Vitamin A: Hero or Villain
NIH Statements on Vitamin A Use In the Body
Vitamin A is a group of compounds (retinol, retinal, and retinoic acid) that play an important role in vision, bone growth, reproduction, cell division, and cell differentiation (in which a cell becomes part of the brain, muscle, lungs, blood, or other specialized tissue.) These vitamin A compounds help regulate the immune system, which prevents or fights off infections by making white blood cells that destroy harmful bacteria and viruses. These fat soluble compounds may help lymphocytes (a type of white blood cell) fight infections more effectively.
They also promote healthy surface linings of the eyes and the respiratory, urinary, and intestinal tracts. When those linings break down, it becomes easier for bacteria to enter the body and cause infection. It also helps the skin and mucous membranes function as a barrier to bacteria and viruses.
In general, there are two categories of these compounds, depending on whether the food source is an animal or a plant.
Strictly speaking the complex is found only in animal sources. It is possible to convert some carotenes found in plants to vitamin A but it cannot be done with many lowfat diets. The preferred fat to make this conversion is animal fat, not vegetable oils, and the conversion rate is 1 part vitamin A to 4 parts or more of carotenes.
This essential compound found in foods that come from animals is is said to be preformed. It is absorbed in the form of retinol, one of the most usable forms of the complex. Sources include liver, butter, raw whole milk, and some fortified food products. Retinol can be made into retinal and retinoic acid which are other active formsin the body.
Since fruits and vegetables don't contain any of the active complex it is called provitamin A carotenoid. They can be made into retinol in the body. In the United States, approximately 26% consumed by men and 34% consumed by women is in the form of carotenoids.
The common carotenoids found in plants that can be chemically changed to the active retinol are beta-carotene, alpha-carotene, and beta-cryptoxanthin. Among these, beta-carotene is most efficiently made into retinol. Alpha-carotene and beta-cryptoxanthin are also converted to retinol, but only half as efficiently as beta-carotene.
The following list from sources other than the NIH contains some specifics about the general statements above.
Vitamin A Use from Other Sources
Retinol, and its metabolites, have critical roles in a number of physiological processes. This is indicated by the many disorders that accompany deficiency or excess states of the vitamin.
• If inadequate quantities of retinal, are present in the rod and cone cells of the eye, vision is impaired. Night blindness, or nyctalopia can result.
• Supplementation in children in Asia and Africa has been effective in reducing rates of infection, diarrhea, anemia and blindness. Such children receiving supplements grow faster, have better hemoglobin values, and die 30-60% less frequently than non-supplemented peers.
• Supplementation can reduce the incidence of malaria in children in susceptible areas.
• It also regulates T-cell (one of the white blood cells of the immune system) production and apoptosis (programmed cell death). This may determine whether a cell dies a normal death or lives on to possibly become a tumor cell.
• Of the many infectious diseases studied deficiency has been shown to increase the severity and frequency of disease. This may mean these important compounds have a necessary part of the immune process.
• Many infections are associated with inflammatory reactions that lead to a decrease in retinol binding protein, and thus to a lesser amount of circulating retinol.
• Retinol supplementation to malnourished children has demonstrated a decrease in the mortality rate from diseases such as measles.
• Normal levels are required for sperm production, and normal reproductive cycles in females.
• In Vitamin A deficiency the skin becomes scaly and mucous secretion is depressed. Epithelial cells appear to require these important compounds for proper differentiation and maintenance of skin. These effects appear to be due to impaired transcription regulation because of a deficiency in retinoic acid signaling.
• Normal functioning of osteoblasts and osteoclasts in bone remodeling depends on adequate levels of these vitamins. Osteoblasts lay down bone and osteoclasts remove bone in the continuous process of bone remodeling.
• Vitamin A is also important in protein utilization. Kwashiorkor is as much a vitamin deficiency disease as it is a protein deficiency. Vitamin deficiency leads to impaired protein utilization. In high protein low fat diets this compound is rapidly depleted. Such diets can lead to blindness as has happened in some food give away programs.
Human Studies of Fat Soluble Vitamins
In his book, Nutrition and Physical Degeneration, (copyright in 1939) Dr Weston A Price DDS, reported that fat soluble vitamins were deficient in practically every case of active tooth decay. The diets were also deficient in minerals, especially phosphorus.
The program that Dr. Price found most effective in controlling dental caries in public school programs included the use of small quantities of very high vitamin butter mixed in equal parts with high vitamin cod liver oil. Half a teaspoonful of this mixture 2-3 times a day with a diet low in sugar and starches, together with a gruel made from freshly ground cereal grains and raw whole milk from pasture fed animals, worked well. The pasture should be on a renewable agriculture system so as to contain adequate content of minerals, especially phosphorus, in the soil.
In his study of isolated peoples around the world, Dr Price found their local diets contained 90% more vitamin A than those in the USA in the 1930s and 40s. These isolated peoples had little or no dental decay while on their local diets. They were also free of many nutritional diseases that plague us today.
Dr. Price insisted that dental decay indicated serious metabolic problems elsewhere in the body.
Primitive peoples seldom ate lean meat alone but included organ meats from their local food supply which insured adequate vitamin A levels. The organ meats are demonized today. Even though they didn’t know one vitamin from another, primitive peoples did know what foods to eat to maintain optimum health.
For more information about these peoples, their local diets, and what happened when they abandoned their local diets for the sugary foods of the white man please click on “Isolated Peoples” on the Navbar at the left of this text, or on the Immunity link at the bottom of this page.
Human beings cannot absorb minerals satisfactorily from inorganic chemicals such as calcium carbonate according to Dr Price.
Some manufacturers provide some calcium in combination with organic substances such as malate or citrate. The best source is in food however.
The second part of this series features animal studies on fat soluble vitamins and sources of vitamin A.
To review the studies on isolated peoples click here.
To continue the study of vitamin A click here.
The Home Page defines the Nutritional Diseases.