Can diabetes affect my work performance? if yes, how is it proven?

NoIf well controlled: Diabetes is a sever metabolic disease , effects every organ and system , fortunately , due to advances in diagnosis , treatment ( and prevention of early on set ) virtually any person can perform normally , unfortunately advanced disease due due to delay , due to organ failure . Will not be able to go to work that is the proof also most of them will choose early retirement.

Yes; checkbloodsugar: Yes, poorly controlled diabetes can affect work performance. If your sugars run low eg hypoglycemia, you can't think straight & can be easily distracted if not seizing or passing out. If too high, then poor vision & urinating all the time due to glucosuria. Consider checking your sugars at various times throughout work day. Go see your doc regularly & check a1c every 3 months. Aim for <7 if possib.