• heart failure
• risk factors
• interaction
• body mass index
• physical fitness

Heart failure affects more than 40 million people worldwide and is a leading cause of hospitalisation and mortality.1 The aetiology of heart failure is often multifactorial and is influenced by both cardiovascular and non-cardiovascular risk factors.1 Although the prevalence of these risk factors vary according to sex, age, ethnicity, presence of comorbidities and environmental factors, the majority of cases remain preventable.1 In their Heart paper, Crump and colleagues2 provide insights into the aetiologic pathways for heart failure as they examine the interplay between body mass index (BMI) and different aspects of physical fitness on the risk of heart failure.

Improvements in medical management of risk factors have stabilised the incidence of heart failure, which in some countries now are even declining.1 3 Nonetheless, due to the ageing of the population and improved survival rates among patients with heart failure,3 the prevalence of heart failure is projected to increase nearly 50% by 2030.1 In contrast to the overall trends of decreasing incidence, the incidence of heart failure in the youngest patient group below 50 years of age is increasing.4 This difference in trends of age-specific incidence rates is likely explained by corresponding increasing obesity prevalence in younger people, now exceeding 30% in the USA. Development of obesity at a young age versus later in life is a particular concern due to early clustering of cardiovascular risk factors, particularly the metabolic syndrome,5 which increases the risk of cardiovascular death. Obesity is associated with congestive heart failure through ischaemic heart disease, but also through haemodynamic, anatomic, metabolic, inflammatory and hormonal changes.6 Obesity will, thus, likely continue to counterbalance the improved trends in incidence and mortality of heart failure unless more effectively dealt within early-life primary prevention strategies.

Using the Swedish Conscription Database, Crump and colleagues identified 1 330 610 military conscripts of ~18 years of age during 1969–1997. The study takes advantage of the unique Scandinavian registries, which are linkable at the individual level through personal identifiers and enable follow-up of all individuals without loss to censoring. Heart failure was identified from hospital diagnoses, and adjustments were made for socioeconomic factors, other chronic diseases and family history of heart failure.

The study confirmed previous studies showing that low aerobic fitness, low muscular strength and obesity at the age of 18 years were independently associated with higher risk of heart failure in adulthood.6 7 The data also supported the increasing body of evidence suggesting that among overweight and obese participants, higher levels of cardiorespiratory fitness attenuate the BMI-associated increased risk of heart failure at a later age.8 A novel finding was that independent of BMI, the combination of low aerobic fitness and low muscular strength was associated with risk of heart failure in a magnitude larger than their individual effects combined (interaction). On the additive scale, this interaction indicated that low aerobic fitness accounted for more heart failure cases among men with low muscular strength compared with high muscular strength.

If causal, these findings imply that improvements in aerobic fitness have the greatest primary prevention potential among persons with low muscular strength. Vice versa, improvements in muscular strength have the largest impact on heart failure prevention in those with low aerobic fitness. The take-home message for patient counselling is that preventive interventions for heart failure should begin early in life and include weight control and aerobic fitness and muscular strength, even among non-obese persons.