Hi Emma,
For several years I suspected that coffee spiked my blood-sugars. I like to take large coffees (black), and if I had a couple in the evening at home I would very often notice high blood-sugars the next day. It didn't happen every time so I could never pin it down exactly, but it seemed like there was a connection.
After I bought a decent water-filter for my kitchen, this connection between evening coffees and higher levels the next day got completely severed.
Unlikely as it sounds, I concluded that there was something (no idea what) in the water supply to my home (but not to my workplace) that my body did not like. Don't know for sure if that was the answer, but I now stick with filtered water anyway.
Regards,
Antony