The importance of beta carotene, as it converts to retinol (vitamin A), and its involvement in health
and disease prevention are well-known. However, another carotenoid, alpha carotene, not only converts to vitamin A in the body, but also has benefits of its own.
Where Can You Find Alpha Carotene?
Like beta carotene, alpha carotene is found in a variety of vegetables and fruits. Alpha carotene (α-carotene) is also found in dietary supplements. Cleavage of alpha carotene in the body produces retinol and alpha retinol whereas cleavage of beta carotene produces two retinol molecules.1 Only a small amount of fat needs to be present for optimal alpha carotene absorption.2 In the National Survey of Dietary Intake in Spain (2009-2010), alpha carotene was determined to represent 12.8% of provitamin A carotenoids.3 Specific locations on three chromosomes were recently identified as being associated with serum alpha carotene levels.4
A study reported in JAMA Internal Medicine that involved 15,318 adults enrolled in the Third National Health and Nutrition Examination Survey Follow-up Study revealed a 23% lower adjusted risk of death from any cause over an average 13.9 year follow-up period among those whose serum alpha carotene levels were 2-3 micrograms per deciliter (mcg/dL) in comparison with participants whose levels were 0-1 mcg/dL.5 For participants whose levels were 4-5 mcg/dL, 6-8 mcg/dL, and 9 mcg/dL or more, the respective risks were 27%, 34%, and 39% lower.
The researchers from the Centers for Disease Control and Prevention and UCLA also uncovered decreasing risks of mortality from cardiovascular disease, cancer, and other causes over follow-up in association with rising alpha carotene levels. Authors Chaoyang Li, MD, PhD, and colleagues note that “Although alpha carotene is chemically similar to beta carotene, in vivo study results suggest that alpha carotene is about 10 times more effective than beta carotene in inhibiting the proliferation of human neuroblastoma cells; that alpha carotene, but not beta carotene, has a potent inhibitory effect against liver carcinogenesis; and that alpha carotene is more effective than beta carotene in inhibiting the tumor-promoting action of glycerol in lung carcinogenesis and skin tumor promotion.
An investigation involving 13,293 men and women enrolled in the National Health and Nutrition Examination Survey (NHANES) III, 1988–1994, uncovered a 46% higher risk of all-cause mortality through 2006 among those whose serum alpha carotene levels were among the lowest 25% in comparison with those whose levels were among the highest.6
An assessment of the effects of carotenoids and vitamin A on the risk of recurring colon polyps (which can be a precursor of colorectal cancer), found that participants in the Polyp Prevention Trial whose serum alpha carotene levels were among the top 25% of subjects had a 45% lower risk of recurrence.7 Those with a higher dietary intake of alpha carotene with or without supplements also had a lower risk of developing new polyps. A case-control study in China that matched 538 individuals with colorectal cancer with 564 subjects who did not have the disease found that those whose serum alpha carotene levels were among the highest 25% had a 51% lower risk of colorectal cancer compared to those whose serum levels were among the lowest 25%.8
An analysis of a case-control study of lung cancer uncovered a 30% lower risk of the disease among subjects with the highest one-third of alpha carotene intake in comparison with those whose intake was among the lowest third.9 When examined according to smoking status, having a high-intake of alpha-carotene was protective against lung cancer in men who were heavy smokers. A meta-analysis of five prospective studies that provided data concerning blood concentrations of carotenoids and retinol among determined a 34% lower risk of lung cancer per each 5 mcg/100 milliliter alpha carotene.10
Moreover, results from a population-based, case-control study of the association between the consumption of fruits and vegetables and risk of lung cancer suggest that consumption of yellow-orange (carrots, sweet potatoes or pumpkin, and winter squash) and dark green (broccoli, green beans, green peas, spinach, turnip greens, collards, and leaf lettuce) vegetables, which have a high alpha carotene content, was more strongly associated with a decreased risk of lung cancer than was consumption of all other types of vegetables.
