How does vitamin D deficiency affect calcium absorption?

For patients with vitamin D deficiency, it is difficult for the body to obtain calcium from the diet. This often leads to a rise in the PTH level, since the parathyroid glands must increase the PTH production in order to increase calcium levels by stealing it from the bones. Therefore, people with a normal blood calcium levels and a high PTH level may have secondary hyperparathyroidism, which means that the high PTH level is a normal response of healthy parathyroids glands to another problem (like vitamin D deficiency or kidney failure).
Vitamin D helps your body absorb calcium to form and maintain strong bones. If you don't consume enough vitamin D, your bones may become thin, weak and brittle. In children, a deficiency causes weak bones, or rickets. In adults, a shortage of vitamin D may cause osteoporosis (brittle bones) and osteomalacia (soft bones), accompanied by bone pain and muscle weakness.

Maintaining a healthy blood level of vitamin D is thought to reduce the risk of falls and fractures in people prone to them.

Jonathan B. Levine, DMD
The human body synthesizes vitamin D through exposure to the ultraviolet B (UVB) rays of the sun. One of the main functions of vitamin D is to promote the absorption of calcium, the most prominent mineral in the body and one that is essential for maintaining strong and healthy bones throughout the entire skeletal system, including our teeth.

There is a correlation between vitamin D levels and calcium absorption. When blood levels of calcium begin to drop, the body responds in several ways. It promotes the conversion of vitamin D into its active form, which then travels to the intestines (to encourage greater calcium absorption into the blood) and to the kidneys (to minimize calcium loss in the urine). 

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.