Urinary phytate (Myo-inositol hexaphosphate) in healthy school children and risk of nephrolithiasis.

OBJECTIVE Although the incidence of urolithiasis is lower in children than in adults, the number of children with urolithiasis is increasing. Phytate, a naturally occurring compound present in legumes, nuts, and whole meals, has antilithiasic activity. The aim of this study was to assess, for the first time, the urinary levels of phytate in children and to correlate these levels with other urinary parameters related to crystallization risk and to general dietary habits. DESIGN AND METHODS This was a cohort study conducted from April 2012 to March 2013 in the Laboratory of Investigation in Renal Lithiasis and at Son Espases Universitary Hospital in Palma de Majorca, Spain. SUBJECTS Subjects included 165 healthy schoolchildren aged 5 to 12 years. INTERVENTION All subjects followed their habitual diet. Information on the main dietary habits of the study subjects was obtained by asking each child's parents to fill out a dietary questionnaire. MAIN OUTCOME MEASURE Phytate and citrate concentration and excretion were measured in 2 urine samples (a spot sample and a 12-hour overnight sample) for each child. Furthermore, common urinary biochemical indicators of stone risk were measured in each sample. RESULTS The urinary phytate concentrations were low in this child population because of low consumption of dietary phytate. The urinary concentrations of phytate and citrate were low in 27.5% of these children. CONCLUSION Because both substances are important inhibitors of crystallization, these finding suggests that these children are at risk of crystallization. Moreover, their diets consisted of foods rich in animal protein, with insufficient consumption of vegetables, legumes, and fruits.