From Ergo Log
Adding the amino acid leucine to protein-rich meals is perhaps the most effective supplementation strategy for strength athletes seeking to speed up muscle growth. Researchers at Clermont Universite in France have discovered that the higher the concentration of vitamin D3 in the blood, the greater the anabolic effect of leucine.
The researchers exposed C2C12 muscle cells in test tubes to leucine, insulin and varying concentrations of 1,25(OH)2-vitamin D3, which also goes by the name of calcitriol. This is the active form of vitamin D.
The researchers also added labelled valine to the test tubes, so they could see whether the muscle cells built the valine into their protein structures. This enabled them to measure the anabolic effect of the leucine-insulin cocktail. The more 1,25(OH)2-vitamin D3 there was in the test tubes, the greater the anabolic effect.
When the researchers looked closely at the production and activity of anabolic signal proteins, they noticed that 1,25(OH)2-vitamin D3 made the insulin receptor more sensitive. The greater the concentration of 1,25(OH)2-vitamin D3, the greater the activity of anabolic signal proteins such as Akt, GSK3, p70-S6K and 4EBP1.
The figures above reveal the way in which 1,25(OH)2-vitamin D3 gets the muscle cell's anabolic machinery to work harder. Vitamin D3 induces muscle cells to manufacture more insulin receptors.
At the same time the muscle cells also produce more vitamin-D receptors as a result of exposure to 1,25(OH)2-vitamin D3, an effect that other researchers had already observed. [Endocrinol Metab Clin North Am. 2010 Jun;39(2):255-69.]
"The transcriptional induction of these genes as well as a potentiation of the insulin and leucine action on key related proteins is likely one of the central mechanisms of action of vitamin D on skeletal muscle anabolism", the researchers write. "Overall, our data open up perspectives for potentially valuable nutritional interventions coupling vitamin D and amino acid supplementation, mainly in situations like sarcopenia where vitamin D and amino acid response is deficient, to support muscle fiber protein synthesis."
The research was funded by Danone.
Mol Nutr Food Res. 2013 Aug 9. doi: 10.1002/mnfr.201300074. [Epub ahead of print].