Overview of fat-soluble vitamin deficiencies

The fat-soluble vitamins (A, D, E and K) require bile for absorption from the gastrointestinal tract, and travel through the lymphatic system before entering circulation. Fat-soluble vitamins are not easily excreted, and the risk of toxicity is greater than with water-soluble vitamins. Excesses are stored primarily in the liver and adipose tissues, so deficiencies may not be seen until weeks or months of inadequate intake. People with conditions causing fat malabsorption (eg cystic fibrosis, pancreatic insufficiency, short bowel syndrome, bariatric surgery) are at higher risk of fat-soluble vitamin deficiencies.

See Clinical aspects of fat-soluble vitamins for the physiological function of fat-soluble vitamins, and the effects and risk factors for deficiency.

Dietary sources of fat-soluble vitamins are listed in Dietary sources of key vitamins, minerals and trace elements.

The evidence for the optimal dosage of fat-soluble vitamins and outcomes is limited; dosages given in this topic are a guide only.

People deficient in multiple fat-soluble vitamins or with a condition causing fat malabsorption can be treated with a water-miscible, high-potency fat-soluble multivitamin formulation such as VitABDECK (contains vitamin A 2500 international units [IU], vitamin D 440 IU, vitamin E 150 IU, and vitamin K 150 micrograms). People deficient in a specific fat-soluble vitamin may only need treatment with a high-dose supplement of that vitamin.

Baseline testing of fat-soluble vitamin blood concentration should only be carried out in people at risk of deficiency. Repeat testing may be used to determine if the patient is having an adequate response to therapy and to ensure that the patient is not receiving an excessive dosage; however, evidence to guide timing of repeat testing is lacking. Disease-specific guidelines may provide recommendations for the frequency of repeat testing. In general, the requirement for and frequency of repeat testing should be individualised based on which micronutrient is supplemented and the severity of the deficiency. For information about the requirement for and frequency of vitamin D testing, see Vitamin D treatment regimens.

Supplementation of fat-soluble vitamins should not continue indefinitely. To avoid toxicity, recheck blood concentration after 3 months, if appropriate, and stop supplementation if the deficiency has resolved. Long-term supplementation may be required in patients with a chronic condition causing fat malabsorption.