Sweet Potato

Scientific Name(s): Ipomoea batatas L. Family: Convolvulaceae.

Common Name(s): Sweet potato , caiapo , nyamis (Africa), yam , kumara (New Zealand), camote (southwest United States)

Uses

Pharmacological investigations on the antidiabetic, antihypertensive, anti-inflammatory, antimicrobial, and antioxidant activity of sweet potato have been conducted.

Dosing

Clinical studies of the efficacy of the nutraceutical caiapo, an extract of sweet potato, used a total of 4 capsules daily, with each capsule containing caiapo 168 to 336 mg. Sweet potato is available in powder and capsule (caiapo) forms. Dosage regimens vary, but most commercial manufacturers suggest 2 capsules 30 minutes before meals, up to a total of 6 capsules daily.

Contraindications

Hypersensitivity to any of the chemical components in the plant species.

Pregnancy/Lactation

There are no case reports or clinical studies relevant to pregnancy or lactation. However, women with hypersensitivity reactions to the plant should avoid use.

Interactions

None well documented.

Adverse Reactions

Historical and clinical data document no serious adverse reactions. Patients with known hypersensitivity reactions to the plant may develop generalized urticaria, hypotension, and edema of the hands and face. Dizziness, loss of consciousness, nausea, vomiting, and a sensation of tickling and tightness in the throat have been documented.

Toxicology

Very little toxicity data are available about the plant.

Botany

The sweet potato plant originated in Central America. Although China is considered the leading producer of sweet potatoes, the plant is widely cultivated and consumed throughout the world. It is a herbaceous perennial vine with alternate heart-shaped, lobed leaves and medium-sized flowers. The root is edible and is often long and tapered. The skin may be red, purple, or brown and white in color. The interior, or flesh, may be white, yellow, orange, or purple. The leaves and shoots sometimes are eaten as greens. 1

History

Sweet potato is the world's sixth largest food crop and is important for the growing populations in Asian and African countries. The plant has been used medicinally in Japan for treating diabetes and other diseases. American Indians used sweet potato to treat thirst and weight loss attributed to diabetes. 2 , 3 , 4 , 5

Chemistry

There are numerous, extensive phytochemical investigations. Most studies focus on the nutraceutical properties and understanding the physiological functions of sweet potato. Only selective studies will be discussed because of the extent of these investigations.

The root and skin contain most of the studied medicinal components. High levels of polyphenols, such as anthocyanins and phenolic acids (eg, caffeic acid), have been isolated from sweet potato. Chlorogenic, dicaffeoylquinic, and tricaffeoylquinic acids are derivatives of caffeoylquinic acid that protect the root from fungal diseases and have potential cancer chemoprotective effects. The numerous acylated anthocyanins are the major color constituents in the storage roots and are important in the plant's use in diabetes. Sesquiterpenoids include 6-myoporol and ipomeamarone. Structural properties of the anthocyanins important for bioactivity include phenolic esters of the sugar, presence of 2 hydroxyl groups on the aromatic ring, and the presence of an unsaturated alkyl chain in the acylated moiety. 4 , 6 , 7 , 8 , 9

The plant's antioxidant activity is associated with its alpha-tocopherol content, which is the most common form of vitamin E, and comprises 25 mg per 100 g of sweet potato shoots. The 2 storage proteins, sporamins A and B, account for more than 80% of the total protein isolated from the roots of sweet potato. 10 , 11

Uses and Pharmacology

Pharmacological investigations on the antidiabetic, antihypertensive, anti-inflammatory, antimicrobial, and antioxidant activity of sweet potato in animals have been conducted.

Cardiovascular effects
In vitro data

An extract was examined for relaxant activity on isolated rat vascular aortic preparations. Sweet potato showed 97% relaxation activity for endothelium-intact aortic ring preparations but only 35% in the mesenteric vascular bed. The vasorelaxation mechanism of action was similar to that of the pharmacological agent acetylcholine. 12

Antioxidant effects
In vitro and in vivo data

The major phenolic components in a 70% methanol extract of sweet potatoes showed strong antioxidant activity in a linoleic acid-aqueous system. 13

Anthocyanins of purple sweet potato (PSP) have antioxidant activity. DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity in collected urine samples increased in PSP anthocyanin-injected rats and in 6 PSP beverage-administered human volunteers. The degree of radical-scavenging activity for some of the anthocyanins was higher than that for ascorbic acid. 14

Immune system effects
Animal data

Sweet potato fiber may be useful in combination with other therapeutic agents used in skin wound therapy. The healing effect of sweet potato fiber was evaluated for burns or decubital wounds in rats over 19 days. Outcome measures included reduction in size and changes in quality of the wounds. Rats treated with the sweet potato fiber covering had reduced wound areas by 21% at day 9, 19.5% at day 11, and 18.7% at day 13, compared with controls. Healing times for both groups were 19 days for treated rats and 21 days for controls. 15

