The impact of a rice based diet on urinary arsenic

Abstract

Rice is elevated in arsenic (As) compared to other staple grains. The Bangladeshi community living in the United Kingdom (UK) has a ca. 30-fold higher consumption of rice than white Caucasians. In order to assess the impact of this difference in rice consumption, urinary arsenicals of 49 volunteers in the UK (Bangladeshi n = 37; white Caucasians n = 12) were monitored along with dietary habits. Total urinary arsenic (As_t) and speciation analysis for dimethylarsinic acid (DMA), monomethylarsonic acid (MA) and inorganic arsenic (iAs) was conducted. Although no significant difference was found for As_t (median: Bangladeshis 28.4 µg L⁻¹) and white Caucasians (20.6 µg L⁻¹), the sum of medians of DMA, MA and iAs for the Bangladeshi group was found to be over 3-fold higher (17.9 µg L⁻¹) than for the Caucasians (3.50 µg L⁻¹). Urinary DMA was significantly higher (p < 0.001) in the UK Bangladeshis (median: 16.9 µg DMA L⁻¹) than in the white Caucasians (3.16 µg DMA L⁻¹) as well as iAs (p < 0.001) with a median of 0.630 µg iAs L⁻¹ for Bangladeshi and 0.250 µg iAs L⁻¹ for Caucasians. Cationic compounds were significantly lower in the Bangladeshis (2.93 µg L⁻¹) than in Caucasians (14.9 µg L⁻¹). The higher DMA and iAs levels in the Bangladeshis are mainly the result of higher rice consumption: arsenic is speciated in rice as both iAs and DMA, and iAs can be metabolized, through MA, to DMA by humans. This study shows that a higher dietary intake of DMA alters the DMA/MA ratio in urine. Consequently, DMA/MA ratio as an indication of methylation capacity in populations consuming large quantities of rice should be applied with caution since variation in the quantity and type of rice eaten may alter this ratio.