Normal blood sugar levels for a person over 20 with diabetes varies throughout the day, with a normal fasting glucose level being below 100, states WebMD. Before a meal, ideal levels are 70 to 130, after a meal less than 180, and at bedtime 100 to 140.
For a person with diabetes who takes insulin, an ideal level before exercise is at least 100, notes WebMD. Keeping track of blood sugar levels throughout the day and logging results, along with time, date and recent activities helps control overall health. Controlling blood sugar levels helps reduce risk of heart attack and stroke as well as complications with the kidneys, eyes and nerves.