Olive oil has been studied as a stand-alone entity in some studies; however, it is generally studied as part of the Mediterranean diet where it is the principal source of fat and considered a key contributor to the diet’s many healthy benefits. As a reflection of this, research into the Mediterranean diet is included in this monograph; however, the contribution of olive oil to these results remains unclear. In contrast, olive leaf extract has not been significantly tested under clinically controlled conditions, so evidence is mainly derived from traditional, in vitro and animal studies.
- 0.1 Clinical note — What is the Mediterranean diet?
- 0.2 CARDIOVASCULAR DISEASE
- 0.3 HYPERTENSION
- 0.4 INFLAMMATORY CONDITIONS
- 0.5 CANCER PREVENTION
- 0.6 DIABETES
- 0.7 LONGEVITY
- 0.8 ANTIBACTERIAL, ANTIFUNGAL AND ANTIVIRAL
- 1 Olive: Other Uses
- 2 Olive: Dosage Range
Clinical note — What is the Mediterranean diet?
The Mediterranean diet studied in most trials is based on the traditional diet of Greece. It is low in saturated fat and high in monounsaturated fat (oleic acid:omega-9 = 18:1), mainly from olive oil; high in complex carbohydrates, from legumes; and high in fibre, mostly from vegetables and fruits. Total fat may be high (>40% of total energy intake), but the monounsaturated to saturated fat ratio is around 2. The high content of vegetables, fresh fruits, cereals, and olive oil guarantees a high intake of beta-carotene, vitamins B6, B12, C, and E, polyphenols, and various minerals.
Prevention It has been speculated that consumption of olive oil reduces the incidence of coronary heart disease, based on the observation that countries where the Mediterranean diet is consumed, chiefly Greece, Italy and Spain, have a lower incidence of coronary heart disease.
In 1999, the Lyon Diet Heart Study was published and is widely claimed to be a landmark study investigating whether a Mediterranean type diet could reduce the rate of myocardial infarction. It was a randomised secondary prevention trial that used a Mediterranean-type diet (with butter and cream replaced by a margarine based on rapeseed/canola oil and rich in alpha-linolenic acid). At a mean follow-up of 27 months, there was a 73% decrease in combined end-points of cardiac death and non-fatal myocardial infarction, with a 70% decrease in cardiac death in the group eating the Mediterranean-style diet. Benefits were maintained for nearly 4 years after follow-up, which translates to 12 lives saved per 300 people in 27 months. Interestingly, these impressive results were obtained without lowering blood pressure, LDL-cholesterol and triglycerides, or raising HDL-cholesterol.
Several years later, data from the CARDIO2000 multicentre study was used to investigate the association between acute coronary syndromes (ACS) and a Mediterranean-style diet. Once again it was shown that the Mediterranean diet reduced the risk of developing ACS regardless of the presence of other risk factors such as hyperlipidaemia, type 2 diabetes or a sedentary lifestyle. In this instance, primary prevention benefits were observed.
Positive results were also seen with the Indo-Mediterranean diet, which has increased intakes of whole grains, walnuts and almonds, fruit and vegetables. The randomised trial involving 1000 patients with angina pectoris, myocardial infarction or other risk factors for coronary artery disease compared the Indo-Mediterranean diet to the Step I National Cholesterol Education Program diet and found total cardiac end-points were significantly fewer with the Indo-Mediterranean diet, as were sudden cardiac deaths and non-fatal myocardial infarctions.
Overall, these results suggest the Mediterranean diet has both primary and secondary prevention effects.
Both olive oil and olive leaf extract have demonstrated blood pressure lowering ability in small intervention trials, and long-term dietary intake of olive oil is associated with reduced incidence of hypertension.
One randomised, double-blind, crossover study compared the effects of monounsaturated (MUFA) (extra-virgin olive oil) and polyunsaturated fatty acids (PUFA) (sunflower oil) in 23 hypertensive patients over 6 months (Ferrara et al 2000). MUFA intake resulted in significantly reduced resting blood pressure compared to the PUFA diet, but most impressively, daily drug dosage was significantly reduced with the MUFA diet (-48% vs -4%, P < 0.005).
