How one gene helps link sunlight to strong bones

Traveling nearly 93 million miles through the vacuum of space, sunlight takes approximately 8 minutes to reach Earth. After all of that, some of those light waves will end their journey when they collide with our skin. It’s phenomenal to think about such a long journey coming to an end right there in front of you—or rather, on you. That’s not quite the end of it, though: When the light contacts our skin, it passes on energy that’s capable of generating an important molecule for our body, vitamin D.
We get our vitamin D primarily through our diet (dairy products and fish oils) and from the sun1. It’s easier to understand how we get vitamins from our diet, but we can’t really eat sunlight, so how does that play into it? Vitamin D is actually produced from a chemical known as 7-dehydrocholesterol, which is found in our skin. When ultraviolet light from the sun hits us, 7-dehydrocholesterol is converted into a compound called pre-vitamin D31. After a series of chemical reactions, we end up with a form of vitamin D that is able to regulate calcium levels; this is known as the active form of vitamin D. But in order for that to work, it needs to be able to travel throughout the body via the bloodstream. This is where the gene GC comes into play.

Longitude and latitude

Because sunlight is so important to the generation of vitamin D, where you live can affect how much vitamin D your body makes (due to fluctuations in the type of sunlight).

For instance, during the months of November to February, the city of Boston receives much less ultraviolet light—resulting in a significant drop in the amount of vitamin D produced by people living there. Meanwhile, people living in the city of San Juan, Mexico produce more consistent levels of vitamin D due to their proximity with the equator which experiences a more steady sunlight all year round.

GC produces a protein known as DBP, short for vitamin D binding protein. This protein escorts the active form of vitamin D around the body where it has its various effects. Among its many activities, vitamin D helps regulate the amount of calcium in our blood1. Calcium serves many roles in our body, but it’s probably best known for helping to build sturdy bones. Additionally, calcium also plays a critical role in physiological processes like muscle contraction and the firing of neurons.
Vitamin D is a hormone which can affect when segments of our DNA are read. It does this by partnering up with other proteins in a cell and traveling together into the cell’s nucleus1. There, vitamin D and the other proteins bind the DNA in specific locations where they can help turn genes on or off. In general, this is how vitamin D and many other hormones (like testosterone and estrogen) work. Researchers suspect that vitamin D influences calcium levels by altering the body’s ability to use genes that are critically involved in the transport of calcium and in building bones1.

Vitamin D regulates the entry of calcium into and out of the blood stream in several locations such as the intestines, bones, and kidneys—all locations where calcium is absorbed, stored, and released1. But these locations are physiologically far from your skin, so we need help from DBP to transport vitamin D to the proper locations.
Like many other genes we’ve discussed, variants can occur in the GC gene which may affect a person’s vitamin D levels. Numerous studies have sought to understand how changes in the DNA affects vitamin absorption and distribution, particularly in terms of vitamin D2-5. Out of these studies came the finding that a particular variant in the GC gene known to researchers as rs2282679 can have a minor impact on a person’s vitamin D levels3. It’s not clear how this link works; it may be due to effects on the amount of DBP protein produced, or it may alter the function of the protein.
Genetic testing can help you understand how your body is predisposed to processing nutrients like calcium and hormones like vitamin D. GoalGetter by InsideTracker analyzes your DNA (including the GC gene) to explore these insights and many others, all with the mission of helping you pursue your performance goals.

1Christakos, Sylvia et al. “Vitamin D: Metabolism, Molecular Mechanism of Action, and Pleiotropic Effects.” Physiological Reviews 96.1 (2016): 365–408. PMC. Web. 5 Feb. 2018.
2Moy, Kristin A et al. “Genome-Wide Association Study of Circulating Vitamin D–binding Protein.” The American Journal of Clinical Nutrition 99.6 (2014): 1424–1431. PMC. Web. 6 Feb. 2018.
3Ahn, Jiyoung et al. “Vitamin D-Related Genes, Serum Vitamin D Concentrations and Prostate Cancer Risk.” Carcinogenesis 30.5 (2009): 769–776. PMC. Web. 6 Feb. 2018.
4Zhang, Zeng, et al. “An analysis of the association between the vitamin D pathway and serum 25-Hydroxyvitamin D levels in a healthy Chinese population.” Journal of Bone and Mineral Research, vol. 28, no. 8, 2013, pp. 1784–1792., doi:10.1002/jbmr.1926.
5Li, Shan-Shan et al. “Genetically Low Vitamin D Levels, Bone Mineral Density, and Bone Metabolism Markers: A Mendelian Randomisation Study.” Scientific Reports 6 (2016): 33202. PMC. Web. 6 Feb. 2018.