Multiple differences between patients who initiate fish oil supplementation post-myocardial infarction and those who...

The utility of fish oil supplements (FOS) in patients who survive an acute myocardial infarction (MI) remains controversial, with randomized trials showing less benefit than observational studies would suggest. The differences in the characteristics of MI patients who use FOS in routine clinical care are unknown but may help explain this discrepancy. We used data from a 24-site registry study in which extensive information was available on 4340 MI patients at admission and 1, 6, and 12 months postdischarge. After excluding those using FOS at admission (n = 651), those who died before the 1-month follow-up visit (n = 63), and those with missing data at 1 month (n = 1228), 2398 remained. Of them, 377 (16%) started FOS within 1 month of their MI. We analyzed 53 patient characteristics associated with FOS use. We observed differences (P < .001) in 20 demographic, socioeconomic, treatment, disease severity, and health status domains. The FOS users were more likely than nonusers to be white, married, financially secure, highly educated, and eating fish. They also had a higher ejection fraction at discharge, were more likely to have had in-hospital percutaneous coronary interventions, and were more likely to have participated in cardiac rehabilitation programs. The FOS users were less likely to have a history of diabetes, alcohol abuse, stroke, MI, and angina. In conclusion, post-MI patients who initiate FOS within 1 month of discharge in routine clinical practice differ substantially from those who do not. These differences are strongly associated with a better post-MI prognosis and may illuminate several sources of unmeasured confounding in observational studies.