Novel findings regarding Alzheimer’s and respiratory disease
Dr. Larsson highlights two novel findings of this study.
First, it showed a 27% reduction in risk of dementia-related mortality for those in the highest versus lowest category of olive oil consumption. “Considering the lack of preventive strategies for Alzheimer’s disease and the high morbidity and mortality related to this disease, this finding, if confirmed, is of great public health importance,” she said.
Second, the study reported an inverse association of olive oil consumption with risk of respiratory disease mortality. “Because residual confounding from smoking cannot be ruled out,” Dr. Larsson said, “this finding is tentative and requires confirmation in a study that is less susceptible to confounding, such as a randomized trial.”
And although the current study and previous studies have found that consumption of olive oil may have health benefits, she identified several remaining questions.
“Are the associations causal or spurious?” she noted. Is olive oil consumption protective for certain cardiovascular diseases like stroke or atrial fibrillation only, as has been shown in other studies, or also for other major diseases and causes of death, she added. What is the amount of olive oil required for a protective effect?
Further, is the potential effect related to monounsaturated fatty acids (MUFAs) or phenolic compounds; that is, “is the protective effect confined to polyphenol-rich extra-virgin olive oil or are refined olive oil and other vegetable oils as beneficial? More research is needed to address these questions,” she concludes.
“Further studies are needed,” the researchers agree, “to confirm the association of olive oil consumption with reduced mortality, clarify the mechanisms responsible, and quantify the dose/volume boundaries around this effect.”
Virgin olive oil has more polyphenols
Olive oil, a key component of the Mediterranean diet, is high in MUFAs, especially oleic acid, as well as vitamin E and polyphenols, which contribute to its anti-inflammatory and antioxidant properties, the researchers explain.
Virgin olive oil, produced by mechanically pressing ripe olives, contains multiple bioactive and antioxidant components and has an acidity of less than 1.5%. And extra-virgin olive oil is produced the same way but has a higher quality, more intense taste, and lower acidity (less than 1%).
Refined or processed olive oil contains less phytochemicals, as some are lost during processing; it usually contains more than 80% refined oil, plus virgin oil added back to enhance flavor, and may also be labeled “pure” or “light.” However, refined olive oil “still has a good amount of healthy fatty acids but less bioactive compounds,” Dr. Guasch-Ferré noted.
Until now, no large prospective study has examined the link between olive oil intake and all-cause and cause-specific mortality in a U.S. population, where olive oil consumption is limited, compared with Mediterranean countries.
The researchers identified 60,582 women in the Nurses’ Health Study and 31,801 men in the Health Professionals Follow-up Study who were free of CVD or cancer in 1990, the first year that food frequency questionnaires in these studies asked about olive oil.
Participants replied to questionnaires every 4 years that asked about use of olive oil (for salad dressing, baking, frying, sautéing, and spreading on bread), other vegetable oils (for example, corn, safflower, soybean, canola oil), margarine, butter, and dairy fat. The researchers averaged the consumption of these fats during the follow-up years.
From 1990 to 2019, the average consumption of olive oil increased from 1.6 g/day to 4 g/day. Margarine in the 1990s contained saturated fat and trans fats, whereas more recently margarine contains beneficial olive oil or vegetable fat, Dr. Guasch-Ferré noted.
Baseline olive oil consumption in this U.S. population “differed remarkably” from that in the Spanish population in the PREDIMED (Prevención con Dieta Mediterránea) trial, which was, on average, 20-22 g/day of extra-virgin olive oil and 16-18 g/day of refined/mixed olive oil, Larsson pointed out.
Because olive oil consumption was so low in this U.S. study, the researchers did not distinguish between virgin/extra-virgin olive oil and refined/processed olive oil.
The participants were almost all White (99%) and were generally healthier than the average U.S. population; on average, they had a body mass index of 25.3-25.8 kg/m2 and ate 4.8-7.2 fruits and vegetables/day.
Those with the highest olive oil consumption were more physically active, had a healthier diet, were more likely to have Southern European or Mediterranean ancestry, and were less likely to smoke.
During 28 years of follow-up, 36,856 participants died. The researchers classified the deaths into five categories: CVD, cancer, neurodegenerative disease (including Alzheimer’s disease, Parkinson’s disease, multiple sclerosis), respiratory disease (such as chronic obstructive pulmonary disease), and all other causes (including suicide, injury, infections, diabetes, and kidney disease).
After adjusting for multiple confounders, compared with participants who rarely or never consumed olive oil, those in the highest quartile for olive oil consumption had a decreased risk of death from all causes (hazard ratio, 0.81; 95% confidence interval, 0.78 - 0.84) and from CVD (HR, 0.81; 95% CI, 0.75-0.87), cancer (HR, 0.83; 95% CI, 0.78-0.89), neurodegenerative disease (HR, 0.71; 95% CI, 0.64-0.78), and respiratory disease (HR, 0.82; 95% CI, 0.72-0.93).
There was no decrease in mortality in models where the researchers substituted olive oil for vegetable oil, suggesting that vegetable oils may provide similar health benefits as olive oil.
The research was supported by grants from the National Institutes of Health. Dr. Guasch-Ferré was supported by the American Diabetes Association. Coauthor Salas-Salvadó is partially supported by the Catalan Institution for Research and Advanced Studies and received the virgin olive oil that was used in the PREDIMED and PREDIMED-Plus studies from the Patrimonio Communal Olivalero and Hojiblanca (Málaga, Spain). The other study authors and Dr. Larsson have reported no relevant financial relationships.
A version of this article first appeared on Medscape.com.