Beta-Carotene

Beta-carotene is a well-known provitamin A carotenoid, acting as a precursor to vitamin A in the body. 

Found abundantly in vibrant fruits and vegetables like carrots, sweet potatoes, and spinach, beta-carotene is enzymatically converted into retinol, primarily in the intestinal mucosa and liver. 

This nutrient is celebrated for its potent antioxidant properties, supporting immune function, eye health, and potentially playing a role in cancer prevention by promoting gap junctional communication among cells. 

However, while beta-carotene offers significant health benefits, high-dose supplementation, particularly in smokers, has been linked to an increased risk of lung cancer, highlighting the need for cautious use.

What is Beta Carotene?

Beta carotene is one type of a molecule called a provitamin A carotenoid. 

Provitamin A carotenoids such as beta-carotene, alpha-carotene, and beta-cryptoxanthin, are plant-derived pigments that serve as precursors to vitamin A in the body.  While there are over 600 carotenoids, only about 50 have provitamin A activity, and one of the most famous is beta-carotene [15.]. 

These carotenoids are found abundantly in fruits and vegetables, particularly those with vibrant orange, red, and yellow colors. Upon ingestion, provitamin A carotenoids are enzymatically converted into retinol by the body, primarily in the intestinal mucosa and liver [8., 17.].

The conversion rate of beta-carotene to retinol varies widely and often falls between 3.6–28:1 by weight [17.].

Beta-carotene is the most well-known and studied provitamin A carotenoid, with potent antioxidant properties and potential health benefits outside of its relationship to vitamin A [9.].

Despite its benefits, beta-carotene supplementation, especially in high doses, has been linked to adverse effects in certain populations, such as smokers, where it may increase the risk of lung cancer [8.].

What is Vitamin A?

Vitamin A, a fat-soluble vitamin, exists in various forms; retinol is the most common active form in dietary sources. 

The main forms of vitamin A include:

Retinol: The most common form of vitamin A found in animal-based foods and supplements, serving as the primary storage and transport form in the body.  Retinol and carotenoids are two dietary forms of vitamin A that must be converted to retinal or retinoic acid in the tissues to support biological function.

Retinal: An intermediate form of vitamin A involved in the visual cycle, converting light signals into electrical signals in the retina.

Retinoic Acid: The biologically active form of vitamin A, playing a crucial role in gene expression regulation and various cellular processes, including cell differentiation and growth.

Provitamin A Carotenoids: Precursors of vitamin A found in plant-based foods, such as beta-carotene, alpha-carotene, and beta-cryptoxanthin, which can be converted into retinol in the body as needed.

Along with retinol, carotenoids must be converted to retinal or retinoic acid in the tissues to support biological function.

Functions of Beta Carotene

Beta-carotene, a potent antioxidant, plays a significant role in human health by neutralizing reactive oxygen species (ROS) and protecting against oxidative stress-related diseases. 

It has well-known health benefits, including: 

Antioxidant Properties

Beta-carotene is a potent antioxidant that helps neutralize reactive oxygen species (ROS), reducing oxidative stress, a critical factor in the development of many chronic diseases [9.].

Cancer Prevention

Adequate beta-carotene intake has been associated with a reduced risk of several types of cancer, particularly lung cancer in non-smokers, and possibly prostate cancer [9.].

Beta-carotene and other carotenoids may help prevent cancer by inducing gap junctional communication (GJC), a process that allows cells to communicate and coordinate their functions [16].

Cardiovascular Health

Beta-carotene can help prevent the oxidation of LDL cholesterol, which is a key factor in the development of atherosclerosis and coronary heart disease [9.].

Photosensitivity and Skin Health

Beta-carotene can protect against sunburn and other photosensitivity disorders due to its ability to quench singlet oxygen and other ROS generated by UV radiation [9.].

Immune System Support

Beta-carotene has been suggested to stimulate the immune system, enhancing the body's ability to fight infections and inflammation [9.].

Beta-carotene enhances various aspects of immune function, including T and B lymphocyte proliferation, effector T cell functions, and natural killer cell activities [6.]. These immunoenhancing properties may contribute to its potential anticarcinogenic effects, which have been observed in epidemiological and animal studies [6.].

