Omega 3 supplement

[Bernadette_Abraham]

@Kkol – can you please share this contradictory study. I have never come across such information, unless they’re referring to rancid omega-3 supplements?

[Kkol]

I’ve been reading and hearing since last year or more about „dangers” of taking it especially for men ( prostate ). I

Atrial fibrillation (AFib) risk: Some studies suggest that high doses of fish-oil/omega-3 supplements (especially above ~1 gram/day) may increase risk of atrial fibrillation in people who are otherwise healthy.

For example, a large UK Biobank observational study (~400,000 people, 12 years follow-up) found that regular users of fish oil supplements who did not have cardiovascular disease had a ~13% higher risk of developing AFib compared to non-users.

Stroke risk in healthy people: The same UK study noted a slightly raised risk of stroke (~5%) for healthy supplement users.

Prostate cancer risk (men): There was a study (from around 2013) that associated higher blood levels of omega-3s (EPA, DHA, etc.) with a somewhat increased risk of prostate cancer, especially high-grade prostate cancer.

Diminishing returns / no benefit for some people: Several large trials (e.g. the VITAL trial) found that for healthy middle-aged people with no strong prior risk factors, taking fish oil (~1 g/day) didn’t significantly reduce risks of heart attacks, strokes, or cardiovascular death, compared to placebo.

[Bernadette_Abraham]

@Kkol can you please link the study directly? I’d really like to read it fully

[Kkol]

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[Daniel]

Hey @Kkol ,

Thanks for raising this. It’s a smart question, because omega-3s are one of those topics where the headlines often confuse more than they help.

I’ve taken a look at the BMJ Medicine study, and maybe this answer can help you to give the right weight to this study

First: how much weight should we give to this study?

This BMJ Medicine paper was an observational study. That means researchers watched a large group of people (~415,000 in the UK Biobank) over many years and looked at patterns: who took fish oil, who didn’t, and what happened to them.

Observational studies are powerful for large numbers and long follow-up, but they cannot proove cause and effect. They only show correlation. Classic example: if you study where people die, you’ll find that many die in hospitals. But the conclusion “hospitals cause death” would obviously be wrong.

That matters here, because the study has several built-in weaknesses:

• Self-reported supplement use. We don’t know dose, formulation, or quality. One person may have taken a single low-dose capsule occasionally, another several grams daily, but the study lumps them together. We don’t know dose, formulation, or quality.
• Hidden Variables: Supplement users differ from non-users in many ways (diet, income, lifestyle, medications). Even with adjustments, you can’t eliminate all bias.
• Outcome measurement limits: Atrial fibrillation (AF) and stroke were identified through hospital records. If someone had mild, brief, or symptom-free (silent) AF, or a small stroke that never reached the hospital, it wasn’t recorded. This means the study will miss cases. Also, people who see doctors more often get diagnosed more, which can inflate differences between groups that aren’t really due to the supplement itself.
• Contradictions with other research. Other analyses of the same UK Biobank and different cohorts sometimes found protective or neutral effects of fish oil. Differences in statistical models and definitions may explain why, but it shows results aren’t consistent.

This study is meant to see a signal, but it is not meant to be proof of anything.

What the study actually found

• People without heart disease who took fish oil were more likely to develop AF and had a slightly higher stroke risk.
• The relative risk sounds big in headlines, but in real numbers it’s ~1–2 extra AF cases per 1,000 people per year.
• People with existing heart disease sometimes did better: lower risk of progressing from AF to serious events, or from heart failure to death.

So the message is nuanced: it’s not “fish oil is bad.” It’s “fish oil may shift risks depending on who you are and how much you take.”

Dosage & supplement quality (things the study didn’t measure)

• The Biobank study had no dose data. Some participants may have taken one capsule a week, others four a day. We just don’t know.
• Other research shows the AF risk grows mainly at higher doses (>1 g/day EPA+DHA): the kind you’d get with prescription fish oil or multiple capsules.
• Quality matters. Cheap fish oils may contain oxidised fats or contaminants, which add stress instead of helping. The best are molecularly distilled oils (purified, concentrated, tested for heavy metals).

But the more important question is, in light of this study, how could the advice change?

A practical plan for fish oil use

If you like a food-based approach, start with food. Two portions
of oily fish per week (salmon, sardines, herring, mackerel). This gives
steady omega-3s plus selenium, vitamin D, and other nutrients.

Supplement if needed, but match to your situation:

• General health, no heart disease: keep dose modest. This avoids the high-dose AF risk seen in trials.
• High triglycerides or diagnosed heart disease: this is where fish oil (sometimes in prescription form) can help, but it should be guided by your doctor.
• History of AF or palpitations: Be cautious with higher doses, and involve your cardiologist before starting.
• Choose quality. Molecularly distilled, third-party tested. Store away from heat and light. If it smells fishy, it’s oxidising: stop using it.

Take-home truth: Observational studies raise questions, and not verdicts. This one adds to the discussion, but it doesn’t overturn decades of evidence on omega-3s. The real risks – and benefits – depend on who you are, what dose you take, and the quality of what you use.

Or to put it in a metaphor: An observational study is like watching ships at sea. You may count how many sink, but you cannot blame the ocean without knowing their cargo, their captain, or the storms they faced.

Numbers alone are never the cause

• This reply was modified 3 weeks, 2 days ago by  Daniel.

[Kkol]

Thank you Daniel!

What about other things like prostate issues

[Daniel]

Great follow-up question! Prostate health has also been studied with omega-3s, but here the picture is similar: more questions than verdicts.

• The 2013 headline study (SELECT trial) suggested higher blood omega-3 levels linked to higher prostate cancer risk, especially aggressive types. But it was an observational snapshot (one blood draw, no info on diet or supplements and no dose data. Dietary omega 3s don’t stay for a long time in the blood). Bias could have played a role in this study as well. For example, people who are consuming fish and omega 3s are probably more health-conscious and might visit the doctor more often. Or people diagnosed with cancer or having pain start consuming Omega 3s. This study sees a signal, but isn’t proof.
• Since then, stronger evidence (large randomised trials like VITAL, genetic studies, and meta-analyses) has not confirmed that omega-3s cause prostate cancer. In fact, some research suggests men who eat more fish may actually have lower prostate cancer mortality, meaning they don’t necessarily get it less often, but if they do, outcomes can be better.

So where does that leave us?

Omega-3s don’t look like a smoking gun for prostate cancer risk. The bigger picture is overall lifestyle: weight, exercise, diet quality, inflammation, and screening matter much more. If you enjoy fish a few times a week, keep going. If you use supplements, stick to moderate doses and good quality.

With research, we see this more often: observational studies show a signal, and once more follow-up studies have been done with better quality, we see that the conclusions made by the media and even other health educators were too premature. I wouldn’t be surprised if the follow-up research on AF would take a similar road, but that’s for the future to decide. The headlines made it sound scary, but the best current data show neutral to helpful effects when omega-3s come from whole foods.

One more piece that rarely gets discussed: most supplement studies don’t account for quality. Many commercial fish oils are already oxidised (“rancid”) by the time people take them, or they contain trace contaminants (like heavy metals). If there are negative health effects, part of the signal could come from poor-quality oils, not from omega-3s themselves.

• This reply was modified 3 weeks, 3 days ago by  Daniel.