VITAMIN D: THE ANABOLIC PROHORMONE
Vitamin D is a fat-soluble, steroid-like vitamin that functions as a prohormone regulating the expression of roughly three percent of the human genome—giving vitamin D influence over most cell types within the human body.1.2 Some of the lean muscle-promoting properties associated with vitamin D likely stem from the similar chemical structure between vitamin D and steroid molecules like testosterone. Studies have shown that vitamin D can directly bind the testosterone receptor3, turning on the same lean muscle-developing genes normally triggered by testosterone. In addition, vitamin D can also bind and activate the vitamin D receptor, turning on several other genes that elicit increased lean muscle.4 Other lean muscle-promoting properties associated with vitamin D are also caused by the rather unique ability of vitamin D to increase the expression of several genes involved in the production of testosterone4, ultimately boosting testosterone biosynthesis. In fact, a strong correlation between vitamin D and testosterone has been shown—where low vitamin D levels correlate with low testosterone measurements, while high amounts of vitamin D correlate with high testosterone—signifying that vitamin D buoys the production of testosterone.
Like many other vitamins, vitamin D also promotes overall health. Some of the health benefits associated with vitamin D include greater absorption and metabolism of calcium and phosphorous for improved bone health. Even more importantly, low levels of vitamin D correlate tightly with several life-threatening diseases such as cancer5, cardiovascular disease6, and obesity7, indicating the requirement of vitamin D to counteract these disorders.
VITAMIN D BURNS BODY FAT
In addition to the lean muscle-enhancing and health-promoting influence of vitamin D, accumulating evidence shows that vitamin D deficiency is prevalent in obese people-indicating that more vitamin D intake could help reduce body fat, particularly as higher levels of vitamin Dtend to reduce body fat.8,9 While the relationship between vitamin D and fat loss is well documented, the mechanisms by which this vitamin reduces body fat have not been very well characterized until recently, in a study by Chang et al.10, which found several key mechanisms affected by vitamin D that reduced fat. More specifically, this investigation showed that the most biologically active form of vitamin D—vitamin D3—caused a substantial decrease in intracellular fat accumulation in isolated fat cells by increasing the expression of several key genes involved in fatty acid oxidation, which effectively increased fatty acid oxidation activity—resulting in more fat being burned for energy. This study also showed that vitamin D3 amplified the expression of numerous lipolytic enzymes that break down fat. Naturally, the higher lipolytic enzyme count contributed even more to the decline in intracellular fat seen in this study.
In addition to all of the fat-burning effects of vitamin D3 seen in isolated fat cells, there is also evidence supporting the fat-torching capacity of vitamin D within the body—thus demonstrating an influence of vitamin D on fat cells in a test tube that is similar to what has been demonstrated in the body. One study in particular demonstrating this was a study by Siddiqui et al.11, which looked at two different groups of obese rats that were fed diets either low in vitamin D or high in vitamin D. After several weeks on both diets, the rats consuming a high vitamin D diet demonstrated reduced body fat mass caused by a greater level of fatty acid oxidation.
VITAMIN D MIMICS LOW-CALORIE DIETS
In addition to increasing lipolysis and fatty acid oxidation to diminish fat, vitamin D3 also has the rather unique capacity to mimic low caloric consumption, further driving fat loss. This effect was shown in the aforementioned study by Chang et al.10, which found that vitamin D3 activated the molecule SIRT1—an energy-sensing enzyme normally activated by low caloric intake, but in this case, SIRT1 was activated by vitamin D3 intake. Interestingly, in order to trigger SIRT1 function, vitamin D3 increased production of the molecule NAD, which is a compound that represents a low energy state within the cell, which therefore turns on SIRT1. As a result, SIRT1 immediately activates several enzymes that oxidize fatty acids for the replenishment of cellular energy, which also diminishes body fat. Vitamin D3 also cranked up expression of the SIRT1 gene, which likely further enhanced SIRT1-driven fatty acid oxidation and fat loss. In addition, an activated SIRT1 also multiplies the number of mitochondrion within the cell. Since mitochondria function as power generators that burn fat and sugar for energy, more mitochondrion provides fat cells with an even greater capacity to scorch body fat. Taken together, this data indicates that vitamin D3 activation of the NAD-SIRT1 pathway potently contributes to the overall ability of vitamin D to reduce fat mass.
SIRT1 can also be activated by resveratrol supplementation, producing favorable effects on body fat composition that are quite similar to vitamin D. Interestingly, recent research showed that resveratrol also stimulates vitamin D3 binding to the vitamin D receptor and the subsequent activation of SIRT1 in certain human cells types in vitro12, implying that the combination of resveratrol with vitamin D3 would be a potent fat-burning stack that should conceivably activate SIRT1 more extensively, generating even more fat loss.
VITAMIN D BLOCKS NEW FAT CELL FORMATION
In addition to the growth of existing fat cells, body fat levels can also increase by forming new fat cells from precursor cells—a process known as adipogenesis. Both fat cell hypertrophy and new fat cell formation provide the additional storage space required to accommodate the freshly biosynthesized fat molecules generated in response to excessive caloric intake. In addition, vitamin D3 reducing the size of the fat cell size in the body, Chang et al.10 also showed that vitamin D3 has one more trick up its sleeve, as it is able to reduce fat levels by blocking the production of new fat cells. This was accomplished by turning off several adipogenic genes required to convert preadipocyte fat cells into mature fat cells, essentially blocking generation of new fat cells.
In summary, the ability of vitamin D3 to reduce the size of the fat cell while concomitantly thwarting the generation of new fat cells clearly supports the consumption of vitamin D as an effective strategy for accelerating fat loss.
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