Do not take ordinary fish-oil supplements to prevent cardiovascular disease
Two large trials enrolled roughly 26,000 people and 15,000 people with diabetes. Taking 1 gram of fish oil daily did not produce a clear reduction in serious cardiovascular events or deaths. Evidence that eating fish is beneficial does not automatically establish that fish-oil capsules are beneficial. Skipping them saves RMB 400–1,000 a year.
What it takes
About RMB 1–3 a day, or 400–1,000 a year. Taking them requires little time.
What you may gain
VITAL enrolled 25,871 people, used 1 gram daily, and followed participants for a median of 5.3 years. Major cardiovascular events had an HR of 0.92 (95% CI 0.80–1.06). An HR of 1 means no difference, and the interval crosses 1, so the trial did not establish a difference. All-cause mortality was similarly unchanged: HR 1.02 (0.90–1.15). ASCEND enrolled 15,480 people with diabetes, also used 1 gram daily, and followed participants for an average of 7.4 years. Serious vascular events had a risk ratio (RR) of 0.97 (0.87–1.08), and all-cause mortality an RR of 0.95 (0.86–1.05). The appeal comes from treating “fish is good for you” as equivalent to “fish-oil capsules are good for you.”
Context & considerations
There is an important exception. REDUCE-IT enrolled 8,179 people with cardiovascular disease or diabetes who were already taking statins and still had elevated triglycerides, 135–499 mg/dL. Taking 4 g of a prescription pure-EPA product daily reduced the event rate from 22.0% to 17.2%: roughly a one-quarter relative reduction, HR 0.75 (0.68–0.83). That was a high-dose prescription medicine for high-risk patients, not ordinary over-the-counter fish oil for the general population. This entry also does not apply to eating fish itself.
Research & references
Manson JE et al. (2019). Marine n-3 Fatty Acids and Prevention of Cardiovascular Disease and Cancer. NEJM. https://doi.org/10.1056/NEJMoa1811403; ASCEND Study Collaborative Group (2018). Effects of n-3 Fatty Acid Supplements in Diabetes Mellitus. NEJM. https://doi.org/10.1056/NEJMoa1804989; Bhatt DL et al. (2019). Cardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia. New England Journal of Medicine. https://doi.org/10.1056/NEJMoa1812792 (the high-purity prescription product discussed below).