Beta-carotene

Beta-carotene is a member of the carotenoid group - a group of plant pigments whose members are known to have antioxidant and other effects. Beta-carotene is found in many plant products such as green leafy, yellow and orange fruits and vegetables (2). Beta-carotene is a plant substance that is rapidly converted to vitamin A in the body, which is why it is often considered a form of vitamin A (1). Normal vitamin A levels are essential for good vision, a strong immune system and general health. Beta-carotene contributes 30 to 35% of daily vitamin A consumption in the Western world, while in developing countries it is the main and in some cases the only source of vitamin A (3, 4).

Potential health benefits of beta-carotene

Beta-carotene is an antioxidant

Similar to other carotenoids, beta-carotene also has antioxidant properties. It helps protect against reactive oxygen species and protects against oxidative stress (5, 6). In one study, when 12 healthy women were placed on a diet low in beta-carotene, they experienced increased oxidative stress and reduced superoxide dismutase (SOD) antioxidant activity (7). In two studies involving a total of 167 workers exposed to elevated levels of lead, the following effects were observed with beta-carotene supplementation (8, 9):

• Increased G6PD, Catalase and SOD activity - these are all enzymes that protect your body from oxidative stress.
• Increased vitamin E levels.
• Reduced malondialdehyde (MDA) levels - a marker for oxidative stress
• Reduced homocysteine levels - homocysteine is a metabolic by-product that is considered a marker for many chronic diseases.

However, beta-carotene reduced glutathione peroxidase (GPx) and glutathione S-transferase (GST) activity. GPx and GST are important for neutralizing certain free radicals (8, 9, 10, 11). Several studies suggest that beta-carotene may be beneficial for patients with cystic fibrosis as it reduces oxidative stress and improves quality of life (12, 13, 14). In addition to circulating in the blood, beta-carotene is also a normal component of human first milk (colostrum) and later breast milk, where it contributes to oxidative protection of the newborn and infant (15).

Beta-carotene is good for the skin

Many studies have shown that beta-carotene and other carotenoids help protect the skin from UV rays through antioxidant effects (6, 16). However, there are also studies that have not found any positive effects (16, 17).

According to a meta-analysis of 7 studies with a total of 135 test subjects, beta-carotene supplementation protected against sunburn. However, the effect only came about after 10 weeks of beta-carotene supplementation (18).

Another study looked at the effects of 2 different beta-carotene doses (30 and 90 mg per day) on wrinkles, skin elasticity, collagen content and UV-induced DNA damage in 30 healthy women. Interestingly, only the lower dosage (30 mg per day) improved wrinkles and skin elasticity and counteracted light-induced skin ageing (19).

Beta-carotene taken through food or supplements is more efficient than beta-carotene applied to the skin because it is more stable (20).

Beta-carotene promotes brain health

Since oxidative stress can contribute to brain aging, antioxidants such as beta-carotene can help protect brain function (21). In a clinical study of nearly 6,000 participants, those who received long-term beta-carotene supplementation performed better on cognitive tasks. They generally had better memory and cognitive function. This was particularly true for people who had taken beta-carotene for more than 15 years. Short-term supplementation, on the other hand, was ineffective (21). In a meta-analysis of 7 studies, beta-carotene intake was associated with a lower risk of Alzheimer's disease (22).

Beta-carotene protects eye health

In a meta-analysis of 22 articles, higher beta-carotene levels reduced the risk of cataracts - a clouding of the lens of the eye that impairs vision. A similar association was observed with higher dietary beta-carotene intake (23). In 29 patients with retinitis pigmentosa, an eye disease that can lead to vision loss, a supplement containing beta-carotene improved retinal function (24). In a clinical study of 3,640 adults, those who took antioxidant supplements (beta-carotene, vitamin E and vitamin C) showed a reduced risk of vision loss (including age-related macular degeneration) (25). However, a study of 22,000 male physicians showed no advantages or disadvantages of 12 years of beta-carotene supplementation when it comes to cataracts. Beta-carotene did, however, appear to reduce the increased risk in smokers by a quarter (26).

Beta-carotene could protect against diabetes

In over 37,000 healthy subjects, higher beta-carotene intake was associated with a reduced risk of diabetes (27). However, when it comes to nutritional studies, it is difficult to say whether the benefits can be directly attributed to beta-carotene or higher consumption of fruit and vegetables in general. In 108 obese, non-diabetic people, higher beta-carotene blood levels were associated with higher adiponectin blood levels. This means that higher beta-carotene blood levels could increase insulin sensitivity (28).

