Vitamin D is most widely known as the sunshine vitamin because the body is able to make vitamin D when exposed to sunlight. Vitamin D plays an important role in supporting bone health, maintaining cardiovascular function and immune function, and promoting an overall sense of well-being.
Vitamin D is available in two different forms, D2 and D3. Vitamin D3 is the preferable form as it has been found to maintain vitamin D levels in the body for a longer period of time when compared to vitamin D2.
Vitamin D 5,000 IU product data sheet
What is Vitamin D?
Vitamin D is a steroid vitamin, a group of fat-soluble prohormones that are best known for the role they play in supporting bone health and aiding in the absorption of calcium and phosphate from the gastrointestinal tract. A growing body of research highlights its important role in supporting other body systems, including cardiovascular and blood sugar balance, musculoskeletal strength and neurological and immune function, enabled by its ability to target over 200 different genes throughout the body. At the same time, deficiency and insufficiency of this important nutrient has reached epidemic proportions around the world, making the achievement of optimal levels extremely important than ever to overall health and wellbeing.
Known as the sunshine vitamin, one of the key roles of vitamin D is maintaining serum calcium and phosphorous balance. Our bodies make vitamin D by converting vitamin D2 to D3, or cholecalciferol (the active form) when exposed to sunlight. D3 is also the form which the body derives from dietary cholesterol. When calcium and phosphorus levels dip in the body, parathyroid hormone (PTH) is released to increase vitamin D conversion to the active form. D3 is then metabolized to calcitriol, a steroid hormone that helps regulate a variety of genes through the vitamin D receptor (VDR). While vitamin D is available in both forms as supplements, studies have found vitamin D3 is the preferable form, as it has been found to maintain active vitamin D levels for a longer period of time. This Vitamin D formulation is delivered as D3 (cholecalciferol) for optimal use by the body and is available in 1,000 and 5,000 IU capsules, to meet a variety of individual needs.
Vitamin D Depletion†
While it has long been assumed that the majority of the population achieves adequate levels of vitamin D through exposure to the sun, the biosynthesis of the nutrient is affected by time of day, seasons, location, smog/pollution, clothing and sunscreen. In addition, those with darker skin require more exposure to the sun to attain adequate levels. These factors all contribute to the insufficiency seen in a growing portion of the population. It takes about 48 hours for vitamin D to be absorbed from the skin into the body and washing skin during that time period can interfere with absorption into the blood. Inadequate intake or levels of cholesterol can also inhibit the adequate production of the nutrient. Depleted levels of vitamin D may interfere with the normal development of teeth and bones, normal cell growth, and contribute to poor regulation of immune and nervous systems. Certain medications have been found to contribute to deficiency of vitamin D, including some anti-seizure medications, bile acid sequestrants, oral corticosteroids, and weight loss medications, which bind fats. 
Bone and Dental Health†
Numerous studies have highlighted the importance of vitamin D to maintaining healthy bone density. In one 2013 study, 52 overweight men and women with suboptimal vitamin D levels were given either 7,000 IU of cholecalciferol daily or a placebo for 26 weeks. The vitamin D group significantly increased vitamin D levels in the blood and improved biomarkers of bone health. [2, 3]
Cardiometabolic Health and Blood Sugar Balance†
In light of the role that vitamin D plays in a variety of tissues and body systems, it comes as no surprise that much research from recent years has underscored its contribution to cardiometabolic wellness.  There is accumulating evidence that calcitriol helps strengthens cardiomyocyte function, vascular smooth muscle cells, and the vascular endothelium. Low levels of 25-hydroxyvitamin D are associated with diminished cardiovascular health.  In a recent study of 222 participants, slow coronary function was significantly higher in those with insufficient blood levels of the vitamin ; optimal vitamin D status has also been linked with a 40% cardiovascular system protective effect  as well as maintenance of healthy blood pressure levels.  Vitamin D has also been shown to support healthy blood sugar metabolism. [9, 10]
Immune Health and Modulation†
One of the more profound functions of vitamin D is its ability to modulate immunity. An important recent study suggested that improving vitamin D status significantly affects the expression of genetic pathways linked to immune activity.  Vitamin D has been shown to boost the immune response by up-regulating specific genes that increase cellular production of natural compounds that protect us against pathogens. 
Numerous studies also point to the key role of vitamin D in supporting musculoskeletal strength and comfort.  In one study, among 62 adult patients with nonspecific musculoskeletal discomfort, over 95% had vitamin D deficiency and responded to replenishment of vitamin D. Moderate deficiency of vitamin D has also been shown to predict knee discomfort over a five year period and hip discomfort over two years. 
1. http://umm.edu/health/medical/altmed/supplement/ vitamin-d
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11. Hossein-nezhad A, Spira A, Holick MF. Influence of vitamin D status and vitamin D3 supplementation on genome wide expression of white blood cells: a randomized double-blind clinical trial. PLoS One. 2013;8(3):e58725.
12. Cannell JJ, Vieth R, Umhau JC, Holick MF, Grant WB, Madronich S, Garland CF, Giovannucci E. Epidemic influenza and vitamin D. Epidemiol Infect. 2006 Dec;134(6):1129-40.
13. Abbasi M, Hashemipour S, Hajmanuchehri F, Kazemifar AM. Is vitamin D deficiency associated with nonspecific musculoskeletal pain? Glob J Health Sci. 2012 Nov 11;5(1):107-11.
14. Laslett LL, Quinn S, Burgess JR, Parameswaran V, Winzenberg TM, Jones G, Ding C. Moderate vitamin D deficiency is associated with changes in knee and hip pain in older adults: a 5-year longitudinal study. Ann Rheum Dis. 2013 Apr 17.