Nearly two-thirds of sexual precocity cases are caused by improper diets that include out-of-season fruits and fast food, say Shanghai experts.

Chen Qimin, a paediatrician at the Shanghai Children's Medical Centre, said some farmers use hormones to accelerate the ripening of out-of-season fruits or preserve fruits.

Some chicken or fish in fast food is also dangerous because the feed is often mixed with hormones. Chen said these hormones are major causes of children's sexual precocity.