Beta-carotene could protect against metabolic syndrome

Metabolic syndrome is a combination of conditions that occur together and increase the risk of diabetes and heart disease. If you have metabolic syndrome, you have at least three of the following symptoms:

• High blood pressure
• High blood sugar levels
• Excessive body fat around the waist
• High cholesterol levels
• High triglyceride levels

In an observational study of 910 people, those with high beta-carotene levels had a low risk of developing metabolic syndrome over the next 10 years. In addition, they had a low risk of high cholesterol levels (29). Beta-carotene may protect against metabolic syndrome by reducing cholesterol absorption in the digestive tract and increasing fecal cholesterol excretion (30).

A study conducted in rats showed that beta-carotene supplementation can reduce total cholesterol levels, non-HDL cholesterol levels and liver fat and cholesterol content. This was accompanied by an increase in fecal excretion of fat and cholesterol (30).

Beta-carotene is associated with lower uric acid levels

High uric acid levels can lead to gout and kidney stones (31, 32). In an observational study of over 14,000 subjects, low beta-carotene levels were associated with higher uric acid levels (33).

Beta-carotene could protect against heart disease

In over 1,000 men followed for 15 years, men with low beta-carotene blood levels were more than twice as likely to die from heart disease (34). In mice fed a high-fat diet, a natural source of beta-carotene - Dunaliella algae - reduced hardening of the arteries and protected against an increase in blood cholesterol levels (35).

Beta-carotene could protect against cancer

Studies support a possible role of dietary and circulating beta-carotene in preventing cancer. These levels generally correspond with a higher intake of fruit and vegetables. However, the results are controversial when it comes to beta-carotene supplementation.

Circulating and dietary beta-carotene

Higher blood levels of beta-carotene have been associated with a lower risk of cancer, including lung cancer, leukemia and bone cancer (36, 37).

A meta-analysis of 19 studies involving over 500,000 people suggests that higher dietary beta-carotene intake may reduce the risk of lung cancer (38). Another meta-analysis of 5 studies with over 3,700 subjects linked a high dietary beta-carotene intake to a 16% lower risk of ovarian cancer compared to a low intake (39). In 540 cancer patients with head and neck cancer treated with radiation, higher blood beta-carotene levels and higher dietary beta-carotene intake were associated with fewer side effects and a lower rate of cancer recurrence (40). A study of 190 healthy individuals showed a U-shaped relationship between beta-carotene intake and genome stability. Both low and high beta-carotene intake (< 4.1 and > 6.4 mg per day) increased DNA mutations, which can potentially lead to cancer (41).

Beta-carotene supplements

Some studies show that beta-carotene supplementation is associated with a minimally reduced risk of cancer, including prostate cancer, throat cancer and colorectal cancer (42, 43). Other studies (involving 39,000 and 29,000 people) found neither positive nor negative effects of beta-carotene on the incidence of cancer (44, 45). However, a meta-analysis of 6 studies with a total of over 40,000 participants found that beta-carotene supplementation increased the risk of bladder cancer (46). According to a meta-analysis of 9 studies, smokers and people exposed to asbestos should avoid beta-carotene supplements, as they could increase the risk of lung or stomach cancer in these groups (47).

Beta-carotene could protect against radiation

Beta-carotene supplements effectively reduced cell damage in 709 children exposed to different doses of radiation during and after the Chernobyl accident (48). In rats, beta-carotene showed significant antimutagenic/radioprotective activity against radioactive iodine, which is used in the diagnosis of thyroid disorders (49).

Beta-carotene could promote longevity

A meta-analysis of 41 observational studies (totaling over 500,000 people) suggests that both higher blood levels of beta-carotene and higher dietary beta-carotene intake may be associated with reduced mortality from all causes (50). According to another meta-analysis involving over 25,000 people, higher beta-carotene blood levels were associated with a reduced risk of death from all causes. In addition, in studies involving a total of 150,000 people, higher dietary beta-carotene intake was associated with reduced mortality from all causes (51). In another study of 29,000 men, those with higher serum beta-carotene levels had significantly lower mortality from all causes, as well as from heart attacks, strokes and cancer (52). In another meta-analysis of 53 studies (with a total of over 240,000 participants), beta-carotene supplementation at doses above 9.6 mg per day was associated with a slight increase in mortality (53). It should also be noted in this context that beta-carotene blood levels and dietary beta-carotene intake reflect fruit and vegetable consumption and that fruit and vegetables are generally beneficial for health.

