A vitamin is an organic compound needed in small quantities that cannot be made in cells. In human nutrition , most vitamins function as coenzymes after modification; for example, all water-soluble vitamins are phosphorylated or are coupled to nucleotides when they are used in cells.  Nicotinamide adenine dinucleotide (NAD + ), a derivative of vitamin B 3 ( niacin ), is an important coenzyme that acts as a hydrogen acceptor. Hundreds of separate types of dehydrogenases remove electrons from their substrates and reduce NAD + into NADH. This reduced form of the coenzyme is then a substrate for any of the reductases in the cell that need to reduce their substrates.  Nicotinamide adenine dinucleotide exists in two related forms in the cell, NADH and NADPH. The NAD + /NADH form is more important in catabolic reactions, while NADP + /NADPH is used in anabolic reactions.
Answer- Fructose does not stimulate the release of insulin. The reduced insulin/glucagon ratio stimulates gluconeogenesis and inhibits glycolysis. That is, glucagon dominates the picture, increasing fructose bisphosphatase activity and leading to formation of glucose. Gluconeogenesis occurs only if fructose in pure form is consumed. However, the more usual situation is consumption of fructose as sugar as a sweetener in a “normal” meal. In other words, fructose is consumed together with starch or sugar. This leads to increases in blood sugar and insulin levels directly with a rapid cessation of gluconeogenesis.