Vitamin D Receptor variants & and ocular risk: Identifying those needing supplementation with individualized nutrition consult
With the expression of the receptor and vitamin D regulatory enzymes throughout the eye, studying vitamin D in relation to ocular tissues and pathologies is biologically significant. Increasing evidence implicates that vitamin D is important in the maintenance of ocular health.
While best known for its role in calcium homeostasis, Vitamin D is now recognized to have many diverse functions: immune regulation, proliferation, differentiation, apoptosis, and angiogenesis. Vitamin D directly or indirectly regulates up to 5% of the human genome, or over 900 different genes! This puts the compound in the prestigious category of a master regulator, similar to Nrf2 and mTOR (stay tuned for future posts). Vitamin D is obtained from dietary consumption (fatty fish, fortified foods, supplements, etc) and local production in the skin on exposure to UV light.
The Vitamin D Receptor (VDR) recruits numerous co-activators and mediators to influence gene transcription. Genetic variation in the VDR is associated with myopia, wherein deregulated calcium homeostasis affects ciliary muscle dysfunction, leading to problems with emmetropization. Vitamin D deficiency and the presence of the BsmI ‘B’ allele and the TaqI ‘t’ allele are risk factors in the development of glaucoma as well, but how these polymorphisms affect disease risk is not clear.
It is NOT simple enough to say that anyone who tests "low" on a serum 25(OH)D test should a high dose supplement to push levels higher than 30ng/mL, in fact doses between 400-1200 IU daily may be safer and more effective. There is considerable controversy regarding whether the serum marker is even a reliable indicator of Vitamin D insufficiency, since it is not the active form of the hormone.
Individualized assessment of gene variants, dietary intakes, sun exposure, ocular pathology history/family history, and detailed symptom review is how I get an entry level picture of status upon which to decide whether conservative supplementation is warranted.
Variant SNP's in VDR need to be analyzed holistically with other pathways that are inter-related. For example: those on very low fat diets or with pancreatic insufficiency could have trouble absorbing any of the fat-soluble vitamin (A, D, E &K). Subsequently, iron-induced oxidative damage has connections to pancreatic function by way of copper-containing ferroxidases, one of which is ceruloplasmin. I will update with posts about iron pathways and iron overload ocular pathophysiology soon.
1. Vitamin D: Implications for Ocular Disease and Therapeutic Potential. Experimental Eye Research 2015
2. The Importance of Vitamin D in systemic and ocular wellness. Journal of Optometry 2013
3. Associations of Vitamin D Deficiency and Vitamin D Receptor (Cdx-2, Fok I, Bsm I and Taq I) polymorphisms and the risk of primary open angle glaucoma. BMC Ophthalmology 2016
4. Ceruloplasmin and hephaestin jointly protect the exocrine pancreas against oxidative damage by facilitating iron efflux. Redox Biology 2018