March 1, 2010

Adiponectin, inflammation, diabetes, and heart disease

Humans, like many animals, evolved to be episodic eaters and spend most of their time fasting. Body fat is the main store of energy in the human body. Excess dietary carbohydrates and fat are stored as body fat, in specialized cells known as adipocytes. Excess dietary protein is not normally stored as body fat.

Adipocytes can be seen as being part of a very important and distributed endocrine organ, being responsible for the release of many different hormones into the bloodstream. One of these hormones is adiponectin. Other important hormones secreted by body fat tissue are leptin and tumor necrosis factor-alpha.

Among hormones, adiponectin is particularly interesting because it is negatively correlated with body fat mass. That is, unlike other hormones such as leptin and tumor necrosis factor-alpha, a decrease in body fat mass (a well known health marker) is associated with an increase in adiponectin. This has led some researchers to speculate that adiponectin is a causative factor that promotes health, in addition to being a health marker.

Jung and colleagues (2008; full reference at the end of this post) studied 78 obese individuals (41 females) who participated in an exercise program during 12 weeks. The exercise program involved mostly low intensity aerobic activities, such as brisk walking. The individuals also took an appetite suppressant, with the goal of reducing their calorie intake by about 500 kcal per day.

The table below (click on it to enlarge) shows various measurements for the participants before and after the 12-week intervention.


From the table above we can say that there were significant reductions in weight, body mass index (BMI), waist and hip circumference, waist-to-hip ratio (WHR), total body fat, and total fasting cholesterol and triglycerides. However, the participants were still obese at the end of the intervention, with an average body fat percentage of 35.5.

The table below shows the concentrations of various hormones secreted by body fat tissue, as well as other types of tissue, before and after the 12-week intervention. These hormones are all believed to be health indicators and/or health causes.


We see from the table above that the hormonal changes were all significant (all at the P < .001 level except one, at the P < .05 level), and all indicative of health improvements. The serum concentrations of all hormones decreased, with two exceptions – adiponectin and interleukin-10, which increased. Interleukin-10 is an anti-inflammatory hormone produced by white blood cells. The most significant increase of the two was by far in adiponectin (P = .001, versus P = .041 for interleukin-10).

One of the most promising effects of adiponectin seems to be an increase in insulin sensitivity. This effect appears to be unrelated to any effects on insulin secretion. That is, adiponectin seems to act directly on various cells, including muscle cells, increasing their ability to clear glucose from the blood. This effect seems to be one of the underlying, and previously unknown, reasons why loss of body fat improves health in those who suffer from diabetes type 2.

Increased serum adiponectin has been found to be significantly associated with: decreased body fat and particularly visceral fat, decreased risk of developing diabetes type 2, decreased blood pressure, and decreased fasting triglycerides.

Adiponectin appears to also have anti-inflammatory and athero-protective properties.

On average, women have higher levels of serum adiponectin than men.

According to Giannessi and colleagues (2007) administration of adiponectin in mice has shown positive results. Since research on adiponectin is new, it will probably be some time until related drugs are developed. Giannessi and colleagues also note that fish oil and vanadium salts may increase the synthesis and release of adiponectin.

So far it seems that the most effective way of increasing adiponectin levels is weight loss, particularly through body fat loss. Even as new drugs are developed, this will likely remain the most natural and safe way of increasing adiponectin levels.

All of this helps in the identification of missing links between body fat loss and health improvement. It seems that losing body fat has an effect similar to that of supplementation; it increases the blood concentration of a health-promoting substance - adiponectin!

References:

Giannessi, D., Maltinti, M., & Del Ry, S. (2007). Adiponectin circulating levels: A new emerging biomarker of cardiovascular risk. Pharmacological Research, 56(6), 459-467.

Gil-Campos, M., Cañete, R., & Gil, A. (2004). Adiponectin, the missing link in insulin resistance and obesity. Clinical Nutrition, 23(5), 963-974.

Jung, S.H. et al. (2008). Effect of weight loss on some serum cytokines in human obesity: increase in IL-10 after weight loss. The Journal of Nutritional Biochemistry, 19(6), 371-375.

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