Vitamin A – Beta-Carotene

   (People have asked why we include 2 types of vitamin A and why beta-carotene is a larger part.  This is the second part, explaining beta-carotene.)

   Harvard studies, and many others, show vitamin A to significantly reduce cancer and heart diseases. Proteins, minerals and water-soluble vitamins need A to be properly utilized by the body. It is also known for helping vision, diabetes, child viral infection resistance, bone formation, cell membranes, and healthy skin. Recent studies have indicated that much higher amounts may be needed.

The pre-formed vitamin A (usually called retinal) can build up to toxic levels in your liver in large amounts. This is the form found in most multi-vitamins and it is rightfully warned against taking too much of it. New studies are recommending that there is a much safer way to get vitamin A.

Beta-carotene is a much safer form – even for pregnant women according to Consumer Lab.  It is derived from plant sources and the body transforms it into vitamin A only as it is needed. As a bonus, it is also a more potent antioxidant than retinal A. Carrots and spinach are good sources but heavy cooking destroys the beta-carotene. This makes substantial supplementation warranted. Some might like to know that a low fat diet (which we do not recommend – see our reports) makes it much harder for the body to convert beta carotenes to A.

A Basic Primer   (Includes excerpts from the NIH Office of Dietary Supplements)

The term “vitamin A” makes it sound like there is one particular nutrient called “vitamin A,” but vitamin A is actually a broad group of related nutrients.  Each of these nutrients provides us with health benefits, but these benefits may be quite different and they may be provided in different ways. Here is a summary chart showing basic relationships between the forms of vitamin A.

Vitamin A-Related Nutrients

*These carotenoid forms of vitamin A may be converted by the body into retinoid forms.

  A. Retinoids

As you can see in the chart above, there are two basic forms of vitamin A:

• Retinoids (found in animal foods)
• Carotenoids (found in plant foods).

   There are some specific immune, inflammatory, genetic, and reproductive-related benefits of vitamin A that can only be obtained from the retinoid forms of the vitamin.  These retinoid forms can be especially important with respect to pregnancy and childbirth, infancy, childhood growth, night vision, red blood cell production, and resistance to infectious disease.

  B. Carotenoids

   Like the retinoid forms of vitamin A, the carotenoid forms also provide us with unique health benefits. Most carotenoid forms of vitamin A function as antioxidant and anti-inflammatory nutrients – as well as special roles in our health.  For example, there are vitamin A carotenoid benefits related to eye health (for example, prevention of age-related macular degeneration).

  C. Conversion of Carotenoids to Retinoids

   The bodies of many individuals may not be well equipped to convert carotenoid forms of vitamin A into retinoid forms.  Many different factors can contribute to problems, including:

• A person’s inherited genetic tendencies,
• Digestive problems,
• Bacterial imbalances in the digestive tract,
• Excessive use of alcohol,
• Excessive exposure to toxic chemicals,
• Imbalanced intake of vitamin A and vitamin D as a result of high-dose supplementation,
• The use of certain over-the-counter and/or prescription medications.

• If a person has problems converting carotenoids into retinoids, beta-carotene is the best carotenoid for the body to work with.
• If a person’s body is effectively able to convert carotenoids into retinoids, there may be some advantages to letting it do so (rather than trying to directly obtain high levels of retinol from food).

How Does Vitamin A Support Health?

  Retinoid Forms:

Vision Support

   The human retina contains a pigment, called rhodopsin, that allows the rod cells to detect small amounts of light, playing a fundamental role in the adaptation of the eye to low-light conditions and night vision.

Support of the Immune and Inflammatory Systems

   Throughout the body, but particularly in our digestive tract, vitamin A plays a key role in support of immune and inflammatory functions.  For example, in order to help neutralize unwanted bacteria and other micro-organisms, our immune system has the ability to:

• Make and release antibodies that can block their activity.
• They also have “braking” function that prevents them overreacting.

Recent research has shown that vitamin A plays a key role in both of these protective processes.  Vitamin A may be equally important for our immune and inflammatory “braking” system, in which our cells are prevented from becoming over-reactive.

Cell Growth Support

   Vitamin A is required for normal cell growth and development.  For example, the production of red blood cells in our bone marrow is a process that is known to require vitamin A in the form of retinoid acid.

Other Roles for Vitamin A

   Vitamin A is essential for reproductive processes in both males and females and plays a role in normal bone metabolism, regulating genetic events and for proper production of sperm.

Carotenoid Forms:

Preventing Vitamin A Deficiency

   From among the more than 600 carotenoids known to exist in plant foods, only three carotenoids – beta-carotene (the best), alpha-carotene, and beta-cryptoxanthin could be converted by the body (under the right circumstances) into retinoids.

Antioxidant, Anti-Inflammatory, and Immune-Enhancing Activity

   Carotenoids have received a large amount of research attention as potential anti-cancer and anti-aging compounds. These potential functions of carotenoids are closely related to their antioxidant and anti-inflammatory activity.

Promoting Proper Cell Communication

   In addition to their antioxidant and immune-enhancing activity, carotenoids have shown the ability to stimulate cell-to-cell communication.  Researchers now believe that poor communication between cells may be one of the causes of the overgrowth of cells, a condition that eventually leads to cancer.

What Food Practices Might Lead to a Dietary Deficiency of Vitamin A?

