Spice plant Allium cepa: Dietary supplement for treatment of type 2 diabetes mellitus

Abstract

Objective

Diabetes mellitus (DM) is associated with significant morbidity and mortality and its prevalence is increasing worldwide. Although conventional antidiabetic agents are known to ameliorate the symptoms of diabetes, they also may cause adverse effects. The purpose of this review was to organize and discuss various studies that have been previously conducted indicating the efficacy of Allium cepa in DM.

Methods

A comprehensive English literature search was conducted using various electronic search databases. Different search terms were used and an advanced search was conducted by combining all the search fields in abstracts, keywords, and titles.

Results

Allium cepa, a spice plant, is commonly known as onion and belongs to the family liliaceae. Since ancient times, it has been used traditionally for the treatment of different diseases. Among various activities of Allium cepa, regulation of hypoglycemic activity is considered one of its important effects in DM. Sulfur compounds including S-methylcysteine and flavonoids such as quercetin are mainly responsible for the hypoglycemic activity of Allium cepa. S-methylcysteine and flavonoids help to decrease the levels of blood glucose, serum lipids, oxidative stress, and lipid peroxidation, as well as increasing antioxidant enzyme activity and insulin secretion. Extracts of onion also have been shown to have hypoglycemic and hypolipidemic effects by normalizing the activities of liver hexokinase, glucose 6-phosphatase and HMG coenzyme-A reductase. In preliminarily clinical trials, patients with diabetes safely consumed slices of Allium cepa, exhibiting sufficient hypoglycemic activity. In the future, further studies must be conducted to investigate and confirm the hypoglycemic activities of Allium cepa and its constituents and/or their synthetic analogs.

Conclusion

This review will not only elucidate the nutritious facts of Allium cepa but may also help in understanding the molecular basis of its effects in DM. This review will explore in particular the medicinal characteristics of Allium cepa supporting that the consumption of dietary onion could lower blood glucose levels, thus contributing to the reduction of risk factors associated with DM.

Introduction

Diabetes mellitus (DM) is a serious chronic and heterogeneous disease of diverse disorders affecting the metabolism of proteins, fat, and carbohydrates [1], [2]. Major factors that contribute to the prevalence and progress of DM include hyperglycemia, dyslipidemia, insulin resistance, impaired insulin secretion, and the activation of proinflammatory mediators [2], [3]. DM is considered one of the most frequent lifestyle diseases [4].

Type 2 diabetes mellitus (T2DM) is known as non-insulin–dependent diabetes mellitus in which resistance to insulin, abnormal insulin secretion, elevated levels of insulin, or all three have been observed. Among diabetic cases diagnosed, >95% are T2DM [2]. Existing conventional and synthetic antidiabetic agents for the treatment of T2DM are well known for potential adverse effects such as weight gain, acute hypoglycemia, edema, hepatic and cardiac defects, and gastric and respiratory complications [2], which have motivated researchers and scientists to investigate new avenues for the treatment of DM [5], [6], [7], [8], [9], [10], [11]. One area being researched is the therapeutic use of medicinal plants that have shown hypoglycemic properties. Herbal plants are less toxic and free from side effects compared with synthetic drugs [12], [13], which are restricted in terms of efficacy and side effects [2], [14], [15]. In Asian communities, herbal agents are most commonly used as an effective remedy for the treatment of many diseases [16], [17], [18]. Use of medicinal plants for treatment of DM is most important where resources are meager and insufficient [19], [20], [21], [22], [23], [24]. The families of plants that have shown potent hypoglycemic effects include Leguminoseae, Lamiaceae, Liliaceae, Cucurbitaceae, Asteraceae, Moraceae, Rosaceae, Euphorbiaceae, Araliaceae and Ranunculaceae [19], [25], [26].

In this present study, we have summarized general properties of Allium cepa. To understand the molecular basis of its effects in DM, we explore Allium cepa's medicinal characteristics by discussing various experimental studies performed to identify the hypoglycemic properties of onion, its extracts, juices, essential oils, and constituents. Here, we have tried to confirm that consumption of dietary onion could help lower blood glucose levels, thus contributing to a reduction in risk factors associated with DM.