Eye Health

While closely related carotenoids like lutein and zeaxanthin are primarily known for their role in eye health, beta-carotene also contributes to protecting vision by acting as an antioxidant [9.].

Beta Carotene and Lung Cancer in Smokers

Beta-carotene has been shown to have a complicated relationship with lung cancer; research has highlighted both positive and negative findings. 

Beta-carotene acts as an antioxidant and enhances immune function, with higher intake and serum levels associated with improved lung function and reduced risk of lung cancer [7., 13.].

Numerous epidemiological studies show that higher consumption of beta-carotene-rich foods correlates with a reduced risk of lung cancer [7., 13.].

However, intervention studies, notably the ATBC and CARET trials, found an increased risk of lung cancer in smokers who took beta-carotene supplements [2., 14.].

The ATBC and CARET Trials

The Alpha-Tocopherol, Beta Carotene (ATBC) Cancer Prevention Study investigated the effects of vitamin E (alpha-tocopherol) and beta carotene supplementation on lung cancer incidence in male smokers [2.].

Conducted as a randomized, double-blind, placebo-controlled trial with 29,133 participants, the study found no reduction in lung cancer incidence among those who received alpha-tocopherol [2.].

Surprisingly, those who took beta carotene had an 18% higher incidence of lung cancer compared to those who did not, raising concerns about the safety of beta carotene supplementation for smokers [2.].

The Beta-Carotene and Retinol Efficacy Trial (CARET) investigated the effects of a combination of 30 mg of beta carotene and 25,000 IU of vitamin A (retinol) on the incidence of lung cancer and cardiovascular disease in 18,314 participants, including smokers, former smokers, and asbestos-exposed workers [14.]. 

This multicenter, randomized, double-blind, placebo-controlled study followed participants for an average of four years.

The trial revealed that the active-treatment group had a 28% higher risk of developing lung cancer compared to the placebo group. Furthermore, the risk of death from any cause increased by 17%, with specific increases in deaths from lung cancer and cardiovascular disease [14.].

Due to these adverse findings, the study's intervention phase was halted 21 months early, although follow-up will continue for another five years [14.].

These unexpected results have not been fully explained, but hypotheses suggest that improved lung function from beta-carotene may lead to deeper inhalation of carcinogens [7.].

While the antioxidant properties of beta-carotene, including free radical scavenging and immune system enhancement, are well-documented, their precise mechanisms in relation to lung cancer remain unclear [7.].

However, not all studies have demonstrated this connection between increased beta carotene intake and lung cancer in smokers. 

A randomized, double-blind, placebo-controlled trial was conducted with 22,071 U.S. male physicians aged 40-84 to test the effect of beta-carotene (50 mg on alternate days) on cancer and cardiovascular disease over 12 years [10.].

Among the participants, 11% were current smokers and 39% were former smokers at the start of the study in 1982. 

The results showed no significant difference in the incidence of malignant neoplasms between the beta-carotene group (1273 cases) and the placebo group (1293 cases) [10.]. There was also no significant difference in lung cancer cases (82 in the beta-carotene group vs. 88 in the placebo group). 

There remains a critical need to understand if and why beta-carotene supplementation may increase lung cancer risk in smokers, despite its general health benefits and positive associations in non-supplemented populations.

Sources of Beta-Carotene [19.]

• Carrots: a major source of beta-carotene, contributing significantly to dietary intake.

• Sweet Potatoes: rich in beta-carotene, often contributing to its intake in diets.

• Spinach: contains beta-carotene along with other carotenoids.

• Kale: another leafy green vegetable high in beta-carotene.

• Collard Greens: provides beta-carotene and other nutrients.

• Turnip Greens: a good source of beta-carotene.

• Butternut Squash: contains significant amounts of beta-carotene.

• Cantaloupe: a fruit contributing to beta-carotene intake.

• Red and Orange Bell Peppers: rich in beta-carotene.

• Apricots: provide beta-carotene in diets.

• Peas: although not as rich as other sources, they still contain beta-carotene.

• Broccoli: contributes to beta-carotene intake among other nutrients.

• Pumpkin: high in beta-carotene, especially when cooked.

• Mangoes: contain beta-carotene, contributing to its dietary intake.

• Papayas: another fruit that provides beta-carotene.

• Tomatoes: contain beta-carotene along with other carotenoids.

