Many children in Britain are also given cows' milk, which has higher levels of salt than breast or formula milk, the researchers say.
High levels of salt can damage developing kidneys, give children a taste for salty foods and establish poor eating practices that continue into adulthood and can result in health problems later in life.
Dr. Pauline Emmett and Vicky Cribb of the University of Bristol say the study is based on almost 1,178 participants in the Children of the 90s study.
The study, published in the European Journal of Clinical Nutrition, found the majority of infants first introduced to solids at around 3 to 4 months. The mean salt intake for the highest group at 8 months was more than double the maximum recommendation for that age group -- 400 mg sodium per day up to 12 months.
Infants in this top group often consumed cows' milk as a main drink, which has a higher sodium content than breast milk or formula. The babies also ate three times the amount of bread compared to the lowest group, and they were given salty flavorings such as yeast extract and gravy, the study says.
"These findings show that salt intakes need to be substantially reduced in children of this age group," the study says.