Can you find beta-carotene in natural foods?

Health experts recommend that beta-carotene and other antioxidants should preferably be obtained from food rather than supplements.

Beta-carotene can be found in the following foods (1, 2, 54, 55):

• Fruit (apricots, peaches, melons, citrus fruits, tomatoes, persimmon, etc.)
• Green vegetables (spinach, broccoli, parsley, collard greens)
• Orange-colored tuber vegetables (carrots, sweet potatoes)
• Animal products (salmon, egg yolk, butterfat)

The beta-carotene content is highest in fresh fruit and vegetables. Frozen foods and canned foods contain less beta-carotene. Studies suggest that the absorption of beta-carotene from plant sources ranges from 5 to 65% in humans (56). This depends on many different factors such as the fat and fiber content of the food. Fat has a positive and fiber has a negative effect on the bioavailability of beta-carotene (57, 58, 59, 60). Steaming increases the availability of beta-carotene, but prolonged cooking has a negative effect (1).

Beta-carotene supplements

Beta-carotene can also be taken in the form of supplements. However, it is advisable to try to meet the need for beta-carotene in the form of whole foods such as fruit and vegetables, as these foods also contain a variety of other healthy ingredients that can have positive effects on the body. When using supplements, it should be noted that excessive amounts of beta-carotene can have negative effects on health, especially for smokers and people who consume alcohol.

Recommended intake?

While there is an official recommended daily intake for vitamin A, there is no official recommended intake for beta-carotene. Doses ranging from 15 to 180 mg per day have been used in scientific studies. Although there is no set upper limit for beta-carotene intake, high doses could be dangerous with long-term use. Many experts recommend a combination of carotenoids such as lutein, carotene, zeaxanthin, lycopene, etc. instead of taking beta-carotene in isolation. However, the correct dose of mixed carotenoids for short or long-term use is unclear.

The normal range of beta-carotene blood levels

Beta-carotene blood levels are not a routine test. However, it is possible to determine them using a simple blood test. Women will usually have slightly higher levels than men (54). Normal levels for men are in the range of 4 - 51 ug/dl (micrograms per deciliter) and for women in the range of 6 - 77 ug/dl. Levels may vary slightly between individual laboratories.

Low beta-carotene levels

Causes of low beta-carotene levels

The following causes are commonly associated with low beta-carotene levels. However, an accurate diagnosis should be made in consultation with a physician.

1) Malnutrition

Beta-carotene levels are a good indicator of fruit and vegetable consumption and general dietary habits (61). Beta-carotene levels are low in poorly nourished children and those who eat few fruits and vegetables (71). A review of 7 articles including 4500 European adolescents showed that beta-carotene deficiency is quite common, affecting 14 to 19% of all adolescents (63).

2) Obesity

Overweight and obese people tend to have lower beta-carotene levels than people of a healthy weight (64, 65).

In a study of 92 healthy, overweight subjects who received beta-carotene supplements, those with higher BMI had lower circulating beta-carotene levels (66).

3) Smoking and alcohol consumption

Smoking lowers beta-carotene levels (61, 67). The same applies to alcohol consumption (61).

4) Diseases that impair nutrient absorption

Cholestatic liver diseases can cause problems with the absorption of nutrients in the digestive tract. In an observational study of 53 children with cholestatic liver disease, more than 80% had low beta-carotene levels (68). Sometimes - and especially in developing countries - parasites can impair the absorption of nutrients in the digestive tract. Studies show that in children, deworming therapy can help increase beta-carotene levels (69). Beta-carotene deficiency is common in all stages of HIV/AIDS. This disease can cause diarrhea and prevent the small intestine from absorbing fats. Which leads to reduced levels of beta-carotene in the blood (70). However, clinical studies have not shown any positive effects of beta-carotene supplementation. Low beta-carotene levels tend to reflect a more active HIV-1 infection than a deficiency that is treatable by intervention (71, 72).

5) Hyperthyroidism

In several studies, patients with hyperthyroidism or an overactive thyroid had reduced beta-carotene levels (73, 74).

