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Table 2 Effect size measures and confounding factors used in the selected studies that were included in the systematic review.

From: Olive oil intake is inversely related to cancer prevalence: a systematic review and a meta-analysis of 13800 patients and 23340 controls in 19 observational studies

Author Effect sizes
(OR = odds ratio)
95% Confidence Interval Confounding factors
Breast cancer
Trichopoulou A, et al [10] Increased olive oil consumption is related with reduced cancer risk (OR = 0.75 for more than once a day versus once a day) 0.57-0.98 Adjustment for age, place of birth, parity, age at first pregnancy, age at menarche, menopausal status, Quetelet index, total energy intake, consumption of fruits and vegetables
Katsouyanni K, et al [11] OR per quintile monounsaturated fat 0.97 0.88-1.07 Adjustment for demographic and reproductive risk factors for breast cancer, as well as for total energy intake and mutual confounding influences among nutrients
Trichopoulou A, et al [12] HR per 21 g in daily intakes of olive oil in the entire cohort (HR = 0.93, P = 0.106) and in the postmenopausal women (HR = 0.85, P = 0.106) 0.80-1.08
Adjusted for age, educational level, smoking status, BMI, height (ordered as quintiles), metabolic equivalents of task hours per day, energy intake, age of menarche, parity, age at first delivery, menopausal status, age at menopause, hormone replacement therapy and an interaction term for the BMI by menopausal status.
Martin-Moreno JM, et al [13] For highest versus lowest quartile of olive oil consumption, OR = 0.66 0.46-0.97 Adjustment for total energy intake and other potential confounders
Landa MC, et al [14] OR for the highest tertile of monounsaturated fat intake compared to the lowest 0.30 0.1-1.08 Not mentioned in the abstract in PubMed
García-Segovia P, et al [15] The OR for women in the three upper quintiles of olive oil consumption (≥ 8.8 g/day) is 0.27
OR for monounsaturated fat intake is 0.52
Not mentioned in the abstract in PubMed
La Vecchia C, et al [16] OR per unit (30 g) is 0.89. The ORs for olive oil compared with the lowest intake are 1.05, 0.99, 0.93 and 0.87 for increasing quintiles of intake. 0.81-0.99 Adjusted for demographic and reproductive breast-cancer risk factors, energy intake and mutually for types of dietary fat
Sieri S, et al [17] The salad vegetables pattern had a RR = 0.66 0.47-0.95 Adjusted for education, parity, height, age at menarche, smoking, menopausal status, energy intake and age
Bessaoud F, et al [18] OR (> 20.5 g/day vs. < 2 g/day) 0.71 (classical method)
OR (> 20.5 g/day vs. < 2 g/day) 0.29 (spline method)
Adjustment for total energy intake, education, parity, breast-feeding age at first full-term pregnancy, duration of ovulatory activity, body mass index, physical activity, and first-degree family history of breast cancer.
Adjustment by monounsaturated fatty acids and total energy intake
Richardson S, et al [20] OR for the highest tertile of consumption of mono-unsaturated fat = 1.7 1.2-2.5 Not mentioned in the abstract in PubMed
Colorectal cancer
Braga C, et al [25] ORs for the highest tertile of olive oil intake, compared
with the lowest one is 0.83 when colorectal carcinoma is analyzed
as a whole/0.81 for colon carcinoma and 0.88 for rectal carcinoma
ORs are 0.94 for colorectal
0.94 for colon carcinoma
0.97 for rectal carcinoma
Estimates from multiple logistic regression equations are presented, including terms for study center, age, sex, education, alcohol, total energy intake, and simultaneously the various types of oils and fats.
After allowance for vegetable intake.
Benito E, et al [29] ORs for the higher available category of monounsaturated fat intake compared for the lowest one is 0.72 Not mentioned in the abstract in PubMed Adjustment for total calorie intake
Galeone C, et al [30] OR for fried olive oil, 0.89, for colon cancer 0.82-0.98 Adjusted for age, center, sex, education, body mass index, tobacco smoking, alcohol drinking, non alcohol energy intake, family history, physical activity and red meat intake.
Prostate cancer
Tzonou A, et al [34] Chi-square linear trend adjusted = 0.44   Adjusted for age, height, Quetelet index, years of schooling and total energy intake.
Norrish AE, et al [35] RR 0.5 (> 5.5 ml MUFA-rich vegetable oil intake per day vs. non-consumption) 0.3-0.9 The multivariate linear regression model included terms for age, total non-steroidal anti-inflammatory drugs, socioeconomic status, intake of total energy, lycopene, and levels of eicosapentaenoic acid and docosahexaenoic acid measured in erythrocytes
Hodge A, et al [36] Higher consumption of olive oil (> 0.25, as well as < 0.25 l/month compared to non consumption) had an OR = 0.8 0.6-1.1 Adjusted for state, age group, year, country of birth, socioeconomic group, total energy intake and family history of prostate cancer
Cancer of the larynx
Gallus S, et al [40] OR for the olive oil higher intake compared to the lower one was 0.28 0.09-0.89 Adjusted for age, year of interview and study center, and including terms for education, BMI, non-alcohol energy intake, tobacco and alcohol consumption
Crosignani P, et al [41] The consumption of olive oil was associated with a better prognosis from laryngeal cancer Not mentioned in the abstract in PubMed Not mentioned in the abstract in PubMed
Bosetti C, et al [43] OR = 0.4 for the highest compared to the lowest quintile
When adjusted for total vegetable consumption: OR = 0.66
Estimates from unconditional logistic regression adjusted for sex, age, center, education, tobacco smoking, alcohol drinking, non-alcohol energy intake, all seasoning fats in the table, as well as for total vegetable consumption in the second model.
