More than 40 percent of Australian women are deficient in iodine, a vital mineral in developing healthy brains in babies.

The finding from the Westmead Institute of Medical Research will cause concern, as iodine deficiency is the single most preventable cause of mental delays globally.

Our modern food supply is depleted in iodine, with best sources including marine seafood, seaweed, bread and iodised salt. But most salt sold in Australia is not iodised, despite World Health Organisation (WHO) recommendations.