Vitamins and why we need them
Vitamin D RDA 400iu. (10ug)
There are two major forms of vitamin D, D2 (ergocalciferol) and D3 (cholecalciferol). D2 is the form added to milk and is used in nutritional supplements.
Both of these substances, ergocalciferol in plants and cholecalciferol in humans, are usually referred to as provitamin D and both can be converted by the liver, and then the kidneys, into fully active vitamin D (called calcitriol). When ultraviolet light falls on the cells of our skin, cholesterol is converted into vitamin D3. Sunlight is the best source of vitamin D but for those exposed to little sunlight, supplements are recommended.
Calcitriol, the most metabolically active form of vitamin D, works with parathyroid hormone (PTH) to maintain proper levels of calcium in the blood. Low levels of calcium in the blood stimulate the secretion of PTH from the parathyroid gland. PTH then stimulates the conversion of inactive forms of vitamin D to calcitriol.
Calcitriol increases the intestinal absorption of calcium, also decreasing calcium secretion by the kidneys. It also stimules the release of calcium from bone, thereby increasing blood calcium levels. Alternatively, when blood levels of calcium are too high, calcitriol decreases the intestinal absorption of calcium and stimulates the bones to take up calcium, thereby decreasing blood calcium levels.
Vitamin D may also play a role in regulating cellular growth and function in our brain cells and helps regulate immune system activity, preventing an excessive or prolonged inflammatory response. Vitamin D deficiency has also been associated with increased risk of certain cancers. These cancers include breast cancer, colon cancer and ovarian cancer.
The production of vitamin D precursors in the skin decreases with age and the kidney is less able to convert vitamin D to its active hormone form. Periodontal disease, a chronic inflammatory gum disease common in those over 50, is another example of a lack of vitamin D resulting in a progressive, inflammatory condition.Symptoms associated with vitamin D deficiency
Rickets - deformed and porous bones - teeth and gum problems - muscular weakness - cramps - tetany - nervous instability - underactive thyroid - depression - overweight - eye problems - calcium deficiency - fatigue - arthritis - stiffness - backache.Best food sources
Fish liver oil - mackerel - sardines - herring - salmon - tuna - eggs.