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Why can excessive amounts of vitamins A and D become toxic?

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rickets, a nutritional disease — nutritional disease Children with rickets. The disease, which most commonly strikes children, causes bone deformities such as bowlegs. Rickets is caused by a lack of vitamin D or calcium.

Excessive amounts of vitamins A and D can become toxic primarily because they are fat-soluble vitamins, which allows them to be stored in the liver and fatty tissue rather than being readily excreted in the urine like most water-soluble vitamins.12

Because the body retains these vitamins, a surplus can accumulate over time, eventually reaching levels that cause toxicity (hypervitaminosis A or D). This risk is particularly high when pharmaceutical vitamin preparations are used in excess.314

Vitamin A: When stored in the liver in excessive amounts, it can lead to symptoms such as nausea, bone pain, fatigue, hair loss, and liver damage. It is also known to cause birth defects if taken in excess during pregnancy.32
Vitamin D: Because it regulates calcium absorption, excess intake can lead to dangerously high blood calcium levels (hypercalcemia), resulting in the widespread deposition of calcium phosphate in soft tissues, including the kidneys and cardiovascular system, which can cause significant organ damage.42