Image caption A child affected by rickets

Greater access to cheap vitamin D supplements would improve the health of at-risk groups, experts say.

The Royal College of Paediatrics and Child Health (RCPCH) says up to 25% of UK children are vitamin D deficient, leading to a rise in rickets cases.

In the BBC's Scrubbing Up column, the college's Prof Mitch Blair called for concerted action to tackle the problem.

The government said those with the greatest need already received free supplements.

The RCPCH said other options to increase vitamin D levels, such as fortifying a wider range of foods, should be considered.

Half of the UK's white population, and up to 90% of the black and Asian people in the country are thought to be affected by vitamin D deficiency.

The first signs of deficiency include muscle and bone pain as well as swelling around the wrists and ribs.

A lack of the nutrient is linked to a higher incidence of diabetes, tuberculosis, multiple sclerosis as well as rickets - a disease that causes bones to become soft and deformed.

Media playback is unsupported on your device Media caption Dr Barbara Murray said children spend too much time indoors and need "more sunlight"

The number of cases of rickets has been rising, from 183 in 1996 to 762 in 2011.

In January this year, the chief medical officer for England, Dame Sally Davies, recommended all pregnant and breastfeeding women, children aged six months to five-years-old and the over-65s should take vitamin D supplements.

'Short supply'

Writing in Scrubbing Up, Prof Blair said: "Vitamin D can be found in some foods such as oily fish, eggs and mushrooms - but only 10% of a person's recommended daily amount is found naturally in food.

"Put bluntly, eating more fish and getting out in the sun a bit more won't make much of a difference to your vitamin D levels."

The RCPCH is also calling for a public awareness campaign to raise awareness of the warning signs of vitamin D deficiency and how to prevent it, and more research into the link between vitamin D deficiency and bone disease.

It says this is needed to help investigations into bone injuries in children.

How much Vitamin D? Vitamin D does not have a recommended daily intake in the same way as other vitamins and minerals as it is primarily made by the body rather than consumed in food. If you look at the concentration of the vitamin in the blood then levels below 25 nanomoles per litre are a sign of deficiency. There is still controversy over the optimal level for health. Around 50 nanomoles per litre is argued for good bones, while some experts champion 75 nanomoles per litre for other conditions such as MS and diabetes, although this remains a source of debate. Diet is a poor source of the vitamin, although it is in fatty fish, eggs and fortified foods. However, 10 to 20 minutes of sunlight for light-skinned people, or more than half an hour for those with darker skins, should be enough for a week's worth of the vitamin. The government advises pregnant or breast feeding women and the over-65s to take a daily supplement containing 10 micrograms of vitamin D. Babies and the under fives should have daily vitamin D drops, unless they are taking formula milk.

Prof Blair added: "The government's Healthy Start programme provides vitamins free to low income families and 'at risk' groups.

"But these vitamins appear to be in short supply and uptake is low. Ensuring people are aware they're available is crucial."

The college is to produce leaflets in a bid to raise awareness of vitamin D deficiency among the profession.

In addition, the Scientific Advisory Committee on Nutrition (SACN) is looking into proposals for further fortification of food and drink, as happens in countries including the US, Canada and Finland.

'Best placed'

Prof Nicholas Clarke, consultant orthopaedic surgeon at Southampton General Hospital, said who has been warning of the dangers of vitamin D deficiency since 2010, said: "I strongly support the use of supplements and widespread fortification of foods."

Dame Sally said doctors and other health professionals were "best placed" to give advice on vitamin D.

She added: "The Department of Health has also made sure vitamin D supplements are available free to pregnant women and young children from low income families through our Healthy Start scheme.

"Local NHS organisations must make sure those eligible for Healthy Start get the supplements they're entitled to, and the department continues to work closely with the NHS on this."