More people should be given vitamin D tablets to counter a hidden epidemic of deficiency, a report says.
The NHS advisory body, the National Institute for Health and Care Excellence (NICE), says 10 million people across England could be deficient, and many are unaware.
Its report says children should get free supplements and calls for supermarkets to sell low-cost tablets.
Deficiency can result in rickets and brittle bones.
Action of sunlight
NICE focused on groups most at risk of having low levels of the vitamin.
The chief medical officer in England has already urged doctors to prescribe tablets to these populations, and similar advice has been issued in Northern Ireland, Wales and Scotland.
But experts are concerned many are still not getting the Vitamin D they need. Official estimates suggest one in five adults and one in six children in England may have low levels.
People get most of their vitamin D from the action of sunlight on their skin. But the amount in food is small, unlike many other vitamins.
The low level of sunlight during winter months means people in the UK must rely on stores built up during the summer.
Professor Mike Kelly, who was involved in producing the NICE guidelines, said: "Around 10 million people in England may have low vitamin D status and so could be at risk of health problems - and they may not know it.
"People with darker skin are particularly at risk - during winter months nearly 75% of adults from Asian or African and Caribbean backgrounds may have low vitamin D levels."
People at risk include:
- Children and babies
- Pregnant women
- People with darker skin, including many people from African, Caribbean and Asian backgrounds
- People who don't get much exposure to the sun, such as those who cover up their skin for most of the year
- People who are housebound.
Free of charge
The NICE report sets out a number of measures, including encouraging local authorities to provide tablets free of charge to children.
The advisory body also urges manufacturers to ensure supplements are sold at the recommended dose - 10 micrograms a day for adults.
And NICE recommends supermarkets stock low-cost vitamin D tablets and promote them to those at risk.
Doctors and other health workers are encouraged to take every opportunity to discuss and record vitamin D intake with any patients who are at risk.
Professor Susan Jebb, who was also involved in developing the guidance, said: "It is really important health professionals are aware of the problem and that everyone understands that for those at risk of deficiency, a good diet alone will not solve the issue.
"People who are at risk can get supplements over-the-counter or speak to their GPs."