Syzygium cumini (L.) Skeels (Myrtaceae) against diabetes – 125 years of research

Syzygium cumini (L.) Skeels (syn. S. jambolanum DC, Eugenia jambolana Lam.) belongs to the medicinal plants most often recommended as an adjuvant therapy in type 2 diabetes. The plant was extensively studied during the last 125 years, approximately 100 case reports were reported already before the discovery of insulin. After the Second World War, research was concentrated on animal studies. Not all, but many of them reported some success in reducing type 2 diabetes symptoms. However, a state-of-the-art clinical study is still missing. In this review, historical literature dating back to the pre-insulin era was evaluated as were more recent in vitro-, animal-, and in vivo studies. Results were screened for information still useful today and compared to study results achieved in more recent decades. In view of the knowledge summarized here, a successful clinical study should use S. cumini seeds, seed kernels or fruit from India in fairly high doses. Reductions on blood sugar levels by about 30% seem reasonably to be expected. Adverse effects to be expected comprise gastrointestinal disturbances.