Non-alcoholic fatty liver disease (NAFLD), which has attracted much attention in recent years, is a chronic liver disease and is known as the major cause of liver enzymes disorder in recent decades. The disease is characterized by an increase in fat accumulation by about 5%–10% of the liver's weight in patients without a history of significant consumption of alcohol [1], steatogenic medication or hereditary disorders [2]. This clinicopathological condition is related to a spectrum of liver disorders ranging from steatosis, steatohepatitis and cirrhosis which can be developed to hepatocellular carcinoma over time. Symptoms of nonalcoholic steatohepatitis are presented in 5%–10% of NAFLD cases, and 1.3% of them are developed to cirrhosis [3]. Risk factors of NAFLD include central obesity, type 2 diabetes, dyslipidemia, high blood pressure, sedentary life-style and unhealthy dietary pattern [4]. The prevalence rate of NAFLD is about 33.9% in the general population of Iran [5]. From the precautionary medical point of view, the early diagnosis of this disease can prevent subsequent liver dysfunctions through screening and following appropriate interventions [67].

Quercetin (3-3-4-5-7 pentahydroxy flavones, C₁₅H₁₀O₇) [8], contains 5 hydroxyl groups and numbers of derivatives including galactoside, glucoside, xylose, rhamnose, and glucuronide [9]. It is a polyphenolic compound, which is widely distributed in edible vegetables such as caper, onion, tea, and apple [8]. Quercetin absorption is mainly mediated using the sodium-glucose transporter or lactase phlorizin hydrolase in the enterocytes (mostly in the upper part of the small intestine) [10].

It is almost totally confirmed that oxidative stress plays a crucial role in the pathogenesis of NAFLD [11]. Studies have demonstrated that red blood cell (RBC) destruction and death are mainly mediated by oxidative stress. The continuous exposure to reactive oxygen species (ROS) might cause RBC membrane to be fragile and make them susceptible to damage [1213]. This oxidative damage is largely caused by the reaction of ROS with membrane lipids and proteins, which can affect membrane structure and function. One of the involved possible mechanisms is that oxidative stress has shown to inhibit Ca-ATPase, which can result in elevation of intracellular calcium concentration and subsequent leakage of potassium from the RBC and finally shrinkage of the cell and impaired deformability [14]. Previous studies have also indicated that one-third of NAFLD patients are iron deficient, and red blood cell distribution width (RDW) is significantly increased in NAFLD cases mainly because of inflammatory conditions of this disease [1516]. We hypothesized that quercetin as a potent antioxidant, could protect RBC membrane against oxidative damage, and improve the hematological parameters [171819]. To the best of our knowledge, this is the first study, which evaluates the effect of quercetin supplementation on hematological parameters in NAFLD patients, in the form of a placebo-controlled trial.

Flavonoids and in particular quercetin have controversial effects on hematological parameters. Reviewing the publications over last years, we could not find any related paper, which have been exclusively focused on this topic. In this study, quercetin supplementation significantly increased RBC in intervention group. Flavonoids can increase the production of RBCs by stimulating the secretion of erythropoietin [2021]. Erythrocytes are highly exposed to oxygen and their membrane has high concentration of polyunsaturated fatty acids, which can make them susceptible to oxidative stress [19]. RBCs can also bind polyphenols to their surfaces and play a crucial role in the distribution of polyphenols and protect the erythrocytes membrane against oxidative damage [22]. Quercetin has a great potential in restoring the content of endogenous glutathione in erythrocytes that was depleted by radical generators [18]. In our study, patients had normal ferritin level at baseline. Ferritin level had been significantly decreased in the quercetin group from the baseline to the end of treatment. In enterocytes, quercetin acts as an electron donor and facilitates inorganic iron absorption. However, quercetin can also repress the expression of ferroportin and hephaestin, and subsequently inhibits basolateral iron absorption [2324]. Another possible mechanism is that quercetin may be able to chelate iron in the enterocytes and the quercetin iron complex being retained in the cytosol [25]. Therefore, the reduction in ferritin level may be as the result of functional cellular iron deficiency [26]. Inconsistent with other findings of our study, including increased levels of RBC and hemoglobin, the levels of MCV and MCH significantly decreased in quercetin group. It is possibly due to erythrocytosis which occur in 3% of patients at the early stage of anemia [27].

Supporting our findings in a study conducted by Keskin et al. [20], supplementation with quercetin in streptozotocin induced diabetic rats has not shown any significant changes on MCV, MCH, and MCHC, but RBC count significantly increased in group receiving quercetin. Similarly in another animal study, rabbits receiving 3 different doses of guercetin for 90 days 3 times a week, exhibited slight changes in some hematological parameters including: RBC, hemoglobin, and hematocrit; however, the differences were not significant between these two groups [28]. In contrast with our results, Kasmi et al. [17] demonstrated that co-administration of quercetin (20 mg/kg) improved the levels of platelet and white blood cells in rats received different doses of difenoconazole to liver injury induction [17]. In similar manner, quercetin supplementation (50 mg/kg) had a significant favorable effect on polychlorinated biphenyls induced hematological changes in adult male Wistar rats [29]. Mahmoud et al. [21] indicated that MCV, MCH, and MCHC increased to near normal amounts in diabetic rats receiving citrus flavonoids.

The effect of flavonoids on hematological profile can be simulated to a 2-edged sword. As we described mechanisms previously, flavonoids might either cause or cure anemia. In this work, RBC increased and ferritin decreased significantly in group receiving quercetin compared to those in placebo group but the values of RBC and ferritin still remained in normal range throughout the study period. It is worth mentioning that none of the patients had reported any side-effects and this indicate that the quercetin treatment was well-tolerated by the patients.