Intervention: Patients will be randomized to one of two treatment groups (placebo and DHA), using a centralized randomization list. The study will be conducted according to the double-blind trial methodology, in which neither the patient nor the physician are unaware of the active substance administered to the patients. The randomization procedure will be performed assigning either strategy according to a randomization scheme generated by the module PROC PLAN SAS (version 8.2) in multiple of 2 blocks and following a pattern 1:1 stratified by center. A list of random assignment will generated according to the above mentioned, and as from the same will be issued a sealed opaque envelope, identified by a sequential number and the name of the center. The envelopes shall be deposited in the center of central data management and analysis, which will act as coordinator of the centralized randomization assignment by telephone contact.