Oleic acid is a major component of olive oil and has been strongly associated with reduced risks of heart disease, diabetes, obesity, and high blood pressure. It can also improve mood, delay aging, and prevent cancer. Keep reading to learn about the many health benefits of oleic acid and why overdoing it is a bad idea. 

What Is Oleic Acid?

Oleic acid is a non-essential fatty acid, which means it is produced naturally by the human body [R].

It is the primary member of the omega-9 class of monounsaturated fatty acids. Oleic acid accounts for 92% of cis-isomer monounsaturated fats in the human diet [R].

Monounsaturated fats have only one double bond and are defined by the number of carbons in their omega side chain. Oleic acid is sometimes abbreviated as (C18:1), referring to its carbon structure [R].

Most naturally occurring monounsaturated fats are of the cis-isomer conformation, referring to the orientation of the double bond. Artificially produced trans-isomers are associated with negative health outcomes [R].

This article focuses on the cis oleic acid isomer.

Olive oil is the largest dietary contributor to human intake of omega-9 monounsaturated fats. Other good sources of oleic acid are in the following table [R].

Oleic Acid in Olive Oil and the Mediterranean Diet

Olive oil is an important component of the Mediterranean diet [R].

In Mediterranean countries, olive oil is the main source of dietary monounsaturated fats. This is compared to the US and northern European countries where meat and dairy products (20 to 40% monounsaturated fats on average) are more common dietary sources, and also include higher levels of saturated fats [R].

The Mediterranean diet has been linked to a variety of health benefits, including improved heart health, lower blood pressure, lower rates of obesity, and lower incidence of type 2 diabetes [R, R].

Oleic acid is responsible for some of the health benefits of this diet, but other potentially beneficial compounds in olive oil (squalene, antioxidant phenolic alcohols, polyphenols, and vitamin E) also contribute to these benefits [R].

Mechanism of Action

Oleic acid plays an active role in many body processes by changing cell membrane composition and altering which receptors are present on the membrane as a result.

By changing receptor presence at the cellular membrane, oleic acid has the following effects. It:

• Blocks transport of cholesterol in the small intestine by reducing cholesterol receptor production [R]
• Increases production of heart-protective factors (platelet aggregation and hemostatic factors) [R]
• Increases production of proteins to promote healthy blood vessel function (PKA and RhoA) [R]
• Assists immune cells (neutrophils) in the identification of inflammation. This leads to a faster immune response and faster resolution of inflammation, including inflammation-related symptoms like pain [R, R].

Oleic acid also serves several functions in neurotransmitter regulation:

• It blocks GABA reuptake, increasing GABA concentration outside the cell, which in turn increases associated nerve transmission in the brain.
• It competes with serotonin for receptor binding to reduce excess serotonin activity in the gut.
• Dopamine forms a product with oleic acid that is necessary for body movement (locomotion) [R, R, R].

An increased level of oleic acid in the cell membrane reduces the oxidative damage caused by free radicals [R].

Oleic acid is an important building block of the brain and nervous system. It is required for the formation of myelin and for nerve growth and repair [R].

Health Benefits of Oleic Acid

1) Oleic Acid Lowers Cholesterol

Patients at risk of heart disease were often prescribed a low-fat, high-carbohydrate diet (Step 1 Diet). Both the high-carbohydrate diet and a high monounsaturated fat diet lowered total blood cholesterol levels. However, patients on the high monounsaturated fat diet saw lower LDL-cholesterol and triglycerides than those on the carbohydrate diet [R, R, R, R].

The cells of the small intestine absorbed less cholesterol when oleic acid was present, because fewer proteins to transport cholesterol were produced [R].

2) Oleic Acid Protects Against Heart Disease

The famous “seven countries study” followed Mediterranean men and women over many decades and compared them to their counterparts in northern Europe, Japan, and the US. Those with diets rich in monounsaturated fats, including oleic acid from olive oil, had lower rates of heart disease [R].

