The honest answer to the question of does fish oil lower cholesterol is "no." However, fish oil does something far more important than changing total cholesterol or LDL cholesterol numbers.
If you have read the literature of natural health, chances are you have come across many references to a "cholesterol myth" or a "cholesterol hoax." These authors accurately assert that medical science has found only a very slight relationship, or no relationship at all, between cholesterol numbers and heart health.
For instance, the first study to find that that higher cholesterol levels raise the risk of heart attacks, the TexCAP study, found that having high LDL cholesterol increased a 50-year-old adult's risk of having a heart attack in any given year from 0.7% to 0.8%. (This study also found that taking a statin drug to lower LDL cholesterol reduced the risk of a heart attack by about 0.5% in any given year.) Many other studies have found no predictive value at all in the cholesterol numbers doctors usually measure.
Omega-3's and Cholesterol Reduction
The cholesterol number that really counts is a measurement called a kind of cholesterol known as the lipoperoxides, or APO-A. These are fragments of cholesterol that have been attacked by free radicals. When cholesterol that has not been attacked by free radicals lodges in the linings of your blood vessels, it stays soft.
When cholesterol that has been oxidized by free radicals lodges in the linings of your blood vessels, it hardens. Even worse, it attracts white blood cells called macrophages, which try to remove it. In smaller blood vessels and at the bends and turns of blood vessels, these white blood cells can also be calcified and harden, causing a kind of clog known as a cholesterol plaque.
Oxidized cholesterol makes arteries stiff, but fish oil helps arteries relax. Cells all over the body use the omega-3 fatty acids provided by fish oil to make hormones that open arteries and allow blood to flow more freely. These hormones lower blood pressure. They stop clotting. They undo many of the harmful effects of high cholesterol that has been attacked by free radicals.(Check out the article “Does Fish Oil Lower Blood Pressure” for more information.)
Fish Oil and the Limitations of Cholesterol Measurement
But taking fish oil by itself won't lower your cholesterol levels. In fact, if your doctor does not pay attention to your triglyceride levels, taking fish oil may appear to raise your LDL (bad) cholesterol levels.
This isn't because fish oil actually raises LDL cholesterol levels. It's because the test doctors usually order doesn't directly measure LDL cholesterol at all.
The lab usually measures your HDL (good) cholesterol and triglycerides and uses a mathematical formula to "guess" what the other measurements are. The relationship between total cholesterol and the various kinds of cholesterol is:
Total cholesterol = HDL + a kind of cholesterol called VLDL + LDL
The way the lab calculates your LDL cholesterol is:
LDL = Total cholesterol - HDL - VLDL
The lab estimates your VLDL cholesterol as being 1/5 as much as your triglycerides. It may be higher, or it may be lower. This is just an estimate. But because it is only an estimate, this means that when you get your triglycerides down, your LDL number goes up whether your actual LDL levels have gone up at all.
One of the ironies of improving your health by using fish oil is that a doctor who does not understand how cholesterol is measured—and there are lots of doctors who don't—may insist you take a statin drug you don't need, thinking your LDL cholesterol has gone up. And this is even though LDL doesn't really predict heart disease very well.
Do your best to work with a doctor who understands how cholesterol really affects your cardiovascular system. Don't automatically accept a prescription for a statin medication if your LDL numbers go up just because your triglycerides go down. At the very least, make sure your doctor understands this relationship. And take fish oil for the real heart-healthy benefits it offers that go beyond just changing cholesterol numbers