Cancer of the oral cavity and pharynx
Lagiou P, et al [44] Center specific median was used as a cut-off. For olive oil above versus below median:
Olive oil (overall) OR 0.78
Olive oil in salads OR 0.84
Olive oil for cooking OR 0.65
Adjusted for centre through stratification and controlled for age, gender, BMI, height, education level, alcohol consumption and smoking status.
Franceschi S et al [46] Olive oil OR = 0.4
(highest vs. lowest quintile)
Vegetable-adjusted OR = 0.6 for the same quintiles
Adjusted for age, centre, sex, education, smoking habit, total intake of alcohol and energy, plus all oils and fats examined.
Nešić V, et al [47] For frequent/moderate consumption vs. rare or never, OR 0.42 0.19-0.91 Variables, which were significantly associated
with nasopharyngeal cancer in each of the multivariate analyses, were included in the final model (consumption frequency of eggs, margarine, olive oil, rice, white bread,
cornbread, peanuts and industrially manufactured food additives for enhancing flavour, as well as "passive smoking" in the family during childhood, chronic rhinosinusitis and
positive family history for malignant tumours outside of the otorhinolaryngology region)
Petridou E, et al [48] Added lipids, which in Greece are overwhelmingly olive oil, OR = 0.75 (per quantile of intake) 0.58-0.99 Adjusted for body mass index, height, years of schooling, condition of teeth, energy intake, tobacco smoking, daily alcohol and coffee consumption and total energy intake.
Cancer of the oesophagus
Tzonou A, et al. [50] OR associated with an increment of a marginal quintile in the frequency of intake of monounsaturated fat is 1.07 for adenocarcinoma of the oesophagus.
The respective OR is 0.74 for squamous cell carcinoma
Adjusted for socio-demographic facts, tobacco smoking, consumption of alcoholic beverages and total energy intake
Bosetti C, et al. [51] OR = 0.36 for the highest compared to the lowest quintile 0.18-0.73 Adjusted for age, sex, area of residence, education, tobacco smoking, alcohol drinking, non-alcohol energy, all added lipids and for total energy consumption
Launoy G, et al [53] OR for consumers versus non-consumers 0.70 0.54-0.90 Adjusted for age, interviewer, smoking, beer, aniseed aperitifs, hot Calvados, whisky, total alcohol, total energy intake and other food groups.
Stomach cancer
Palli D, et al [54] OR = 0.6, for the highest versus the lowest tertile (MSI-)
OR = 0.5, for the highest versus the lowest tertile (MSI+)
Adjusted for age, sex, social class, family history of gastric cancer, area of residence, and BMI tertiles, and total energy.
Lung cancer
Fortes C, et al [56] Exclusive use of olive oil OR = 0.67 0.45-0.99 Adjusted for smoking variables and also considering all food items simultaneously
Ovarian cancer
Tzonou A, et al [60] The adjusted OR associated with an increment of about 1 SD of the energy-adjusted residual of monounsaturated fat
was 0.80
0.65-0.99 Adjusted for age, years of schooling, parity, age at first birth, menopausal status, as well as for energy intake and other nutrients in the same model, such as crude fiber.
Bosetti C, et al [61] A reduced risk of ovarian cancer was observed for the highest quintile of olive oil OR = 0.68 compared to the lowest one.
OR were 0.85 for olive oil per 12 gr.
Allowance for total vegetable intake attenuated the effect
OR = 0.82
Adjusted for study centre, year at interview, age, education, parity, oral contraceptive use, and total energy intake, various types of added oils and fats simultaneously, plus total vegetable intake, when indicated.
Endometrial cancer
Levi F, et al [65] OR for the highest versus the lowest tertile of olive oil intake OR = 0.82 Not mentioned in the abstract in PubMed Not mentioned in the abstract in PubMed
Tzonou A, et al [66] Increasing intake of monounsaturated fat, mostly olive oil, by about one standard deviation was associated with a OR = 0.74 0.54-1.03 Adjusted for age, schooling years, age at menopause, number of liveborn children, number of miscarriages, number of abortions, history of use of menopausal estrogens, smoking, alcohol intake, coffee drinking, height, body mass index and energy intake, as well as for protein, saturated and polyunsaturated fat
Petridou E, et al [67] Highly suggestive protective effect of added lipids, which in the Greek diet are primarily represented by olive oil Not mentioned in the abstract in PubMed Not mentioned in the abstract in PubMed
Pancreatic cancer
Kalapothaki V, et al [68] OR = 1.04 (hospital controls)
OR = 0.97 (visitor controls)
These are associated with an increment of about one standard deviation of the energy-adjusted residual of monounsaturated fat intake
Controlling for age, gender, hospital, past residence, years of schooling, cigarette smoking, diabetes mellitus and energy intake
Soler M et al [69] OR = 0.58 0.35-0.97 Adjusted for socio-demographic factors and smoking
La Vecchia and Negri [70] OR 0.76 for the intermediate
OR 0.60 for the highest score of intake
Not mentioned in the abstract available in Pubmed Not mentioned in the abstract in Pubmed
Bladder cancer
Brinkman MT, et al [74] Comparing the highest with the lowest tertiles of olive oil intake between cases and controls using unconditional logistic regression. Middle versus the lowest tertile (OR: 0.62; and the highest versus the lowest tertile (OR: 0.47, p-trend = 0.002) 0.39-0.99
Adjustment was made for age, sex, smoking characteristics, occupational exposures and calorie intake
Riboli E et al [75] Moderate increases in the risk for higher intake of monounsaturated fat were found, which disappeared after correction for saturated fat Not mentioned in the abstract in PubMed Adjusted for tobacco smoking and energy intake.