The seven countries study was the first to definitively link saturated fat intake to total cholesterol levels and heart disease. Many of the modern dietary recommendations about fat intake are based on this study. Men and women in the “seven countries study” with elevated cholesterol levels had higher risks of death due to heart disease [R, R].

These protective effects are largely due to a decrease in total blood cholesterol levels, especially “bad” LDL-cholesterol. Limited evidence from an 8-week study of 23 patients with high heart disease risk connects a high monounsaturated fat diet to other heart-protective roles (blood clotting and circulation) [R].

Because oleic acid also acts on insulin sensitivity, blood pressure, inflammatory markers, and blood vessel function those who consume it are protected against heart disease. Oleic acid also lowered cholesterol levels in a study of 180 patients randomly assigned to high- and low-monounsaturated fat diets over 2 years [R].

3) Oleic Acid Lowers Blood Pressure

In a study of 23 patients with elevated blood pressure, those assigned to high monounsaturated fat diets all had significantly reduced blood pressure after 6 months. Eight patients were able to stop taking blood pressure medication entirely while on the diet [R].

However, the drop in blood pressure observed in that 23-patient study was also linked to reduced saturated fat intake, and to increased nitric oxide levels stimulated by polyphenols present in olive oil, not just to the high monounsaturated fat content [R].

Rats with high blood pressure fed a different form of oleic acid (bioactive 2-hydroxyoleic acid) decreased their blood pressure to normal levels after 7 days of treatment. These effects were attributed to changes in the production of proteins that control blood vessel contraction (increase in PKA and decrease in Rho A kinase proteins) [R].

Integration of oleic acid into cellular membranes can alter their structure to allow certain receptors to be present or absent at the membrane (G-protein coupled receptors, specifically members of the adrenergic receptor family) [R].

Increased levels of oleic acid in the vessels of rats fed a high olive oil diet were associated with an increase in receptors that lower blood pressure (via PKA) [R].

4) Oleic Acid Improves Insulin Sensitivity

When a group of adults (162 healthy people) was put on a 3-month high saturated fat diet, their insulin sensitivity decreased, compared to a high monounsaturated fat group [R].

Ten overweight patients with non-insulin-dependent diabetes improved their glycemic profiles (blood glucose and insulin value correlation) when placed on a high monounsaturated fat diet for 15 days [R].

In mice with diet-induced diabetes and obesity, substitution of oleic acid for saturated fats in the diet improved symptoms (hypothalamic inflammation, insulin resistance, and body fat) [R].

Eleven pre-diabetic patients were fed 3 diets, each for 28 days, one diet high in monounsaturated fats, another high in saturated fats, and a third high in carbohydrates. These patients had less belly fat and better insulin sensitivity on the high monounsaturated fat diet [R].

5) Oleic Acid Prevents Obesity

According to the World Health Organization, a high monounsaturated fat diet was the best predictor of low obesity rates worldwide [R].

A 28-day diet high in monounsaturated fats decreased belly (central) fat, which is associated with obesity, in 11 insulin-resistant patients [R].

Obese mice directly injected with oleic acid into the hypothalamus had reduced food intake and fat gain and improved symptoms associated with obesity, like hypothalamic inflammation and body fat [R].

6) Oleic Acid May Improve the Immune System and Resolve Inflammation

Oleic acid is incorporated into cell membranes and can directly interact with the immune cells (neutrophils) responsible for controlling the duration and intensity of tissue inflammation [R].

Part of the inflammatory response in the human body requires the formation of reactive oxygen species by neutrophils at the site of inflammation. This recruits other molecules necessary for healing. This response is increased in the presence of oleic acid leading to faster resolution of inflammation including the release of cytokines (IL1-b) [R, R].

Neutrophils are also responsible for pathogen identification and defense. They more efficiently engulfed (phagocytosed) and killed microorganisms when incubated with oleic acid [R].

