Carotenoids in plants are the phytonutrients that help plants absorb light energy for photosynthesis. As reported by the Linus Pauling Institute at Oregon State University, carotenoids function as antioxidants in the human body. They have cancer-fighting properties, as reported by the Physicians Committee for Responsible Medicine. Some carotenoids are converted into vitamin A, utilized in vision, growth, and development. Carotenoids are reported to have an immune system and anti-inflammatory benefits. They are sometimes found to play a role in the prevention of cardiovascular disease.
Pro-vitamin A Function
Vitamin A is considered essential for normal growth and development, vision, and immune system function. The essential function of carotenoids in humans is that of pro-vitamin A carotenoids, alpha-carotene, beta-carotene, and beta-cryptoxanthin acting as a source of vitamin A. Pro-vitamin A carotenoids are not easily absorbed compared to the preformed vitamin A. They have to be converted to retinol and retinoid by the body. The conversion of pro-vitamin A carotenoids into retinol is variable and depends on food preparation, food matrix, one's absorptive capacity, and digestive capacity.
Antioxidant Function
The primary antioxidant function of deactivating singlet oxygen, which is formed during photosynthesis, in plants is possessed by carotenoids. Among the carotenoids, lycopene is the effective deactivating agent of singlet oxygen. Carotenoids could also stop fat oxidation in some cases, but their function in humans seems more complex. This deactivation of singlet oxygen which is important for plants is not equally important to humans.
There is little evidence to suggest that carotenoids and their metabolites might stimulate the antioxidant expression and enzyme detoxification through the activation of nuclear factor E2-related factor 2 (Nrf2)- dependent pathway.
Immune Function
Vitamin A is considered to be useful for the normal functioning of the immune system. It is not easy to establish whether the effects of pro-vitamin A carotenoids are associated with vitamin A activity or other activities of carotenoids. Some clinical trials found that beta-carotene supplementation enhances various immune system biomarkers, high intake of lutein and lycopene carotenoids devoid of vitamin A activity. Increased intake of Beta-carotene supplementation did not lead to similar enhancements in the biomarkers of the immune function.
Intercellular Communication
Carotenoids facilitate communication between the neighboring cells grown in culture; this happens by triggering the synthesis of connexin proteins. Connexins create pores in the cell membranes, driving the cells to communicate through the exchange of small molecules. This intercellular communication is present in cells in the state of differentiation, while cancer cells do not possess this communication. The gene coding of the connexin protein is expressed highly through intercellular communication facilitated by the carotenoids. Expression of gene coding connexin protein is not associated with vitamin A or with the antioxidant properties of different carotenoids. It involves a retinoic acid receptor (RAR)-independent mechanism.
To unlock this lesson you must be a Study.com Member.
Create your account
The absorption of carotenoids is influenced by the type of fat, presence of soluble fiber, type and amount of carotenoids in the food. The cells lining the intestines absorb the carotenoids by passive diffusion. The apical membrane transporters like scavenger receptor class B type-I and cluster determinant 36 aid in the active uptake of carotenoids.
Most of the carotenoids in food are available in the all-trans form while cooking converts them into other forms of isomers. The low bioavailability of carotenoids from foods compared to supplements is related to the plant's proteins. Cutting and cooking the vegetables disturb the plant matrix making the carotenoids bioavailable. Heating tomatoes enhances the bioavailability of lycopene in tomatoes in the oil.
Carotenoids foods
| Alpha-carotene rich foods | Beta-carotene rich foods | Beta-cryptoxanthin rich foods | Lycopene rich foods | Lutein and zeaxanthin rich foods |
| Pumpkin, carrots, mixed vegetables, winter squash, plantains, collards, tomatoes, tangerines, and peas. | Carrot, pumpkin, spinach, sweet potato, collards, kale, turnip, pumpkin, green dandelions, and cantaloupe. | Pumpkin, papayas, sweet red peppers, orange juice, tangerines, carrots, yellow corn, watermelon, paprika, oranges, and nectarines. | Tomatoes, watermelon, pink grapefruit, and baked beans. | Spinach, kale, turnip, collards, dandelion, mustard greens, summer squash, peas, winter squash, pumpkin, Brussels sprouts, broccoli, sweet yellow corn, avocado, and egg yolk. |
To unlock this lesson you must be a Study.com Member.
Create your account
Alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein, zeaxanthin, and lycopene are the most common carotenoids available in diets. Alpha-carotene, beta-carotene, and beta-cryptoxanthin are pro-vitamin A carotenoids that can be converted into retinol by the body. Lutein, zeaxanthin, and lycopene are non-pro vitamin A carotenoids that cannot be converted to retinol.
