Hyperinsulinemia is an abnormally high level of insulin in the bloodstream. This condition is not a disease, but its presence may indicate an underlying disorder.

Chronic hyperinsulinemia often occurs several years before the development of type 2 diabetes. It is most often caused by insulin resistance, which is itself a factor in the development of prediabetes, type 2 diabetes and metabolic syndrome.

Another cause may be insulinoma, a tumor of the pancreas that causes excess production of insulin.

By itself, hyperinsulinemia lacks symptoms, but it can lead to symptoms caused by other conditions. For instance, if hyperinsulinemia causes the level of glucose (blood sugar) to drop, symptoms of hypoglycemia or insulin shock may appear.

Other causes of and contributors to hyperinsulinemia include:

• Obesity
• Impaired liver function
• Smoking
• Pregnancy or breastfeeding
• Polycystic ovarian syndrome

In addition, recent research found that mice injected with a female hormone (estradiol) or a synthetic chemical called bisphenol-A (BPA), which is a common ingredient in consumer plastics, developed chronic hyperinsulinemia after four days. Some other common plastics ingredients including phthalates have been tentatively linked to insulin resistance, male hypogonadism (low levels of testosterone), obesity and hyperinsulinemia.

Short-term (acute) hyperinsulinemia may be due to an overdosage of insulin medication, unusual physical exertion or a large carbohydrate load that requires extra insulin in the blood to process.

Chronic hyperinsunemia is becoming more common in the general population, along with obesity, according to research based on the National Health and Nutrition Examination Survey (NHANES).

Complications of chronic hyperinsulinemia and insulin resistance can include:

• Elevated triglycerides and reduced HDL “good” cholesterol, raising the risk of  heart attack and stroke

• Elevated blood pressure due to increased renal production of the hormone angiotensin
  
  
• Increased cancer risk
  
  
• Higher risk of blood clots due to increased plasminogen activator inhibitor activity
  
  
• Higher risk of gout and kidney stones due to excess uric acid

Hyperinsulinemia manifests most often in children as transient hyperinsulinemia or persistent hyperinsulinemic hypoglycemia of infancy (PHHI). Transient hyperinsulinemia usually occurs when the mother’s diabetes is not under control during Pregnancy and her high glucose levels move across the placenta to the fetus. The fetus responds to this hyperglycemia by secreting extra insulin.

Normally, the increase in insulin secretion does not cause problems until after birth, when the constant supply of high glucose from the placenta is cut off and the newborn’s blood glucose levels fall. This form of hyperinsulinemia usually resolves after a few days of intravenous drip-feeding of glucose. After effective treatment, the problem generally does not recur.

PHHI, which may be due to a genetic defect, can be especially dangerous in infants.  It can lead to hypoglycemia that prevents the brain from receiving glucose, ketones and lactate. This leaves critical brain cells without the energy needed to work. When not promptly and effectively treated, this form of hyperinsulinemia can lead to brain damage. Seizures and coma may precede the death of the cells, which manifests as learning disabilities, cerebral palsy, blindness and even death.