Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) can cause vitamins, herbs, and other nutritional supplements to be broken down more quickly in the body reducing absorption and rendering them less effective. According to the Arthritis Foundation, to help minimize interactions, take your supplements two to three hours before or after taking an NSAID. The idea is to wait for one to be ingested and absorbed before taking the other.
(Source: Arthritis Today, November-December 2002, pg. 69)