Body mass index and mental health in young people - predictors of early heart failure and cardiomyopathy

Background Heart failure is a medical condition in which the heart muscle cannot maintain an adequate cardiac output, due to structural and/or functional impairment. It is a disorder with a major impact on quality of life and has a poor prognosis, comparable to those of many common forms of cancer. Heart failure among young people is rare, but in contrast to decreasing incidence rates overall, some studies have shown increasing rates among younger people. Accordingly, the rates of cardiomyopathy, which is often the condition underlying heart failure in the young, have more than doubled in Sweden during the last few decades, for unknown reasons. These increases in early heart failure and cardiomyopathy raise questions about the causes. One factor that coincides with this phenomenon is a marked rise in body weight and obesity among young people. At the same time, depression, anxiety, and hospitalizations for alcohol and drug use are becoming more frequent among young Swedes. Considering these coinciding trends, we hypothesized that being overweight and suffering from a mental illness at a young age are associated with an increased risk of future heart failure and cardiomyopathy. Aim, subjects and methods The overall aim of this thesis was to determine whether body mass index (BMI), nonpsychotic mental disorders, and stress resilience (susceptibility to stressful events) at a young age are associated with early heart failure and cardiomyopathy. We performed nationwide cohort studies using the Swedish Military Service Conscription Register and the Medical Birth Register. In Papers I-III, we obtained baseline data on 1.7 million young men who enlisted for mandatory military service in the period 1968–2005. Information on BMI, blood pressure, and medical history were extracted, along with test results of physical fitness, stress resilience, and cognitive ability. In Paper IV, we obtained information on BMI, smoking, and baseline disorders collected at the first antenatal visit during pregnancy for 1.4 million women, in the period 1982–2014. By linking the data to the National Patient and Cause of Death registers, which is a unique possibility in Sweden thanks to our personal identification numbers, we identified cases of early heart failure and cardiomyopathy in these large population cohorts for a follow-up period of up to 46 years. Results We found that higher BMI in young people was associated with an increased risk of early heart failure and cardiomyopathy (Papers I, III, and IV). The increased risk was present already at BMI values that are considered midto high-normal for adolescent men (i.e., BMI 20–25), whereas, for cardiomyopathy, women of childbearing age had an elevated risk from BMI 25. The risk increased in line with increasing BMI, regardless of gender, such that severe obesity (i.e., BMI ≥35) was associated with a nine-fold increase in risk for early heart failure and cardiomyopathy among men, and a five-fold higher risk for cardiomyopathy among women. Furthermore, we found that nonpsychotic mental disorders in adolescent males, as well as low stress resilience, were associated with higher risk of early heart failure (Paper II). Conclusions Given the current trends towards increased body weight and mental illness among young people globally, physicians need to be aware of the potential future risk for increased numbers of heart failure and cardiomyopathy cases. The present findings emphasize the importance of weight control in youths, which is essential to curb the obesity epidemic and to prevent the consequences related to it. This should go hand in hand with intensified efforts to prevent mental illness in young people.