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Peer-reviewed scientific article Orange sweet potatoes are an excellent source of vitamin A TAMI TURNER, BETTY J. BURRI* Betty J. Burri *Corresponding author United States Department of Agriculture (USDA), Agricultural Research Service Western Human Nutrition Research Center, 430 West Health Sciences Drive, Davis, CA 95616, USA AgroFOOD industry hi-tech - July/August 2011 - vol 22 n 4 Functional food ABSTRACT: Vitamin A is an essential nutrient required for proper growth and development, vision, red blood cell production, and immune function. An estimated 208 million women and children suffer from vitamin A deficiency worldwide, making vitamin A deficiency a public health problem in numerous countries. Several carotenoids, including beta-carotene, can convert to vitamin A in the body. Orange-fleshed sweet potatoes contain high concentrations of beta-carotene, and have succeeded in improving human vitamin A status in several small-scale food-based interventions. We estimated the amounts of orange sweet potatoes needed to provide sufficient vitamin A for individuals and at the international level. The amounts required can reasonably be provided by orange sweet potato making it an excellent source of vitamin A. VITAMIN A VITAMIN A DEFICIENCY Vitamin A (VA) is an umbrella term for compounds that have VA activity in the body (1). VA is an essential nutrient needed for proper growth and development, vision, red blood cell production, immune function, and numerous roles in genetic regulation (1-3). Rich sources of dietary VA are found in animal products which contain preformed retinol, that is ready to use in the body. Thus, liver, fish oils, and organ meats are excellent sources of VA (4) but are often expensive and inaccessible to much of the world’s population. The amount of dietary VA needed by an individual depends on their age, gender, life stage (i.e. pregnant, lactating), and presumably on genetics, lifestyle, and immune system status. Recommended VA intakes are shown in Table 1. Vitamin A deficiency (VAD) is a public health problem in numerous countries, affecting approximately 208 million people (3, 6, 7). The highest burden of VAD is in women and children often in Sub-Saharan Africa and South East Asia. Providing VA to at risk people decreases the severity of diarrhoea, influenza, and measles (3). VAD is also the leading cause of preventable blindness (3, 6-9). Child mortality decreased by 23 percent (3) and maternal mortality decreased by about 30 percent with VA supplementation (10, 11). VAD prevention and intervention has included large-scale supplementation programs, foodfortification, bio-fortification, and food-based programs. Large-scale, synthetic VA capsule programs have provided a cost-effective way to alleviate and prevent VAD in many countries (e.g. Bangladesh, Nepal). However, these programs are usually funded by national governments and international organizations. Funding issues mean these programs can be difficult to sustain and can fail to cover some of the population at risk, especially the rural poor (12). There are also potential toxic effects in some infants receiving more than one high-dose supplement (13). Highdose capsules are also contraindicated in reproductiveaged women, and due to potential teratogenic effects, they can only be given within 6-8 weeks postpartum (3). Fortifying food with VA could reach more people, since it is often done at the national level, but there are inherent problems in fortifying food: 1) the type of food chosen should be consumed and available by most, including those at highest risk for deficiency, 2) the food needs to be compatible with the nutrient added, 3) the dose must be safe but also provide enough VA to prevent deficiency in both children and adults, and 4) monitoring must be on-going for safety and effectiveness. Bio-fortified or genetically engineered foods also have common issues, such as the amount of VA actually provided to the consumer, consumer acceptance, and underlying environmental issues. Using fruits and vegetables rich in PVA compounds in prevention and treatment of VAD is a good alternative to supplements or food fortification (14, 15). Not only can it provide income to farmers but also it offers longterm sustainable ways to improve VA status. Fruits and vegetables also provide a variety of nutrients along with VA. Many small-scale food-based interventions to improve VA status have been successful (16-20). Table 1. Recommended intake of vitamin A. Carotenoids are orange, red, and yellow pigments; over 700 naturally occurring carotenoids have been described. There are three primary carotenoids in the human diet that can be converted to VA: β-carotene (BC), α-carotene (AC), and β-cryptoxanthin (CX). These are termed provitamin A (PVA) carotenoids. Orange-fleshed sweet potatoes (OFSP), tangerines, carrots and mangoes, as well as dark-leafy green vegetables such as kale and mustard greens are excellent sources of VA. The conversion of carotenoids to VA can be poor, so the amount of VA provided by these carotenoids is controversial. Conversion ratios range from 2:1 to over 24:1 (carotenoid: VA) (1) due to food factors (e.g. species, growing conditions, food matrix, cooking, storage) and host factors (i.e. digestive health, VA status, dietary fat). 