Insulin Resistance Is Not Just About Obesity

2010-12-06 | |
Last updated: 2010-12-06

Aside from the well known sex hormones, testosterone and estrogen, our general awareness of the many hormones that exist in our bodies is, for the most part, relatively limited. One other hormone that most people will recognize, however, but may not identify as a hormone is insulin. For the millions of diabetics that must take insulin injections several times per day, it can simply be seen as medicine.

In both diabetics taking insulin and in individuals whose bodies naturally produce correct levels of the hormone, insulin serves to control the rate at which the body processes fats and carbohydrates. More generally, it contributes to controlling the rate of energy use. Being that it is a hormone and that hormones often serve numerous roles, insulin is also involved in managing other aspects of bodily function.

In the body, the three types of cells that react the most to insulin levels are muscle, fat and liver cells. Under normal conditions, insulin tells these cells when to absorb glucose (blood sugar) from the blood or when to supply blood with glucose. In some situations, however, the sensitivity of these cells to the levels of insulin in the blood can be reduced and the resulting medical condition is called insulin resistance. When the condition occurs, the levels of glucose in the blood become high resulting in Type 2 diabetes.

For quite some time, the relationship between obesity and resistance to insulin has been known to exist, but the reasons for this connection have been harder to pin down. At the same time, insulin resistance can occur in those of normal weight so the development of the syndrome in patients is not always associated with carrying excess weight. While obesity and a related condition called metabolic syndrome are significant contributors to insulin resistance, in recent years research has started to identify a number of other potential causes for the condition.

Among the contributors to insulin resistance, some are based on factors caused by the body itself while others are related to external conditions. One of the internal causes of the syndrome relates to the existence of chronic inflammation in the body. Researchers from the Xeral-Calde Hospital in Spain found that people with untreated Rheumatoid Arthritis experienced higher levels of insulin resistance than those taking appropriate drugs to control the autoimmune disease. Since the drugs used to control Rheumatoid Arthritis work to reduce inflammation, the researchers theorized that inflammation promotes insulin resistance.

In related research efforts, scientists from the Walter and Eliza Hall Institute determined that the immune system can affect the sensitivity of certain cells to insulin. In particular, they found that specific immune cells that normally target foreign invaders can move into fat tissue and release communication chemicals that cause the fat cells to become insulin resistant. What all this means is that chronic inflammation in the body caused by autoimmune disease or by obesity can result in improper responses to insulin by fat cells.

Another internal cause of insulin resistance, only recently identified, is due to an elevated level of a specific liver hormone. When researchers from Kanazawa University performed genetic analysis on mice with Type 2 diabetes, they found that those mice with the highest levels of insulin resistance also had the greatest level of activity in a specific gene. Knowing that these active genes are responsible for a particular liver hormone, they injected normal weight mice with the hormone and found that the mice developed insulin resistance. This finding means that genetic factors could cause the liver to promote insulin resistance in certain people.

With respect to the external influences that can result in insulin resistance, poor quality sleep is an important factor. Research from Leiden University Medical Center has determined that only a single night with insufficient sleep causes more than 20% overproduction of glucose by the liver. At the same time, insulin sensitivity is reduced by almost 20%. Given that many people survive on a chronic shortage of sleep, there is considerable risk for many individuals to develop resistance to insulin based on this lifestyle factor.

A related research finding regarding the effect of sleep on insulin resistance comes from research published in the American Journal of Respiratory and Critical Care Medicine. There, researchers discovered those with the sleep breathing disorder, sleep apnea, experienced reduced effectiveness in the ability of the body to process glucose. Insulin sensitivity was reduced, glucose was processed less efficiently and the cells of the pancreas worked less effectively in producing insulin all as a result of low levels of oxygen in the blood of those with sleep apnea. The relationship between sleep apnea and insulin resistance existed regardless of the BMI of the patient.

One further external influence that can lead to insulin resistance is air pollution. From research at Ohio State University, scientists studying air particulate pollution found that small animals exposed to such air pollution tended to have more body fat even when fed the same diet as other animals in the study breathing clean air. Within the bodies of these animals, they found that the air particulate caused immune reactions and inflammation by the immune cells within fatty tissues. As in the case of autoimmune disease mentioned earlier, this causes the fat cells to become less sensitive to the controls exerted by insulin. The result is insulin resistance.

With 1 in 3 American adults exposed to high levels of air pollution according to the EPA, air pollution is potentially a significant contributor to both the obesity and diabetes epidemics.

Although insulin resistance is largely a result of obesity, it is not, by any means, the only cause. As a result, for individuals struggling with resistance to insulin, it is important to understand the different factors that can contribute to the condition. Though not all of the contributors are under our direct control, the impact of some factors can be reduced and knowing this allows patients to explore different options for achieving better control of their health.

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Category: Disease Information, General Health, Health Risks

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