Does Fish Oil Raise Cholesterol?

Katie had an LDL of 87 mg/dl, HDL of 48 mg/dl, triglycerides of 201 mg/dl. By conventional standards, not too bad.

Reading about the heart health benefits of omega-3 fatty acids, Katie added fish oil. With the preparation she bought, 4000 mg per day provided 1200 mg the omega-3 fatty acids, EPA and DHA. Three months later her LDL was 118 mg/dl, HDL 54 mg/dl, triglycerides 92 mg/dl.

In other words, LDL cholesterol increased by 31 mg. What happened?

Several studies have, indeed, confirmed that fish oil raises LDL cholesterol, usually by 5-10 mg/dl. Occasionally, it may be as much as 20 or more milligrams, as in Katie's case, enough for some people to be scared away from continuing this supplement.

Unfortunately, many physicians often assume that it's the (minor) cholesterol content of fish oil capsules, or some vague, undesirable effect of fish oil. It's nothing of the kind. And, if you were to rely on basic cholesterol values, it does indeed appear to be the case.

But it's not.

What has happened is that triglycerides have been reduced. Triglycerides occur in particles called very low-density lipoproteins (VLDL) and intermediate-density lipoproteins (IDL). Given Katie's high triglyceride level of 201 mg/dl before fish oil, we can safely assume that VLDL and perhaps IDL (a less common pattern) were also elevated in Katie's blood. Fish oil effectively reduces triglycerides, as it did in Katie, and VLDL and IDL are also reduced. Since LDL particles start out as VLDL particles (the first particle that emerges from the liver), fish oil can cause a "shift" of particles from VLDL to LDL. Thus, the apparent rise in LDL.

Another factor: Conventional LDL cholesterol is a calculated value, not measured. (Many people are surprised when they first hear this.) The calculation for LDL is thrown off-sometimes considerably-by any reduction in HDL or rise in triglycerides from average values. In Katie's case, the rise in HDL from 48 to 54 mg/dl along with the reduction in triglycerides from 201 to 92 mg/dl mean that calculated LDL has become more accurate and rises towards the true measured value. The actual rise in true LDL cholesterol may be small to none.

Omega-3 fatty acids from fish oil therefore provide the appearance of raising LDL cholesterol, but the actual-measured-rise is usually small to none.

Omega-3 fatty acids have been convincingly shown to reduce risk of heart attack, stroke, heart rhythm disorders, and are powerful tools to reduce triglycerides. It's a shame to avoid this wonderfully effective and healthy tool because of the appearance of rising cholesterol.