Impact of Introducing High-Selenium Lentils on Everyday Diet for Mitigating Arsenic Related Health Problems in Bangladesh

Abstract

Background: Chronic arsenic (As) toxicity (arsenicosis) due to consumption of ground water polluted with higher level of As is a major global environmental problem. Worldwide, above 100 million people are found to be chronically exposed to As through drinking water. Despite major international and national efforts to reduce As contamination in drinking water, millions of Bangladeshis are still at risk of high As exposure via consumption of As contaminated tube-well water as well as food. The micronutrient selenium (Se) is known to be an essential element for humans. Selenium has been suggested to counteract As-induced toxicity through its antioxidant properties by promoting the excretion of As from the body. Low blood Se level increases the risk of As-induced health problems such as skin lesions, cancers in different organs, black foot disease (an exceptional peripheral vascular disease affects the lower extremities of the body) etc. It has also been reported that Bangladeshis have a low intake of Se due to the deficiency of Se in Bangladeshi soil similar to many parts of the world. Therefore, crops grown in Bangladesh contain a low level of Se. Lentils grown in western Canada, especially in Saskatchewan, are rich in Se mainly in the form of L-selenomethionine, which is exclusively bioavailable. Incorporation of these high Se lentils into the daily meals of As-exposed Bangladeshi families has the potential to reduce As-induced morbidity without having to change people's food habit as Bangladeshis eat lentils daily as "dahl." The beneficial impact of high Se lentils to mitigate As induced toxicity has been shown in a number of experimental studies, including various animal models like rats, mice, and rabbits. In several human trials, investigators also used Se pills to reduce As toxicityrelated health problems.

Hypothesis: In this study, we hypothesized that the consumption of high-Se containing lentils would decline the body load of As and reduce As exposure related toxicity in a chronically exposed Bangladeshi population compared to those consuming low-Se lentils. Aim: The aim of this thesis was to demonstrate if the daily intake of lentils, naturally biofortified with Se for six months could result in health benefits in an As-exposed rural Bangladeshi population who had been chronically exposed to As through contaminated drinking water. Method: This thesis was a part of a randomized, double-blinded, placebo-control, community-based supplementation trial conducted in Shahrasti, a rural area of Bangladesh where people are frequently exposed to a very high level of As (>100 ppb) through their tube well water. A total of 405 participants chronically exposed to As were enrolled in the trial. Each participant was taken 65 g of lentils per day during the intervention period of 6 months. Participants from the intervention arm (Se-group) consumed Se-rich lentils (55μg Se/day, the recommended dietary allowance (RDA) dose of Se) while from the control group received placebo lentils of similar nutrient profile except with low Se (1.5μg Se/day). Anthropometric measurements (height, weight, blood pressure), blood, urine, hair and stool samples were collected at baseline, month 3(except for hair) and end of the intervention at month 6. Morbidity data were collected fortnightly. Total urinary As (U-As, specific gravity adjusted), stool-As (subsample, n= 132), and hair-As from all the collected samples were measured by hydrogen vapor generated atomic absorption spectrometry (HVG-AAS) while urinary Se (U-Se) at all the three-time points, erythrocyte As (Ery-As), erythrocyte Se (Ery-Se) at baseline and month 6 were measured by inductively coupled plasma mass spectrometry (ICP-MS). The fractionated nitric oxide level (FENO) in exhaled air was measured at the three-time points to assess lung inflammation by NIOX MINO. Total glutathione content in erythrocytes (Ery-GSH) was measured by recycling assay method, and plasma levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG) were analyzed by a competitive immunoassay by ELISA. Plasma C-reactive protein and lipids levels were measured by a biochemistry analyzer. Results: Consumption of Se bio-fortified lentils resulted in increased urinary As excretion (p=0.001), improved body mass index (p≤0.01), and reduced frequency of asthma (p=0.05) and allergy (p=0.02) among the study participants in the intervention arm (Se-group) compared to those in the control arm (control group). It was also linked with higher levels of Se in the erythrocyte (p <0.001). Recommended dietary allowance dose of Se supplementation through lentils did not alter the levels of oxidative stress, antioxidant defense, lung inflammatory marker (FENO) and the biomarkers of cardiovascular diseases in the current population, while lentil supplementation for six months reduced lung inflammation and regulate biomarkers of cardiovascular diseases (particularly blood pressure and plasma lipids except for triglycerides) after six months of supplementation. Conclusion: Daily consumption of RDA dose of Se through lentils for six months can increase As excretion, blood Se content and thereby improve some of the health indicators, while lentil supplementation regardless of Se content can provide a number of health benefits to the chronically As exposed rural Bangladeshi population.