ABSTRACT
Although most of the current evidence on myocardial infarction focuses on obesity, there is growing evidence that patients who are underweight have unfavorable prognosis. This study aimed to explore the prevalence, clinical characteristics, and prognosis of this population at risk. Embase and Medline were searched for studies reporting outcomes in populations who were underweight with myocardial infarction. Underweight and normal weight were defined according to the World Health Organization criteria. A single-arm meta-analysis of proportions was used to estimate the prevalence of underweight in patients with myocardial infarction, whereas a meta-analysis of proportions was used to estimate the odds ratio of all-cause mortality, medications prescribed, and cardiovascular outcomes. Twenty-one studies involving 6,368,225 patients were included, of whom 47,866 were underweight. The prevalence of underweight in patients with myocardial infarction was 2.96% (95% confidence interval 1.96% to 4.47%). Despite having fewer classical cardiovascular risk factors, patients who were underweight had 66% greater hazard for mortality (hazard ratio 1.66, 95% confidence interval 1.44 to 1.92, p <0.0001). The mortality of patients who were underweight increased from 14.1% at 30 days to 52.6% at 5 years. Nevertheless, they were less likely to receive guideline-directed medical therapy. Relative to subjects with normal weight, Asian populations who were underweight had greater mortality risks than those of their Caucasian counterparts (p = 0.0062). In conclusion, in patients with myocardial infarction, those who were underweight tend to have poorer prognostic outcomes. A lower body mass index is an independent predictor of mortality, which calls for global efforts in addressing this modifiable risk factor in clinical practice guidelines.