Vitamin D The Sunshine Vitamin

Vitamin D

The Sunshine Vitamin

The main function of Vitamin D is regulating calcium and phosphorus to make bones strong. Vitamin D is an unusual vitamin. Vitamin D is necessary in the diet only for people who get too little sun to make their own vitamin D. For the billions of people who do get enough sun, it is not a vitamin because it is not needed in the diet. Vitamin D is also very hard to find in a natural diet as it occurs in only a few foods. Vitamin D is a fat-soluble vitamin. Vitamin D is also unusual because its most active form is one of the most powerful hormones in
the human body.

Vitamin D was first named in 1922 by researchers who learned of a fat soluble substance that played an important role in bone growth. Researchers went on to learn that ultraviolet light could activate vitamin D. By 1925 it was
suspected that a cholesterol derivative in skin was activated by sunlight. In 1931 vitamin D2 was synthesized, and the structure of vitamin D was established by 1936.

How Vitamin D Controls Calcium

Blood calcium levels must be maintained within a narrow range for normal nervous system functioning and maintenance of bone density. Blood calcium levels are especially vital in childhood during bone growth. Vitamin D as calcitriol is an essential part of the regulation of blood calcium and phosphorus levels. Bone growth and regulation is also assisted by vitamin A, vitamin C, vitamin K, the hormone calcitonin, parathyroid hormone,
and magnesium.

Calcium levels are sensed by the parathyroid glands. If blood levels of calcium fall too low, the parathyroid glands secrete parathyroid hormone. The parathyroid hormone stimulates production of an enzyme in the kidneys. This enzyme increases the transformation of calcidiol to calcitriol. Calcitriol is a potent hormone that increases blood calcium levels.

Increased blood levels of calcitriol cause increased absorption of calcium from food in the intestines. The kidneys also reduce losses of calcium in the urine in response to increased levels of calcitriol. In addition, calcium can be mobilized from bones if dietary levels of calcium are insufficient. Increased release of calcium from the bones requires parathyroid hormone in addition to calcitriol.

Vitamin D and Immunity

Calcitriol has a powerful ability to aid the functioning of the immune system. Immune system cells such as Tcells and macrophage cells need calcitriol. Macrophages have the ability to make calcitriol from calcidiol. In  autoimmune diseases an excess of macrophages may produce an excess amount of calcitriol.