Lesson 14: Vitamin A – Carotenoids

Vitamin A – Carotenoids

Vitamin A is a group of similar molecules that includes retinol, retinal, and retinoic acid. It is an essential nutrient that we need to get from our diets.  It is needed for growth, healthy skin and hair, mucus membranes, digestive juices, our immune system, and also for good eye health and vision.  Its name, retinol or retinal, comes from its abundance in the retina of the eye.  Vitamin A works with vitamin D to normalise immune tolerance and vitamin A deficiency predisposes individuals to gut mucosal damage.1 Vitamin A levels are also important in thyroid health as it is needed for the uptake of Iodine2 and is required for the thyroid hormone triiodothyronine (T3) to bind to intracellular receptors.

The most important fact about vitamin A is the difference between retinoid and carotenoids. The vitamin A from animal sources is retinoid, also called retinol, while plant sources of vitamin A is carotenoids, specifically three forms which are α-carotene, b-carotene and β-cryptoxanthin which can be from food or supplements and converted to Retinol. There are three other carotenoids, Lycopene, Lutein, and Zeaxanthin all of which cannot be converted into retinol but also have their own specific role in human health. Whilst fat assists in the absorbtion of carotenoids and conversion to Vitamin A, Fibre can inhibit this process. Whilst cooking some foods can give a higher carotenoid and higher antioxidant level with great absorption and therefore greater conversion to Vitamin A, the heating process will diminish other vitamin properties within the food source such as Vitamin C which unlike the Fat soluable Vitamin A, Vitamin C is water soluable.

a-Carotenoids – converts at a ratio of 1/24 (24mcg of a-carotenoids = 1mcg of retinol)

b-Carotenoids – converts at a ratio of 1/12 (12mcg of b-carotenoids = 1mcg of retinol)

b-Cryptoxanthin – Converts at a ratio of 1/24 (24mcg of b-cryptoxanthin = 1mcg Retinol)

Lycopene – Does not convert to Vitamin A ( Trans-Lycopene / Cis-Lycopene)

Lutein – Does not convert to Vitamin A

Zeaxanthin – Does not convert to Vitamin A


Animal sources of retinol are bio-available, which means the body can utilize it. The vitamin A from plant sources, in contrast, must first be converted to retinol to be useful in the body. This poses two big problems.

First, when we are in pristine health, it requires at least six units of carotenes to convert into 1 unit of retinol (source). To put this in perspective, that means one must eat 4 1/2 pounds of carrots to potentially get the amount of useable A as in 3 oz. of beef liver (source). What happens if we have digestive issues, hormone imbalances, or other health problems? It requires even more units of carotene in the ratio.

Second, the carotene-to-retinol conversion is HIGHLY compromised. As a matter of fact, this conversion is negligible for many individuals.

This conversion is virtually insignificant:

1)In infants
2)In those with poor thyroid function (hypothyroidism)
3)In those with diabetes
4)In those who are on a low fat diet or have a history of low fat dieting
5)In those who have compromised bile production (gallbladder and digestive issues)

α-Carotene and β-carotene are provitamin A carotenoids, meaning they can be converted in the body to vitamin A. The vitamin A activity of β-carotene in foods is 1/12 that of retinol (preformed vitamin A). Thus, it would take 12 mcg of β-carotene from foods to provide the equivalent of 1 mcg (0.001 mg) of retinol. The vitamin A activity of α-carotene from foods is 1/24 that of retinol, so it would take 24 mcg of α-carotene from foods to provide the equivalent of 1 mcg of retinol. Orange and yellow vegetables like carrots and winter squash are rich sources of α- and β-carotene. Spinach is also a rich source of β-carotene, although the chlorophyll in spinach leaves hides the yellow-orange pigment. Some foods that are good sources of α-carotene are pumpkins and carrots and β-carotene are pumkins, carrots, spinach and sweet potato. For example 1 cup of carrot juice is 10.2mg which would be 0.425 mg of Vitamin A

