NEFL and diabetes mellitus: The novel findings include (i) elevated levels of NfL in individuals with T2D and PD, (ii) diabetes diagnostic status as a significant determinant of plasma NfL levels even after adjusting for confounders such as age, sex, BMI, HOMA-IR, physical activity and CRP, (iii) plasma NfL levels positively correlated with fasting plasma glucose, (iv) no correlation between plasma NfL levels and fasting insulin and IR, suggesting that in people at risk of T2D and newly diagnosed T2D, glycaemic control may be the primary modifiable risk factor for neurodegeneration.