A new study out of Italy has found that vitamin D supplementation increases adiponectin levels in pediatric obesity.
Adiponectin is a protein hormone secreted from adipose tissue into the bloodstream. Adipose tissue is body fat. You need adiponectin for various metabolic processes including regulating blood glucose and oxidizing fatty acid which provides energy to cells. Low levels of adiponectin has been associated with increased insulin resistance and an increased risk for cardiovascular disease and type 2 diabetes.
Individuals with obesity often have low levels of adiponectin. The mechanism behind this still remains relatively unclear. It is known that there is an inverse relationship between body fat and serum adiponectin level. A few studies have shown that obesity is associated with a down regulation of the adiponectin gene expression, which may be the mechanism at play.
Additionally, people with obesity are often vitamin D deficient, most often the case because the more you weigh, the more vitamin D you need. The heavier you are, the more difficult it is to fulfill your vitamin D requirements.
Because of the link between vitamin D deficiency and obesity, and the link between low adiponectin and obesity, researchers in the present study wanted to know, is there then a link between vitamin D and serum adiponectin levels in obese children?
So, they recruited 97 participants between the ages of 5 and 18 years old. Participants were included if they were healthy, had a BMI exceeding the 95th percentile and had vitamin D levels either less than 15 ng/ml or greater than 30 ng/ml.
In total, 42 participants were included in the final analysis. They split the group up with 18 vitamin D deficient participants (levels of 5.4 – 14.2 ng/ml) in one group and 24 vitamin D sufficient participants (levels of 31.20 – 50 ng/ml) in another group.
After a 12 hour overnight fast, the researchers took blood samples for a proteomic, glucose, insulin and vitamin D analysis.
After baseline comparison between groups, the researchers found:
- Participants in the vitamin D deficient group were more obese, more insulin-resistant, and had higher fasting glucose compared to the sufficient group.
- A two-dimensional electrophoresis analysis used to analyze proteins suggested that adiponectin was the protein downregulated in both groups.
- After additional analysis, it was confirmed that adiponectin was even lower in the vitamin D deficient group.
Next, the researchers conducted a follow-up study to see the effect of vitamin D supplementation on adiponectin levels. Ten individuals from the vitamin D deficient group were given 3,000 IU/week for one year. In this study, the researchers found:
- Average vitamin D levels increased from 10.6 ng/ml to 20.4 ng/ml.
- Fasting glucose decreased from 88.0 mg/dl to 81.5 mg/dl.
- A significant gradual and modest improvement in total adiponectin over the twelve month period.
- After measuring visceral adiposity index, body adiposity index, and ghrelin, it was determined that there was no weight loss over the duration of the study.
Finally, the researchers analyzed these effects at the cellular level to find that 1,25(OH)2D, the activated form of vitamin D, directly led to a significant increase in total adiponectin secretion over time.
The researchers concluded,
“In the present study, we used a proteomic approach to study the global plasmatic changes between vitamin D deficient and normal obese pediatric subjects identifying that the multimeric forms of adiponectin, in particular the high molecular weight form are plasmatic biomarkers that could provide a mechanistic link between vitamin D deficiency and pediatric obesity, with total plasma levels increasing with cholecalciferol supplementation.”
The researchers also noted a few limitations. For one, they didn’t measure true body fat measurements, however they state that measuring BMI and visceral adiposity index are good alternative measurements. Also, since this was just a pilot study, more studies are needed to fully understand this biological mechanism and to see if more than just adiponectin is involved.
So why is this study important? Theoretically, adiponectin may be able to help those with obesity in protecting against cardiovascular disease and help manage or improve type 2 diabetes through glucose regulation and increased insulin sensitivity. If vitamin D supplementation may be able to increase adiponectin levels, then it may be of help to certain obesity related complications. Larger and longer randomized controlled trials are sorely needed so we can confirm this mechanism.