Vitamin A – increase nutrition value of a product (part 1). General information.
Imagine your vision (especially at night) is weaker and weaker and you feel sick of that. For example, you have difficulties to recognise people in the evening. Imagine, how difficult is driving a car during the night for people with a similar issue you are experiencing. You are starting looking for help. You are going to doctors, you asking for an advice but couldn’t find a quick solution. They told you that you will feel this discomfort for a longer time. Why not protect your family, your colleagues and your clients before this happened? Why not fortify the food products with ingredients containing Vitamin A or Provitamin A? Why not add Vitamin A to your products and present them to customers with a vision support function?
What is Vitamin A?
Vitamin A is the name of vitamers representing a group of fat-soluble retinoids, including Retinol, Retinal, Retinoic Acid and Retinyl esters. Two forms of Retinyl esters are the most important from the industrial perspective – there are Retinyl Acetate and Retinyl Palmitate. Vitamin A can be obtained also from Carotene, by cleaving it to Retinal and a further reduction to Retinol or oxidation to Retinoic Acid. For this reason beta-Carotene, alpha-Carotene and beta-Cryptoxanthin are called Pro-Vitamins A.
Functions of Vitamin A.
Vitamin A is involved in immune functions, vision, reproduction, and cellular communication.
The most significant sign of Vitamin A deficiency is weakening of a night vision. This vitamin is critical for vision as an essential component of rhodopsin, a protein that absorbs light in the Retinal receptors.
Many of the non-visual functions of Vitamin A are mediated by Retinoic Acid, which regulates gene expression by activating intracellular Retinoic Acid receptors. Vitamin A is also essential in the immunological function, reproduction and embryonic development of vertebrates as evidenced by the impaired growth, susceptibility to infection and birth defects observed in populations receiving suboptimal Vitamin A in their diet.
Vitamin A is also needed for the correct functioning of epithelial cells. In Vitamin A deficiency, mucus-secreting cells are replaced by keratin producing cells, leading to xerosis.
Also, glycoprotein synthesis requires adequate Vitamin A status. In severe Vitamin A deficiency, lack of glycoproteins may lead to corneal ulcers or liquefaction.
Vitamin A is essential to maintain intact epithelial tissues as a physical barrier to infection, as well. It is also involved in maintaining a number of immune cell types from both the innate and acquired immune systems. These include the lymphocytes (B-cells, T-cells, and natural killer cells), as well as, many myelocytes (neutrophils, macrophages, and myeloid dendritic cells).
An activity of Vitamin A in a human body.
An activity of Vitamin A is expressed on the food or supplement labels in International Units or as an equivalent of 1IU, which is equal to:
- 0.3 mcg Retinol,
- 0.344 mcg Retinyl acetate,
- 0.55 mcg Retinyl palmitate,
- 0.6 mcg beta-Carotene,
- 1.2 mcg alpha-Carotene.
An activity of Vitamin A can be expressed also as Retinol Equivalents (RE). 1 mcg RE is equal to:
- 1 mcg Retinol,
- 1.15 mcg Retinyl Acetate,
- 1.83 mcg Retinyl Palmitate,
- 12 mcg all-trans-beta-Carotene,
- 24 mcg another provitamin A carotenoids.
Based on above conversion rates between mcg RE and IU are as follows:
- 1 IU Retinol = 0.3 mcg RE,
- 1 IU beta-Carotene from dietary supplements = 0.15 mcg RE,
- 1 IU beta-Carotene from food = 0.05 mcg RE,
- 1 IU alpha-Carotene or beta-Cryptoxanthin = 0.025 mcg RE.
Under FDA's new labelling regulations for foods and dietary supplements that take effect by July 26, 2018 (for companies with annual sales of $10 million or more) or July 26, 2019 (for smaller companies), vitamin A will be listed only in mcg and not IUs (Food and Drug Administration. Food labelling: Revision of the Nutrition and Supplement Facts labels. Federal Register 2016; 81:33741-999).
A level of Vitamin A in a body.
Retinol and carotenoids levels are typically measured in plasma. Plasma Retinol levels are useful for assessing Vitamin A inadequacy. However, their values for assessing marginal Vitamin A status are limited because they do not decline until vitamin A levels in the liver are almost depleted. Reserves of Vitamin A in a liver can be measured indirectly through the relative dose-response test, in which plasma Retinol levels are measured before and after the administration of a small amount of Vitamin A. A plasma Retinol level increase of at least 20% indicates an inadequate Vitamin A level. Also a plasma Retinol concentration lower than 0.70 micromoles/L (or 20 mcg/dL) reflects Vitamin A inadequacy.
