Physical Activity and Work Productivity in Response to Iron and Iodine Double‐Fortified Salt Trial in Indian Tea Estate Workers

Iron deficiency is the most common micronutrient deficiency in the world, with prevalence estimates for women in low‐income countries ranging between 15 and 50%. Iron is essential for oxygen transport through hemoglobin (Hb), and iron deficiency can lead to decreased physical work capacity. The relationship between iron and work capacity suggests that iron deficient individuals could experience reduced work productivity. We used accelerometry data to determine whether improvements in iron status from an intervention of salt double‐fortified with iron and iodine (DFS) increased the physical activity (PA) and efficiency of work performed by female tea pluckers. Population Participants were 212 experienced tea pluckers between 18 and 55 years from a large tea estate in Darjeeling District of northern West Bengal, India. Methods Two groups were randomly assigned to receive either salt fortified with potassium iodate, or iodized salt that was additionally fortified with microencapsulated ferrous fumarate (3.3 mg/g salt). Over the 10‐month intervention, women received salt only from the study. All measurements were taken at both baseline and end line. Participants self‐reported ethnicity as Adivasi or Nepali. Weight, height, mid‐upper arm circumference (MUAC) and age were measured by trained research staff. Venous blood was analyzed for Hb, serum ferritin (sFt), and soluble transferrin receptor. Physical activity levels were assessed with ActiGraph GT3x tri‐axial accelerometers worn on the hip daily for six days, except when sleeping or bathing. Energy expenditure during the work day was estimated from heart rate, and productivity was measured as the amount of tea plucked (kg) from morning and afternoon weighing. Results Mean (SD) change in minutes from baseline to endline spent at sedentary (<1 MET), light (1–3 MET), and moderate‐to‐rigorous (>3 MET) physical activity during plucking were 32.7 (160.8), 5.6 (75.5), and 6.7 (44.2) respectively. Neither the intervention, change in iron status, energy expenditure, energetic efficiency, nor amount of tea plucked were consistent predictors of PA, even after controlling for potential confounders. Conclusion We found that, contradictory to previous findings, improvements in iron status did not improve physical performance or worker productivity in these Indian tea estate workers. The results should be interpreted in light of the very different tea plucking conditions observed during the study period. Our results may highlight the need for measures of work productivity that are more sensitive to changes in iron status. Support or Funding Information Funded by the Micronutrient Initiative (MI) of Canada