Insulin resistance in horses: Part 2: How food turns into elevated insulin and leads to laminitis

Let’s look at insulin resistance in horses. Research released in June 2011 suggests that any elevation in insulin levels in a horse is dangerous.

A horse with elevated insulin and would be similar to a prediabetic person.

There don’t seem to be hard numbers on how many laminitis horses exist in the United States, but there were at least 57 million U.S. adults ages 20 or older who had prediabetes in 2007, according to the Department of Health and Human Services. The United States has about 313 million residents in 2011, which would indicate about one in five people is prediabetic.

Another sobering statistic: Diabetes was the seventh leading cause of death in humans in 2006, according to the National Diabetes Information Clearinghouse.

In people, type 1 diabetes results in the pancreas producing little or no insulin. Type 2 diabetes results in the body not using that insulin effectively and blood glucose reaching dangerous levels.

Horses normally don’t reach the point of being so insulin resistant that they develop diabetes. The problem is what elevated insulin does to their feet.

So what is insulin and blood glucose and why is it killing humans and horses alike?

Insulin is a hormone, a chemical substance produced by the body that is carried to target cells waiting for that hormone to give them instructions. Hormones control and regulate the activity inside those cells and are essential for digestion, metabolism, growth, reproduction and mood control.

The pancreas produces insulin to regulate glucose (the pancreas also produces enzymes to digest food).

Glucose is a carbohydrate. Carbohydrates are found in plants and can be simple or complex.

Glucose is the most simple carbohydrate, the smallest possible sugar molecule. Glucose is a major source of energy for cells.

Starches are complex carbohydrates and can be made up of hundreds or thousands of glucose molecules.

In the small intestine, starch is broken down into individual glucose molecules. The glucose then enters the bloodstream, and the blood glucose level rises. Blood glucose levels rise considerably after a meal.

Blood glucose is carried throughout your body. As elevated blood glucose hits the pancreas, beta cells in the pancreas release insulin. The insulin transports glucose into the cells for use as energy, at which point blood glucose levels drop back to normal. Cells cannot access glucose without the help of insulin.

Glucose that is not needed for energy is turned into glycogen and stored in the liver and muscles. Glycogen is used for brain functioning, maintenance of the central nervous system and performing high-intensity physical activity.

If blood glucose levels get too low, alpha cells in the pancreas release glucagon. Glucagon is a hormone that tells the liver to release glycogen for energy. Insulin and glucagon maintain consistent levels of blood glucose using this pattern.

If blood glucose levels rise too rapidly due to high sugar and starch intake, and the pancreas churns out more insulin, the cells can become less receptive to the onslaught of insulin; over time, it may take more insulin to transport glucose into the cells. This is one form of insulin resistance and leads to excess insulin and glucose in the bloodstream.

Horses have no insulin receptors in their feet. According to research released in 2011 by researchers in Australia, excess insulin in the bloodstream can bind with receptors in the equine foot that were designed to receive insulin-like growth factor 1. Scientists theorize the insulin-like growth factor 1 may have limited use in making the hoof grow outward as a foal turns into a horse. In adult horses, these receptors are fooled by the insulin and bind to it, leading to abnormal hoof growth and laminitis. Insulin-like growth factor 1 also has been shown to be responsible for metastitis of malignant tumors in humans, according to the Animal Health Foundation, which funded the equine insulin research in Australia (http://www.ahf-laminitis.org/2011/06/major-breakthrough-in-understanding.html).

Meanwhile, the excess glucose in the bloodstream due to insulin resistance is converted into fat and stored in adipose tissue, leading to weight gain.

According to the website of Dr. Frank Reilly of Equine Medical and Surgical Associates, after a grain meal, the insulin level goes up three to four times the regular level due to insulin responding to glucose pouring into the bloodstream.  This is normal and lasts a few hours.

In insulin resistance, the base level of insulin can be constantly elevated three times higher, and a grain meal can cause the insulin level to go up 30, 40, 50 or more than 100 times the usual level and remain there for longer periods.

Reilly says people with insulin resistance and diabetes have their lifespans shortened by seven to 12 years; for horses, this translates to 2.5 to 4.5 years, he says.

Horses that develop laminitis may have a considerably shorter lifespan.

Insulin resistance also can be caused by excess fat. Fat cells can release a toxin that interferes with insulin’s action on the cells. The higher the insulin and blood sugar levels, the more excess glucose is converted to fat in adipose tissue, and the fatter the horse gets.

Insulin resistance creates yet another vicious cycle by lowering thyroid levels. The thyroid gland produces hormones that regulate the body’s metabolism. When the thyroid gland produces less of these hormones – thyroxine (T4) and tri-iodothyronine (T3) – metabolism slows, leading to weight gain.

Other causes of insulin resistance are Cushing’s disease and stress (stress leads to increased cortisol, which increases blood glucose and interferes with insulin).

 

 

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