Quick look for recommended intakes
Recommended Dietary Allowances for Vitamin A has been published in 2001. As you can see from table and graph below the amount of needed vitamin A is increasing with age.
Because Vitamin A can be toxic (read below) if overdosed, upper limits of uptakes for Vitamin A has been well established.
General adequate intakes for infants (Institute of Medicine - 2001) are:
- Infants (0-6 months) 400mcg RE/day,
- Infants (7-12 months) 600mcg RE/day.
Vitamin deficiency and hypervitaminosis.
The optimal level of Vitamin A in the body is important at every age. Too low and too high concentrations of Vitamin A are undesirable, however, can be observed. Especially in developing countries, Vitamin A deficiency typically begins during infancy. Chronic diarrhea also leads to excessive loss of Vitamin A in young children. A lack of Vitamin A has a negative influence on vision (a function of a night-photoreceptor Rodopsin), bone growth (osteoporosis) and functioning of immune systems. The most common symptom of Vitamin A deficiency in young children and pregnant women is xerophthalmia. One of the early signs of xerophthalmia is, mentioned above, night blindness, or the inability to see in low light or darkness. Vitamin A deficiency is one of the top causes of preventable blindness in children.
Vitamin A can also be toxic, especially if it is present in concentrations above the limits (mentioned above). Because Vitamin A is fat soluble, the body stores excess amounts, primarily in the liver, and these levels can accumulate. Chronic intakes of excess Vitamin A lead to increased intracranial pressure (pseudotumor cerebri), dizziness, nausea, headaches, skin irritation, pain in joints and bones, coma, and even death. When people consume too much Vitamin A, usually in supplements, are in a risk. Even they discontinue uptake, their Vitamin A tissue levels take a long time to fall, and the resulting liver damage is not always reversible.
Unlike Vitamin A in form of retinoid, beta-Carotene is not known to be toxic even at higher intakes (20–30 mg/day). The most significant effect of long-term, excess beta-Carotene is carotenodermia, a reversible and harmless condition in which the skin becomes yellow-orange.
Natural sources of Vitamin A.
There are two sources of dietary Vitamin A. Active forms (retinoids), which are immediately available to the body, are present in animal products including dairy products, fish, and meat (especially liver and eggs). Precursors of Vitamin A (provitamins, carotenoids), which must be converted to active forms by the body, are obtained from fruits and vegetables containing yellow, orange and dark green pigments. Especially, plants, like carrots and spinach, are rich sources of carotenes. In a table below are present products, which are the richest in the Vitamin A.
To correctly understand “the Vitamin A world”, we have to remember, that Vitamin A in food products is present in different forms:
- Retinol (and dehydroRetinol and Retinol esters),
- Retinal (and dehyroRetinal),
- Retinoic Acid,
- Carotenoids (primarily α, β, and γ Carotene).
The U.S. Department of Agriculture's (USDA's) Nutrient Database lists the nutrient content of many foods and provides a comprehensive list of foods containing Vitamin A in IUs arranged by nutrient content and by food name, as well as, a list of foods containing beta-Carotene in mcg arranged by nutrient content and by food name (U.S. Department of Agriculture, Agricultural Research Service. USDA National Nutrient Database for Standard Reference, Nutrient Data Laboratory Home Page, 2011).
We have to also consider bioavailability of Vitamin A. In the intestine, Vitamin A is absorbed if it is protected from being chemically changed by Vitamin E. During the absorption process in the intestines, Retinol is incorporated into chylomicrons as the ester form, and in this form is transported to the liver. Liver cells store Vitamin A as the ester, and when Retinol is needed in other tissues, it is de-esterified and released into the blood as the alcohol (Retinol). Retinol then attaches to a serum carrier, Retinol binding protein, for transport to target tissues.
In relation to Carotenoids, their bioavailability ranges between 1/5 to 1/10 of Retinols. Important here is known, that Carotenoids are better absorbed when ingested as part of a fatty meal.
- properties of different forms of Vitamin A,
- available industrial Vitamin A ingredients,
- food composition or fortification with Vitamin A.