Recruitment of neutrophils to the site of inflammation increased when oleic acid was present in lung-injury model mice but decreased when tested in a second study in cells outside the body. So, it remains unclear when or where oleic acid may assist with this early response to inflammation [R, R, R].

7) Oleic Acid May Help with Rheumatoid Arthritis

Forty-three rheumatoid-arthritis patients given a dietary supplement of fish oil (high in omega-3) and olive oil (high in oleic acid) had the best improvements in both pain and mobility compared to fish oil alone or a placebo (soy oil) [R].

8) Oleic Acid May Decrease Chronic Nerve Pain

Oleic acid inhibits a receptor (TRVP1) involved in pain perception (sensing of spiciness, hot temperatures, and itchiness). This is part of oleic acid’s natural role in inflammation [R].

Injection of oleic acid and albumin at the injury site in mice reduced the pain and involuntary movements associated with paralysis after spinal injury [R].

Albumin and oleic acid also promoted new nerve cell (dendritic) growth in normal mice and in mice genetically modified to have human TRVP1 [R].

Injections of oleic acid in a mouse pain-model reduced pain and inflammation similar to that observed in human arthritis patients [R].

9) Oleic Acid Is Essential for Brain Function

Oleic acid is produced during the repair of nerves (mature axons) and plays a role in the production of myelin [R].

Adrenoleukodystrophy, a rare genetic disorder that leads to the breakdown of myelin, can be treated with a mixture of fatty acids, including oleic acid, to slow the disease and reduce brain inflammation [R].

10) Oleic Acid Improves Mood

A small 3-week study (14 to 18 people per test group) associated an oleic acid-rich diet with higher resting energy expenditure (mitochondrial activity), lower anger levels, and increased physical activity [R].

In 20 adolescent boys with ADHD, oleic acid levels in the blood were positively linked with brain plasticity and with the openness and extraversion of the boys’ personalities [R].

11) Oleic Acid Decreases Age-Related Cognitive Decline

High monounsaturated fat intake was correlated with reduced risk of cognitive decline in a survey of over 5,000 elderly Italians (over age 65) [R].

This decreased risk is probably due to oleic acid’s role in the maintenance of neuron structural integrity [R].

The brain’s need for monounsaturated fatty acids increases with age in rats [R].

12) Oleic Acid May Slow Aging

Long-lived species like humans typically have higher levels of oleic acid in their membranes than shorter-lived species like rodents [R].

Aging is often linked with oxidative stress in cellular membranes and with DNA damage caused by free radicals released during energy production (glycolysis and electron transport). Rats that consumed more olive oil and probably have more oleic acid in the membranes had less age-related oxidative stress because these fatty acids are less susceptible to free radical damage [R].

13) Oleic Acid May Prevent Cancer

Oleic acid’s ability to decrease oxidative stress in the cell and thus to protect DNA from oxidative damage also lowers cancer risk [R].

Two studies interviewed more than 5,000 women with and without breast cancer about their dietary habits. Women with high levels of oleic acid in their diets were less likely to have cancer [R, R].

Mice with induced lung cancer (adenocarcinoma) fed an oleic acid-rich diet had increased rates of survival and longer disease-free periods [R].

However, mice with salivary gland tumors fed an oleic acid-rich diet increased tumor progression, possibly due to a lack of other monounsaturated fats in the diet [R].

Negative Effects

1) Oleic Acid at Very High Levels Is Bad

Omega-9 concentrations (expressed as percent of the cell membrane) in red blood cells of 3,000 patients were correlated with the risk of dying after 10 years. The relationship was nonlinear (U-shaped), indicating that both low and high levels of omega-9 could increase the risk of heart failure and death, with the optimal level close to 14% of red blood cell membrane (low levels less than 13% and high levels greater than 15% of cell membrane content) [R].

Mice fed an exclusively omega-9 diet developed deficiencies in the necessary fatty acids (linoleic and alpha-linolenic acids used to build omega-3 and omega-6 fatty acids) [R].

