Abstract and Introduction
Abstract
Background: Both aging and obesity are related to dysregulated immune function, which may be responsible for increased risk of infection and also chronic non-infectious diseases. Dietary lipids have been shown to impact immune and inflammatory responses and cardio-metabolic risk factors. No information on the impact of olive oil on immune responses of overweight and obese older adults is available.
Objective: We aimed to determine the effect of replacing oils used in a typical American diet with extra virgin olive oil for 3 months on immune responses and cardio-metabolic risk factors in overweight and obese older adults.
Methods: This was a randomized, single-blinded and placebo-controlled trial in 41 overweight or obese participants (aged ≥ 65) who consumed a typical American diet. Participants in the control (CON, n = 21) group were provided with a mixture of corn, soybean oil and butter, and those in the olive oil (OO, n = 20) group, with extra virgin olive oil, to replace substitutable oils in their diet. At baseline and 3 months, we measured blood pressure, biochemical and immunological parameters using fasting blood, and delayed-type hypersensitivity (DTH) skin response.
Results: Compared to the CON group, the OO group showed decreased systolic blood pressure (P < 0.05), a strong trend toward increased plasma HDL-C concentrations (P = 0.06), and increased anti-CD3/anti-CD28 -stimulated T cell proliferation (P < 0.05). No differences were found in T cell phenotype, cytokine production, and DTH response between the two groups.
Conclusions: Our results indicate that substitution of oils used in a typical American diet with extra virgin olive oil in overweight and obese older adults may have cardio-metabolic and immunological health benefits. This trial was registered at clinicaltrials.gov as NCT01903304.
Introduction
Olive oil, which is part of the Mediterranean diet (Med-diet), has been shown to have several health benefits including a capacity to lower the risk of cardiovascular disease (CVD), stroke, and certain forms of cancer. The health benefits of olive oil have been linked mostly to its high content of oleic acid and phenolic compounds.[1–4]
It is well known that aging is associated with dysregulated immune function and increased susceptibility to infectious diseases as well as higher incidence of non-infectious diseases such as CVD, dementia, arthritis, diabetes, cancer, and autoimmune disorders.[5,6] Changes in both cell-mediated immunity and inflammatory responses have been reported with aging. While age-associated changes are observed in almost all aspects of the immune system, a decline in T cell function is believed to be the central defect in immunosenescence.[7–10] Age-related decline in ex vivo antigen and mitogen-stimulated T cell proliferation[11,12] as well as in vivo T cell responses to immunization,[13] and delayed-type hypersensitivity (DTH) skin response[14] have been reported across all species. The decline in T cell-mediated function is attributed somewhat to phenotypic changes in lymphocytes,[15–17] decline in IL-2 production[18] and increase in production of T cell suppressive eicosanoids.[19,20]
On the other hand, aging is associated with chronic inflammation as indicated by higher levels of inflammatory markers such as IL-6 and tumor necrosis factor-alpha (TNF-α), both of which may cause substantial tissue damage and dysfunction[5,21,22] and are believed to be key players in the pathogenesis of several diseases including CVD, rheumatoid arthritis (RA), neurodegenerative diseases, and cancer.[23,24]
Similar to aging, obesity is associated with low-grade, chronic inflammation, which is thought to contribute to the development of several inflammatory diseases.[25,26] Obesity is also shown to impair T cell function and resistance to infection.[26,27] Evidence in both humans and mice has shown that metabolic tissues in the obese (including adipose, liver, muscle, pancreas and brain) compared to those in lean controls secrete more inflammatory mediators/markers such as TNF-α, IL-6 and C reactive protein.[28–32] Studies have shown that increased adherence to the Med-diet enriched by extra virgin olive oil (EVOO) is associated with lower incidence of obesity,[33,34] hypertension[35] and hyperlipidemia.[36]
The limited studies conducted on the immuno-modulatory effect of olive oil have shown inconsistent results.[37,38] Additionally, the majority of these studies have reported the anti-inflammatory and antioxidant effects of olive oil[39–42] with little information available on the impact of olive oil on T cell-mediated immune response in humans. Moreover, few studies have evaluated olive oil's effect on both T cell-mediated function and inflammatory responses, and none of them have been conducted in overweight or obese older adults. Given that both obesity and aging are associated with increased inflammation and impaired T cell function, it is critical to determine the health benefits of olive oil in this particular population. Further, all previous studies focusing on immune function have used refined olive oil rather than EVOO, which contains phenolic compounds that have antioxidant properties not found in refined olive oil. These components have been suggested to be key factors contributing to EVOO's beneficial effects.[1–3]
There is growing evidence that olive oil has some beneficial effects on CVD through different mechanisms including effects on lipid profile, blood pressure, inflammation, and arterial wall function;[35,36,43–45] but to our knowledge, none of those studies have been conducted in overweight or obese older adults. Thus, the current study was conducted to evaluate whether substituting oils in a typical American diet with EVOO would improve T cell-mediated immune function and inflammatory responses as well as factors related to cardio-metabolic status in overweight or obese older adults such as lipid profile and blood pressure.
Nutr Metab. 2015;12(28) © 2015 BioMed Central, Ltd.