• Swiss Chard: includes beta-carotene among other vitamins and minerals.

• Watermelon: contains smaller amounts of beta-carotene.

• Lettuce: especially varieties with darker leaves like romaine.

• Asparagus: contains beta-carotene among other nutrients.

• Beet Greens: rich in beta-carotene.

• Grapefruit: particularly the pink and red varieties.

• Herbs: such as parsley and cilantro, though in smaller amounts.

Recommended Daily Amounts of Beta Carotene [20.]

The recommended daily amount (RDA) of beta-carotene, converted to retinol activity equivalents (RAE), varies by age and sex. The following ranges are given by the National Institutes of Health, Office of Dietary Supplements: [20.]

• Infants: the RDA is 400-500 mcg RAE

• Children aged 1-8 years: the RDA is 300-400 mcg RAE

• Children aged 9-13 years: the RDA is 600 mcg RAE 

• Teens aged 14-18 years: the RDA is 900 mcg RAE for males and 700 mcg RAE for females

• Adult males: the RDA is 900 mcg RAE 

• Adult females: the RDA is 700 mcg RAE. 

• Pregnant teens and adults need 750-770 mcg RAE

• Breastfeeding teens and adults need 1200-1300 mcg RAE. 

There are no established upper limits for beta-carotene from food sources, but for preformed vitamin A, the upper limits are 600-3,000 mcg RAE, depending on age.

However, research continues to try to refine the recommended dosage due to concerns over vitamin A toxicity. 

Lab Testing for Beta-Carotene

Test Information, Sample Collection and Preparation

Beta-carotene levels are typically measured through blood tests. These tests analyze the concentration of beta-carotene in serum or plasma samples. 

Sample collection requires a venipuncture. Fasting is often required, and avoidance of alcohol for at least 24 hours may also be recommended [1.].

Interpretation of Beta-Carotene Results

Optimal Levels of Beta-Carotene in Blood

It is important to interpret beta-carotene levels in the context of an individual’s overall health and medical history, and to take into account any symptoms that may be present. 

One laboratory reports the following reference range: 3-91 ug/dL [1.].

Clinical Significance of Elevated Beta-Carotene Levels

Elevated beta-carotene levels may be seen in individuals eating the highest amounts of fruits and vegetables, as well as in some cases of diabetes mellitus, hypothyroidism with or without myxedema, chronic nephritis, nephrotic syndrome, liver disease, type I, IIA, and IIB hyperlipoproteinemia, and in a group of amenorrheic hypogonadotropic women [1.].

Carotenemia may be confused with jaundice, so ordering liver function tests and bilirubin alongside beta-carotene may be recommended in some settings to clarify the causative condition [1.].

Clinical Significance of Low Beta-Carotene Levels

Low beta-carotene levels may be seen in nutritional deficiency, and in some cases of steatorrhea and/or fat malabsorption [1.]. Low levels may also be caused by oral contraceptive use and/or smoking [1.].

Related Biomarkers to Test

Liver Function Tests and Bilirubin

In cases of suspected carotenemia, assessing liver function and bilirubin is recommended alongside beta-carotene levels to rule out jaundice. Both jaundice and carotenemia can present with yellowing of the skin and palms. 

Vitamin A Levels

As beta-carotene is a precursor to vitamin A, measuring vitamin A levels in conjunction with beta-carotene can offer insights into the body's ability to convert and utilize these nutrients. 

Vitamin A is essential for vision, immune function, and cellular communication. Assessing both beta-carotene and vitamin A levels can help identify potential deficiencies or imbalances in the vitamin A pathway.

Antioxidant Status Markers

To fully evaluate antioxidant status, it's beneficial to test for other antioxidant markers alongside beta-carotene. These may include vitamin C, vitamin E, and selenium levels. 

Additionally, measuring markers of oxidative stress, such as malondialdehyde (MDA), can provide information on the overall balance between antioxidants and oxidative damage in the body [3.].

Beta-Carotene Supplements

While beta-carotene is naturally present in many foods, supplements have become increasingly popular as a means to boost intake. This section explores the various aspects of beta-carotene supplementation, including types available, recommended dosages, and potential risks associated with their use.

Types of Supplements Available

Beta-carotene supplements are available in various forms, including capsules, tablets, and liquid formulations. 