A randomised, placebo-controlled, crossover study of 40 subjects with stable coronary heart disease compared the antioxidant and antihypertensive effects of two different olive oil supplements with different phenolic compound levels (refined: 14.7 mg/kg vs virgin: 161.0 mg/kg). Treatment with virgin olive oil rich in phenolic compounds resulted in significantly lower plasma oxidised LDL and lipid peroxide levels, together with higher activities of glutathione peroxidiase. Additionally, SBP was significantly decreased in the hypertensive patients; however, no changes in DBP were observed.
Another randomised study involving elderly patients found that increased dietary intake of virgin olive oil significantly reduced total and LDL-cholesterol in normotensive but not hypertensive volunteers, whereas virgin olive oil consumption normalised SBP in this group (136 ± 10 mmHg) compared to treatment with sunflower oil (150 ± 8 mmHg).
In 2004, results from two large observational studies were published that further suggested olive oil intake has significant effects on blood pressure.
One study involved assessing data from the Greek arm of the European Prospective Investigation into Cancer and Nutrition study, which included 20,343 participants. Intakes of olive oil, vegetables, and fruit were significantly inversely associated with both SBP and DBP, whereas cereals, meat and meat products, and ethanol intake were positively associated with arterial blood pressure. Mutual adjustment between olive oil and vegetables indicated that olive oil has the dominant beneficial effect on arterial blood pressure in this population.
Another study investigated whether dietary olive oil consumption over time affected the incidence of hypertension. Data from 6863 participants with at least 2 years follow-up was used and the study found that olive oil consumption was associated with a reduced risk of hypertension among men; no association was observed among women. The researchers suggested this might be attributed to the overall lower incidence of hypertension among females and the resulting lower statistical power.
A study of olive leaf extract involving 30 subjects with essential hypertension was conducted by the Service de Cardiologie, Hospital Militaire in Tunis. Olive leaf extract (1600 mg daily) was administered for 3 months, after 15 days treatment with a placebo. Active treatment resulted in a statistically significant decrease in blood pressure (P < 0.001) in all patients and was considered well tolerated. Other interesting observations were that patients previously treated with beta-blockers noted a disappearance of gastric symptoms during treatment with olive leaf extract.
Olive leaf extract is used to promote symptomatic relief in various inflammatory conditions, such as osteoarthritis and asthma, and as a gargle in tonsillitis and pharyngitis. The anti-inflammatory effects demonstrated by several major components in olive leaf provide a theoretical basis for its use; however, clinical trials are notyet available to determine whether effects are significant and efficacy remains speculative.
Alternately, olive oil supplementation has been tested in some clinical studies.
In some studies of RA in which fish oil supplements have been investigated, olive oil has been used as a placebo because it was generally regarded as containing neutral fatty acids; however, in some instances olive oil produced significant improvements in disease activity, prompting further research.
Supplementation for 12 weeks with olive oil resulted in a significant decrease in pain intensity, duration of morning stiffness, time taken to walk 18 metres, and fibrinogen levels and improved trends in erythrocyte sedimentation rate, C3, and right grip strength according to an early study. A later double-blind study found subjective measures of mean duration of morning stiffness and analogue pain score improved to the same extent as treatment with fish oil supplements after 12 weeks.
A 24-week double-blind, randomised study of two different dosages of fish oil (3 g/day and 6 g/day) and a single dosage of olive oil (6.8 g/day of oleic acid) was conducted with 49 subjects with active RA. The fish oil treatment produced better results overall; however, improvement in patients’ global assessment was only observed with olive oil supplementation.
Another double-blind study of 90 patients comparing treatment with fish oils (2.6 g/day), or fish oils and olive oil (1.3 g/day and 3 g/day, respectively) or olive oil (6 g/day) over 12 months found a significant decrease in Ritchie’s articular index of pain and the number of painful joints after 12 months of olive oil and also after the combined use of fish oil (1.3 g/day) and olive oil (3 g/day).
