Around 25 percent of children in Britain is suffering from Vitamin D deficiency, making them prone to develop rickets, finds a study.
The shocking finding is now a "major problem" according to consultant pediatrician Dr Benjamin Jacobs from the Royal National Orthopedic Hospital.
His research revealed that 74 per cent of parents know nothing about guidelines advising that children under the age of five are given vitamin D supplements.
More worryingly, more than half of healthcare professionals lack awareness.
Many wrongly believe that rickets - which softens the bone and can lead to skeletal deformities - is a disease of the past. Though common in Victorian times and up to the 1930s, it was all but eradicated with vitamin D supplements by the 1940s.
But, unlike other Western countries, Britain stopped these supplements in the 1950s because of fears that too much vitamin D could be harmful.
In a TV interview Dr Jacobs said this had been a "major mistake".
"We see about one case of rickets a month in our hospital, but that's the very severe end of the disease," the Daily Express quoted him as saying.
"There are many other children who have less severe problems - muscle weakness, delay in walking, bone pains - and research indicates that in many parts of the country the majority of children have a low level of vitamin D.
"It's really only over the past 10 years or so that I've noticed children with vitamin D deficiency and still I would say the majority of doctors, health visitors, midwives, nurses, are not aware enough," he said.
We get most of our vitamin D from sunlight, but it is also found in foods like cod liver oil, oily fish and eggs.
Government advice recommends vitamin D supplements for pregnant and breastfeeding women, children under five, and the over-65s.
But Dr Jacobs says the 400 units a day recommended for pregnant women may be far from enough.
A US study suggested 4,000 units a day.
Chief medical officer Professor Dame Sally Davies said the Government has ordered a review of the current dietary recommendations on vitamin D.