Vitamin A for Reproductive and Immune Health
Vitamin A is a key nutrient essential for good health. It’s commonly known for preserving eyesight but is important for so much more. Let’s first review some basics about the nutrient itself.
Vitamin A is actually a group of fat-soluble compounds which provide the body with activators that assist with mineral assimilation. There are two general categories of dietary Vitamin A. The provitamin or building block forms, which include all members of the carotenoid family such as beta-carotene. These are available from plant sources—most notably red, orange, yellow and dark green fruits and vegetables—and must be converted to a usable form in the GI tract and liver. Efficient conversion is dependent on good digestive health, and factors such as diet. Digestive problems, chronic disease, lipid metabolism disorders, alcohol use, and certain medications can impact how well beta-carotenes are converted for absorption. In addition, our research into the human genome suggests that up to 45% of the population has some form of genetic variation that inhibits the production of the enzyme responsible for the provitamin A conversion.
The preformed or retinoid forms of Vitamin A, on the other hand, are already active and are therefore more bioavailable. In their natural form, these can only be obtained from animal foods such as full-fat dairy, egg yolks, liver, fish liver oils, and other oily fishes. However, there are synthetic versions commonly employed for topical use and vitamin supplements. Be aware there is a downside to excessive use of the synthetic supplement form.
The body stores Vitamin A in the liver, adipose tissue and gonads so it can be available as needed. The liver, therefore, plays an important role in its regulation and metabolism. True Vitamin A deficiency tends to be rare in the US, however, suboptimal levels can lead to suboptimal health over time.
Because the retinoid form can accumulate in the body, it’s possible to achieve a toxic level so it’s helpful to be aware of your supplemented sources in order to avoid large doses of synthetic forms. In general, natural (i.e., non-fortified) food forms are considered safe, but you can overdo it with concentrated, synthetic supplement versions. Supplement levels up to 10,000 IU (3,000 mcg) are generally considered safe as a daily upper limit for adults, although this is quite a high dose. For comparison, the RDA for adult females is 700 mcg (or up to 1,300 mcg if pregnant or lactating), and 900 mcg for adult males. As with many nutrients, focusing on meeting the bulk of your nutrient needs via your diet may be most beneficial and have less risk of complications.
Sticking with a variety of quality food sources should be the primary method of consumption. Including a natural supplement form like cod liver oil can provide an added nutrient buffer for those with relevant health objectives. As a bonus, natural forms such as cod liver oil often include other fat-soluble nutrients like an animal-based source of omega-3 fatty acids and Vitamin D that work synergistically in the body.
Vision: Vitamin A makes vision possible by powering the retinas and producing pigments that allow them to work properly. It helps forestall age-related macular degeneration and lower the risk of cataracts. Signs of deficiency include visual disturbances, dry eyes and poor night vision.
Skin: Vitamin A is important for our skin and mucosal membranes, which can be thought of as our internal skin. Vitamin A plays a role in the expression of mucins and keratins, which help maintain the structure and moisture of skin and mucosal membranes, and regulate the differentiation of epithelial tissues. Its function in the structural integrity of our barrier membranes means it is important for our first-line immune defenses. Some forms of Vitamin A are used on the skin topically for cosmetic purposes, such as the use of retinol creams for the treatment of severe acne and wrinkles. Many of these are by prescription, although milder versions are available over the counter. Be aware that these are absorbed through the skin and thus add to the accumulation of Vitamin A in the body.
Immunity: Vitamin A is involved in the regulation and generation of various types of blood cells, and plays a powerful role in helping to regulate the innate and adaptive immune systems. For instance, roughly 70-80% of our immune cells reside in the mucosal lining of our gut. Vitamin A is also known to decrease the replication of RNA viruses. Carotenoids help mitigate the negative effects of oxidative stress and thus have a regulating effect on inflammation. A deficiency in Vitamin A is known to decrease the activity of the immune system’s natural killer cells, which are important for controlling microbial infections and tumor cells. Supplementation with Vitamin A has been shown to decrease the risks of serious illnesses in preschool-aged children.
Reproduction: Vitamin A is essential for both male and female reproductive systems, as well as ensuring normal embryo development. Males deficient in Vitamin A can have blocked sperm development, resulting in higher percentages of immature gametes. In females, Vitamin A plays an important role in egg quality, placental and several aspects of embryo development. Studies show that female Vitamin A deficiency prior to conception can yield unsuccessful implantation. In pregnant women, Vitamin A deficiency is associated with increased levels of infant disease and mortality.
Resources
Cañete, A., Cano, E., Muñoz-Chápuli, R., & Carmona, R. (2017). Role of Vitamin A/Retinoic Acid in Regulation of Embryonic and Adult Hematopoiesis. Nutrients, 9(2), 159. https://doi.org/10.3390/nu9020159
Clagett-Dame, M., & Knutson, D. (2011). Vitamin A in reproduction and development. Nutrients, 3(4), 385–428. https://doi.org/10.3390/nu3040385
Hogarth, C. A., & Griswold, M. D. (2010). The key role of vitamin A in spermatogenesis. Journal of Clinical Investigation, 120(4), 956962. https://doi.org/10.1172/JCI41303
Leung, W. C., Hessel, S., Méplan, C., Flint, J., Oberhauser, V., Tourniaire, F., Hesketh, J. E., von Lintig, J., & Lietz, G. (2009). Two common single nucleotide polymorphisms in the gene encoding beta-carotene 15,15′-monoxygenase alter beta-carotene metabolism in female volunteers. FASEB journal : official publication of the Federation of American Societies for Experimental Biology, 23(4), 1041–1053. https://doi.org/10.1096/fj.08-121962
Ross, A. C., Chen, Q., & Ma, Y. (2011). Vitamin A and retinoic acid in the regulation of B-cell development and antibody production. Vitamins and hormones, 86, 103–126. https://doi.org/10.1016/B978-0-12-386960-9.00005-8
Rubin, L. P., Ross, A. C., Stephensen, C. B., Bohn, T., & Tanumihardjo, S. A. (2017). Metabolic Effects of Inflammation on Vitamin A and Carotenoids in Humans and Animal Models, Advances in Nutrition, 8(2), 197–212. https://doi.org/10.3945/an.116.014167
