Rickets is on the rise and children face serious health problems because they are not getting enough vitamin D, research reveals.
A quarter of all toddlers in the UK lack vitamin D - and breastfeeding mothers and the elderly are at risk too.
Despite a recommendation that all children under five should take vitamin D supplements, 74 percent of parents are unaware of the guidelines. More than half of health professionals are also unaware of them.
The majority of our vitamin D comes from sunlight and is also found in food such as oily fish, eggs, breakfast cereals and powdered milk.
Dr Benjamin Jacobs, consultant paediatrician at the Royal National Orthopaedic Hospital, described the vitamin deficiency issue as a "major problem".
"We see about one case of rickets a month in our hospital, but that's the very severe end of the disease," he said.
In an interview with BBC Breakfast, Dr Jacobs said there were many children who have less severe problems, including muscle weakness, delay in walking and bone pains.
"Research indicates that in many parts of the country the majority of children have a low level of vitamin D," he told the broadcaster.
He explained that 100 years ago, when most children in London suffered from rickets, it was discovered that vitamin D helped to prevent the disease, which was later eradicated.
Then, in the 1950s, there was concern that children were receiving too much vitamin D in food supplements and cod liver oil, so supplements were stopped, though they continued in other Western countries, Dr Jacobs said.
"We thought they were unnecessary, possibly harmful, and that was a major mistake."
England's chief medical officer, Dame Sally Davies, is concerned that young children and some adults are lacking in vitamin D.
She will contact medical professionals about government guidelines, which recommend that some groups, including children under five, may require daily vitamin D supplements, according to the BBC.
A deficiency in vitamin D can lead to a number of serious health problems, including rickets, broken bones, muscle weakness and infections like tuberculosis.
Research last year suggested that a quarter of Britain's toddlers did not have enough vitamin D in their bloodstreams.
Davies said the government plans to review the issue.
"We know a significant proportion of people in the UK probably have inadequate levels of vitamin D in their blood," she said.
"Our experts are clear - low levels of vitamin D can increase the risk of poor bone health, including rickets in young children."
Davies said many health professionals, such as midwives, GPs and nurses, give advice on supplements and it is crucial they continue to offer this advice as part of routine consultations, as well as to ensure disadvantaged families have access to free vitamin supplements through the Healthy Start scheme.
"People at risk of vitamin D deficiency, including pregnant women and children under five, are already advised to take daily supplements," she said.
"It is important to raise awareness of this issue and I will be contacting health professionals on the need to prescribe and recommend vitamin D supplements to at-risk groups."
The Department of Health has asked the Scientific Advisory Committee on Nutrition to review the issue of current dietary recommendations on vitamin D.
The warning from health experts comes after a recent study by the University of Bristol found that vitamin D could reduce depression in children aged between nine and 13.
It also follows other research conducted by the Institute of Opthamology at the University College London, which found that increasing the intake of vitamin D could significantly improve the vision of elderly people.