What makes carrots orange, watermelon pink, corn yellow, or tomatoes deep red? Carotenoids! The colorful plant pigment family of the carotenoids can put a rainbow on your plate. The vivid carotenoids can do more than brighten up your dishes: different carotenoids have different health benefits. It is a good idea to include a healthy mix of carotenoid-rich foods in your diet, to extract the maximum goodness from each type of carotenoid.
Orange Carotenes as a Vitamin A Source
Three carotenoids have an essential role in the diet as a plant-based source of pro-vitamin A. These carotenoids are alpha-carotene, beta-carotene and beta-cryptoxanthin. Many orange and yellow fruits and vegetables get their intense coloring from alpha- and beta-carotene. Green leafy vegetables often contain both as well, but the color is masked by the presence of dark green chlorophyll. Few fruits and vegetables contain beta-cryptoxanthin, although it is found in some tropical fruits such as papaya and mango.1
In industrialized countries, one third of vitamin A requirements are estimated to be met by carotenoids, and this proportion is higher in vegetarians.2 The structure of alpha-carotene, beta-carotene and beta-cryptoxanthin means that they can be converted easily by the body to retinol, one of the active forms of vitamin A. Vitamin A has various diverse roles in the body: it is required for vision, normal immune function, and the growth and specialization of cells.3
Foods containing pro-vitamin A carotenoids are given a conversion factor that indicate how well they can be converted to retinol, called a Retinol Activity Equivalent. This estimates how much pro-vitamin A carotenoids are needed to produce a certain amount of retinol. In general, to get 1 microgram of retinol, 2 micrograms beta-carotene from a dietary supplement, 12 micrograms beta-carotene from foods or 24 micrograms alpha-carotene or beta-cryptoxanthin are needed. A medium orange carrot weighing 60 grams (2 oz) contains about 3,000 micrograms beta-carotene and 4,000 micrograms alpha-carotene, together providing around 400 micrograms of retinol.4 This is about half the vitamin A requirements of adult men and women.3
Yellow Xanthophylls for Eye Health
The xanthophylls get their name from the Greek word for yellow, and are found in many yellow, orange and green leafy vegetables such as sweet corn, yellow bell peppers and kale.5 Three xanthophylls, lutein, zeaxanthin and meso-zeaxanthin, are being studied for their possible role in eye health. Out of the hundreds of carotenoids that are found in nature, only 50 are absorbed from humans’ normal diet,6 and these three are found in a very specific area of the eye that is responsible for detailed vision, and are prevalent throughout other parts of the eye. This has lead researchers to suggest that they may be important for normal visual function because they are selectively deposited in the eye.7
There are two ways that lutein and zeaxanthin are thought to support our vision. First of all, their yellow color means that they act as a yellow filter over the delicate vision cells at the back of the eye. Just as wearing glasses with yellow lenses blocks blue-colored light, the yellow xanthophylls lutein and zeaxanthin stop damaging blue light from reaching the retina.8 This can lead to improvements vision in bright light situations, as has been found in clinical trials.9,10 Like the other carotenoids, lutein and zeaxanthin are strong antioxidants. The process of vision in the eye results in oxidative stress, which antioxidants can protect against. As lutein and zeaxanthin are found throughout the eye, they are suggested to prevent damage and maintain vision during the aging process.7
Carotenoid content of selected foods11
Alpha-carotene in 1 cup canned pumpkin: 11.7 mg
Beta-carotene in 1 cup carrot juice: 22 mg
Beta-carotene in 1 cup cooked kale: 11.5 mg
Beta-cryptoxanthin 1 medium papaya: 2.3 mg
Lycopene in 1 wedge of watermelon: 13 mg
Lutein and zeaxanthin in 1 cup of cooked-from-frozen spinach: 19.8 mg
Could eating your fruit and vegetables actually make you smarter? Well, you might not be able to boost your results with a beetroot and broccoli binge the night before an exam, but associations between fruit and vegetable intake and a reduction in cognitive decline in older adults have been found in several research articles.12-15 It is thought that carotenoids from fruit and vegetables could help to reduce oxidative stress in the brain, high levels of which are linked to a fall in cognitive abilities due to aging.16
Whether this could be due to the carotenoid content of fruits and vegetables has been tested recently in clinical studies using a dietary supplement containing lutein, with either zeaxanthin or meso-zeaxanthin. For example, in a one-year clinical trial with 91 healthy adults with low levels of carotenoids, the group who took at dietary supplement containing 10 mg lutein, 10 mg meso-zeaxanthin and 2 mg zeaxanthin had a significant improvement in their memory and a significant reduction in errors during a standardized memory test. There were no significant changes in memory score or errors in the placebo group.17 In a second study conducted in 62 older adults, the group receiving a dietary supplement containing 12 mg lutein and zeaxanthin experienced improvements in cognitive function after one year of supplementation compared to a placebo group.18 In a third clinical trial conducted in young, healthy adults, the group that received a dietary supplement containing 12 mg lutein and zeaxanthin for 12 months showed improvements in spatial memory, reasoning ability, and complex attention, compared to the placebo group.19 These encouraging results show the importance of a carotenoid-rich diet.
An expression used widely in the nutrition world is “you are what you eat,” and this applies especially to the carotenoids. People who consume a lot of carotenoid-rich foods or dietary supplements can experience a harmless condition called “carotenodermia,” in which the skin develops an orange hue due to the carotenoids being deposited throughout each skin layer.20,21 Carotenoids make a subtle contribution to overall skin color, and measuring the color of the skin reflects intake of carotenoid-rich fruits and vegetables.21
The carotenoids alpha- and beta-carotene, lycopene, lutein and zeaxanthin are found in the skin.20 As carotenoids are antioxidants and their bright colors indicate that they absorb light, they have been researched to determine their effect on skin health. Due to their ability to absorb light from the UVA and UVB wavelengths, carotenoids have been investigated for their ability to reduce sunburn. Various carotenoids including beta-carotene, lycopene, lutein and mixtures, were able to reduce skin redness after exposure to UV light.22-24 Sun protection afforded by carotenoids offer a small yet constant protection from sun exposure, and may assist in overall protection from sunburn.23
Carotenoids may also enhance the appearance of the skin. In a clinical trial, a combined topical and oral dietary supplement containing lutein and zeaxanthin enhanced skin hydration and elasticity compared to a placebo group.25 Lutein and zeaxanthin isomers, when taken as a dietary supplement as part of a double-blind placebo-controlled study, were able to improve skin tone.24 In a third clinical study using zeaxanthin supplements alone and with a skin cream, zeaxanthin was able to reduce wrinkle count, and improve skin hydration.26
A colorful life: for health!
We have seen that the carotenoids not only make our mealtimes more colorful, they are also linked with certain health benefits. Carotenoids are a source of pro-vitamin A, they contribute to healthy skin color, they may help support normal vision, and there are some tantalizing reports of improvements in cognitive function after intake of certain carotenoids. Make sure your plate is loaded high with carotenoid-rich fruits and vegetables!