Carotenoids are natural colored pigments found in plants, including fruits and vegetables. About 600 such carotenoids have been identified. Examples of some carotenoids are Beta-carotene, Alpha-carotene, astaxanthin, cryptoxanthin, lycopene, lutein and zeaxanthin etc.
The absorption and utilization of carotenoids varies. After much debate over the conversion factors, the US Food and Nutrition Board revised the conversion factors and stated that 1 microgram retinol (preformed Vitamin A) is equivalent to 12 microgram beta-carotene or 24 microgram of other provitamin-A carotenoids. One unit of beta-carotene is defined as the activity of 0.6 microgram beta-carotene and henceforth, 1 microgram beta-carotene is equal to 1.67 units of beta-carotene.
Carotenoids have lot many functions such as –
- It quenches the singlet form of oxygen and helps in preventing the formation of free radicals in the body. Natural form (Cis) of beta-carotene acts as an antioxidant whereas synthetic form (Trans) acts as pro-oxidant.
- It scavenges the free radicals directly to give antioxidant property.
- Enhances some aspects of immune system.
- Acts as precursor for Vitamin A.
Dietary sources of carotenoids – found in wide variety of fruits and vegetables. Alpha-carotene is found in palm oil, maize, carrots and pumpkin. Lycopene is found in red fruits like tomatoes, particularly cooked and pureed ones; guava; watermelon; apricots; peaches and red grapefruit. Lutein and zeaxanthin are found in dark green vegetables, red pepper and pumpkin. Cryptoxanthin is found in mangoes, oranges and peaches. Beta-carotene in found in apricots, cooked carrots, canned and drained mango, cooked sweet potato, cooked spinach, and cooked kale etc.
About the metabolism part of carotenoids, research on beta-carotene is more done and hence beta-carotene is discussed further. Beta-carotene contains two molecules of Vitamin A that gets hydrolyzed in the gastrointestinal tract and absorbed from the mucosal cells of the small intestine to get converted to retinol. This conversion of beta-carotene is regulated by Vitamin A stores of the individual. The intact form of beta-carotene is transported in very low density lipoprotein (VLDL) and low density lipoprotein (LDL) cholesterol. To a less extent carotenoids are stored in liver but most of them are deposited in adipose tissue, epidermal and dermal layers of skin and adrenals; there are also high levels in the corpus luteum and in colostrum. Beta carotene is finally excreted in faeces.
Possible health benefits of various carotenoids –
- Beta-carotene for cancer – epidemiological studies have indicated that foods rich in carotenoids or increasing serum concentration of carotenoids are useful in reducing the risk of certain types of cancer such as lung cancer, cancer of cervix, endometrium, breast, oesophagus, mouth and stomach. However, so far evidence of carotenoids supplementation for beneficial effect in cancer is very little.
- Beta-carotene for cardiovascular disease (CVD) – it is also reported that beta-carotene might be associated with a lower risk of CVD. However, placebo trials of beta carotene supplementation did not prove useful in angina. Also incidence of myocardial infarction is not reduced through beta-carotene. So use of carotenes is not active in this field.
- Beta-carotene for cataract – beta-carotene may protect cataract formation as trials suggest. However, beta carotene treatment for long time had no beneficial or harmful effect on cataract.
- Beta-carotene for diabetes – serum beta-carotene level may be reduced in diabetic patients and there is a negative co-relation between beta carotene levels with glycaemic control. However, trials showed inefficient result in reducing the risk of type-2 diabetes.
- Beta-carotene in immune function – effect of beta-carotene towards immunity has a conflicting response. One study proved its role in increasing proportion of monocytes whereas other showed immunity unaffected by beta-carotene supplementation.
- Lutein for eye- lutein is shown to have protective role in visual apparatus and vascular supply. It filters out the blue light. It helps to prevent ARMD and cataracts. It is also reported that supplements helped to improve the visual function in patients with retinal degeneration. But studies have also shown finally that lutein is not a direct cure for ARMD, but it reverses some of the symptoms thereby improves visual function.
- Lycopene as an antioxidant- lycopene acts as free radical scavenger and shows antioxidant property. It is reported to protect against macular degeneration, atherosclerosis, and cancer especially prostrate cancer. Although it has a beneficial role but it was seen through trials that the effect is very small.
Adverse effects and Precautions
Carotenoids are generally non-toxic. Even large doses do not cause any critical manifestations. Diarrhea, dizziness, and arthralgia may occur occasionally with supplementation. Allergic reactions like hay fever and facial swelling have been reported. Also amenorrhea and leucopenia have also been reported rarely.
Hypercarotenaemia (increased level of carotenoids) is characterized by yellowish coloration of the skin i.e. palms of hands and soles of feet. This is harmless and gradually disappears once the level is corrected.
Possible interactions – none reported so far.
- No serious effects are reported but if you have hypersensitivity towards carotenoids then you must avoid it.
- No problem have been reported for pregnant and breast feeding women on beta-carotene supplementation.
Dose- beta-carotene, lutein, lycopene and mixed carotenoids are available in the form of tablets and capsules. Beta-carotene as a single supplement should not be recommended, it is given in combination with other products as per your physician.
As discussed above carotenoids have been improving their potential in treating various diseases though continuous trials and research is still going to find more of its ability and beneficial role in medicinal field.