Diabetes mellitus, also known simply as diabetes, is a chronic metabolic disorder (De Silva et al. 2012). People who suffer from diabetes cannot produce or effectively use insulin in the body. Due to this insulin imbalance, they have high amounts of glucose in their blood. There are two common types of diabetes, i.e. type 1 diabetes (insulin dependent diabetes mellitus) and type 2 diabetes (noninsulin-dependent diabetes mellitus).

Patients with type 1 diabetes cannot produce insulin, due to the lack of functions of the insulin-secreting beta cells in the pancreas (Meier et al. 2005). They must take insulin continuously every day to stay alive. Type 1 diabetes mostly affects children and adolescent patients, and it represents 5–10% of total diabetes cases worldwide. Patients with type 2 diabetes cannot produce sufficient insulin or cannot effectively metabolize it. This form of the disorder commonly affects elderly people and accounts for 90–95% of all diabetes cases (Hameed et al. 2015). People worldwide suffer from diabetes mellitus and 7% of the world’s adult population is affected by the disease (Philippe and Raccah 2009). In 2017, the largest number of diabetic patients, around 114 million, was recorded in China. Roughly 73 million diabetic patients were recorded in India, and 30 million were recorded in the United States.

There are many negative consequences for patients if diabetes remains untreated, such as blindness, kidney failure, depression, cardiovascular diseases, cancer and even death (Gerstein et al. 2011; Hansen et al. 2012; Huang et al. 2018). Retinopathy (damage of the retina, leading to blindness) and neuropathy (damage of the nervous system) are some of the most severe complications that have been attributed to diabetes (De Silva et al. 2012; Sobngwi et al.

Many Basidiomycota, such as Agaricus bisporus, Cyclocybe aegerita, C. cylindracea and Tremella fuciformis are used as medicine for the treatment or prophylaxis of type 2 diabetes. These mushrooms help patients avoid high levels of glucose because they contain the least amount of digestible carbohydrates in the diet (Poucheret et al. 2006). Bioactive metabolites, which are isolated from medical mushrooms and their cultured mycelia, act as biological antihyperglycemic agents in diabetes treatment (De Silva et al. 2012). Extracts of Inocutis levis (Hymenochaetaceae) have been reported to possess utility as a remedy for diabetes because they increase insulin resistance, insulin sensitivity and glucose uptake in tissues and hence help to control blood glucose levels (Ehsanifard et al. 2017). The fruiting bodies of Antrodia cinnamomea can be used to produce healthy foods and drugs that have anti-diabetes properties (Huang et al. 2018). Grifola frondosa has been used as medicine for type 2 diabetes, and its extracts can effect both hyperglycemia (when a high amount of glucose circulates in the blood) and hyperinsulinemia (when a high level of insulin circulates in the blood) (Poucheret et al. 2006).

Fungal products are sold as remedies for diabetes. Ophiocordyceps sinensis capsules, SX-Fraction, Reishi-Max capsules and Tremella are some of the examples of anti-diabetic products made with medicinal mushrooms (Li et al. 2004; De Silva et al. 2012) and is claimed to decrease fasting blood glucose levels in type 2 diabetes. This medicine can also be used to reduce blood pressure and body weight. SX-Fraction is considered a major alternative for enhancing insulin sensitivity (Preuss et al. 2007). Tremella is a medicinal product used in Chinese medicine; produced from Tremella fuciformis (silver ear mushroom/ white jelly leaf mushroom), it is mainly used for reducing blood glucose and cholesterol levels (Li et al. 2004).

Future investigation is needed to clarify the long-term effects of taking medicinal mushroom products with other drugs. It is necessary to justify the use of medicinal mushroom products as anti-diabetes (De Silva et al. 2012).