β-CaroteneBecause it is has vitamin A activity, β-carotene may be used to provide all or part of the vitamin A in multivitamin supplements. The vitamin A activity of β-carotene from supplements is much higher than that of β-carotene from foods. It takes only 2 mcg (0.002 mg) of β-carotene from supplements to provide 1 mcg of retinol (preformed vitamin A). The β-carotene content of supplements is often listed in international units (IU) rather than mcg; 3,000 mcg (3 mg) of β-carotene provides 5,000 IU of vitamin A. Most commercial supplements contain 5,000-25,000 IU of β-carotene. Although β-carotene can be converted to vitamin A, the conversion of β-carotene to vitamin A decreases when body stores of vitamin A are high. This may explain why high doses of β-carotene have never been found to cause vitamin A toxicity. High doses of β-carotene (up to 180 mg/day) have been used to treat erythropoietic protoporphyria, a photosensitivity disorder, without toxic side effects. For example 1 cup of carrot juice is 22mg which would be 1.83 mg of Vitamin A

β-CryptoxanthinBecause of the free radical quenching ability and effects on cell differentiation and proliferation, multiple recent studies have suggested that β-cryptoxanthin protects against certain diseases such as cardiovascular disease, osteoporosis, and cancer (Uchiyama and Yamaguchi 2005; Lian and others 2006; Voutilainen and others 2006; Lorenzo and others 2009). Like α-and β-carotene, β-cryptoxanthin is a provitamin A carotenoid. The vitamin A activity of β-cryptoxanthin from foods is 1/24 that of retinol, so it would take 24 mcg of β-cryptoxanthin from food to provide the equivalent of 1 mcg (0.001 mg) of retinol. Orange and red fruit and vegetables like sweet red peppers and oranges are particularly rich sources of β-cryptoxanthin. Some foods that are great sources of β-cryptoxanthin are cooked sweet red peppers and cooked pumpkin. For example 1 cup of cooked pumpkin is 3.6mg of  β-Cryptoxanthin which is just 0.15 mg when converted to Vitamin A. 1 medium Orange raw is just 0.2mg of β-Cryptoxanthin whilst it is double for fresh orange juice at 0.4 mg due to its better bioavailability without the fibre. So a Fresh Orange Juice of 5 oranges would be 2 mg of β-cryptoxanthin which would be 0.083mg of Vitamin A

Lycopene is a naturally occurring chemical that gives fruits and vegetables a red color. It is one of a number of pigments called carotenoids. Lycopene is a powerful antioxidant that may help protect cells from damage. Lycopene is found in watermelons, pink grapefruits, apricots, and pink guavas. It is found in particularly high amounts in tomatoes and tomato products. Heat and fat makes lycopene more bioavailable such as cooking tomatoes in oil. Although when heat treated the antioxidant levels increase and continue to increase the longer exposure to heat, which is also true for the carotenoid level, the vitamin c level drops and continues to drop the longer the exposure to heat. There are two forms of Lycopene which are Cis-Lycopene and Trans-Lycopene. Studies suggest that some cis-lycopene isomers are more bioavailable than the trans-lycopene isomer. We hypothesized that tangerine tomatoes, which predominantly contain the tetra-cis isomer, should be a good source of bioavailable lycopene. We fed lunches containing 300 g tangerine or red tomato sauce per day to 21 healthy adults in a double-blind crossover design. We collected blood at baseline and after each treatment and washout period. We measured tetra-cis, other cis, and trans lycopene, as well as other carotenoids, by reversed-phase high-performance liquid chromatography. Both tomato sauces increased lycopene concentrations in blood, but the tangerine tomato sauce caused a greater increase of total and tetra-cis-lycopene. The cis isomer(s) may also have facilitated absorption of the trans-lycopene isomer. Indices of oxidative damage decreased as serum lycopene concentrations increased. Our results suggest that total lycopene concentrations can be increased by substituting tetra-cis-lycopene-rich tangerine tomatoes for common red tomatoes in the diet. Absorption of carotenoids is a complex issue involving release from the food microstructure matrix, dissolution into mixed micelles, intestinal uptake, incorporation into chylomicrons, distribution to the tissues, uptake by liver and resecretion into VLDL, which are progressively transformed into LDL. Lycopene absorption from food sources is widely documented. The best food sources providing lycopene in a bioavailable form are tomato paste and tomato sauce, whereas lycopene from other sources such as fresh tomatoes and unheated tomato juice is poorly absorbed. According to Harvard Medical School, one slice of raw tomato contains approximately 515 micrograms lycopene, while 2 tablespoons of tomato paste contains 13,800 micrograms of lycopene or One cup of canned tomato paste provides 75 mg of lycopene, compared to 5 mg in one cup of raw tomatoes. 1 medium pink grapefruit is 4.9mg and 1 slice of watermelon is 14.7mg, patients being treated with prostate cancer are given 10 mg of lycopene daily. Scientific studies show that lycopene helps prevent prostate, lung, and stomach cancers.3 There is also some evidence that cancers of the pancreas, colon and rectum, esophagus, oral cavity, breast, and cervix could be reduced with increased lycopene intake.3 This hearty antioxidant provides a two-for-the-price-of-one deal as it may help reduce your risk of developing cardiovascular disease by reducing LDL (“bad”) cholesterol and lowering blood pressure.

