Placebo daily 12 weeks

Folic acid 800 ug/day 12 weeks

Folic acid supplementation to assess for increased arsenic metabolite excretion

Inorganic As (InAs) within humans undergoes a stepwise biotransformation reaction in which it is methylated to monomethyl-arsonic acid (MMAsIII), and dimethylarsinic acid (DMAsV) facilitating urinary excretion. This occurs via arsenic methyltransferase (AS3MT) using a methyl donor S-adenosylmethionine (SAM). In this pathway the one-carbon unit carried by 5-methyl-tetrahydrofolate (5-MTHF) is transferred to homocysteine to form methionine, which is activated to SAM. Complete methylation to DMAsV is critical as higher proportion of MMAs(III+V) are associated with skin lesions, peripheral vascular disease, atherosclerosis, and cancers.

We will measure levels of InAs, total DMA and MMA in the urine and blood of the study subjects at baseline and 12 weeks. Outcomes will be reported in percentage (%) of InAs, DMA and MMA in blood and urine.

The Respiratory Symptom Questionnaire (RSQ) is an instrument that assesses the frequency of respiratory symptoms and their impact on patients' activity over the previous four weeks, without requiring a specific diagnostic label of asthma or chronic obstructive pulmonary disease (COPD). The four questions assess the frequency of respiratory symptoms (shortness of breath, wheezing, coughing, and/or chest tightness) during the day and, in response to these respiratory symptoms, frequency of rescue inhaler use, activity limitations and frequency of night-time awakening. We will administer the RSQ to participants at the baseline screening. Maximum value 16, minimum value 4, higher scores represent increased symptom burden.