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The blood sug­ar con­cen­tra­tion or blood glu­cose lev­el is the amount of glu­cose (sug­ar) present in the blood of a human or ani­mal. The body nat­u­ral­ly tight­ly reg­u­lates blood glu­cose lev­els as a part of meta­bol­ic home­osta­sis. With some excep­tions, glu­cose is the pri­ma­ry source of ener­gy for the body’s cells, and blood lipids (in the form of fats and oils) are pri­mar­i­ly a com­pact ener­gy store. Glu­cose is trans­port­ed from the intestines or liv­er to body cells via the blood­stream, and is made avail­able for cell absorp­tion via the hor­mone insulin, pro­duced by the body pri­mar­i­ly in the pan­creas. Glu­cose lev­els are usu­al­ly low­est in the morn­ing, before the first meal of the day (termed “the fast­ing lev­el”), and rise after meals for an hour or two by a few mil­limo­lar. Blood sug­ar lev­els out­side the nor­mal range may be an indi­ca­tor of a med­ical con­di­tion. A per­sis­tent­ly high lev­el is referred to as hyper­glycemia; low lev­els are referred to as hypo­glycemia. Dia­betes mel­li­tus is char­ac­ter­ized by per­sis­tent hyper­glycemia from any of sev­er­al caus­es, and is the most promi­nent dis­ease relat­ed to fail­ure of blood sug­ar reg­u­la­tion. Intake of alco­hol caus­es an ini­tial surge in blood sug­ar, and lat­er tends to cause lev­els to fall. Also, cer­tain drugs can increase or decrease glu­cose levels.