Diabetes Mellitus: Primary & Secondary Causes

Maya Barake, MD
Specialist in Endocrinology, Metabolism & Neuroendocrinology
Bellevue & Clemenceau Medical Centers

Glucose level in the blood is usually maintained normal by two hormones produced by the pancreas: insulin and glucagon. Insulin is secreted when glucose is high. It helps glucose enter our cells where it is the main source of energy, and as a result glucose decreases in the blood. Glucagon has the opposite effect; it is secreted when glucose is low. It then helps glucose stored in our liver to be released in blood.

Diabetes is a disease, which involves a persistent elevation in blood glucose be- cause of a problem in the above system. We can divide the causes of diabetes into two large categories: Primary (where diabetes develops alone) and secondary (where diabetes results from another disease or from taking a medication).


There are two main types of diabetes that people can develop: type 1 & type 2.

90% of people who have diabetes have type 2. In this condition, the pancreas produces insulin but cells do not respond to it as they should. This is called “insulin resistance”. Type 2 diabetes usually occurs in people who are obese; who are not very active, or is inherited.

Type 1 diabetes accounts for 5-10% of cases. It occurs when the pancreas is unable to produce insulin.


While most people who develop diabetes have type 1 or type 2, around 5% of people develop diabetes because of another disease they have or because of a medication they are taking.


Since the pancreas is responsible of controlling glucose levels, any disease that occurs in the pancreas (like repetitive inflammation, trauma, etc) may cause diabetes. However, not all patients who have problems in the pancreas will become diabetic. This is related to the part of the pancreas that is diseased. Diabetes that occurs in this condition most often requires insulin. Surgeries to the pancreas may also result in secondary diabetes.


Although insulin and glucagon are the main hormones that control glucose, other hormones can also increase blood glucose levels when produced in excess. In this case, treating the endocrine disease may also treat and/or cure diabetes.

Endocrine diseases that can cause diabetes include Cushing’s syndrome, a condition where the body has excess cortisol. Cortisol can be produced in the body or it can be taken as a medication. In this case, diabetes usually comes with elevated blood pressure, increase in weight, and skin and/or bone problems. Other diseases include acromegaly (where the body produces excess growth hormone), and pheochromocytoma (presence of excess adrenaline or noradrenaline). Sometimes excess thyroid hormone may also affect blood glucose. In all these cases, diabetes usually comes with other complaints.


Certain medications can cause diabetes in certain individuals as they affect insulin production or action. The drug that most commonly increases glucose levels is cortisol, usually given for diseases of the skin, lungs and sometimes allergies. Medications that suppress immunity like cyclosporine and tacrolimus (given after kidney transplant) can also cause diabetes. Certain antibiotics, some of the drugs given for HIV infection and some drugs that treat psychiatric diseases are also known to cause increased glucose. It is important to note that these medications do not cause diabetes in everyone but usually in individuals with risk factors for diabetes.

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