Linoleic acid is found in soybeans and corn, sunflower, and safflower oils. While recent studies have suggested that higher levels of this essential fatty acid reduce the risk of stroke, other research has yielded conflicting results. Now, a new study published in the August issue of Stroke: Journal of the American Heart Association suggests that higher levels of linoleic acid in the blood are associated with a lower risk of stroke.

About the study

Japanese researchers studied 7450 Japanese men and women between the ages of 40 and 85, who had participated in cardiovascular risk surveys between 1984 and 1992. As part of the survey studies, researchers interviewed them about their risk factors for heart attack and stroke, such as smoking, alcohol intake, high blood pressure, and high cholesterol. In addition, a blood sample was taken from each participant and stored at below freezing temperatures. Researchers monitored participants until 1998 through annual questionnaires to determine which people had strokes. Reported strokes were confirmed through medical records and death certificates.

This recent study of linoleic acid was a case-control study conducted using participants from the cardiovascular risk surveys. For each of the 197 people who had strokes in the first study (cases), the researchers selected three people from the study who did not have a stroke (controls). Three controls were matched to each case on the basis of age, sex, the community they lived in, and years their blood was stored.

Researchers thawed the blood samples and measured their levels of various fatty acids, including linoleic acid. Finally, researchers compared the linoleic acid levels in the blood of cases versus the blood of controls.

The findings

On average, controls had higher levels of linoleic acid in their blood than cases. Specifically, each 5% increase in linoleic acid reduced the risk of stroke by 28%. This was true even after adjusting for other factors associated with stroke risk—smoking, blood pressure, cholesterol, triglycerides, alcohol intake, body mass index (BMI), and diabetes.

As expected, saturated fatty acids were associated with an increased risk of stroke.

Although these results imply that increasing linoleic acid intake reduces the risk of stroke, this study has its limitations. First, the participants were Japanese men and women so it’s unknown whether these findings are applicable to people of other ethnic and racial groups. For example, Japanese adults tend to suffer different types of stroke than Western adults. Second, blood samples remained frozen for as many as 9 years, and it’s not known whether this affected their composition of fatty acids. In addition, participants did not fast before providing their blood samples and the time elapsed since the last meal they ate before testing varied. Third, researchers measured the levels of linoleic acid in the blood, but they did not correlate these levels with the amount of linoleic acid in the diet. It’s possible, though unlikely, that subjects who consumed diets rich in linoleic acid actually did not have higher blood levels of the essentially fatty acid, due to the body’s metabolism process. Finally, even carefully conducted case-control studies like this one are generally less reliable than other types of studies in determining cause and effect.

How does this affect you?

Do you need to get more linoleic acid in your diet? It’s too soon to say. These findings suggest that people with more linoleic acid in their blood are at lower risk of stroke than people with lower blood levels of linoleic acid. However, the study did not measure intake of foods containing linoleic acid, so we still don’t know if dietary intake of linoleic acid reduces the risk of stroke.

One important point this study makes is that not all fats are bad for you. Quite the contrary. Linoleic acid is an essential fatty acid, which means that the body needs it but cannot manufacture it from other substances. So the only way to get linoleic acid is through food. Good sources of linoleic acid include corn oil, sunflower oil, safflower oil, and soybeans. But there’s no need to focus on just one substance in your diet. A balanced diet rich in fruits, vegetables, and whole grains, and low in saturated fat leaves plenty of room for vegetable oils rich in essential fatty acids.