In obesity, cells called adipocytes increase. Adipocytes are fat cells and are the main make-up of adipose, or fat, tissue. These cells, along with adipose tissue as a whole, help store energy from food as fat. An increase in food consumption leads to an increase in storage of energy and a subsequent increase in total adipocytes.
It has been hypothesized that a decrease in the number of adipocytes can help in weight loss and help with weight maintenance. This decrease in adipocytes would be achieved through inducing apoptosis, or cell death, of the adipocytes.
Researchers have been curious if vitamin D plays a role at all in adipocyte apoptosis (death of adipocyte cells). Vitamin D receptors are found on cells all over the body. With cancer cells in particular, vitamin D has been shown to help induce apoptosis.
If vitamin D did play a role in adipocyte apoptosis, then vitamin D may indeed have a minor role in weight management and loss.
In the present study, researchers set out to investigate this potential mechanism.
They fed mice a high fat diet to induce obesity. The researchers then randomly assigned the mice to either a treatment or control group. The treatment group consisted of three separate diets. One of the diets consisted of high calcium intake, one consisted of high vitamin D intake, and one consisted of high calcium and vitamin D intake. The mice receiving vitamin D received ten times the recommended amount usually given to mice. The control group, on the other hand, received a diet containing the recommended amount of calcium and vitamin D.
The mice were fed these diets for 10 weeks. After the 10 weeks, the researchers measured weight, vitamin D status and calcium metabolism. Here is what the researchers found:
- The mice that received calcium, vitamin D or both had less body weight gain and total body weight compared to the control mice.
- The mice fed calcium and/or vitamin D had lower fasting glucose concentrations compared to the control mice.
- The mice on all three treatments showed induced apoptosis of adipocytes.
- Overall, the mice on either calcium, vitamin D or both showed more apoptosis of adipocytes compared to the control group.
The researchers concluded,
“The results obtained show that mice fed a [high fat] diet with an increased level of Ca (1.2%) and high oral intake of vitamin D3 (25 mcg/kg of body weight) demonstrate a decrease body and fat weight gain (epididymal and peritoneal [white adipose tissue] depots) and significant improved markers of adiposity and vitamin D status.”
The researchers suggest a possible detailed mechanism for this induced apoptosis. Previously, the researchers showed that the active form of vitamin D, 1,25(OH)2D3, induced apoptosis of adipocytes in mice and that the active form was mediated by Ca2+ signaling. Ca2+ is the ion form of calcium and is an important messenger for various processes in the cell, including inducing cell death.
Two enzymes signaled by Ca2+ are calpain and caspase-12. Calpain, in particular, has been suggested to play a direct role in inducing apoptosis. In this study, the researchers found that both calpain and caspase-12 were increased to normal levels by vitamin D but not by calcium. Thus, the researchers propose that the mechanism behind apoptosis of adipocytes is through vitamin D’s ability to increase levels of calpain and caspase-12.
We have covered vitamin D and obesity many times before on this blog. While research shows there is a link between vitamin D and obesity, research shows that obesity more so causes vitamin D deficiency than vitamin D deficiency causes obesity. However, mechanistic research continues to suggest that vitamin D plays a causal role in obesity, albeit it may be minor. Further research is needed to understand how vitamin D affects obesity.