A quarter of all toddlers are lacking Vitamin D, according to new research in the UK.
Vitamin D supplements are recommended for those people at risk of deficiency, including all pregnant and breastfeeding women, children under five, and the elderly, but 74% of parents know nothing about them and more than half of healthcare professionals are also unaware, the BBC said.
Dr Benjamin Jacobs, consultant paediatrician at the Royal National Orthopaedic Hospital, described the issue as a "major problem".
He told BBC Breakfast: "We see about one case of rickets a month in our hospital, but that's the very severe end of the disease.
"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."
He explained that it was discovered that Vitamin D prevents rickets about 100 years ago when most children in London suffered from the disease, and it was later eradicated.
But then, in the 1950s, there was concern that children were getting too much Vitamin D in food supplements and cod liver oil and supplements were stopped. This was unlike in other Western countries where they continued, he said.
Dr Jacobs said: "We thought they were unnecessary, possibly harmful, and that was a major mistake."
He said parents are largely unaware of the risk of the condition, while health professionals are often taught that rickets is a disease of the past.
"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 today, the majority of doctors, health visitors, midwives, nurses, are not aware enough of the problem," he said.
Asked about how vulnerable people can be given more Vitamin D, Dr Jacobs said current guidelines suggest taking drops or tablets, but experts are also looking into food supplementation.
He said it would not be harmful if people ended up with too much Vitamin D in their diet.
Current guidelines suggest that children and pregnant women should have 400 units a day, but he described this as a "conservative" level compared to the US, where he said a study suggested pregnant women should have 4,000 units.
"In my view, it is extremely safe," he added.
Last month a young couple walked free from court after being cleared of killing their four-month-old son after it was found he had been suffering from rickets.
Rohan Wray and Chana Al-Alas of Islington, north London, fell under suspicion when baby Jayden died suddenly two years ago.
But, following a six-week trial at the Old Bailey, charges of murder and causing or allowing his death were dropped.