To examine the association between 24 h urinary water-soluble vitamin levels and their intakes in free-living Japanese schoolchildren.

All foods consumed for four consecutive days were recorded accurately by a weighed food record. A single 24 h urine sample was collected on the fourth day, and the urinary levels of water-soluble vitamins were measured.

An elementary school in Inazawa City, Japan.

A total of 114 healthy, free-living, Japanese elementary-school children aged 10–12 years.

The urinary level of each water-soluble vitamin was correlated positively to its mean intake in the past 2–4 d (vitamin B1: r = 0·42, P < 0·001; vitamin B2: r = 0·43, P < 0·001; vitamin B6: r = 0·49, P < 0·001; niacin: r = 0·32, P < 0·001; niacin equivalents: r = 0·32, P < 0·001; pantothenic acid: r = 0·32, P < 0·001; folic acid: r = 0·27, P < 0·01; vitamin C: r = 0·39, P < 0.001), except for vitamin B12 (r = 0·10, P = NS). Estimated mean intakes of water-soluble vitamins calculated using urinary levels and recovery rates were 97–102 % of their 3 d mean intake, except for vitamin B12 (79 %).

The results show that urinary levels of water-soluble vitamins, except for vitamin B12, reflected their recent intakes in free-living Japanese schoolchildren and could be used as a potential biomarker to estimate mean vitamin intake.