CST3 and vitamin D deficiency: Previous studies identified clinical parameters, such as ageing, long duration of diabetes [29], high HbA1c and GA [30], raised body mass index, hypertension, dyslipidaemia [31], insulin resistance [32], low serum total bilirubin [33], elevated serum cystatin C [34], C-peptide and vitamin D deficiency [35, 36], high thyroid-stimulating hormone [37], increased urinary albumin and decreased glomerular filtration rate (GFR) [38], anaemia [39] and arterial stiffness [40], as potential risk factors for DPN.