Carotenes
Alpha-carotene and Beta-carotene: These carotenoids are pro-vitamin A types that the body can convert into vitamin A. The vitamin A activity of beta-carotene in the food is 1/12 as that of retinol. So, it would take up around 12 micrograms of beta-carotene from food to create an equivalent of 1 microgram of retinol. The vitamin A activity of alpha-carotene in the food is 1/24 as that of retinol. So, it would take up around 24 micrograms of beta-carotene from food to create an equivalent of 1 microgram of retinol.
Beta-cryptoxanthin: This is a pro-vitamin A carotenoid. The vitamin A activity of beta-cryptoxanthin in the food is 1/24 as that of retinol. So, it would take up around 24 micrograms of Beta-carotene from food to create an equivalent of 1 microgram of retinol.
Xanthophylls
Lycopene: This is not a pro-vitamin A carotenoid as the body cannot convert it into retinol.
Lutein and Zeaxanthin: These compounds are classified as xanthophylls and non-pro vitamin A carotenoids. The methods used to quantify lutein and zeaxanthin will not separate these two compounds. Both these pigments are present in various fruits and vegetables. Rich sources of lutein are dark green vegetables like kale and spinach. These are poor sources of zeaxanthin. The highly bioavailable sources of lutein are avocados and egg yolks, and they are low in lutein content.
Purified carotenoids are commercially available as dietary supplements in the US without any prescription. Carotenoids are absorbed well if the meal is rich in fat.
To unlock this lesson you must be a Study.com Member.
Create your account
One of the beneficial roles of carotenoids on human health is their antioxidant property. Other benefits also include their impact on the gap junction potentials and insulin-like growth factors. The antioxidant activity is against the free radicals. Research has found beta-carotene to be a micronutrient that prevents effectively lethal hematoporphyrin photosensitization in mice. It was also found to be able to treat protoporphyrin-induced photosensitivity in human genetic disease erythropoietic protoporphyria.
Lutein and zeaxanthin effectively reduce the risk of age-related macular degeneration, a leading cause of blindness. These carotenes reduce cataract incidence and light sensitivity if they are consumed in sufficient quantities regularly. Lutein is known to prevent the formation of plaques that restrict the flow of blood to the heart. Lutein has an antioxidant effect on cholesterol, preventing it from building up in the arteries and clogging them. Studies have shown that individuals who added lutein supplements to their diets did not find too much thickening of their arterial walls than those who did not add.
A few research studies have shown that beta-cryptoxanthin is associated with preventing lung cancer. Beta-cryptoxanthin might be associated with reducing the risk of inflammatory polyarthritis, which includes rheumatoid arthritis. Scientists consider that its antioxidant capacity is probably reducing chronic inflammation. Beta-carotene showed a positive effect by converting it into vitamin A, which helps in improving vision. Beta-carotene shows a negative effect by increasing the risk of lung cancer when taken by smokers. It is found to reduce the risk of metabolic syndrome. After Beta-carotene, Alpha-carotene can be converted into vitamin A.
Lycopene is associated with reducing the risk of prostate cancer risk and has been linked to having a role in promoting bone health and preventing the development of osteoporosis. Diets that have lycopene incorporated resulted in a decrease in free radicals in postmenopausal women.
To unlock this lesson you must be a Study.com Member.
Create your account
Carotenoids are red, yellow, and orange pigments and phytonutrients synthesized by plants. The common dietary carotenes are Alpha-carotene, beta-cryptoxanthin, beta-carotene, lutein, lycopene, and zeaxanthin. Alpha-carotene, beta-carotene, and beta-cryptoxanthin are pro-vitamin A carotenoids converted by the body enzymes into retinol. Lutein, lycopene, and zeaxanthin are non-pro vitamin A carotenoids. Some observational studies have shown the role of a few carotenoids in reducing the risk of cardiovascular disease and cancer. However, a few randomized controlled trials did not conclude that beta-carotene in high doses could reduce the risk of cardiovascular disease and cancer.
Some observational studies have shown that blood lycopene concentration has an inverse association with the risk of developing prostate cancer. Some research studies have shown that a diet rich in lutein and zeaxanthin might aid in delaying the development of age-associated macular degeneration. Carotenoids are absorbed with fat taken through a meal. Cutting and cooking vegetables consisting of carotenoids increase the bioavailability of carotenoids present in them. Some of the food sources of carotenoids include pumpkin, carrots, winter squash, tomatoes, peas, kale, turnip green, collards, cantaloupe, dandelion green, watermelon, paprika, nectarines, yellow corn, sweet peppers, tangerine, grapefruit, beans, broccoli, Brussels sprouts, avocado, egg yolk, summer squash, and mustard greens, etc. Carotenoids have the antioxidant property.
To unlock this lesson you must be a Study.com Member.
Create your account
Video Transcript
What are Carotenoids?