In the United States, about two-thirds of all vitamin A in-take from food comes in the form of retinyl esters found in animal products.  Butter, cheese, eggs, and organ meats like liver are among the top 10 sources of vitamin A for U.S. adults.  Persons who seldom consume any of these foods may be a greater risk of vitamin A deficiency.

Outside of the Unites States, dietary deficiency of vitamin A in its retinoid form is common in many non-industrialized countries, and it is associated with the high incidence of blindness, viral infections, and child mortality.

Carrots, tomatoes, leafy greens, sweet potatoes, and margarines colored with beta-carotene are found in the top 10 pro-vitamin A-containing foods in the U.S.  However, U.S. adults eat relatively small amounts of vegetables in general.

U.S. adults who take vitamin A supplements have a much lower rate of deficiency than non-supplement users.  However, even when vitamin A from food and supplements is added together, about one-third of all U.S. adults still fail to get the vitamin A they need.

If regular intake of green leafy vegetables or brightly orange- or red-colored vegetables like carrots, tomatoes, sweet potatoes, or red bell peppers in not part of your meal plan, your risk of carotenoid deficiency is increased. Similarly, if you do not regularly consume orange-, red- or pink-colored fruits like watermelon, cantaloupe, papaya, and pink grapefruit, you are also likely to have increased risk of carotenoid deficiency.

Risk of Dietary Toxicity

Retinoid Forms:

   It is almost impossible for ordinary intake of animal foods to result in vitamin A toxicity.  Foods simply do not contain enough preformed vitamin A to expose us to toxicity-producing amounts.

 While vitamin A toxicity can be a problem for our health, it comes from improper use ofretinoid-containing supplements, not from our diet.  Most causes of vitamin A toxicity are due to accidental ingestion of supplemental doses exceeding 660,000 IU (200,000 mcg retinol equivalents) and 330,000 IU (100,000 mcg retinol equivalents) by adults and children, respectively.

Carotenoid Forms:

   A telltale sign of excessive consumption of beta-carotene is a yellowish discoloration of the skin, most often occurring in the palms of the hands and soles of the feet. This condition is called carotenodermia and is generally considered to be reversible and harmless.

References:

Bailey RL, Fulgoni VL, Keast DR et al. Examination of Vitamin Intakes among US Adults by Dietary Supplement Use. J Acad Nutr Diet. 2012;112:657-663.

Bloomfield L. Food irradiation and vitamin A deficiency: Public health implications. Food Policy, Volume 18, Issue 1, February 1993, Pages 64-72.

Brandtzaeg P. The gut as communicator between environment and host: Immunological consequences. European Journal of Pharmacology, Volume 668, Supplement 1, September 2011, Pages S16-S32.

Campbell AA, Thorne-Lyman A, Sun K et al. Indonesian women of childbearing age are at greater risk of clinical vitamin A deficiency in families that spend more on rice and less on fruits/vegetables and animal-based foods. Nutrition Research, Volume 29, Issue 2, February 2009, Pages 75-81.

Gautam S, Platel K and Srinivasan K. Influence of β-carotene-rich vegetables on the bioaccessibility of zinc and iron from food grains Original Research Article

Food Chemistry, Volume 122, Issue 3, 1 October 2010, Pages 668-672.

Grune T, Lietz G, Palou A et al. Beta-Carotene Is an Important Vitamin A Source for Humans. J Nutr. 2010 December; 140(12): 2268S–2285S. Published online 2010 October 27. doi: 10.3945/jn.109.119024.

Hogarth CA and Griswold MD. The key role of vitamin A in spermatogenesis. J Clin Invest. 2010 April 1; 120(4): 956–962. Published online 2010 April 1. doi: 10.1172/JCI41303.

Mata-Granados JM, Cuenca-Acevedo R, Luque de Castro MD et al. Vitamin D deficiency and high serum levels of vitamin A increase the risk of osteoporosis evaluated by Quantitative Ultrasound

Measurements (QUS) in postmenopausal Spanish women. Clinical Biochemistry, Volume 43, Issues 13–14, September 2010, Pages 1064-1068.

Semba RD, de Pee S, Sun K et al. Low intake of vitamin A–rich foods among children, aged 12–35 months, in India: association with malnutrition, anemia, and missed child survival interventions.

Nutrition, Volume 26, Issue 10, October 2010, Pages 958-962.

Shi J and Le Maguer M. Lycopene in tomatoes: chemical and physical properties affected by food processing. Crit Rev Biotechnol. 2000;20(4):293-334.

Spencer SP and Belkaid Y. Dietary and commensal derived nutrients: shaping mucosal and systemic immunity. Current Opinion in Immunology, In Press, Corrected Proof, Available online 31 July 2012.

Tang G. Bioconversion of dietary provitamin A carotenoids to vitamin A in humans. Am J Clin Nutr. 2010 May; 91(5): 1468S–1473S. Published online 2010 March 3. doi: 10.3945/ajcn.2010.28674G.

Unlu NZ, Bohn T, Francis DM et al. Lycopene from heat-induced cis-isomer-rich tomato sauce is more bioavailable than from all-trans-rich tomato sauce in human subjects. Br J Nutr. 2007 Jul;98(1):140-6. Epub 2007 Mar 29.

van Jaarsveld PJ, Marais DW, Harmse E et al. Retention of β-carotene in boiled, mashed orange-fleshed sweet potato. Journal of Food Composition and Analysis, Volume 19, Issue 4, June 2006, Pages 321-329.