There is growing awareness about the importance of the "sunshine vitamin" - vitamin D - for health.
But Professor Mitch Blair, from the Royal College of Paediatrics and Child Health, says more action is needed - potentially including fortifying more foods and even cutting the cost of the vitamin to make it more easily available,
Vitamin D is an essential nutrient that contributes to healthy, strong bones and helps to control the amount of calcium in the blood.
Unlike many other vitamins, getting your recommended daily amount of vitamin D is not that easy.
The main source is sunlight; but with short days, long nights and limited sunlight even during the summer, it's not easy to get your fix that way.
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.
Unfortunately, there is limited national research on the true extent of vitamin D deficiency in the UK population.
But we do know that there has been a four-fold increase in admissions to hospital with rickets in the last 15 years and that some groups are more 'at risk' than others - namely children, pregnant women and certain ethnic minority groups.
Pilot studies and regional monitoring suggests that vitamin D deficiency is likely to affect at least half the UK's white population, up to 90% of the multi-ethnic population and a quarter of all children living in Britain.
A recent study in Australia revealed that a third of under-25s are vitamin D deficient - perhaps surprising in a country blessed with plenty of sunshine.
Vitamin D deficiency has been linked to a range of debilitating diseases in children and adults - including diabetes, tuberculosis, multiple sclerosis and rickets, a bone disease associated with poor children in Victorian England.
Lack of vitamin D is often cited as a contributory factor in broken bones and fractures, with obvious implications for some child protection cases.
The National Institute of Clinical Excellence (NICE) recommends supplements for pregnant or breastfeeding women and their children from six months to four years.
The Chief Medical Officer recommends supplements for children up to the age of five and the government's Healthy Start programme provides vitamins free for people on income support.
'Out of the shadows'
But we believe more needs to be done.
Firstly, Vitamin D supplementation should be widely available at low-cost.
In some countries, supplements are free for all.
Whilst the Healthy Start programme of free supplements for low income families is a positive step, evidence suggest the vitamins are in short supply and uptake is low - with many eligible people unaware that they are available or of the need to take them.
Secondly, we need to look at fortifying more foods with vitamin D.
Currently, many brands of cereal and orange juice contain added vitamin D which helps boost daily intake.
In the USA most milk is supplemented with vitamin D, which has helped reduce deficiency, particularly in children. The Scientific Advisory Committee on Nutrition is currently looking into this.
We also need to make sure healthcare professionals - including GPs, paediatricians, doctors and nurses - know the signs and symptoms of vitamin D deficiency, but more importantly give appropriate advice to patients who are 'at risk' to prevent problems developing.
And it's important that the public are aware of the implications of vitamin D deficiency, where they can get supplements and how they can boost their intake.
In addition, we need more research into the links between vitamin D deficiency and bone disease - and there must be better surveillance to monitor the prevalence and incidence of vitamin D deficiency across the population.
Only by knowing the true extent of the problem can we develop the most appropriate preventions - and ensure that vitamin D is brought out of the shadows and into the sun.