Olive Leaf Extract: Benefits & Side Effects Of This Mediterranean-Diet-Approved Ingredient

If you ask most doctors how to eat for optimal health and longevity, chances are they'll point you to a Mediterranean diet. For starters, it's light on processed foods, but researchers also believe that olive oil plays a major role in delivering its health benefits, thanks to one of its main compounds known as oleuropein.

Oleuropein is responsible for that slightly spicy, pungent flavor you'll encounter in a quality extra-virgin olive oil. But supplement manufacturers are able to produce something called olive leaf extract, which contains a stable, standardized form of oleuropein so you can reap the benefits (in concentrated form) without having to consume huge quantities of olive oil.

The first known record of olive leaf comes from Ancient Egypt, where its antimicrobial oils were used to mummify kings. It has since been used extensively in traditional medicine1 to treat a variety of ailments and is still popular across many cultures today. In Japan, olive leaves are taken orally for stomach and intestinal diseases, while in Greece and the Canary Islands, a hot water extract of olive leaves is taken orally to treat high blood pressure. In Italy, people reach for a tincture of olive leaves to reduce fever, and in several countries, olive leaf extract has been used to treat malaria.

In addition to major metabolic and cardiovascular perks, taking olive leaf extract has also been shown to provide antiviral, anticancer, and neuroprotective benefits. "Its bioactive compounds are not only antioxidant and anti-inflammatory, but they can lower blood pressure, improve blood glucose levels, reduce cholesterol levels, and improve lipid ratios," says integrative neurologist Ilene Ruhoy, M.D., Ph.D. "These actions are powerfully cardioprotective and can reduce the risk of diabetes, hypertension, heart attack, and stroke."

Numerous studies3 have shown that olive leaf extract significantly reduces blood pressure in people with hypertension or borderline hypertension—to the point that those who are already on blood-pressure-lowering medication should consult with their doctor before supplementing with the oil since their levels could potentially drop too low.

In fact, olive leaf extract may be just as effective as prescription blood pressure medication for some people. In this study4, participants who took 500 mg of olive leaf extract twice a day for eight weeks experienced a comparable drop in blood pressure to those who took the medication Captopril.

Olive leaf extract is thought to lower blood pressure by acting as a calcium channel blocker, which relaxes and widens the blood vessels. In the same study, olive leaf extract also lowered triglyceride levels (i.e., levels of fat in the blood), while Captopril did not. This is important for heart health, as high triglyceride levels contribute to hardening of the arteries, or atherosclerosis, which increases the risk of heart attack and stroke.

Olive leaf extract may be just the thing to help prevent or shorten your next flu. This research review suggests that olive leaf compounds interact with the protein of virus particles and reduce their ability to infect us. They also slow the replication of viruses known to cause colds, influenza, and lower respiratory infection.

Olive leaf extract has an antimicrobial effect against bacteria and fungi, too. In this lab study6, various bacteria and fungi were immersed in an olive leaf extract solution, and after three hours, the extract killed almost all of them, including dermatophytes, which cause skin, nail, and hair infections, and E. coli, which can cause severe diarrhea and candida.

The polyphenols in olive leaf extract are antioxidant and anti-inflammatory. In fact, olive leaves and their extracts have long been used (orally and topically) throughout the Mediterranean to combat painful, inflamed joints1, and arthritis. In this animal study8, rats with osteoarthritis (OA) that were given olive leaf extract experienced a significant reduction in paw swelling, leading researchers to believe that it holds promise as a treatment for human OA too.

Research shows9 that olive leaf polyphenols are anti-inflammatory and protect against DNA damage initiated by free radicals, which are characteristic of many types of cancer. Also, thanks to their structure, which is similar to estrogens, they're thought to interact with estrogen receptors and thus reduce the prevalence and progression of hormone-related cancers, like breast cancer.

Olive leaf extract seems to help manage type 2 diabetes in several ways. One study13 tested the effects of olive leaf extract on rats and found that it slowed the digestion of starches into simple sugars. This, researchers speculate, may be why olive leaf extract supplementation helps stabilize blood sugar in humans. The same study found that human participants with type 2 diabetes who took 500 mg of olive leaf extract daily experienced a significant reduction in fasting insulin levels and hemoglobin A1c, a marker of long-term exposure to elevated blood sugar.

The Mediterranean region consistently has low rates of dementia, and this might be thanks to olive leaf too. Research6 suggests that oleuropein, present in olive leaf extract, may be one of the most important neuroprotective polyphenols, with studies6 finding that it helps counteract the creation of amyloid plaque in the brain (which collects between neurons and disrupts cell function) that is characteristic of Alzheimer's disease.

"Most people should be able to safely take olive leaf extract at appropriate doses," says Ruhoy. But there are a few key exceptions. Oleuropein, the active ingredient in olive leaf extract, may exacerbate low blood pressure16 in people whose blood pressure is already lower than average. It can also interact with16 prescription drugs that are designed to lower blood pressure or regulate diabetes. So, as is the case with all supplements, it's important to consult with your doctor before taking olive leaf extract in order to avoid interactions and side effects.

Olive leaf extract is available in both capsule and liquid form. "While some think the liquid formulations are more potent due to better absorption, which can be true17, the capsules are more standardized for dosing that is effective," says Ruhoy.

For capsules, experts typically recommend 500 to 1,000 mg of olive leaf extract per day—a range that's been shown to deliver significant blood pressure and blood sugar benefits in human studies (however, even higher amounts seem to be well-tolerated). To ensure you're getting a potent product, look for capsules that are standardized to 18 to 25% oleuropein.