Pregnant or breastfeeding women have been urged to boost their vitamin D intake amid warnings that cases of rickets in children are increasing.
Most pregnant women should take vitamin D, say experts
Rickets is a bone disease mainly caused by a lack of the vitamin. It can lead to deformities, stunted growth and general ill-health.
Some minority ethnic groups in the UK, including Asians, are particularly at risk, says the Department of Health.
Doctors want pregnant women to take more vitamin D during winter months.
It is made by the skin in response to sunlight, but can also be found in certain foods.
Officials are urging women to check if they are eligible for free supplements from their GP or health visitor under the government's Healthy Start scheme.
It provides vitamin D-rich milk and fresh fruit and vegetables as well as supplements for those on benefits or women who are under the age of 18 years old and pregnant.
Common at the start of the last century, rickets was thought to be eradicated in the 1950s because of better nutrition.
But research suggests the incidence of rickets could be as high as one in 100 children among Asian, Afro-Caribbean and Middle Eastern ethnic minority groups.
Dark-skinned people do not absorb as much sunlight through the skin and may also wear clothing that limits exposure to the sun for cultural reasons.
Most people in the UK should get enough vitamin D from sunlight - it only takes 15 minutes of sun exposure to the arms, head and shoulders each day during the summer months to make enough vitamin D for good health.
But in winter months at latitudes of 52 degrees north (above Birmingham), there is no ultraviolet light of the appropriate wavelength for the body to make vitamin D in the skin, research shows.
There have been several reports of a "resurgence" of rickets in recent years.
In June 2007, doctors in Dundee said they had seen several cases and warned that guidelines on vitamin D for pregnant women were being ignored.
Health Minister Dawn Primarolo said the Healthy Start scheme was designed to improve the health of the most vulnerable families.
"We encourage people who are eligible to take advantage of the free vitamins, to minimise the risk of developing vitamin D deficiency and other conditions.
"We particularly encourage women who are pregnant or breastfeeding to take vitamin D, to protect the health and wellbeing of their baby and help them get the best possible start in life."
She added that children under the age of four may also benefit from a supplement containing 10 micrograms of vitamin D.
Dr Colin Michie, a paediatrician at Ealing Hospital, says the biggest problem is maternal shortage of vitamin D.
"Mothers and babies are simply not getting enough of this important vitamin.
"If a pregnant or breastfeeding woman is lacking in vitamin D, the baby will also have low vitamin D and calcium levels which can lead babies to develop seizures in the first months of life."