Vitamin D deficiency is a global public health problem and is prevalent among all ages and ethnic groups. Nevertheless, it is preventable cost-effectively, if proper public health interventions are implemented. Only a handful of expensive foods, such as fatty fish, contain sufficient amounts of vitamin D. Moreover, it is difficulty to change people`s attitude concerning sun exposure and lifestyles, such as food preference. Therefore, an inexpensive supplements and food-fornication programs have been recommended. Nearly all requirement for vitamin D should generate from human skin, but sun avoidance behaviors prevent this. In combination with lifestyle and environmental issues, decreased exposure to sunlight have led to vitamin D insufficiency. This affects approximately 50% of the global population and estimated 1.5 billion people worldwide have vitamin D deficiency.
While it is best to obtain vitamin D through sunlight, vitamin D3 is the preferred supplement. Irrespectively, if vitamins D3 is obtained by endogenous production in the skin or by diet, it needs to be activated. A first hydroxylation step occurs in the liver generating 25(OH)D3 and its final hormonal form, 1,25(OH)2D3 is generated in kidneys. Serum 25(OH)2D3 levels below 30 ng/mL (75 nmol/L) are considered as insufficiency, i.e. hypovitaminosis D. The key functions of vitamin D are to facilitate intestinal absorption of calcium and phosphorus for proper skeletal mineralization. Moreover, vitamin D modulates both innate and adaptive immunity by increasing the defense against the invading microbes and protecting against autoimmune disease. Improved immunity could also be the main mechanisms for the cancer protective function of vitamin D. The molecular basis of all these physiological functions is vitamin D-dependent modulation of gene expression.
Beyond its use to prevent osteomalacia and rickets, and prevention of falls and fractures, the evidence for other health effects of vitamin D supplementation are increasing, but still inconsistent. However, provision of vitamin D supplementation to deficient elderly and institutionalized persons have been unequivocally shown to decrease falls, increases bone mineral density and decrease fractures. Additional exciting biological and physiological functions of vitamin D are in the horizon.