6) The contraceptive pill

In an observational study of 150 women, women taking oral contraceptives had lower beta-carotene levels than women not taking oral contraceptives (67).

Methods to increase beta-carotene levels

The most important step is to work with a doctor to find the cause of low beta-carotene levels and treat the underlying conditions. The lifestyle changes described below should be discussed with the treating physician. None of these strategies should be used in place of what the treating physician has recommended or prescribed.

The best way to increase beta-carotene levels is to increase the amount of beta-carotene rich foods in the diet, as described above. Fiber can interfere with beta-carotene absorption, which is why fruit and vegetable juices may be a better source of beta-carotene than whole fruits and vegetables (57). However, it is even better to consume fats together with beta-carotene-rich foods. Dietary fats increase the bioavailability of carotenoids in meals. For example, one study showed that avocado can increase both beta-carotene absorption (by a factor of 2.4 to 6.6) and conversion to vitamin A (by a factor of 4.6 to 12.6) (58). Mayonnaise can also increase the absorption of beta-carotene. One study concluded that a meal containing mayonnaise is a better source of beta-carotene than fruit and vegetable juices (59, 60) and, interestingly, processed vegetables such as carrots and spinach are a better source of beta-carotene than their raw counterparts (75). Consumption of higher amounts of plant sterols, which reduce cholesterol absorption, also reduce the bioavailability of beta-carotene (76). Plant sterols are found in wheat germ, vegetable oils (corn oil, sesame oil, canola oil and olive oil), peanuts, almonds and sterol-enriched foods. Overweight people should lose weight, as overweight/obese people have lower beta-carotene levels (64). Smoking and alcohol should also be avoided, as both lower beta-carotene levels (61, 67). Lutein supplements should also be avoided as they reduce the absorption of beta-carotene (77, 78).

Elevated beta-carotene levels

Causes of elevated beta-carotene levels

The following causes are commonly associated with high beta-carotene levels. However, an accurate diagnosis should be made in consultation with a physician.

1) Excessive dietary intake

Excessive intake of beta-carotene rich foods will lead to an increase in beta-carotene levels and potentially cause vitamin A poisoning (79). However, this is extremely rare and only occurs with very specific diets. The conversion of beta-carotene to vitamin A decreases with increasing dietary intake, which in most cases protects against vitamin A intoxication (80).

2) An underactive thyroid

People with an underactive thyroid have significantly higher beta-carotene levels (73, 74).

Symptoms of excessive beta-carotene levels

Excessive consumption of beta-carotene-rich foods can cause vitamin toxicity. Symptoms include the following (79, 81, 82):

• Headache
• Nausea and vomiting
• fatigue
• Dizziness and lightheadedness
• weight loss
• Hair loss
• Dry skin
• Diarrhea
• Muscle pain

How to reduce excessive beta-carotene levels

The most important step is to work with a doctor to find the cause of excessive beta-carotene levels and treat the underlying conditions. In the case of vitamin poisoning, the treating doctor may recommend reducing the amount of beta-carotene-rich foods in the diet over a period of time. In this case, fruit and vegetable juices should be avoided in favor of whole fruits and vegetables (57). In addition, larger amounts of plant sterols can be consumed, which reduce the bioavailability of beta-carotene (76). Plant sterols are found in wheat germ, vegetable oils (corn oil, sesame oil, rapeseed oil and olive oil), peanuts, almonds and foods enriched with sterols.

Risks

Although the benefits are generally unclear, beta-carotene supplements appear to carry serious risks. Smokers or people who have been exposed to asbestos should not use beta-carotene supplements, as even low doses have been associated with an increased risk of cancer, heart disease, stroke and death in these groups (85, 86, 87, 88, 89). These risks are further increased when smoking is combined with alcohol consumption (84). High alcohol consumption in combination with beta-carotene supplements can increase the risk of liver disease, heart disease and cancer (83). In high doses, vitamin A and presumably also beta-carotene can be toxic to the liver. In addition, a meta-analysis of 53 studies with a total of over 240,000 participants suggests that beta-carotene supplementation at doses above 9.6 mg per day may slightly increase mortality (53).

Interactions

If you are taking medication, you should discuss beta-carotene supplementation with your doctor in advance. Beta-carotene supplements may interact with drugs used to treat high cholesterol and other medications. Due to the lack of data regarding safety, children and pregnant and breastfeeding women should only take beta-carotene supplements on the recommendation of a doctor.

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