More recently, a study of 43 patients investigated the effects of placebo (soy oil), fish oil (3 g/day), and a combination of fish oil (3 g/day) and 9.6 mL/day of olive oil as an adjunct to standard treatment. The groups receiving fish oil and the fish oil/olive oil combination experienced a statistically significant improvement in joint pain intensity, hand grip strength, duration of morning stiffness, and onset of fatigue compared with placebo. Parameters that responded after 24 weeks were Ritchie’s articular index for pain joints, the ability to bend down to pick up clothing from the floor, and getting in and out of a car. The group using the fishoil/olive oil combination also experienced improved ability to turn taps on and off and decreased rheumatoid factor after 24 weeks. When groups were compared, the combination treatment was found to be superior, showing a significant improvement in patient global assessment after 12 weeks.
It has been speculated that consumption of olive oil, chiefly as an ingredient of the Mediterranean diet, may reduce the incidence of some cancers, based on the observation that the incidence of cancer overall in Mediterranean countries is lower than in Scandinavian countries, the United Kingdom, and the United States.
One review calculated that up to 25% of the incidence of colorectal cancer, approximately 1 5% of the incidence of breast cancer, and approximately 10% of the incidence of prostate, pancreas, and endometrial cancers could be prevented if the populations of highly developed Western countries shifted to the traditional healthy Mediterranean diet. Although these figures are only estimates, data from observational studies are now considered strong enough to suggest that the traditional Mediterranean diet should be actively promoted in order to reduce the incidence of cancer.
There is anecdotal evidence that people with type 2 diabetes are using olive leaf extract as an adjunct to dietary modification. One report from Morocco found that 80% of people surveyed used herbal medicines for diabetes, hypertension and cardiac disease, and olive leaf was one of the most popular treatments. Once again, hypoglycaemic activity reported in animal models provides a theoretical basis for its use; however, clinical testing is not yet available to determine whether effects are significant and efficacy remains speculative.
In 2002, Panagiotakos et al found that adherence to a Mediterranean diet and healthy lifestyle (non-smoking, physically active, moderate drinking) is associated with a greater than 50% lower rate of all-cause and cause-specific mortality, such as from coronary heart disease, cardiovascular diseases, and cancer. The cohort study involved 1507 apparently healthy men and 832 women, aged 70-90 years in 11 European countries and was conducted from 1988 until 2000.
A year later, Trichopoulou et al also reported a positive association between longevity and the Mediterranean diet, with their study showing that the benefits are significant in people aged 55 years and older.
More recently, a 2004 review of five cohort studies further confirmed these findings and concluded that there is now sufficient evidence to show that diet does indeed influence longevity and that the optimal diet for the prevention of both coronary heart disease and cancer is likely to extensively overlap with the traditional Mediterranean diet. Although it is uncertain which specific components in the Mediterranean diet are most important for its protective health benefits, olive oil, fish, plant foods and moderate wine consumption are likely candidates.
ANTIBACTERIAL, ANTIFUNGAL AND ANTIVIRAL
Based on evidence of its broad-spectrum antimicrobial activity, olive leaf extract is used for the treatment of common bacterial infections such as bronchitis and tonsillitis, common fungal infections such as vaginal candidiasis, Tinea pedis and Tinea capitis, and viral infections such as herpes simplex. Currently, controlled studies are not available to determine whether treatment is effective.
Olive: Other Uses
Olive oil is an emollient and used externally to relieve pruritis and inflamed surfaces and is used to soften and remove dry scales in eczema and psoriasis. Taken internally, it is used as a laxative to soften impacted faeces. As a folk remedy, the plant is used as a diuretic, hypotensive, emollient, febrifuge and tonic, for urinary and bladder infections and for headaches. Olive leaf extract is also used as a general tonic to improve energy and provide a sense of wellbeing.
Olive: Dosage Range
• Olive leaf extract (according to manufacturer’s recommendations): 5 mL three times daily diluted with water or juice if necessary (Olive Leaf Australia)
• Olive oil: should replace dietary intake of saturated fats and be consumed as part of a Mediterranean style diet
ACCORDING TO CLINICAL STUDIES
• Hypertension: 1600 mg/day of olive leaf extract or 50 mL/day of virgin olive oil.
• Rheumatoid arthritis: 6-10 g/day of olive oil long term