Carotenoids

Carotenoids - background and overview

Carotenoids are a class of compounds that represent the most widespread group of naturally occurring plant pigments. Largely responsible for the yellow, red and orange colors of fruits and vegetables, these phytonutrients are also found in many dark leafy green vegetables. Among the most abundant carotenoids in the North American diet are beta-carotene, alpha-carotene, gamma-carotene, lycopene, lutein, beta-crpytoxanthin, zeaxanthin, and astaxanthin.

Physiological functions of carotenoids

• Protect cells from the damaging effects of free radicals
• Serve as a dietary source of vitamin A
• Enhance immune system functioning
• Contribute to reproductive system health

Physiological events that may signal a need for greater carotenoid intake

• Low intake of fruits and vegetables
• Regular alcohol consumption
• Smoking

Functions of carotenoids

Prevention of vitamin A deficiency

Approximately 50 members of the carotenoid family can be converted into retinol, an active form of vitamin A. Intake of these carotenoids, referred to as provitamin A compounds, can help to prevent vitamin A deficiency. The most common consumed provitamin A carotenoids in the North American diet include beta-carotene, alpha-carotene, beta-crpytoxanthin, gamma-carotene, lycopene, lutein, zeaxanthin, and astaxanthin. Until late in the 20th century, the vitamin A activity of carotenoids was researchers\' main focus when it came to investigating the health benefits of these phytonutrients.

Antioxidant & immune-enhancing activity

Carotenoids have potent antioxidant activity, enabling them to protect cells from free radical damage. Additionally, carotenoids, notably beta-carotene, are also suggested to play a role in supporting immune system function. Due to these actions, carotenoids have received a great amount of attention as potential anti-cancer and anti-aging compounds.

Enhancing proper cell communication

Carotenoids have also been shown to stimulate cell-to-cell communication. Since researchers now believe that poor cell-to-cell communication may be one of the factors leading to proliferation of cells, a condition that eventually leads to cancer, carotenoids may play an important role in cancer prevention.

Supporting female reproductive system

Carotenoids are also believed to play a role in female reproduction, although their exact function has yet to be determined. This hypothesis is partially based upon the finding that the corpus luteum has the highest concentration of beta-carotene of any organ in the body.

Causes and symptoms of carotenoid deficiency

Fat malabsorption as well as extremely low fat diets can negatively impact carotenoid status since carotenoids are fat-soluble compounds. Pancreatic enzyme deficiency, gallbladder disease, liver disease, Crohns disease, celiac disease, cystic fibrosis and surgical removal of part or all of the stomach are conditions that can cause fat malabsorption.

Adolescents and young adults generally have a lower consumption of fruits and vegetables and therefore are at risk of carotenoid deficiency. Individuals who smoke cigarettes as well as those who regularly drink alcohol are at risk for carotenoid deficiency since these individuals have been noted to eat fewer carotenoid-containing foods and cigarette smoke has been found to destroy carotenoids. However, if you drink or smoke, it is important to use carotenoid supplements with care (see Toxicity: Causes and Symptoms section).

There do not seem to be any short-term deficiency symptoms specifically associated with carotenoids. Yet, if your intake of both vitamin A and the provitamin A carotenoids (including beta-carotene, alpha-carotene and beta-cryptoxanthin) is low, it may result in symptoms associated with vitamin A deficiency.

Research indicates that diets low in carotenoids can increase the bodys susceptibility to free radical damage. Therefore, over a period of many years, inadequate intake of carotenoids may increase tissue damage from free radical activity and set the stage for the development of several chronic diseases including heart disease and cancer.

Causes and symptoms of carotenoid toxicity

Carotenodermia, a reversible and harmless condition characterized by a yellowish discoloration of the skin that most often occurs in the palms of the hands or soles of the feet, is caused by excessive consumption of beta-carotene. Lycopenodermia, caused by excessive consumption of the carotenoid lycopene, can cause a deep orange discoloration, but like carotenodermia, it is a harmless and reversible condition.

As high intake of carotenoid-containing foods or supplements is not associated with any toxic side effects, in 2000, when the Institute of Medicine at the National Academy of Sciences reviewed these compounds, they did not establish a Tolerable Upper Intake Level (UL) for carotenoids. Yet, it should be noted that two research studies have suggested that individuals who take isolated beta-carotene supplements in doses greater than 20-30 milligrams per day and who smoke heavily and regularly drink alcohol may increase their risk of developing heart disease and/or lung cancer.

The effect of cooking, storage and processing on carotenoids

In most cases, extended cooking of vegetables decreases the availability of carotenoids since it changes their structure from the natural trans-configuration to the cis-configuration. Fresh carrots, for example, contain 100% all-trans beta-carotene. Yet, in canned carrots, only 73% all-trans beta-carotene remains.

There are certain cases with individual carotenoids in select foods where cooking can actually improve bioavailability of the nutrient. One example is lycopene whose availability is increased when tomato products are processed at high temperatures. This results in lycopene being able to be better absorbed in canned, pasteurized tomato juice, for instance, compared with fresh tomatoes. Additionally, lightly steaming spinach and carrots enhances the absorption of carotenoids from these foods.

Interactions between medications and carotenoids

Medications that may reduce carotenoid status in the body:

• Bile acid sequestrants such as Cholestyramine, Colestipol and Colestid
• Olestra, a fat substitute
• Plant sterols as found in Benecol and Take Control margarines

Interactions that occur between carotenoids and other nutrients

Certain carotenoids have been suggested to compete with certain others for absorption as reflected in studies where beta-carotene supplements were shown to reduce blood levels of the carotenoid lutein. Pectin supplementation is thought to decrease carotenoid absorption.

Health conditions that require special emphasis on carotenoids

Individuals who have the following health conditions should pay special attention to their carotenoid status:

• Age-related macular degeneration
• Angina pectoris
• Acquired immunodeficiency syndrome (AIDS)
• Asthma
• Cataracts
• Cervical cancer
• Cervical dysplasia
• Chlamydial infection
• Coronary heart disease
• Laryngeal cancer (cancer of the larynx)
• Lung cancer
• Male and female infertility
• Osteoarthritis
• Photosensitivity
• Pneumonia
• Prostate cancer
• Rheumatoid arthritis
• Skin cancer
• Vaginal candidiasis

Forms in which carotenoids are found in dietary supplements.

Carotenoids are generally available as either synthetic all-trans beta-carotene, beta- and alpha-carotene from the algae Dunaliella, or mixed carotenes from palm oil. Additionally, individual carotenoids such as lutein and lycopene can be found in supplements.

Due to the inconsistent results from research intending to evaluate the health benefits of beta-carotene supplements, the National Academy of Sciences cautions individuals not to take high dose carotenoid supplements, except if they are using beta-carotene to prevent vitamin A deficiency.

Foods that are concentrated sources of carotenoids

• Apricots, carrots, mangoes, squash, sweet potatoes, yams and other orange-colored fruits and vegetables contain significant amounts of beta-carotene, alpha-carotene, and beta-cryptoxanthin.
• Collard greens, kale, spinach and other green vegetables contain beta-carotene and are among the best sources of lutein.
• Guava, pink grapefruit and tomatoes are sources of lycopene.
• Egg yolk, milk, salmon and shellfish are some other food sources of carotenoids.