Insulin

When blood glucose levels rise after a meal, insulin is released to allow glucose to move into tissue cells, especially muscle and adipose (fat) cells, where is it is used for energy production.  Insulin then prompts the liver to either store the remaining excess blood glucose as glycogen for short-term energy storage and/or to use it to produce fatty acids. The fatty acids are eventually used by adipose tissue to synthesize triglycerides to form the basis of a longer term, more concentrated form of energy storage. 

Without insulin, glucose cannot reach most of the body's cells.  Without glucose, the cells starve and blood glucose levels rise to unhealthy levels. This can cause disturbances in normal metabolic processes that result in various disorders, including kidney disease, cardiovascular disease, and vision and neurological problems. Thus, diabetes, a disorder associated with decreased insulin effects, is eventually a life-threatening condition.

People with type 1 diabetes produce very little insulin and so eventually require insulin supplementation therapy. Type 2 diabetes is generally related to insulin resistance, which increases with time. People with type 2 diabetes may initially be managed only with lifestyle modifications such as diet and exercise. Eventually, they may require oral medications that increase the sensitivity of their body's cells to insulin or that stimulate their body to produce more insulin. Type 2 diabetics may also eventually need to use insulin injections to achieve normal glucose levels. 

Insulin resistance may also be seen in those with polycystic ovarian syndrome (PCOS), pre-diabetes or heart disease, metabolic syndrome, and with disorders related to the pituitary or adrenal glands.

Insulin and glucose levels must be in balance.  Hyperinsulinemia is an excess amount of insulin in the blood. Other than in insulin resistance, this is most often seen in people with insulinomas or with an excess amount of administered insulin. Hyperinsulinemia causes low blood sugar (hypoglycemia), which can lead to sweating, palpitations, hunger, confusion, blurred vision, dizziness, fainting, and seizures.  Since the brain is totally dependent on blood glucose as an energy source, severe glucose deprivation due to hyperinsulinemia can lead fairly quickly to insulin shock and death.