Vitamin D is essential for the efficient utilization of calcium by the body (1). Maintenance of blood calcium levels within a narrow range is vital for normal functioning of all cells in the body, including the nervous system, as well as for bone growth and maintenance of bone density.
If calcium levels drop too low, a hormone (‘parathyroid hormone’) stimulates the production of 1,25(OH)2D, which binds to the vitamin D Receptor (VDR) and thus modulates gene expression in a way that the blood calcium gets back to normal by 1) increasing the absorption of dietary calcium in the digestive tract, 2) increasing the reabsorption of calcium filtered by the kidneys, and 3) mobilizing calcium from bone when there is insufficient dietary calcium (6).
Differentiation of cells results in their specialization for specific functions. In general, the differentiation process leads to a decrease in the speed of cell division. While rapid cellular division (‘proliferation’) is essential for growth and wound healing, uncontrolled proliferation of cells with certain mutations may lead to diseases like cancer. The active form of vitamin D, 1,25(OH)2D, inhibits proliferation and stimulates thedifferentiation of cells (1).
Vitamin D in the form of 1,25(OH)2D is a potent immune system modulator. There is considerable scientific evidence that 1,25(OH)2D has a variety of effects on immune system function, which may enhance innate immunity and inhibit the development of autoimmunity (7).
While animal studies suggest that 1,25(OH)2D plays a role in insulin secretion under conditions of increased insulin demand (8), emerging data in humans suggest that insufficient vitamin D levels may have an adverse effect on insulin secretion and glucose tolerance in type 2 diabetes (9, 10, 11).
Research in mice suggests that the expression of the gene coding for the enzyme renin is regulated by 1,25(OH)2D (12). Renin plays an important role in the regulation of blood pressure via the so-called ‘renin-angiotensin system’ (13, 14). Since inappropriate activation of the renin-angiotensin system is thought to play a role in some forms of human hypertension, adequate vitamin D levels may be important for decreasing the risk of high blood pressure.
The European Food Safety Authority (EFSA), which provides scientific advice to assist policy makers, has confirmed that clear health benefits have been established for the dietary intake of vitamin D in contributing to:
In addition, vitamin D plus calcium are needed for the maintenance of normal bone.
Authored by Dr Peter Engel in 2010, reviewed and updated by Dr Igor Bendik-Falconnier on 18.06.2017