Beta-carotene supplements are available in synthetic and natural forms, with ongoing debate about their relative efficacy and safety. 

Studies have compared the bioavailability of synthetic all-trans beta-carotene with natural sources like palm oil and algae-derived carotenoids. 

While both forms can significantly increase plasma beta-carotene levels [18.], some research suggests that natural beta-carotene mixtures may be more bioavailable, have greater antioxidant capacity, and accumulate to higher levels in the liver of rats and chicks [4.].

Recommended Dosages

The recommended dosage for beta-carotene supplements can vary depending on the intended use and individual health status.

The safety and efficacy of beta-carotene supplementation have been extensively studied. While an upper limit (UL) for beta-carotene cannot be definitively established, a tentative upper level of 4 mg/day has been proposed [12.]. 

However, clinical trials have used beta-carotene supplements in the range of 15-50 mg/day without adverse effects, and doses up to 180 mg/day have been safely used to treat photosensitivity disorders [5.].

Potential Risks and Side Effects

While beta-carotene is generally considered safe when consumed through dietary sources, high-dose supplementation can pose risks for certain individuals. Some studies have shown that beta-carotene supplements may increase the risk of lung cancer in smokers and individuals exposed to asbestos [2., 14.].

Additionally, excessive beta-carotene intake can lead to carotenodermia, a harmless but cosmetically concerning condition that causes yellowing of the skin. [11.]

While diet and over supplementation are common causes, metabolic factors such as hypothyroidism, diabetes mellitus, and genetic predisposition may also contribute to hypercarotenemia [11.].

Given these potential risks, it's essential to approach beta-carotene supplementation with caution and under professional guidance.

Beta-Carotene FAQ

Beta-carotene, a vibrant pigment found abundantly in nature, is a precursor to vitamin A and a powerful antioxidant.

This FAQ section addresses common questions about beta-carotene including its sources, benefits, and potential applications in cancer prevention and skin health. 

We'll explore the latest research findings and provide evidence-based answers to help you better understand this important nutrient and its role in human health.

What is Beta-Carotene?

Beta-carotene is a pigment found abundantly in nature, particularly in fruits and vegetables. It's a precursor to vitamin A and acts as a powerful antioxidant in the body. 

Beta-carotene is known for its ability to scavenge free radicals, potentially reducing oxidative stress.

What are Main Beta-Carotene-Containing Foods?

Beta-carotene is found in many fruits and vegetables, especially those with yellow, orange, and dark green colors. 

Common sources include carrots, sweet potatoes, spinach, kale, butternut squash, mangoes, and apricots. It's also present in some other foods, though in lower concentrations.

What are Beta-Carotene’s Benefits to Human Health?

Beta-carotene offers several health benefits. 

It acts as an antioxidant, supports immune function, and contributes to eye and skin health. 

Some studies suggest it may play a role in cancer prevention, particularly in the early stages of carcinogenesis. 

Beta-carotene also affects cell proliferation and differentiation and may help control intercellular messages via gap junctions [16.].

Are Beta-Carotene Supplements Recommended?

Beta-carotene supplements are available, but they should be used under the guidance of a licensed healthcare professional.

While dietary sources of beta-carotene are generally safe, high-dose supplementation can pose risks for certain individuals, particularly smokers. 

The tolerable upper intake level for beta-carotene from supplements is set at 4 mg per day, although higher doses have also been suggested and are often used in research settings. 

Always consult with a healthcare professional before starting any supplementation regimen.

How Does Beta-Carotene Benefit the Skin?

Beta-carotene can contribute to skin health due to its antioxidant properties. It helps protect the skin from UV radiation damage and oxidative stress. 

Some people report that beta-carotene intake can contribute to a healthy skin tone and may improve the appearance of skin by providing a natural, subtle glow. 

However, it's important to note that beta-carotene should not be considered a substitute for proper sun protection measures.

Can Beta-Carotene Help Prevent Cancer?

The role of beta-carotene in cancer prevention is complex. While some epidemiological studies suggest that diets rich in beta-carotene may help prevent precancerous and neoplastic lesions, large-scale clinical trials have produced mixed results. 

Some studies have even shown an increased risk of lung cancer in smokers who took high-dose beta-carotene supplements. 

More research is needed to fully understand beta-carotene's role in cancer prevention.

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