Scientific Name(s): Ipomoea batatas L.
Common Name(s): Caiapo, Camote, Kumara, Nyamis, Sweet potato, Yam
The sweet potato plant is an herbaceous perennial vine that 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 has 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. The interior, or "flesh," may be white, yellow, orange, or purple. The leaves and shoots are sometimes eaten as greens. Synonyms include Convolvulus tiliaceus auct. non Willd.; Ipomoea fastigiata (Roxb.) Sweet; Ipomoea tiliacea auct. non (Willd.) Choisy; Ipomoea triloba auct. non L.1, 2
Sweet potato is one of the world's largest food crops 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.3, 4, 5, 6
Numerous extensive phytochemical investigations focusing on the nutraceutical properties and physiological functions of sweet potato have been conducted.7, 8 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 play a major role in the plant's antidiabetic properties. Sesquiterpenoids include 6-myoporol and ipomeamarone. Structural properties of the anthocyanins important for bioactivity include phenolic esters of the sugar, 2 hydroxyl groups on the aromatic ring, and an unsaturated alkyl chain in the acylated moiety.5, 9, 10, 11, 12
The plant's antioxidant activity is associated with its alpha-tocopherol content, alpha-tocopherol being the most common form of vitamin E and comprising 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.13, 14
Uses and Pharmacology
Animal and in vitro data
The major phenolic components in a 70% methanol extract of sweet potato showed strong antioxidant activity in a linoleic acid–aqueous system.15
Anthocyanins of purple sweet potato have antioxidant activity. Levels of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity were increased in collected urine samples of purple sweet potato anthocyanin–injected rats and in 6 human volunteers administered a purple sweet potato beverage. The degree of radical scavenging activity for some of the anthocyanins was higher than that for ascorbic acid.16
A clinical trial reported modulation of antioxidative status and decreased exercise-induced oxidative damage in healthy young males (N=15) following 7 days of purple sweet potato leaf consumption after completing a running exercise protocol.17
The bioavailability of polyphenols in purple sweet potato leaves was demonstrated in a clinical study, with reported potential for enhanced antioxidant defense and decreased oxidative stress in young healthy adults.18
A sweet potato leaf extract was examined for relaxant activity in 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.19
Research reveals no clinical data regarding the use of I. batatas in cardiovascular disease; however, a sweet potato/footbath/acupressure massage intervention to prevent constipation was conducted among hospitalized patients with acute coronary syndromes.20
Blood glucose-lowering activities of sweet potato have been demonstrated in animal studies.8
In a free-glucosidase (AGH) assay system, potent AGH inhibitory activity was observed with anthocyanin extracts from the storage roots of purple sweet potato (50% inhibitory concentration [IC50]=0.36 mg/mL). The extracts also inhibited alpha-amylase activity, indicating a potential role in suppressing the increase in postprandial glucose levels.21
The antidiabetic activity of white-skinned sweet potato versus troglitazine was examined in Zucker fatty rats over 8 weeks. Oral dosing of white-skinned sweet potato reduced hyperinsulinemia 23%, 26%, 60%, and 50%, at 3, 4, 6, and 8 weeks, respectively. White-skinned sweet potato 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 white-skinned sweet potato was unsuccessful.3, 22
A sweet potato leaf extract given for 5 weeks decreased glucose levels in mice with type 2 diabetes; additional studies demonstrated stimulated secretion of glucagon-like peptide-1, resulting in increased insulin secretion.23
Evidence and similar experiments in rats indicate that acylated anthocyanins (eg, caffeoylsophorose) are responsible for alpha-glucosidase inhibitory activities of the extract. The production of adiponectin, a protein produced and secreted only from adipose tissue as a cytokine and found in human plasma, by transgenic sweet potatoes has gained pharmaceutical interest. Low levels of this cytokine or protein are associated with type 2 diabetes mellitus, obesity, and hypertension.11, 24
A Cochrane review evaluated randomized clinical trials comparing sweet potato with a placebo or a comparator intervention in type 2 diabetes. In 2 of the included trials (N=122), administration of sweet potato (caiapo tablets) produced significant improvement in glycosylated hemoglobin A1c at 3 to 5 months compared with placebo (mean difference, −0.3% [95% confidence interval, −0.6 to −0.04]; P=0.02). Included trials were all conducted by the same group of researchers.8
Immune system effects
Sweet potato fiber, in combination with other therapeutic agents, may be useful 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. In rats treated with the sweet potato fiber covering, wound areas were reduced 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.25
In a mouse model, purified sweet potato polysaccharide (PSPP) isolated from the roots acted as a biological response modifier. In mice treated with PSPP (50, 150, and 250 mg/kg body weight for 7 days), phagocytic function, hemolytic activity, and serum immunoglobulin concentration increased in a dose-dependent manner.2
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 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 diet consisting of 200 g daily of purple sweet potato leaves, and the control group consumed a diet consisting of low polyphenols and carotenoids adjusted to the same level as those of purple sweet potato leaves. A washout diet followed during week 4. During weeks 5 and 6, the experimental and control groups switched diets. Results from blood and urine samples indicate that dietary intervention in the form of purple sweet potato leaf 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 lytic activity of natural killer cells.26 Similarly, a clinical trial in healthy young males (N=15) reported decreased proinflammatory cytokine secretion after 7 days of consuming purple sweet potato leaves after completing a running exercise protocol.17
Immune system effects have also been documented for white-skinned sweet potato.27
Chemoprotective effects may be associated with the anthocyanins and phenolic acids in sweet potato. Intake of an anthocyanin-rich purple sweet potato beverage improved serum hepatic biomarkers in Japanese men with borderline hepatitis who were otherwise healthy.28
Clinical studies document use of sweet potato, due to its provitamin A (or beta-carotene) content, as a potential long-term, food-based strategy to improve vitamin A deficiency in children in many developing countries.29, 30, 31, 32, 33, 34
4 g/day of a sweet potato preparation (caiapo tablets) given for 3 to 5 months has been used in clinical studies.8
Clinical studies regarding efficacy of the nutraceutical caiapo used 2 g (low dose) or 4 g (high dose) daily, for a total of 4 tablets daily (each containing either 168 or 336 mg of powdered white-skinned sweet potato). Sweet potato supplements are available in powder and tablet (caiapo) forms.6, 35 Dosage regimens vary, but most commercial manufacturers suggest 2 tablets 30 minutes before meals, up to a total of 6 tablets daily.
Vitamin A deficiency
Pregnancy / Lactation
Information regarding safety and efficacy in pregnancy and lactation is lacking. Women with a history of hypersensitivity reactions to the plant should avoid use.36
None well documented.
Historical and clinical data report no serious adverse reactions. No serious adverse effects were reported in a Cochrane review of clinical trials of caiapo use in type 2 diabetes.8
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.36
Limited toxicity data are available. Animal studies document temporary neurological effects followed by extensive liver necrosis for 3 sesquiterpenoids in sweet potato, with a median lethal dose ranging from 184 to 266 mg/kg.12 Sweet potato consumption should be avoided in individuals hypersensitive to any of the chemical components of the plant species.36
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