In this task, you are given two sentences in the English language (Sentence 1 and Sentence 2). Your task is to identify the connecting word between the two sentences.

Sentence 1:They improve sleep - related problems by shortening the time spent in bed before falling asleep , prolonging the sleep time , and , in general , reducing wakefulness . Sentence 2:However , they worsen sleep quality by increasing light sleep and decreasing deep sleep .
however