Glycaemic control and insulin therapy are significant confounders of the obesity paradox in patients with heart failure and diabetes mellitus.

Background: A high body mass index (BMI) confers a paradoxical survival benefit in patients with heart failure (HF) or diabetes mellitus (DM). There is, however, controversy whether an obesity paradox is also present in patients with HF and concomitant DM. In addition, the influence of glycaemic control and diabetes treatment on the presence or absence of the obesity paradox in patients with HF and DM is unknown.

Methods: We identified 2936 patients with HF with reduced ejection fraction (HFrEF) in the HF registries of the universities of Heidelberg, Germany, and Hull, UK (general sample). Of these, 598 (20%) were treated for concomitant DM (DM subgroup). The relationship between BMI and all-cause mortality was analysed in both the general sample and the DM subgroup. Patients with concomitant DM were stratified according to HbA1c levels or type of diabetes treatment and analyses were repeated.

Results: We found an inverse BMI-mortality relationship in both the general sample and the DM subgroup. However, the obesity paradox was less pronounced in patients with diabetes treated with insulin and it disappeared in those with poor glycaemic control as defined by HbA1c levels > 7.5%.

Conclusion: In patients with HFrEF, a higher BMI is associated with better survival irrespective of concomitant DM. However, insulin treatment and poor glycaemic control make the relationship much weaker.