The Department of Health (DH) is encouraging pregnant and breastfeeding women to boost their intake of vitamin D in the darker winter months.
Some general practices have started offering free vitamins for women and children to beneficiaries of the Healthy Start scheme, for families on certain benefits.
Healthcare professionals say more children than ever are presenting with vitamin D deficiency, which can cause seizures and rickets.
The DH says many cases of rickets in the UK occur in Asian, Afro-Caribbean and Middle Eastern children, as 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.
Vitamin D status is lowest during winter, when we rely on body stores and dietary intake to maintain adequate levels.
Health Minister Dawn Primarolo said: "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."
The DH has advised people who think they may be at risk of vitamin D deficiency to check with their GP and possibly obtain a blood test to diagnose this deficiency.