Relações entre medidas antropométricas, peptídeo natriurético tipo B e mortalidade em dez anos de idosos do estudo de Bambuí sobre saúde e envelhecimento

Abstract

The demographic, nutritional and technological transition phenomena that have been taking place in Brazil in the last two decades led to a dramatic increase in the number of older adults with excessive weight. The impact of obesity on the health conditions of the elderly is animportant issue both in clinical practice and in public health. Additionally, the elderly are the age group with the highest prevalence of cardiovascular diseases. Biomarkers, such as the Btype natriuretic peptide, have been studied with the aim to diagnose cardiovascular diseases, stratify the risk of subjects with these diseases and evaluate the response to treatment. The Btype natriuretic peptide (BNP), which is secreted by the cardiomyocites under hemodynamic (pressure or volume) overload, is among these biomarkers. Although obesity is associated with hemodynamic overload, low BNP levels have been described in obese subjects. Combined with evidence of lipolytic and metabolic action of the natriuretic peptides, the role of these peptides on the biological mechanisms of obesity and the usefulness of BNP as abiomarker in obese individuals are put into question. The aims of this thesis were to investigate the impact of overweight and obesity on mortality and also the relationship between BNP and anthropometric measures in Brazilian elderly. These issues were investigated in the Bambuí (Brazil) Cohort Study of Ageing, which is a ongoing cohort study in Bambuí, Minas Gerais, Brazil, since 1997. The region was endemicfor Chagas disease, despite the interruption of the vectorial transmission by 1970, there is a high prevalence of elderly who were infected at young ages. The Bambuí Study was designed to study the isolated and combinated consequences of Trypanossoma cruzi infection ndnoncommunicable diseases on the health of adults aged 60 or older. Weight, height, body mass índex (BMI), waist circumference and triceps skinfold thickness were some of the anthropometric measures assessed at baseline and repeated in the third and fifth years offollow-up. The outcome studied in this thesis was death until the 31st December 2007, which was ascertained by death certificates in the majority (98.9%) of the cases. Plasmatic BNP was measured in blood samples colected at baseline and stored under -80ºC. We found that overweight and class I obesity, as measured by BMI and defined according to WHO criteria, were associated with the lowest rates of death in the follow-up of 10 years of the elderly of the BHAS. This suggests that the cut-off points used to indicate weight control and loss interventions in adults do not grade appropriately the risk of death in Brazilian elderly individuals. Additionally, we found that BNP levels were inversely associated with the anthropometric measures at baseline regardless of Trypanossoma cruzi infection status. This finding is probably related to BNP metabolic actions and suggests that neither BNP might reflect the hemodynamic burden nor predict adequately the risk of death in elderly obese individuals. This is an issue of great clinical importance, which needs to be clarified by further prospective studies.