Lutein and zeaxanthin are two types of carotenoids, which are yellow to red pigments found widely in green leafy vegetables and other green or yellow vegetables. Among these, cooked kale and cooked spinach top the list. For example 1 cup of cooked spinach is 20.4 mg whilst 1 cup of raw spinach is just 3.7mg. It is suggested that these antioxidants and carotenoids are needed for eye health but no recommended daily allowance has been developed.

Example of Dietary conversion of carotenoids to Vitamin A with Raw Vegan Diet

1 Cup of Raw Spinach juiced – 5.6mg Beta carotene / .46mg (460mcg of Vitamin A)

1 Cup of Orange Juice – 2 mg of β-cryptoxanthin / 0.083mg (83mcg of Vitamin A)

1 Cup of carrot Juice with teaspoon of Hemp oil – 22mg of b-carotenoid and 10.2 of a-carotenoid which is 2.255mg (2255mcg Vitamin A)

How to Get Enough Vitamin A 

Total Potential Vitamin A from 1 cup of orange juice (5 oranges), 1 cup of carrot juice and 1 cup of spinach juiced is 2798mcg Retinol (Vitamin A) which is 2.8mg (9326 Iu of Vitamin A) – The RDA of Vitamin A is 3000 IU.

Enhance Absorption by

Combining carotene rich foods with Fat (Hemp oil , Avocado, Coconut butter)

Do not Mix carotene rich foods with fibre as this will inhibit absorption (so juiced oranges and carrots are better sources than smoothies for Vitamin A)

For Lycopene you can eat water melon or slow cooked tomatoes and sundried tomatoes for greater absorption

Fermented Vegetables will greatly increase bioavailablility of carotenoids in foods ( ferment spinach, carrot, red and yellow peppers, squash and tomatoes For a high bioavailable mix of carotenoids )


Further Reading:

Read more about Carotenoids
For Lutein and Zeaxanthin food content analysis 
Read More about nettles, which are fantastic for Calcium, Vitamin K and Vitamin A (b-carotene).
Read More here about oranges 
View Vitamin Conversion Chart 

Vitamin Conversion chart 

Vitamin A: 1 IU is the biological equivalent of 0.3 mcg retinol, or of 0.6 mcg beta-carotene
Vitamin C: 1 IU is 50 mcg L-ascorbic acid
Vitamin D: 1 IU is the biological equivalent of 0.025 mcg cholecalciferol or ergocalciferol
Vitamin E: 1 IU is the biological equivalent of about 0.67 mg d-alpha-tocopherol, or 0.9 mg of dl-alpha-tocopherol.