In an investigation that included 2,188 participants in the Nurses’ Health Study who developed breast cancer over a 20-year period who were matched with women who did not develop the disease, having a plasma level of alpha carotene that was among the top 20% of subjects was associated with a 26% lower risk of breast cancer during follow-up than subjects whose levels were among the lowest 20%, and for recurrent or lethal breast cancer, the risk was 46% lower.11
A prospective analysis of 185,885 adults enrolled in the Multiethnic Cohort Study found an 8% lower adjusted risk of invasive bladder cancer in men and a 48% lower adjusted risk in women whose alpha carotene intake was among the top 25% in comparison with those whose intake was among the lowest quarter of subjects.12
In a meta-analysis of 10 studies that examined the associations between carotenoid intake and non-Hodgkin’s lymphoma, subjects whose intake of alpha carotene was highest had a 13% lower risk of the disease compared to those whose intake was among the lowest.13 Of the carotenoids examined, a significant inverse dose-response relationship existed only between alpha carotene and non-Hodgkin’s lymphoma risk, which was 13% lower per each 1,000 mcg per day increment of intake.
In a study that included 34 subjects with coronary heart disease and 40 control subjects, plasma alpha carotene and gamma-tocopherol levels were significantly lower in the heart disease patients.14 “These data suggest that plasma levels of alpha carotene and gamma-tocopherol may represent markers of atherosclerosis in humans.,” A. Kontush and colleagues conclude. “Measuring these antioxidants may be of clinical importance as a practical approach to assess atherogenesis and/or its risk.”
Bone Health and Eye Health
In addition to cancer and heart disease, consuming more alpha carotene may also help protect the bones and eyes. Among participants in the prospective European Prospective Investigation into Cancer and Nutrition-Norfolk, a lower risk of hip fracture was observed among men with higher plasma alpha carotene levels, and increased bone density among women who had a higher intake.15 A 2015 study found that people with the highest intakes of α-carotene maintained macular health better than those with lower intakes of α-carotene.16
Obesity and Chronic Disease
Research suggests further roles for alpha carotene. “Serum alpha carotene may provide a deeper and clinically relevant purpose, beyond previous suggestions for its use as a biomarker for fruit and vegetable consumption, in that alpha carotene may be a biomarker for chronic disease risk frequently linked with obesity,” note E. T. Nuss and colleagues at the University of Wisconsin-Madison. “As humans begin to live over a century, determining biomarkers of ultimate health is important. Alpha carotene does not have the same distribution in the food supply as beta carotene and therefore is often overlooked in surveys.”1
- Nuss ET et al. Exp Biol Med (Maywood). 2017 Jan 1:1535370217706962.
- Roodenburg AJC et al. Am J Clin Nutr. 2000 May;71(5):1187-93.
- Beltrán-de-Miguel B et al. Int J Food Sci Nutr. 2015;66(6):706-12.
- D’Adamo CR et al. J Nutrigenet Nutrigenomics. 2016;9(5-6):254-264.
- Li C et al. Arch Intern Med. 2011 Mar 28;171(6):507-15.
- Shardell MD et al. Nutr Res. 2011 Mar;31(3):178-89.
- Steck-Scott S et al. Int J Cancer. 2004 Nov 1;112(2):295-305.
- Huang J et al. Mol Nutr Food Res. 2017 Jun 12.
- Shareck M et al. Front Oncol. 2017 Feb 28;7:23.
- Abar L et al. Cancer Med. 2016 Aug;5(8):2069-83.
- Eliassen AH et al. Am J Clin Nutr. 2015 Jun;101(6):1197-205.
- Park SY et al. J Nutr. 2013 Aug;143(8):1283-92.
- Chen F et al. Ann Hematol. 2017 Jun;96(6):957-965.
- Kontush A et al. Atherosclerosis. 1999 May;144(1):117-22.
- Hayhoe RPG et al. Br J Nutr. 2017 May;117(10):1439-1453.
- Wu J et al. JAMA Ophthalmol. 2015 Dec;133(12):1415-24.