In a mouse model, purified sweet potato polysaccharide (PSPP) isolated from the roots acted as a biological response modifier. In a dose-dependent manner, mice treated with PSPP (50, 150, and 250 mg/kg body weight for 7 days) had increased in phagocytic function, hemolytic activity, and serum IgG concentration. 1

Clinical data

A randomized, crossover study involving 16 healthy, nonsmoking adults (7 men and 9 women) examined the effects of physiological doses of purple sweet potato leaves (PSPL) over 6 weeks. During week 1, control and experimental groups were subjected to a low-polyphenol diet. During weeks 2 and 3, the experimental group consumed a PSPL diet consisting of 200 g daily of PSPL, and the control group consumed a diet consisting of low polyphenols and carotenoids adjusted to the same level as that of PSPL. The washout diet followed week 4. During weeks 5 and 6, experimental and control groups switched diets. Results from blood and urine samples indicate that dietary intervention in the form of PSPL consumption modulated various aspects of immune function, including increased proliferation responsiveness of peripheral blood mononuclear cells, secretion of cytokines IL-2 and IL-4, and increased lytic activity of natural killer cells. 16

Similar immune system effects also have been documented for the white-skinned sweet potato (WSSP). 17

Diabetes
In vitro data

In a free-glucosidase (AGH) assay system, potent AGH inhibitory activity was seen with anthocyanin extracts from the storage roots of PSP (IC 50 = 0.36 mg/mL). The extracts also inhibited alpha-amylase activity, indicating a potential role in suppressing the increase in postprandial glucose levels. 18

Animal data

The antidiabetic activity of WSSP versus troglitazine was examined in Zucker fatty rats over 8 weeks. After starting oral dosing with WSSP, hyperinsulinemia was reduced 23%, 26%, 60% and 50%, at 3, 4, 6, and 8 weeks, respectively. WSSP also inhibited increases in blood sugar levels after administration of a glucose challenge test during week 7. Histology of the pancreas showed regranulation of pancreatic islet B cells. Isolation and purification of the antidiabetic component in WSSP was unsuccessful. 2 , 19

Evidence and similar experiments in rats indicate that acylated anthocyanins, such as caffeoylsophorose, are responsible for alpha-glucosidase inhibition of the extract. The production of adiponectin by transgenic sweet potatoes has gained pharmaceutical interest. Adiponectin is a cytokine produced and secreted only from adipose tissue and is found in human plasma. Low levels of this cytokine or protein are associated with type 2 diabetes mellitus, obesity, and hypertension. 8 , 20

Clinical data

Caiapo, an extract of WSSP, improves glucose tolerance by reducing insulin resistance without affecting body weight or insulin secretion and clearance.

A 6-week, prospective, placebo-controlled, randomized, double-blind study involving 18 men examined the effects of caiapo. Patients were randomized into 3 groups and received a total of 4 tablets daily containing placebo, caiapo 168 mg, or caiapo 336 mg. Outcome measures assessed included an intravenous glucose tolerance test and oral glucose tolerance test. Overall, only high-dose caiapo improved metabolic control by decreasing insulin resistance without affecting body weight. No serious side effects were observed. 5 , 21

Results from an uncontrolled study in 145 Japanese patients with type 2 diabetes treated with the nutraceutical caiapo indicated a decrease in blood glucose levels. 5

Other pharmacological activity

Chemoprotective effects may be associated with the anthocyanins and phenolic acids in sweet potato. Sweet potato contains provitamin A or beta-carotene and clinical studies document its potential role as a long-term, food-based strategy in reducing vitamin A deficiency in children in many developing countries. 3 , 4 , 22 , 23

Dosage

Clinical studies of the efficacy of the nutraceutical caiapo used a total of 4 tablets daily, with each tablet containing caiapo 168 to 336 mg. Sweet potato is available in powder and capsule (caiapo) forms. Dosage regimens vary, but most commercial manufacturers suggest 2 capsules 30 minutes before meals, up to a total of 6 capsules daily.

Pregnancy/Lactation

There are no case reports or clinical studies relevant to pregnancy or lactation. However, women with a history of hypersensitivity reactions to the plant should avoid use. 24

Interactions

No drug interaction data could be found in medical literature.

Adverse Reactions

Historical and clinical data document no serious adverse reactions. Patients with known hypersensitivity reactions to the plant may develop generalized urticaria, hypotension, and edema of the hands and face. Other case reports also document dizziness, loss of consciousness, nausea, vomiting, and a sensation of tickling and tightness in the throat. 24

Toxicology

Very little toxicity data are available for the plant. Animal studies document temporary neurological effects followed by extensive liver necrosis for 3 sesquiterpenoids in sweet potato with a median lethal dose varying from 184 to 266 mg/kg. 9 Sweet potato consumption should be avoided by individuals hypersensitive to any of the chemical components in the plant species. 24

