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Vitamin D protects bone, preserves muscle strength, and regulates cell growth and energy metabolism. It also offers some protection against cancer and other disease, but are these effects really important for health and life expectancy? The answer seems to be a resounding yes.

What can high-vitamin D foods do for you? * Help prevent a growing list of chronic diseases, including type 2 diabetes, heart disease, hypertension, osteoporisis, breast cancer, colon cancer, and ovarian cancer * Help keep your bones and teeth strong and healthy * Regulate the growth and activity of your cells * Reduce inflammation What events can indicate a need for more foods rich in vitamin D? * Bone pain and/or soft bones * Frequent bone fractures * Bone deformities or growth retardation in children

Bioactive vitamin D or calcitriol is a steroid hormone that has long been known for its important role in regulating body levels of calcium and phosphorus, and in mineralization of bone. More recently, it has become clear that receptors for vitamin D are present in a wide variety of cells, and that this hormone has biologic effects which extend far beyond control of mineral metabolism. The active form of vitamin D binds to intracellular receptors that then function as transcription factors to modulate gene expression. Like the receptors for other steroid hormones and thyroid hormones, the vitamin D receptor has hormone-binding and DNA-binding domains. The vitamin D receptor forms a complex with another intracellular receptor, the retinoid-X receptor, and that heterodimer is what binds to DNA. In most cases studied, the effect is to activate transcription, but situations are also known in which vitamin D suppresses transcription. Each of the forms of vitamin D is hydrophobic, and is transported in blood bound to carrier proteins. The major carrier is called, appropriately, vitamin D-binding protein. The halflife of 25-hydroxycholecalciferol is several weeks, while that of 1,25-dihydroxycholecalciferol is only a few hours. The vitamin D receptor binds several forms of cholecalciferol. Its affinity for 1,25-dihydroxycholecalciferol is roughly 1000 times that for 25-hydroxycholecalciferol, which explains their relative biological potencies

Vitamin D and calcium insufficiency-related chronic diseases: molecular and cellular pathophysiology. Peterlik M, Cross HS. Eur J Clin Nutr. 2009 Dec;63(12):1377-86. Epub 2009 Sep 2. PMID: 19724293 doi:10.1038/ejcn.2009.105 A compromised vitamin D status, characterized by low 25-hydroxyvitamin D (25-(OH)D) serum levels, and a nutritional calcium deficit are widely encountered in European and North American countries, independent of age or gender. Both conditions are linked to the pathogenesis of many degenerative, malignant, inflammatory and metabolic diseases. Studies on tissue-specific expression and activity of vitamin D metabolizing enzymes, 25-(OH)D-1alpha-hydroxylase and 25-(OH)D-24-hydroxylase, and of the extracellular calcium-sensing receptor (CaR) have led to the understanding of how, in non-renal tissues and cellular systems, locally produced 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) and extracellular Ca2+ act jointly as key regulators of cellular proliferation, differentiation and function. Impairment of cooperative signalling from the 1,25-(OH)2D3-activated vitamin D receptor (VDR) and from the CaR in vitamin D and calcium insufficiency causes cellular dysfunction in many organs and biological systems, and, therefore, increases the risk of diseases, particularly of osteoporosis, colorectal and breast cancer, inflammatory bowel disease, insulin-dependent diabetes mellitus type I, metabolic syndrome, diabetes mellitus type II, hypertension and cardiovascular disease. Understanding the underlying molecular and cellular processes provides a rationale for advocating adequate intake of vitamin D and calcium in all populations, thereby preventing many chronic diseases worldwide.

"Vitamin D is not just a sun-derived vitamin, but is a crucial steroid precursor that is transformed into one of the most potent hormones in the human body for strength, power, lung function and regulating gene expression in every organ system. Athletes need Vitamin D. Dr. Cannell has written quite extensively about the role of vitamin D in athletes"

Sweat gland epithelial and myoepithelial cells are vitamin D targets. Koike N, Stumpf WE. Exp Dermatol. 2007 Feb;16(2):94-7. PMID: 17222221 DOI: 10.1111/j.1600-0625.2006.00513.x Nuclear receptor binding of 1,25(OH)2-vitamin D3 (vitamin D) in skin keratinocytes of epidermis, hair sheaths and sebaceous glands was discovered through receptor microscopic autoradiography. Extended experiments with 3H-1,25(OH)2-vitamin D3 and its analog 3H-oxacalcitriol (OCT) now demonstrate nuclear receptor binding in sweat gland epithelium of secretory coils and ducts as well as in myoepithelial cells, as studied in paws of nude mice after i.v. injection. The results suggest genomic regulation of cell proliferation and differentiation, as well as of secretory and excretory functions, indicating potential therapies for impaired secretion as in hypohidrosis of aged and diseased skin.

"Numerous studies link Vitamin D and influenza, as well as Vitamin D and respiratory infections more generally. This vitamin up-regulates genetic expression of various endogenous antimicrobial peptides (AMP), which exhibit broad-spectrum microbicidal activity against bacteria, fungi, and viruses. Reports discussed below indicate that susceptibility to influenza is reduced with higher levels of sun exposure or vitamin D supplementation. Seasonal variation of vitamin D levels in humans can help explain the seasonality of flu epidemics."

"If you're running low on vitamin D - as an estimated 70 percent of the U.S. population is - your immune system may not be functioning as well as it should. As a result, you may be more vulnerable to infectious diseases than you would if your vitamin D levels were optimal. Worse, you could be at higher than normal risk of a long list of diseases including heart disease and several kinds of cancer. A report recently published journal, Future Microbiology, highlighted research at the Linus Pauling Institute at Oregon State University, which has shown that vitamin D induces expression of an antimicrobial peptide gene called cathelicidin that is the "first line of defense" in the immune system's response to minor wounds, cuts and bacterial and viral infections. The regulation of cathelicidin by vitamin D could help explain its vital role in immune function. The report noted that vitamin D is a key cofactor in reducing inflammation, in blood pressure control and helping to protect against heart disease. Author Adrian Gombart explains that there is still much to explore about D's mechanisms of action, the potential use of synthetic analogs of it in new treatments, and its duty in fighting infection."

Evolution and function of vitamin D. Holick MF. Recent Results Cancer Res. 2003;164:3-28. Review. PMID: 12899511

Dusso AS, Brown AJ, Slatopolsky E. Vitamin D. Am J Physiol Renal Physiol. 2005 Jul;289(1):F8-28. Review. PMID: 15951480 [PubMed - indexed for MEDLINE]