A 52-year-old male farmer from rural Maharashtra undergoes elective open cholecystectomy for symptomatic cholelithiasis. On postoperative day 5, the surgical wound shows erythema, warmth, and purulent discharge. Culture grows Staphylococcus aureus. The patient's haemoglobin is 9.2 g/dL (preoperative: 13.8 g/dL), serum albumin 2.8 g/dL, and blood glucose (random) 280 mg/dL. Which of the following is the MOST significant modifiable risk factor contributing to impaired wound healing in this patient?