The results of this study would suggest that as a
primary prevention strategy, fish oil supplementation may not be useful and may in fact be harmful. But as a
secondary prevention strategy among people who have developed early-stage or late-stage cardiovascular disease, fish oil use may provide
protection.
Should you stop using fish oil if you’re healthy?
Before jumping to that conclusion, let’s put these risk increases in perspective. The healthy fish oil users had a 13% higher risk of Afib and a 5% higher risk of stroke compared to non-users — but this is in terms of
relative risk. Relative risk represents a ratio of the risk of a cardiovascular event in the fish oil users compared to the risk in non-users. But relative risk doesn’t tell us much about
absolute risk, or the absolute difference in the risk of a cardiovascular event between groups.
Without the raw data on the event rates in each group (how many participants experienced each event compared to those who didn’t), we can’t calculate the absolute risk for fish oil users and non-users in this study. But some personal correspondence with Dr. Bill Harris indicates that they may be much lower than the relative risks. For example, the actual incidence of Afib in the non-fish oil users was around 4.2%, while that in the fish oil users was 4.8% — this represents an
absolute risk increase attributable to using fish oil of just 0.6%
Not to mention, the study also found that even though fish oil users were at a greater risk of developing Afib, fish oil use
protected them from transitioning to more severe cardiovascular disease.
Arguably, preventing stroke, heart failure, myocardial infarction, and certainly death are
more important outcomes than atrial fibrillation, which we should want to avoid nonetheless. But it’s interesting that most of the media headlines — and even the study authors themselves — choose to focus on the detrimental result in fish oil users rather than the four beneficial results also observed.
Instead of going into some of the other technical issues of the study, I think it would be best to discuss the vast literature (and it is quite vast)
supporting the use of omega-3 supplements to promote heart health and prevent cardiovascular disease. Observational studies and randomized controlled trials have largely converged on the idea that fish oil is cardioprotective, and I want to focus on one particular study that seems incredibly relevant to our discussion.
This study was published in 2020 and included nearly the
exact same group of participants as the current UK Biobank study and similarly, used self-reported fish oil supplementation as the independent variable.
What did this study find? The exact opposite. Regular use of fish oil was associated with a
13% lower risk of all-cause mortality,
a 16% lower risk of dying from cardiovascular disease, and
a 7% lower risk of incident cardiovascular disease events (i.e., myocardial infarction or stroke).
The evidence for fish oil use strengthens when we look at what is arguably a much more robust measure than self-reported fish oil use — omega-3 fatty acid levels in the blood. One large meta-analysis of cohort studies (including a UK Biobank cohort) found that
higher blood DHA levels were associated with a lower risk for all-cause mortality and a lower risk of dying from cardiovascular disease.
Even data from randomized controlled studies of omega-3 supplementation support its benefits, finding that doses of 2–4 grams per day
protect against all-cause mortality, cardiovascular disease mortality, and stroke.
It’s important to underscore that
other than a slightly elevated risk of Afib,
no other studies have found detrimental effects of fish oil supplementation or self-reported fish oil use on cardiovascular outcomes. In my opinion, focusing on this single observational study and ignoring the rest of the literature is missing the forest for the trees. Be careful about what you might read in the headlines about this study, and
certainly don’t use it to make decisions about whether or not to supplement with fish oil.
Want more information on fish oil? I’ve put together
The Omega-3 Supplementation Guide, a free 12-page guide that has everything you need to know about how to choose the highest-quality omega-3 supplement.
I also talk about fish oil in my most recent Q&A episode (#61), which
you can watch in full here. This Q&A also covers hyperbaric oxygen therapy, supplements for kids, sleep strategies, and the impact of curcumin on testosterone.
