Milk in tea/coffee - why did it cause a spike?

Milk contains naturally occurring sugar.

Milk contains a natural sugar (carbohydrate) called lactose. Lactose is composed of two carbohydrates: glucose and galactose.

Different people have different reactions to carbohydrates and you’ll even have different reactions on different days based on a number of factors.There are many things that can impact your blood glucose - from how tired you are to how much water is in your body.