Abstract
Objective: Studies have reported controversial findings regarding the flaxseed oil effect on antioxidant status biomarkers. The present meta-analysis aimed to determine the impact of flaxseed oil on the serum level of biomarkers of oxidative stress. Methods: A systematic search was conducted up to November 2020 on PubMed, Embase, Web of Science, Scopus, and Cochrane Central Library. Random-effects model was employed to perform meta-analysis. Subgroup analysis was carried out to determine the effect across different ranges of dosages and durations. Results: Eight trials were included with a total sample size of 429 individuals with a mean age range of 25 to 70 years. The results indicated that flaxseed oil supplementation led to a significant decrease in malondialdehyde (MDA) levels (SMD: -0.52 μmol/L; 95% CI: -0.89, -0.15; P=0.006, I 2 = 71.3, P < 0.001) and increase in total antioxidant capacity (TAC) levels (WMD: 82.84 mmol/L; 95% CI: 19.80, 145.87; P=0.006, I 2 = 92.7, P < 0.001). No significant effect was observed on glutathione (GSH). Conclusion: Our findings revealed that flaxseed oil supplementation might play a beneficial role in the reinforcement of the antioxidant defense system and amelioration of oxidative stress in adults.
Link to Full Text
Key Points
Oxidative stress (OS) is an imperfection in the balance between reactive oxygen/nitrogen species (ROS/RNS) and the total antioxidant capacity of organisms. An increase in the oxidation of the biomolecules and dysfunction of the antioxidant system subscribe the pathogenesis of the chronic disease including atherosclerosis, type 2 diabetes (T2DM), fatty liver diseases, hypertension, and neurological diseases. Different markers have been used in studies to evaluate this balance between ROS/RNS production and antioxidant system function such as total antioxidant capacity (TAC), malondialdehyde (MDA), and glutathione (GSH). MDA, as the main determinant of the oxidation status in the body, is a by-product in the lipid peroxidation pathway.
A previous meta-analysis published in 2020 assessed the antioxidant effects of flaxseed oil supplementation on biomarkers of oxidative stress using 5 studies. The results showed that flaxseed oil reduces MDA and increases TAC levels, but no significant effect was observed on GSH levels although changes of some biomarkers of oxidative stress have not been assayed in detail. Therefore, the present meta-analysis was conducted to summarize current evidence and estimate the direction and magnitude of the effects of flaxseed oil supplementation on oxidative stress biomarkers in adults.
In this meta-analysis, the results showed that flaxseed oil supplementation significantly decreases MDA serum levels and increases the TAC levels significantly. No significant effect was observed on GSH levels. After subgroup analysis based on administered dosage, sample size, mean age, and duration, the level of heterogeneity was reduced. Flaxseed oil supplementation for ≤8 weeks significantly reduced MDA levels, whereas interventions for >8 weeks did not. In addition, the dose-dependent subgroup analysis showed that a flaxseed oil dosage of ≤2000 mg/day led to a significant decrease in the MDA level. Some leading causes of the observed variation in the findings may be food intake, physical activity, and the participant’s clinical state. Flaxseed oil affects MDA via its significant content of omega-3 and phytochemicals.
Increasing TAC levels via flaxseed oil supplementation was another important finding of this meta-analysis. The mean age of participants and flaxseed type were found to be potential sources of heterogeneity in subgroup analysis.
Results obtained from the analysis showed that flaxseed oil supplementation had no significant effect on the GSH level. The mean age of participants was found to be a possible source of heterogeneity in subgroup analyses. The heterogeneity was more considerable in studies with mean age >48. However, GSH levels were significantly increased in participants aged <48 and in the studies that used flaxseed oil-derived omega-3 fatty acids.
Overall, the results of this meta-analysis showed that flaxseed oil supplementation reduced MDA levels. Moreover, flaxseed oil supplementation increased the TAC levels but was not effective on GSH levels. It seems that flaxseed oil could be considered as an effective agent in augmenting the antioxidant defense system which indicates the efficiency of being set in the regular diet. However, additional clinical trials with larger sample sizes in various health conditions are required to clarify this more accurately.