**1. Introduction**

The prevalence of diabetes has increased rapidly over the past few years, mainly in low to middle-income countries, and became one of the major causes of premature death worldwide. According to the WHO statistics, 422 million people were estimated as diabetes in 2014, and 1.6 million deaths were reported [1]. The International Diabetes Federation estimated that the world's diabetic population has increased to 592 million by 2035. The largest number of diabetes cases was reported in the Western Pacific region (132 million), while 71.4 million diabetes cases were reported in the South Asian area [2].

Diabetes mellitus is a chronic metabolic disease characterized by hyperglycemia due to defects in insulin secretion, insulin action, or both. It is mainly classified

as insulin-dependent diabetes mellitus (Type 1 DM) and non-insulin-dependent diabetes mellitus (type 2 DM). Type 1 DM is associated with deficiency of insulin, which occurs due to the destruction of pancreatic ß-cells via an autoimmune process. In contrast, type 2 DM is linked with insulin resistance, which reduces insulin utilization by peripheral tissues and results in hyperglycemia and obesity [3]. Type 2 DM became a major health problem worldwide associated with microvascular and macrovascular health complications. Microvascular and microvascular complications include diabetic retinopathy, neuropathy, nephropathy, and cerebrovascular diseases, peripheral arterial diseases, respectively [4]. Therefore, natural therapeutic approaches [5] should be developed to maintain the blood glucose level and long-term complications in patients with type 2 DM.

As currently available treatment regimens for type 2 DM have adverse side effects, it is necessary to search for an effective drug that helps maintain the blood glucose level and complications in patients with type 2 DM. Even though most of the researchers focused on herbal medicine, none have a full beneficial effect on curing patients with type 2 DM [6]. Hence, it is worth emphasizing marine seaweeds as they have been identified as a rich source of promising bioactive compounds synthesized from their biochemical and physiological mechanisms. Besides, most marine seaweeds are survived in extremely harsh environments, which provide enormous potential to produce complex bioactive compounds to withstand extreme conditions. As a result, the composition of the bioactive compounds in marine seaweeds can vary depending on the geographic area and seasonal changes [7]. As most marine seaweeds are a potential source of bioactive compounds with various therapeutic effects, this chapter mainly emphasizes the pharmacological uses of marine algae as an anti-diabetic therapy.
