Science doesn't fare as well for pessimists. They not only have lower levels of happiness compared to optimists, but research shows that people with negative thoughts are 3 times as likely to develop health problems as they age.
I am an ESL student. I can't get the meaning of 'as' here (in bold), and what part of speech it is. And also want to know if the sentence doesn't make sense without 'as', and if so, why. Please advise.