Anaemia and its causes at the Brazilian Longitudinal Study of Adult Health: a cross-sectional analysis of baseline data.

Background: Most anaemia studies focus on children and women of childbearing age. We assessed the frequency and main aetiologies of anaemia according to sociodemographic characteristics at the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil), a cohort of middle-aged adults.

Methods: The primary analyses included 15,051 participants aged 35-74 years with a valid blood cell count. We built logistic models to analyse the association between socioeconomic characteristics and anaemia diagnosis. We also described the main aetiologies in a subset (n = 209) of participants with anaemia.

Results: Anaemia was present in 3.0% (95% confidence interval [95%CI]: 2.6-3.4%) of men and 7.4% (95%CI: 6.9-8.0%) of women. The frequency of anaemia diagnosis was higher in women in all subgroups except for the oldest age stratum (65-74 years). The frequency of anaemia was particularly high in Blacks (6.0% and 15.5% in men and women, respectively). The most common causes of anaemia were iron deficiency (in women), chronic kidney disease, and chronic inflammation (in men). The frequency of unexplained anaemia was respectively 33.3% and 34.2% for men and women, and this condition was more frequent among participants of Black or Mixed races.

Conclusions: Anaemia was associated with age, female sex, Black race, and low socioeconomic status. Unexplained anaemia was common and more frequent in individuals of Black and Mixed races. ELSA-Brasil follow-up data may provide further insight into the relevance of unexplained anaemia in this setting.