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How does vitamin D deficiency cause rickets?

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USDA MyPlate dietary guidelines — human nutrition MyPlate, a revised set of dietary guidelines introduced by the U.S. Department of Agriculture (USDA) in 2011, divides the four basic food groups (fruits, grains, protein, and vegetables) into sections on a plate, the size of each section representing the relative dietary proportions of each food group. The small blue circle shown at the upper right illustrates the inclusion and recommended proportion of dairy products in the diet.

Vitamin D deficiency causes rickets by impairing the body's ability to maintain the mineral density required for bone rigidity.

In a healthy state, the active form of vitamin D, known as calcitriol, acts on the small intestine to increase the absorption efficiency of dietary calcium and phosphorus. These minerals are essential for the deposition of calcium phosphate, which provides structural strength to the skeleton.12

When vitamin D is deficient, intestinal calcium absorption decreases, leading to lower levels of ionized calcium in the blood. This drop triggers the parathyroid glands to secrete parathyroid hormone (PTH). While PTH attempts to restore blood calcium levels by mobilizing calcium from the bones, it also causes increased excretion of phosphorus into the urine.123

Consequently, although the body continues to produce the protein matrix (osteoid) for bone growth, the matrix remains poorly calcified. This lack of mineralization results in the softening of bones characteristic of rickets in children.12