Why a daily pill doesn’t work the same for everyone
You take your fish oil pill every morning. Your friend takes the same one. But your blood tests show big improvements, while theirs barely change. Why?
It’s not just about diet or lifestyle. New research suggests your DNA plays a major role in how your body responds to fish oil supplements.
Scientists studied nearly 200,000 people and found that your genes can change how fish oil affects your blood levels of healthy fats. This could explain why some people get heart benefits from fish oil, while others don’t.
The problem with fish oil today
Omega-3 fatty acids are healthy fats found in fish. They help lower inflammation, support brain health, and may reduce heart disease risk. Many people take fish oil supplements to get these benefits.
But here’s the frustrating part: studies show fish oil supplements don’t work for everyone. Some people see their omega-3 levels rise sharply. Others take the same dose and see almost no change.
Doctors don’t fully understand why. It’s not just about how much you take or what you eat. Something else is at play.
This leaves many people wondering: Is fish oil worth it for me? Should I take more? Should I stop?
What we used to believe vs. what’s new
For years, scientists focused on how genes affect your baseline omega-3 levels. They looked for genes that directly raise or lower these fats.
But this study took a different approach. Instead of looking for genes that change your starting point, they looked for genes that change how much your levels vary after taking fish oil.
Think of it like this: some genes act like a dimmer switch. They don’t just set your omega-3 level—they control how much your levels can swing up or down when you take a supplement.
This is called a “variance quantitative trait locus,” or vQTL. It’s a genetic spot that affects how much a trait changes, not just what it is.
How genes and fish oil interact
The researchers looked at 14 different blood fats, including omega-3 and omega-6 fatty acids. They screened the DNA of 200,478 people from the UK Biobank.
First, they found genetic spots (vQTLs) that affect how much these blood fats can change. They found 172 such spots across all 14 fats.
Then, they checked if any of these spots interact with fish oil supplements. Do certain genes make fish oil more or less effective?
They found six key interactions. These involve genes like FADS1/2, ZPR1, and SUGP1/TM6SF2. These genes are known to help process fats in the body.
For example, people with certain versions of the FADS1/2 gene may see a bigger boost in omega-3 levels after taking fish oil. Others might see little change.
What the study looked at
The study used data from the UK Biobank, a massive health database in the United Kingdom. Researchers analyzed blood samples from over 200,000 people.
They measured 14 different unsaturated fatty acids in the blood. Then, they scanned the participants’ DNA to find genetic spots linked to changes in these fats.
They also checked who took fish oil supplements. This allowed them to see how genes and supplements interacted.
The study didn’t test new treatments. It analyzed existing data to find patterns.
The researchers found 172 genetic spots linked to changes in blood fat levels. Sixteen of these spots had no effect on the starting level of the fat—only on how much it changed.
They also found 46 unique genetic regions that affect these changes. Some fats, like omega-6, had many genetic spots (24). Others, like DHA (a key omega-3), had only one or two.
Most importantly, they found six gene-supplement interactions. These show how certain genes change the effect of fish oil on specific blood fats.
For example, one interaction affects DHA levels. Another affects the omega-3 to omega-6 ratio, which is important for heart health.
These findings suggest that your genes can make fish oil more or less effective for you.
But there’s a catch
This is where things get interesting. The study found strong patterns, but it’s not ready for real-world use.
The research is based on data from one group of people—mostly of European descent. We don’t know if these findings apply to other groups.
Also, the study didn’t test whether these genetic differences lead to real health outcomes, like fewer heart attacks. It only looked at blood levels.
This doesn’t mean this treatment is available yet.
What experts think
Researchers say this study is a step toward personalized nutrition. In the future, genetic tests might help doctors recommend the right dose of fish oil for each person.
But for now, experts caution that more research is needed. We need to see if genetic testing improves health outcomes, not just blood levels.
If you take fish oil and wonder why it’s not working, your genes might be part of the answer. But you can’t get a genetic test to guide your fish oil use today.
Talk to your doctor if you’re concerned about omega-3 levels. They can check your blood levels and help you decide if fish oil is right for you.
The study has several weaknesses. It only included people of European ancestry, so results may not apply to other groups. It also relied on self-reported fish oil use, which can be inaccurate. Finally, it looked at blood levels, not actual health outcomes like heart attacks.
Next, researchers need to test these findings in diverse populations. They also need to see if genetic testing can improve health outcomes. If successful, this could lead to personalized fish oil recommendations in the future. But that’s likely years away.