Rickets, the bone disease that causes bowed legs and stunted growth in children and is associated with Victorian England, is making a comeback.
Health staff in Cardiff have reported a surge in cases among the children of ethnic groups who do not get enough exposure to the sun for religious or cultural reasons. Similar reports have come from cities in the North of England, including Newcastle and Bradford, and from Southampton.
Vitamin D, made by the action of sunlight on the skin, is essential to prevent rickets and people who spend a lot of time indoors and cover up when they go out may become deficient.
Half the population is deficient by the end of winter, when there is little sun, and public-health doctors have called for children to be given vitamin D supplements to prevent deficiency. The vitamin is found in certain foods such as margarine, oily fish and Marmite, but not in sufficient quantity.
In Cardiff the disease is being seen in children born to women who have progressively lower levels of vitamin D with each birth.
Dr Elspeth Webb, a reader in child health at Cardiff University, said: "You get women living in certain communities that perhaps don't go out much because of religious, cultural traditions. They're covered up when they do. They don't get enough access to sunlight. So they get vitamin D deficient.
"Every pregnancy, you use up your vitamin D stores and if you're not making enough to replenish them, you gradually get more and more depleted. By your third or fourth child, that child is born already without enough vitamin D. So they'll be presenting with rickets at around 18 months."