Scientists say women who cover themselves almost completely for religious or cultural reasons when outside are at risk of severe vitamin D deficiency.
They say if these women breast feed they can also put their children in danger of developing the bone disease, rickets.
Professor John Eisman from the charity Osteoporosis Australia says other at-risk groups at the centre of a new awareness campaign are dark skinned migrants and the housebound elderly.
He says they all need more exposure to sunshine, but especially the children.
"When you don't have enough Vitamin D, particularly if you are a child, the bones don't develop properly."
"They are softer, more bendy, and they deform, which can have major long-term problems in terms of the skeleton."