When you are in the produce section at the local market, do you ever stop to notice the variety of color in the fruits and vegetables around you? From vibrant orange and yellow peppers to deep red tomatoes and dark leafy greens, bursts of color are everywhere. Thanks to a group of pigments known as carotenoids, we can eat a virtual rainbow of food.
 |
Carotenoids don't simply exist just to make our food look pretty; they also have a wealth of health benefits, such as giving us vitamin A. This provides our bodies with antioxidants, which stabilize harmful molecules in the body called free radicals. In fact, an enormous variety of fruits and vegetables contain carotenoids that are crucial in our diets for our overall health. In this lesson, you will get to learn more about these compounds and gain an understanding of how they help us.
Types and Function of Carotenoids
There are over 600 known carotenoids found in nature. Carotenoids are fat-soluble compounds, meaning they are broken down in the presence of fat. Whether or not you love fruits and vegetables, you have most likely consumed many foods containing these compounds. If you have munched on carrots or choked down a dish of creamed spinach, you have indeed eaten them. Let's take a deeper look at the different categories of carotenoids and which foods they encompass.
There are two main groups of carotenoids: the carotenes and the xanthophylls. These two categories differ in molecular structure and composition. Let's look first at the carotenes, which are molecules known as hydrocarbons. Carotenes are the carotenoids found in the yellow and orange fruits and vegetables such as pumpkin, sweet potatoes, cantaloupe, apricots and, yes, carrots. If you associate the word carrot with carotene, you will certainly be able to remember the color of these pigments.
 |
One of the more familiar carotenes is beta-carotene. Beta-carotene is known as a provitamin A carotene because it can be converted by the body to a usable form of vitamin A. In fact, many of these orange and yellow foods are the primary source of vitamin A in a diet. Remember when your parents told you to eat your carrots so you would have good eyesight? This was not just a ploy to get you to eat your vegetables. Vitamin A is essential for our bodies for many reasons that we will discuss a little later.
Another very well-known carotene is lycopene. Bringing the rich, red color to tomatoes, lycopene has many antioxidant properties. One interesting fact about lycopene is that its properties and availability to the body are enhanced when tomatoes are cooked. Typically, cooking fruits and vegetables takes away some of their nutritive properties, but not with tomatoes. So keep making those delicious simmered sauces to gain even more health benefits. And lycopene isn't exclusively found in tomatoes, but also in pink grapefruit as well as watermelon.
 |
Xanthophylls, the other type of carotenoid, are oxygen-containing molecules. They are found in dark leafy greens such as spinach and kale, as well as broccoli. If you pay attention to healthy food at all, you are sure to recognize these vegetables as some of the healthiest around. Xanthophylls are also antioxidants, and two in particular have great importance in the health of our eyes.
 |
Lutein and zeaxanthin are two xanthophylls that are found in green leafy vegetables and in some fruits as well. They also have antioxidant properties, especially regarding the eyes. These two carotenoids have the ability to absorb the blue light that enters our eyes. This type of light can be damaging when it reaches the inner structures of the eye. Because they protect the eyes from this type of damage, lutein and zeaxanthin reduce the likelihood of cataracts and macular degeneration.
Benefits of Carotenoids
As previously mentioned, carotenoids provide us with numerous health benefits. Provitamin A carotenes such as beta-carotene are a source of vitamin A for our bodies. Vitamin A is essential for us because it is necessary for many cellular functions and for good eyesight. It also helps keep our immune system strong.
Carotenoids also have many antioxidant properties. Antioxidants work by stabilizing harmful molecules in our bodies called free radicals. These molecules can cause cancer, and when we eat foods with antioxidant properties, it takes away the destructive nature of these molecules. Lycopene, lutein, and zeaxanthin are all antioxidants. Studies have shown that eating foods with these compounds does help prevent cancer and cardiovascular disease as well cataracts and macular degeneration, as we talked about earlier.
You may have heard that it is healthy to eat a variety of color when it comes to fruits and vegetables. You now probably understand why this is a good idea. With the variety of color comes the variety of antioxidants and health benefits. So keep eating that rainbow of fruits and veggies.
Lesson Summary
Carotenoids are the various yellow, orange, red and green pigments that are found in many fruits and vegetables. The two main types are carotenes and xanthophylls. Carotenes are typically yellow and orange. Beta-carotene is a well-known carotene, and it is a provitamin A carotene. Lycopene is a red carotene, and it has antioxidant properties. Xanthophylls are typically found in leafy greens. Lutein and zeaxanthin are two examples of xanthophylls, and they are also antioxidants. Antioxidants work by stabilizing harmful molecules in our bodies called free radicals. Eating foods that contain carotenoids can help prevent cancer, cardiovascular disease, as well as promote good eye health.