Converting one’s diet exclusively to any single fat source can be detrimental.

2) Oleic Acid May Have Negative Effects on Reproduction

In mice, increased dietary intake of omega-9 fatty acids (like oleic acid) have been linked to poor reproductive outcomes, including smaller litters of pups and shorter gestation periods. This is likely due to changes in steroid hormone synthesis during gestation [R].

When mothers consumed high oleic acid diets during pregnancy, lowered sperm count and motility were observed in male offspring due to increased DNA damage (fragmentation and oxidative stress) in mice [R].

3) Oleic Acid May not Play a Role in Skin Care

Oleic acid is often marketed as an ingredient in skin care products. But there is little scientific evidence to support any positive claims about preventing UV (ultraviolet) damage, eliminating free radicals, or other skin benefits as either a dietary supplement or in topical applications [R].

Limitations and Caveats

Dietary Studies Include Many Factors

Many of the dietary studies for monounsaturated fats used olive oil as a source of oleic acid. This does not distinguish between omega-9 fatty acids (like oleic acid) or other monounsaturated fatty acids (like omega-3 or omega-6). Other compounds present in olive oil and other monounsaturated fatty acids in the diets also have positive health effects.

Determining which components contribute the most to those effects can be very difficult without tightly controlled studies, especially when diets were self-reported by participants [R].

Men and Women Respond Differently

Population (epidemiological) studies often did not distinguish between men and women, and many intervention studies had exclusively male participants. In the cases where data for men and women were analyzed separately, the effects on blood cholesterol levels were often smaller in women than in men [R].

Drug Interactions

Oleic acid has potential interactions with blood pressure medication or diabetes medications. When taken with one of these medications the combined effect could cause blood pressure or blood sugar levels to drop too low [R, R, R].

Some chemotherapy treatments for breast-cancer (paclitaxel) can be enhanced (greater cell death) in the presence of high levels of oleic acid and its derivative compounds when studied in cells [R].

Nutritional Supplements

Most adults receive enough oleic acid in their normal diet [R].

However, you might consider a supplement to increase oleic acid in your diet if you’re interested in one of its positive health effects.

For some patients with high blood pressure (hypertension), olive oil or oleic acid supplementation can be as effective as prescriptions at lowering blood pressure [R].

Olive leaf extracts and other olive supplements are often normalized by their oleuropein content to indicate what portion of the supplement is derived from olives.

Olive Oil

The recommended dosage for dietary supplementation for patients with high blood pressure is 2 to 4 tablespoons of olive oil, or 10 to 20 olives per day [R].

Olive Leaf Extract

Olive leaf extract supplements have also been effective in reducing blood pressure in a comparison study of twins [R].

The recommended dosage is 500 mg twice daily [R].

Other Common Supplements High in Oleic Acid

The following oils and extracts are often sold as oils or in capsules. Blends of vegetable oils are common as well.

• Sunflower 0il
• Flaxseed 0il
• Omega complex (usually a mix of omegas-3, 6, and 9). Note that “essential omega” or “essential fatty acid” (EFA) supplements often contain only omega-3 and omega-6, not omega-9
• Macadamia oil
• Sesame oil
• Rice bran oil
• Other vegetable oils (coconut, safflower, etc.) also contain oleic acid, but in smaller quantities

User Experiences

User reviews on olive oil or olive leaf extract supplements were overwhelmingly positive. Many consumers attributed health improvements to these supplements, including reductions in blood pressure and cholesterol.

The most common complaint was receiving oxidized olive oil. This happens when oil is old and has been exposed to air for a period of time, possibly reducing the supplement’s effectiveness.

A few consumers reported allergic reactions to these supplements, but it was not immediately clear whether they were allergic to the oil being consumed (olive and other vegetable allergies are possible) or if some supplements contained gluten or other filler compounds.