Like magnesium, vitamin D is important for maintaining bone density through its interaction with the parathyroid gland. When calcium concentration in the blood begins to fall, increasing amounts of a hormone are released from the parathyroid gland. This causes the activation of vitamin D in the kidneys, and the vitamin D then signals cells lining the walls of the intestines to absorb calcium.
If sufficient calcium is available from the diet, the effect of vitamin D activation is to increase the amount of calcium in the body and to restore what may have been taken from the bone. If there is a lack of calcium in the diet, blood calcium concentration is maintained by reabsorbing calcium from the bone. This will reduce bone density and can lead to osteoporosis.
Recent research has shown that vitamin D also has a direct effect on increasing bone density. It is required to induce a protein called osteocalcin, which binds calcium in the bones. This protein also requires vitamin K for its formation and activation.
Most of the vitamin D in the body is synthesised from cholesterol by the action of sunlight on the skin. Vitamin D is also available from dietary sources such as liver, fish liver oils, egg yolk, sprouted seeds and milk.
Excessive intake of vitamin D can produce toxicity and supplementation should not be undertaken without professional advice.
