The World Health Organisation recommends we have less than 25g of "free sugar" a day. That's not very much at all. There's 4g in a teaspoonful. I think that would be a rounded teaspoon not a level one. I've been trying to achieve this but it is sooo difficult.
By "free sugar" they mean plain sugar, and sugar added to food, and the sugar in fruit juice. And those fruit shakes made in blenders with ice. And honey too.