There is no harm in eating blueberries in moderation for a long time, but the harm of eating large quantities of blueberries for a long time is indigestion, unfavorable to the blood sugar control of diabetic patients, and damage to the teeth. 1. indigestion: blueberries are rich in dietary fiber, a small amount of daily consumption can promote gastrointestinal motility, but if long-term, large amounts of blueberries, may increase the burden on the stomach and intestines, causing indigestion. 2. Not conducive to blood sugar control in diabetes: blueberries contain a lot of fructose and other sugary substances, although not a high sugar fruit, but if consumed over a long period of time, a large number of fructose substances within the same will affect the blood glucose concentration of diabetic patients, resulting in an increase in blood glucose. 3. Damage to the teeth: blueberries themselves are rich in calcium, phosphorus, potassium and other trace elements, as well as fruit acids and other nutrients, daily consumption can be supplemented to a certain extent the elements needed by the human body. However, fruit acids and other substances are acidic substances, if the normal population long-term, large quantities of blueberries, and after eating without timely cleaning of the mouth, the accumulation of fruit acids and other substances in the mouth may corrode teeth, tooth enamel damage. In summary, long-term large quantities of blueberries will have some harm, daily attention to control the amount of food, generally will not appear the above harm.