Doctors in Bristol are to prescribe vitamin D supplements after a rise in the number of rickets cases.
Rickets weakens the bones
The new guidance was prompted by 264 cases in four Bristol GP practices over the last two years.
Vitamin D deficiency, known as rickets in children or osteomalacia in adults, is caused by a lack of sunlight.
The Somali community in the city is most at risk because its use of traditional dress means little of a person's skin is exposed to the sun.
Dr Julie Mytton, from Bristol North PCT, said: "Vitamin D is needed in the body for many reasons, but the main one is to keep our bones strong.
"If you don't have enough Vitamin D in your body, the bones become weaker and painful, and joints can become swollen."
Vitamin D comes from sunlight and foods such as oily fish, margarine and cereals with added vitamin D, or from vitamin supplements.
Free prescriptions will be available for Bristol's residents on low incomes.