Abstract
Salt intake in Japan as reported in the National Nutrition Survey decreased consistently from the start point of the survey, but began to increase after 1987. To investigate the reason for the increase, the trends in food intake and all nutrients intakes other than vitamins, were compared, taking into account a revision of tables of food composition in 1988 (which changed from a table of food composition by weight average to the standard tables of food composition in Japan-fourth revised edition), and to a revision to the food classification system in 1990, namely separation of 'other seasonings' from 'other food'. The trends for food intake and for each nutrient intake, with the exception of sodium intake, showed similar patterns rapid increase in 1988 and rapid decrease in 1990 corresponding to the changes in 'other seasonings'.
Sodium intake from 'other food' in 1988 and 1989 was corrected by adjusting using the average ratios of sodium : food intake and sodium : intake of each nutrient for 'other food' including 'other seasonings' from 1990 to 1994. Sodium intake from total food amended using the adjusted sodium intake of 'other food', increased rapidly in 1988 and reached a plateau.
It is concluded that this rapid increase is not a real increase but an apparent increase that was caused by the change of the method for estimating amounts of nutrients, due to the change of the tables of food composition or changes of the classification system of foods.
