Diabetes impairs your body’s ability to produce or use insulin, which regulates blood glucose levels and generates energy. In type I diabetes, the pancreas does not produce insulin. Without insulin, too much sugar remains in the blood and becomes toxic, leading to fatigue, neuropathy, headaches, blindness and death if left untreated. Type II diabetes is developmental and involves cellular resistance to insulin, which doctors usually don't diagnose until patients report obvious symptoms such as chronic headaches.
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Hyperglycemia occurs when too much glucose circulates in the blood owing to either lack of insulin production in the pancreas or cellular resistance to insulin. Hyperglycemia is a hallmark of both types of diabetes and is a serious condition because high concentrations of glucose are toxic to nerves and blood vessels.
According to the Mayo Clinic, headache is an early symptom of hyperglycemia and frequently includes blurred vision, fatigue and confusion. In the absence of insulin therapy, hyperglycemia can cause a buildup of ketones, which are waste products in the blood and urine, leading to coma and death.
Hypoglycemia occurs when too little glucose is in the blood or getting into cells, where the body uses it for energy. If you have diabetes, hypoglycemia can occur if you mismanage your insulin therapy and take too much. If you don't have diabetes, failure to eat enough nutrients such as carbohydrates that the body can easily break down to glucose molecules can result in hypoglycemia. Hypoglycemia is a serious condition because glucose is the primary source of energy for brain function.
According to the American Heart Association, a dull headache is a common, early sign of hypoglycemia and often includes related symptoms such as dizziness, cloudy vision, sweating, tremors and confusion. If you don't consume simple carbohydrates, such as fruit, pasta juice or breads in response, hypoglycemia can result in convulsions, loss of consciousness and death.
If you have diabetes, especially type II, you are more prone to developing glaucoma, according to the “Professional Guide to Diseases.” In glaucoma, the optic nerve is damaged, which leads to progressive, irreversible blindness. Diabetes is accompanied by a higher incidence of glaucoma because the optic nerve is sensitive to high levels of blood glucose.
Glaucoma is often associated with increased pressure within the eye, which can cause eye pain and headaches. Glaucoma-related headaches often feature stabbing or sharp pain above and behind the eye and sometimes include blurred or sudden loss of vision, halo-like visual phenomena, nausea and vomiting.
Diabetes often leads to neuropathy, which is nerve injury and irritation caused by high levels of glucose in the blood. The brain contains many neurons, including the larger cranial nerves, which can develop neuropathy as a consequence of diabetes. Neuropathy in these nerves results in severe, pounding headaches. As a 2003 case history published in the “Journal of the Royal Society of Medicine” illustrates, diabetic neuropathy–related headaches can be severe and disabling, but doctors often misdiagnose them as migraines.