Introduction to vitamin D deficiency

The main source of vitamin D (colecalciferol or vitamin D₃) in humans is ultraviolet B radiation from the sun acting on 7-dehydrocholesterol in the skin. Vitamin D₃ is converted in the liver to 25-hydroxyvitamin D, the form of vitamin D that is measured in the serum. 25-hydroxyvitamin D is converted in the kidneys to the active form of vitamin D, 1,25-dihydroxyvitamin D (calcitriol), which promotes absorption of calcium and phosphate from the gut, and assists bone mineralisation by interacting with parathyroid hormone. Dietary sources provide less than 10% of total requirements of vitamin D.

Adequate exposure to sunlight is the best way to prevent vitamin D deficiency. The amount of exposure required depends on the season, the location (ie distance from the equator) and the person’s skin tone. Suggested exposure times depending on location in Australia can be found on the Healthy Bones Australia website.

Vitamin D deficiency is usually asymptomatic, but can present with mild bone pain and muscle weakness. Severe deficiency can cause defects in bone mineralisation leading to osteomalacia in adults or rickets in children.