NADPH, or nicotinamide adenine dinucleotide phosphate, is a cofactor used in anabolic reactions, such as the Calvin cycle and lipid and nucleic acid syntheses, which require NADPH as a reducing agent. NADPH is the reduced form of NADP+, the oxidized form, and is used by all forms of cellular life. NADPH provides the reducing equivalents, usually hydrogen atoms, for biosynthetic reactions and the oxidation-reduction involved in protecting against the toxicity of reactive oxygen species (ROS), allowing the regeneration of glutathione (GSH). It is also used for anabolic pathways, such as cholesterol synthesis, steroid synthesis, ascorbic acid synthesis, xylitol synthesis, cytosolic fatty acid synthesis. NADPH is often kept at higher concentration in the cytosol than NADP+, to allow for the easy reduction of small molecules into larger macromolecules. NADPH is a cofactor, used to donate electrons and a hydrogens to reactions catalyzed by some enzymes, typically enzymes involved in anabolic pathways that create large molecules. It acts as an electron and hydrogen donor.