Essential omega-3 fats from fish oil may help reduce your risk for heart disease, at least in part by lowering your triglyceride levels and your blood pressure. They also decrease abnormal heartbeats, slow down the clogging of your arteries and improve the functioning of your blood vessels. In some cases, people who take fish oil experience an increase in low-density lipoprotein, or LDL cholesterol, which is the type that may increase heart disease risk.
Increase in LDL
Studies often show an increase in LDL when people supplement their diets with fish oil or omega-3 fats, notes an article published in "Vascular Health and Risk Management" in 2006. Taking 4 grams per day of fish oil may increase your LDL by as much as 5 to 15 percent, according to an American Heart Association statement published in "Arteriosclerosis, Thrombosis, and Vascular Biology" in 2003. These effects may be dose dependent, but even a lower dose of 1.2 grams per day has increased LDL to some extent.
Type of LDL
The increase in LDL that comes with taking fish oil appears to be mainly due to an increase in the less risky, fast-floating types of LDL that are more buoyant. This is often accompanied by a decrease in the riskier, slow-floating types that are more dense, according to a review article published in "Vascular Health and Risk Management" in September 2006. These denser types of LDL are the ones that are more likely to clog your arteries and increase your risk of heart disease.
Type of Omega-3 Responsible
The authors of the 2006 "Vascular Health and Risk Management" review article note that while not all studies show an effect of EPA or DHA on cholesterol levels, these two types of omega-3 fats may affect your LDL cholesterol in different ways. The increase in LDL cholesterol may be due to EPA, while increases in the size of LDL particles may be due to DHA.
LDL versus HDL
Even with the potential increase in LDL, fish oil exerts potential heart health benefits. The increase in LDL cholesterol is sometimes accompanied by an increase in high-density lipoprotein, or HDL, which is the beneficial type of cholesterol. These increases can be as much as 15 percent, according to the 2006 "Vascular Health and Risk Management" article. This means that overall your ratio of "bad" to "good" cholesterol could improve, depending on the exact change in your LDL and HDL levels.
LDL versus Non-HDL
An article published in "Drugs of Today" in 1998 notes that while LDL cholesterol may go up, non-HDL cholesterol levels usually go down with omega-3 supplementation. Total non-HDL cholesterol levels, which includes both LDL and VLDL, are a better predictor of heart disease risk than LDL cholesterol alone. This decrease in total non-HDL cholesterol levels may be a result of omega-3 fats decreasing very-low-density lipoprotein levels.