Mannitol is a six carbon polyol extracted from brown algae cells. It has two configurations: D and L. L configuration is a synthetic product, which does not exist in nature. D configuration is widely distributed in the plant kingdom. In particular, the content of mannitol in marine brown algae of kelp family is very high. Mannitol is a storage material in brown algae cells. Kelp and other large brown algae are the main raw materials for the extraction of mannitol. Mannitol extracted from kelp and nicotinic acid mannitol ester synthesized from nicotinic acid can significantly alleviate angina pectoris and have a good curative effect on hyperlipidemia. It can treat diseases such as high cholesterol, hypertension and arteriosclerosis. Mannitol is also a dehydrating agent, which can be used in medical treatment. When its 20% solution is injected into the vein, it is rarely decomposed in the body, resulting in a temporary increase in blood osmotic pressure, so as to make the water in the tissue enter the blood, so as to reduce the edema of the tissue. When mannitol is filtered from the glomerulus, it is not easy to be reabsorbed in the renal tubules, which increases the osmotic pressure of the original urine in the renal tubules and brings out a large amount of water to play a diuretic role.