

More than 90% of vitamin D comes from ultraviolet B rays hitting the skin and converting a type of cholesterol into vitamin D. If you have fair skin you need to be outside for only 13 minutes between 10am and 3pm, two to three times a week in summer, to get enough – any longer and you'll need sunscreen. If you have darker skin, you need at least twice as much sun.

The problem with getting vitamin D from food is that most children aren't mad on oily fish, mushrooms and egg yolks. Colin Michie of the Royal College of Paediatrics and Child Health is adamant all children under five need vitamin D supplements: "The diet of the average under-five does not provide enough," he says. They "don't run around and play in the sunshine. Our lifestyles are putting us in the position where we have to buy supplements."

Guidelines from the health watchdog Nice say children under five should have vitamin D supplements. I don't give them to my child and I don't know many doctors who do. But if it's good enough for Nice and the Royal College, then maybe we should all start.