Bibliography

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2. Kusano S , Abe H , Tamura H . Isolation of antidiabetic components from white-skinned sweet potato ( Ipomoea batatas L.) . Biosci Biotechnol Biochem . 2001;65:109-114.
3. Yoshimoto M , Okuno S , Yoshinaga M , Yamakawa O , Yamaguchi M , Yamada J . Antimutagenicity of sweetpotato ( Ipomoea batatas ) roots . Biosci Biotechnol Biochem . 1999;63:537-541.
4. Konczak-Islam I , Yoshimoto M , Hou D , Terahara N , Yamakawa O . Potential chemopreventive properties of anthocyanin-rich aqueous extracts from in vitro produced tissue of sweetpotato ( Ipomoea batatas L.) . J Agric Food Chem . 2003;51:5916-5922.
5. Ludvik B , Waldhausl W , Prager R , Kautzky-Willer A , Pacini G . Mode of action of Ipomoea batatas (Caiapo) in type 2 diabetic patients . Metabolism . 2003;52:875-880.
6. Konczak I , Okuno S , Yoshimoto M , Yamakawa O . Caffeoylquinic acids generated in vitro in a high-anthocyanin-accumulating sweet potato cell line . J Biomed Biotechnol . 2004;5:287-292.
7. Goda Y , Shimizu T , Kato Y , et al. Two acylated anthocyanins from purple sweet potato . Phytochemistry . 1997;44:183-186.
8. Matsui T , Ebuchi S , Fukui K , Matsugano K , Terahara N , Matsumoto K . Caffeoylsophorose, a new natural alpha-glucosidase inhibitor, from red vinegar by fermented purple-fleshed sweet potato . Biosci Biotechnol Biochem . 2004;68:2239-2246.
9. Wilson BJ , Burka LT . Toxicity of novel sesquiterpenoids from the stressed sweet potato ( Ipomoea batatas ) . Food Cosmet Toxicol . 1979;17:353-355.
10. Ching LS , Mohamed S . Alpha-tocopherol content in 62 edible tropical plants . J Agric Food Chem . 2001;49:3101-3105.
11. Maeshima M , Sasaki T , Asahi T . Characterization of major proteins in sweet potato tuberous roots . Phytochemistry . 1985;24:1899-1902.
12. Runnie I , Salleh MN , Mohamed S , Head RJ , Abeywardena MY . Vasorelaxation induced by common edible tropical plant extracts in isolated rat aorta and mesenteric vascular bed . J Ethnopharmacol . 2004;92:311-316.
13. Hayase F , Kato H . Antioxidative components of sweet potatoes . J Nutr Sci Vitaminol . 1984;30:37-46.
14. Kano M , Takayanagi T , Harada K , Makino K , Ishikawa F . Antioxidative activity of anthocyanins from purple sweet potato, Ipomoera batatas cultivar Ayamurasaki . Biosci Biotechnol Biochem . 2005;69:979-988.
15. Suzuki T , Tada H , Sato E , Sagae Y . Application of sweet potato fiber to skin wound in rat . Biol Pharm Bull . 1996;19:977-983.
16. Chen CM , Li SC , Lin YL , Hsu CY , Shieh MJ , Liu JF . Consumption of purple sweet potato leaves modulates human immune response: T-lymphocyte functions, lytic activity of natural killer cell and antibody production . World J Gastroenterol . 2005;11:5777-5781.
17. Miyazaki Y , Kusano S , Doi H , Aki O . Effects on immune response of antidiabetic ingredients from white-skinned sweet potato ( Ipomoea batatas L.) . Nutrition . 2005;21:358-362.
18. Matsui T , Ueda T , Oki T , Sugita K , Terahara N , Matsumoto K . α-Glucosidase inhibitory action of natural acylated anthocyanins. 1. Survey of natural pigments with potent inhibitory activity . J Agric Food Chem . 2001;49:1948-1951.
19. Kusano S , Abe H . Antidiabetic activity of white skinned sweet potato ( Ipomoea batatas L.) in obese Zucker fatty rats . Biol Pharm Bull . 2000;23:23-26.
20. Berberich T , Takagi T , Miyazaki A , Otani M , Shimada T , Kusano T . Production of mouse adiponectin, an anti-diabetic protein, in transgenic sweet potato plants . J Plant Physiol . 2005;162:1169-1176.
21. Ludvik BH , Mahdjoobian K , Waldhaeusl W , et al. The effect of Ipomoea batatas (Caiapo) on glucose metabolism and serum cholesterol in patients with type 2 diabetes: a randomized study . Diabetes Care . 2002;25:239-240.
22. Haskell MJ , Jamil KM , Hassan F , et al. Daily consumption of Indian spinach ( Basella alba ) or sweet potatoes has a positive effect on total-body vitamin A stores in Bangladeshi men . Am J Clin Nutr . 2004;80:705-714.
23. van Jaarsveld PJ , Faber M , Tanumihardjo SA , Nestel P , Lombard CJ , Benade AJ . Beta-carotene-rich orange-fleshed sweet potato improves the vitamin A status of primary school children assessed with the modified-relative-dose-response test . Am J Clin Nutr . 2005;81:1080-1087.
24. Velloso A , Baeza M , Tornero P , et al. Anaphylaxis caused by Ipomoea batatas . J Allergy Clin Immunol . 2004;113:S242.

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