If you think about what vitamin A is needed for in the body, eye health typically comes to mind. Or maybe it provokes the thought of cod liver oil you were given as a kid during the winter months. Vitamin A provides many different actions of support to your body. While crucial for vision health, vitamin A is also critical for intestinal and immune barrier health, lungs and respiratory health, the gut microbiome, pancreas and insulin endocrine function, growth and development, thyroid and iodine function, and more.
Vitamin A Basics
Vitamin A is an essential nutrient that must obtained in the diet. The active metabolite of vitamin A is retinoic acid. Beta carotene and other carotenes are related to vitamin A. Some of these carotenes, but not all types, are converted into vitamin A in the intestines. The conversion of carotenoids into vitamin A is not always very efficient, as it depends on the plant source, the amount present, and if healthy fats were included in the meal.
Beta-carotene absorption from dietary plant sources ranges from 5 – 65 percent depending on individual nutrient status, gut integrity, thyroid function and gene mutations (SNPs) linked with its absorption. Vitamin A absorption occurs primarily in the upper small intestine and needs healthy gallbladder and liver function for this to happen.
The best sources of bioactive vitamin A are found liver, cod liver, eggs, dairy products, and fish. Green-leafy, and red, orange, yellow, and purple colored vegetables and fruits are good sources of carotenes but higher amounts are needed due to lower conversion rates. A balance between animal sources of vitamin A and plant-sources of carotenes is best. Vitamin A is stored in the body and needs to be balanced in the right amounts. Carotenes are water-soluble and are not stored long-term in the body.
Over 20 percent of the population in Western countries fails to consume even two-thirds of the recommended daily intake (RDI) of vitamin A. Common dietary patterns of calorie-rich, nutrient poor foods and poorly planned vegetarian diets have led to low levels of vitamin A being stored in the body.
Vitamin A for Vision
Early research focused on the critical relationship between vitamin A and vision. Vitamin A is needed for rhodopsin, a protein that absorbs light in retina receptors, which then sends signals to the brain for visual processing. Vitamin A is also used by the cornea and other tissues within the eye. In low-income countries where vitamin A intake is low in expectant mothers or young children, there are high rates of childhood blindness.
Vitamin A and Respiratory Health
As discoveries were made, scientists found out just how critical vitamin A is to normal physiology and function throughout the body. For example, during pregnancy and infancy, vitamin A is required for lung development. Beyond infancy, individuals of all ages need vitamin A for respiratory health, as it aids in maintenance and regeneration of the air sacs called alveoli.
The architectural structure of the respiratory tract and lungs require vitamin A. Within the lungs and alveoli, signaling mechanisms between immune and nerve cells use vitamin A. Vitamin A also works together with collagen and elastic-like materials to help air movement in and out of lungs.
Vitamin A Critical for Immune Cells, Mucosal Linings, and Defense
Your body has several mucosal barriers, which are the front lines of defense that provide a buffer between your internal tissues and the outside environment. There are four different types: immune, mechanical, chemical, and biological mucosal barriers.
The respiratory tract (mouth, sinus, bronchioles, and lungs) and digestive tract (mouth, esophagus, stomach, small and large intestine) have the two largest mucosal barriers. Mucosal barriers are also found with the eyes, urinary tract, or birth canal.
The immune portion of mucosal barriers uses specialized immune compounds called secretory IgA (sIgA), gut associated lymphoid tissue (GALT) and other specialized immune cells to provide an immune defense. sIgA identifies antigens from things that we ingest or breathe and recognizes them as safe or problematic.
Vitamin A is necessary for sIgA production and is also required for numerous immune cell functions in the mucosal barriers and GALT. Astaxanthin, which is part of the carotenoid family, also aids in sIgA production.
Vitamin A is essential for the immune barrier within the mucosal barrier as it promotes mucin, a protective immune secretion. Mucin helps the immune system manage its defense against antigens and maintain the overall integrity of the mucosal barriers. Vitamin A levels help keep barriers in the eyes, throat, skin and others moist rather than being dry and irritated.
Vitamin A influences and regulates immune cells (T cells, B cells, T-regs, etc) and dendritic cells in the gut. Dendritic cells are highly specialized, powerful, skillful front-line defense cells that orchestrate immune responses by interacting with the gut microbiome. Vitamin A provides antioxidant, immune-regulatory, and wear and tear support to these dendritic cells and is integral to the microbiome homeostasis.
Vitamin A Affects Your Gut Microbiome
Vitamin A affects another dimension of gut health and immune function. Vitamin A helps your gut flora or microbiome variety, diversity and composition. When vitamin A status is low, the microbiome population or beneficial flora shrinks, causing an unhealthy imbalance of the gut flora. This is highly unfavorable, as immune health requires microbiome diversity.
Vitamin A is also needed for the mechanical barriers (tight junctions) in the gut lining. Tight junctions are tiny doors inside the gut lining that selectively open and close to allow nourishment to move from the digestive tract to the remainder of your body. If the tight junctions don’t work properly, then increased intestinal permeability or leaky gut syndrome happens.
Pancreas and Gut Microbiome
As researchers continue to discover the inter-relationships between internal organs and the gut microbiome, they have found that the balance of gut flora affects pancreas function, affecting insulin and blood sugar management. Vitamin A is believed to be one of the connecting elements for healthy gut flora-pancreas-insulin-metabolism relationship.
Your pancreas requires vitamin A for beta- and alpha-cells to make insulin. Pancreatic islets cells need vitamin A to keep their normal size and shape, which affects insulin production and overall blood sugar metabolism.
Vitamin A Partnership with Thyroid and Other Nutrients
Vitamin A works in partnership with other nutrients and systems. Thyroid metabolism requires adequate vitamin A for iodine uptake in the body. Zinc works as a cofactor in vitamin A functionality. Vitamin D and vitamin A work together for immune mucosal barrier function throughout your body. Adequate protein and iron are also needed for vitamin A to work in the body.
Alcohol, low-fat/no-fat diets, xenobiotics stress, and malabsorption difficulties impact vitamin A status. Some individuals don’t convert carotenes very well into vitamin A because of gene SNPs, which increases dietary need.
If you get your vitamin A levels checked by a blood test, know that obesity may affect vitamin A test results. Animal studies showed that vitamin A blood levels differ from tissue stores in obesity. Blood levels were elevated, but actual vitamin A content in tissues like the liver, lungs, pancreas, and kidneys were substantially reduced. Vitamin A use and transport throughout the body was altered in obesity. When weight loss occurred, vitamin A levels in the blood correlated more accurately with actual tissue levels.
Your immune system and barriers, along with numerous other critical functions in the body, require vitamin A. If twenty percent of the population fails to consume a minimal two-thirds of the basic RDI, how many others do not meet the full RDI for daily needs? Does this include you?
