Vitamin A is a fat-soluble vitamin critical for immunity, eye health and vision, and healthy skin. Vitamin A binds the retinoid X nuclear receptors (RXR), responsible for the expression of hundreds of genes that influence hormone metabolism, cellular differentiation, and reproduction.
For immunity, vitamin A is especially critical. Retinol and retinol derivatives regulate a broad range of immune processes, such as the adaptive immune response, cytotoxicity and T-cell proliferation through influences on cytokine release and expression of receptors. Vitamin A metabolites also modulate TH1–TH2-cell balance and the differentiation of TReg cells and TH17 cells. Vitamin A deficiency correlates with decreased TH2-cell responses and is associated with impaired intestinal immune responses and increased mortality associated with gastrointestinal and respiratory infections.1
Vitamin A exists in two major forms: active vitamin A (retinol), which can be found in high quantities in animal liver, and pro-vitamin A (most commonly beta-carotene), found in orange fruits and vegetables as well as green leafy vegetables. In order for the body to use pro-vitamin A, it must first be converted into retinol, which can then carry out its functions.
The gene, BCMO1 (beta-carotene monooxygenase) is responsible for the conversion of beta-carotene into retinol, the active form of vitamin A. Genetic variations in the BCMO1 gene can reduce the enzyme function by up to 69%, leading to 240% higher levels of beta-carotene in the blood. 2 Presumably decreasing cellular concentrations and bioavailability of retinol.
In those who are poor converters of BC to retinol, it is important to provide dietary sources of retinol, and reduce the over consumption of beta-carotene rich foods. Studies show that in those with low BCMO1 activity, high consumption of beta-carotene rich foods shuts down intestinal BCMO1 activity, contributing to retinol deficiency.
Follow up labs
The following strategies have been shown to improve beta-carotene absorption and BCMO1 activity:
- Increase protein consumption to 40% of total caloric intake
- Avoid gluten
- Avoid additives (MSG)
- Reduce beta-carotene rich foods and increase dietary retinol
- Retinol supplementation
- Mora, J. R., Iwata, M. & von Andrian, U. H. Vitamin effects on the immune system: vitamins A and D take centre stage. Nat. Rev. Immunol. 8, 685–698 (2008).
- Leung, W. C. et al. Two common single nucleotide polymorphisms in the gene encoding β-carotene 15,15′-monoxygenase alter β-carotene metabolism in female volunteers. FASEB J. 23, 1041–1053 (2009).
Dr. Robyn Murphy, ND
Scientific Advisory Board Member