14 ORANGE-FLESHED SWEET POTATOES IN VITAMIN A DEFICIENCY PREVENTION AND INTERVENTION OFSP are well-suited for VA interventions since they contain large amounts of BC. They are low in fat and protein, high in antioxidants (21), fibre, some B vitamins, many minerals, and have been efficacious VAD interventions (16, 18, 20). They grow well in hot, humid climates generally from root cuttings and are a high yielding crop. OFSP store well and retain most of their carotenoids for at least 50 days (22). The amount of BC depends heavily on the species grown and ranges anywhere from trace amounts to 31450 µg BC/100 g (OFSP having higher BC than yellow, cream, and purple varieties). Cooking can cause loss of BC, but also may help soften the food matrix allowing carotenoids to be released with a general trend of higher temperatures and longer time causing more loss of BC (Table 2). Bioaccessibility of BC from OFSP is also influenced by dietary fibre and fat concurrently consumed. Functional food Table 2. The effects of variety and processing on the amount of betacarotene measured in 100 grams of sweet potato. AgroFOOD industry hi-tech - July/August 2011 - vol 22 n 4 Amount of sweet potatoes needed to provide vitamin A The VA requirement of individuals varies by age and life stage (Table 1). We calculated the amount of OFSP needed to provide 100 percent VA per day, assuming a range of BC in OFSP (4-23mg/100g), loss from storage and cooking of 10 percent, a bioaccessibility fraction (0.25), a conversion of BC to VA of 3:1 for deficient and 12:1 for adequately nourished people, and the weight of one cup of sweet potatoes (255g/cup) (25). Figure 1 shows the amounts of OFSP needed to meet the dietary VA requirement at different life stages. The results show that OFSP provide an excellent source of VA. A person can reasonably consume 100 percent of their VA from OFSP. Figure 1. The amount of orange sweet potatoes needed per day to meet vitamin A requirement. 15 Functional food AgroFOOD industry hi-tech - July/August 2011 - vol 22 n 4 Overall, the effectiveness of OFSP in food-based nutritional interventions to improve VA status in populations is mainly based upon the variety of the potato, since BC concentrations vary greatly. Smaller factors that improve the effectiveness of BC-rich OFSP to provide VA include as ranked: the presence of fat in the meal consumed with the potato > growing, harvesting > cooking and storage > consumer preference (25). To estimate the amount of OFSP needed to supply VA worldwide for the 190 million children and 19.1 million pregnant and lactating women at risk for VAD, we assumed 75 percent of preschoolers were 1-3 years old, and 20 percent pregnant women were also lactating. The smallest amount of OFSP needed to supply these people was 2.083 million metric tons per year whereas a higher, and maybe more realistic amount, was 11.681 million metric tons. Current production worldwide is approximately 106.5 million metric tons (26). Surprisingly, most sweet potatoes are produced in low-income, food-insecure countries with populations that have moderate VAD (6, 8, 9, 11). However, many sweet potato growing countries eat cream or white sweet potatoes, and much of the crop is used for animal feed. Although production and consumption values do not separate the different varieties of sweet potatoes, worldwide production is much higher than our estimated amounts needed to supply VA to VAD people worldwide. Feasibility of orange sweet potatoes to improve vitamin A status The distribution and consumption data of sweet potatoes suggest they are accepted and available among many VAD populations. Studies assessing switching to OFSP have shown low resistance with only a small impact of 5-10 percent on consumer preference (26, 27). There is also little evidence of especially unfavourable environmental impacts if one were to increase the production of sweet potatoes (28, 29). Although growing large quantities of any single crop may have ecological, societal, or economic impacts that must be taken into account, this indicates that encouraging farmers and consumers to substitute OFSP for other varieties, or to increase OFSP production, may be successful in preventing VAD. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. CONCLUSION Orange sweet potatoes are excellent sources of VA. VAD is a public health problem in numerous developing countries. Providing foods naturally rich in VA to alleviate VAD can improve the health of millions of people. In low-income countries, approximately 82 percent of total dietary VA intake is via the consumption of carotenoid-rich plants (7). OFSP varieties commonly grown provide high amounts of BC which can provide a considerable amount of VA and thus, are excellent sources of this essential nutrient. Production of sweet potatoes for human consumption is encouraging, since these could be a considerable nutritious and sustainable source of VA. Improvement in agricultural practices in developing countries to increase yields and the replacement of other varieties of sweet potatoes as white-fleshed, yellow, or purple potatoes with OFSP could allow further improvements in nutrition, especially in VAD-insecure countries. REFERENCES AND NOTES 1. 16 2. Dietary reference intakes for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc, eds. U.S. Institute of Medicine, Food and Nutrition Board, National Academy Press (2000). 22. 23. 24. 25. 26. 27. 28. 29. R. Blomhoff, H.K. Blomhoff, J of Neurobiol., 66, pp. 606-630 (2006). Vitamin A Supplementation, World Health Organization, online: http://www.who.int/vaccines/en/vitamina.shtml, accessed April 20, 2011. 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