Hi Cinzia,
Both words of course are available in the dictionary, but they bear different meanings which are used similarly in both American and British English.
Simply put :
To lose would be to be unable to catch up with something, to stop being the owner, or to have a reduction (of something).
Loose on the other hand could also be used as a verb which would mean to make free or less tight.
You might want to check the context in which the word was supposed to be used so you can decide the right one to choose. A typographical error could have led to the wrong usage in the book.
Regards.