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Background: Despite the emergence of diverse programs in Mexico to address anemia and micronutrient deficiencies in disadvantaged groups, progress on reducing their prevalence has stagnated. In Mexico, anemia surveillance at the population level is conducted through the National Health and Nutrition Survey ENSANUT (for its acronym in Spanish). Objective: To overview the trends in anemia and iron deficiency (ID) from 1999 to 2018-19 in the Mexican population before COVID-19 pandemic. Methods: Data from five nationwide surveys in Mexico were used. Where available, data on anemia, ID, and ID anemia (IDA) were extracted from ENSANUTs 1999, 2006, 2012, 2016, and 2018-19 in participants from 1 to 99 years old. Blood sample collection methods were similar across surveys (1999-2018) where capillary drop blood was used to estimate Hb using a HemoCue and serum blood samples to measure ferritin and C-reactive protein concentration. Results: The trend in anemia prevalence shows a U-shape from 1999 to 2018-19 in <60 years old. In older adults (≥60 years), an increasing trend was observed. Anemia declined progressively from 1999 to 2012 but increased from 2016 to 2018-19 in comparison with 2012. In contrast, ID declined from 2006 to 2018-19, mainly in children, while IDA did not change over this period. In older adults, ID prevalence remained constant over time. Conclusions: The shifting trend in anemia prevalence across ENSANUTs 1999 through 2018-19 did not mimic the decreasing trend of ID over the same period of time. Other noncausal factors seem to play an important role in the variability of hemoglobin measurements. Plain language title: Overview of Trends in the Prevalence of Anemia and Iron Deficiency in the Mexican Population From 1999 to 2018-19 Plain language summary: In Mexico, anemia surveillance has been monitored through the National Health and Nutrition Survey since 1999. Nonetheless, progress on reducing their prevalence seems to be stagnated despite the emergence of diverse social programs in Mexico to tackle micronutrient deficiencies in children and women. The main cause of anemia in children and women is iron deficiency (ID). Any progress in tackling ID should be reflected in anemia prevalence. To investigate the prevalence trend, we used information about anemia (based on hemoglobin concentration) and ID (based on serum ferritin levels) where available, from 5 nationwide surveys in Mexico among participants from 1 to 99 years old, to discuss some of the potential factors behind anemia and ID trends. From 1999 to 2018-19, we observed an ¨U" shape in the prevalence of anemia in all age groups <60 years old, contrasting with the prevalence of ID, which trend is in decline. No major changes in terms of social programs can explain the trend in anemia. In fact, other nutritional indicators seem to have improved in Mexican children. A major difference in the measurement of anemia and ID is that hemoglobin was measured in situ using drop of capillary blood in HemoCue, a portable photometer, while ferritin was measured in venous blood in the central laboratory. While many external factors might influence the hemoglobin measurement in the field setting, it seems that the technique of finger prick capillary introduces more errors to the measurement of hemoglobin than other techniques (e.g., pool capillary or venous blood using HemoCue). This difference, in turn, affects anemia diagnosis. Since the drop of capillary blood has been widely acceptable, we did not perform any validation of hemoglobin measurement in those past surveys, so we cannot role out the contribution of other factors that affected hemoglobin measurement. Future studies should use venous blood to improve anemia classification; otherwise, validation studies should be carried out to improve hemoglobin measurement when using capillary blood. [ABSTRACT FROM AUTHOR]