A 74-year-old man comes to the clinic because of a 6-month history of worsening dyspnea. He has a 15-year history of type 2 diabetes mellitus, colon adenocarcinoma diagnosed 2 years ago, and a pulmonary embolism 2 years ago treated with enoxaparin for the first 6 months and then edoxaban, which he is still taking. He is currently also on metformin 1g twice a day. Physical examination shows bibasilar crackles. Laboratory results show N-terminal-prohormone BNP (NT-proBNP) 428 pg/mL (< 125), blood group type O and the presence of MTHFR C677T mutation. Echocardiogram shows dilated right heart chambers, normal valve morphology and function, normal biventricular systolic function, pulmonary artery systolic pressure (PASP) 38 mmHg (<20), and tricuspid regurgitant velocity 2.8 m/s (<2.8). Which of the following is a risk factor for his likely diagnosis?