Analysis of spot urine biomarkers and association with body weight in Japanese elementary school children

Abstract

Purpose Childhood obesity is rapidly increasing world-wide and is largely the consequence of adoption of unhealthy diets excessive in calories and salt (NaCl) as well as devoid in pivotal micronutrients such as potassium (K) and magnesium (Mg). Education-based programs aiming to encourage healthy food knowledge and behaviors are crucial at a young age, and for this purpose, convenient ways to assess daily dietary intake are warranted. We therefore attempted to evaluate the dietary intake of Okinawan school children in Japan by analyzing a series of biomarkers in morning spot urine samples and explore whether these biomarkers correlate with body weight and a series of metabolic parameters. Methods We enrolled 98 third-grade elementary school children in Okinawa, Japan. Morning spot urine samples were collected and analysed using high performance liquid chromatography (HPLC) to assess dietary intake. Results We found that estimated daily NaCl intake was higher in obese/overweight children as compared to healthy-weight children (p = 0.0001). There was also a significant positive correlation between body mass index (BMI) and NaCl intake (Spearman) (ρ = 0.45, p < 0.0001) and a negative correlation between BMI and Mg/Cr (ρ=-0.27, p = 0.01). Furthermore, Na/K ratio was higher in samples collected on Monday (weekend) as compared to samples collected on Thursday or Friday (weekday) (p < 0.0001). Conclusion Via the use of morning spot urine analyses, our results show that NaCl intake was associated with obesity, and Mg excretion negatively correlated with BMI in Japanese school children, highlighting the potential role of these micronutrients in maintaining a healthy body weight.