Insulin resistance is a condition in which the body’s insulin receptors are not as receptive to the hormone insulin, causing the pancreas to produce more insulin in order for the body to appropriately convert blood glucose to energy. The condition is thought to be caused by genetic and environmental factors, such as weight and diet. It is also associated with pre-diabetes, a condition of increased blood glucose (hyperglycemia) that increases a person’s risk for diabetes, and metabolic syndrome, a set of conditions related to obesity, diabetes and heart disease. The National Diabetes Information Clearinghouse has more information on the differences between and lab values that define the conditions.
Though some of the factors involved in insulin resistance are known, the exact causes of the disorder are not known. As such, the effect of insulin resistance on other body processes (versus simultaneous pathological processes) is not entirely clear. It is akin to asking, “what came first, the chicken or the egg?” However, some conditions are known to be associated with insulin resistance and to share hormone signals.
The dysfunction in glucose metabolism caused by insulin resistance also leads to dysfunctional fat (lipid) metabolism. The accumulation of fat leads to fatty liver. Tumor necrosis factor (TNF) alpha is an inflammatory hormone that has been linked to both fatty liver and insulin resistance (example: Borst, The role of TNF-alpha in insulin resistance, Endocrine, 2004). In addition, a number of cytokines and inflammatory mediators have been associated with the dietary components of insulin resistance (see figures from Shoelsen, Lee and Goldfine, Journal of Clinical Investigation, 2006).
Studies of sports supplements have found increased insulin levels (due to ingested carbohydrates) to effect the production of testosterone. An inverse relationship has been considered though – low testosterone levels have been suggested to decrease insulin sensitivity (i.e. lead to insulin resistance). A similar role has been suggested for estrogen.
As outlined by MedicineNet, women with insulin resistance tend to have reproductive disorders, such as infertility or difficulty conceiving, polycystic ovarian syndrome and irregular menses, further suggesting a link between insulin resistance and the female hormones. Insulin resistance is also thought to cause an abnormal production of male hormones (called androgens) by the ovaries, resulting in hyperandrogenism, though the exact mechanism is not yet clear. Sex hormones have also been associated with atherosclerosis, a known complication of insulin resistance and a risk factor for heart attack and stroke, which are also considered to be complications of insulin resistance.
The sport supplement studies also found that carbohydrate ingestion (which increases insulin levels) increases growth hormone levels. Patients with the disorder have been found, for yet unknown reasons, to have increased skin tag growth. What is known is that insulin resistance has been associated with increased signaling via insulin-like growth factor, which is linked to the activity of growth hormone and potentially associated with the increased cell growth seen in insulin resistance.
Insulin resistance and hormones
As pointed out by research, insulin resistance affects not only insulin, but also a range of other hormones. Work is ongoing to discern its role in metabolic syndrome and other inflammatory imbalances.