The spice sumac is prepared from the fruit of the shrub or small deciduous tree R. coriaria L. (family Anacardiaceae) that grows mainly in the Mediterranean region, North Africa, and the Middle East. The word sumac is derived from the Arabic word sumaq, which means red or dark red, a term that aptly describes the colored fruit of this flowering plant (Figure 1). R. coriaria is also known as Sicilian sumac and tanner's sumac due to the use of its tannin-rich leaves and bark in leather tanneries.1,2 Moreover, black and yellow dyes are prepared from these leaves and bark. A relative of this plant, Rhus vernix or Toxicodendron vernix Kuntze (R. vernix L.) also called poison sumac, is not edible and is well known to produce an allergic skin reaction upon contact. However, the genus Rhus contains well over a hundred individual species of flowering plants, some varieties of which are edible. Besides R. coriaria, other examples are R. glabra L. (or smooth sumac) used by the indigenous people of North America, R. typhina L. (staghorn sumac), R. integrifolia (Nutt.) Benth. & Hock. f. ex. Rothr (lemonade berry), R. aromatica Aiton (fragrant sumac), R. ovata S. Watson (sugar bush), and R. trilobata Nutt. (skunkbush sumac, sourberry, three-leaf sumac, squawbush).3–5
In the Middle East and Turkey, sumac is widely added to diverse food preparations. The fruits of this plant are composed of compact clusters of red berries that are dried and ground to yield the dark red/purple spice, the taste of which has been described as tangy, astringent, and lemony. The Arabic spice blend Za'atar has sesame seeds, thyme, and sumac as core ingredients, with other possible components such as oregano, marjoram, coriander, and cumin as additions. In Turkish piyaz salad, the sumac fruit is ground with salt, mixed with olive oil and lemon juice, and combined with red onions, tomatoes, and parsley.
One classic Palestinian food, musakhan roll or sumac chicken roll, is made with shredded chicken, caramelized onions, and multiple spices including sumac, plus olive oil, all then wrapped in flatbread. The Middle Eastern bread salad, fattoush, uses sumac in the preparation of the baked, bite-sized bread pieces as well as in the vinaigrette that is drizzled over salad greens. Sumac is a common flavoring in grilling of kebabs of ground meat skewered along with vegetables and/or fruit. The Iranian dish, mahi ba somagh or sumac roasted fish, calls for drizzling sumac, lime and orange juices, and olive oil over butterflied fish portions before baking. Persian yellow rice is often sprinkled with sumac to impart a tangy, citruslike flavor. This spice can even season yogurt that is used as a dip or condiment.1–5
R. coriaria contains diverse classes of chemicals, the relative amounts of which vary depending on the location of cultivation, environmental conditions, and methods of harvesting and processing the fruit. The fruit is abundant in organic acids, such as malic and citric acids, hydrolysable tannins, phenolic acids, and flavonoids. In the essential oil ß-caryophyllene, cembrene, n-nonanal, p-anisaldehyde, limonene, and α-pinene6–8 are among the main constituents (Figure 2). None of these phytochemicals have been identified as a primary bioactive contributing to sumac's reported biological actions. R. coriaria has an extensive history as a traditional medicine primarily in the Middle East. Maladies treated with sumac extracts have included diarrhea, diseases of the mouth and throat, gastrointestinal distress, headaches, inflammatory conditions of the skin, liver disease, and pain, to name a few.1,2,5 Recent human studies examining the potential health benefits of sumac are limited and mainly explore the actions of R. coriaria toward cardiometabolic risk factors. This narrative overview summarizes these clinical trials, as well as relevant associated animal experiments, and suggests opportunities for future research.
To provide evidence for potential health benefits of foods, ingredients, and plant constituents, data are gathered from a variety of scientific methods such as cell culture experiments, animal studies, and human clinical trials. Human studies are particularly important in determining public health recommendations, especially randomized controlled trials testing well-characterized treatments and applying appropriate statistical analyses. With this in mind, a search of the PubMed and Science Direct databases was conducted through September of 2022, using terms that included “R. coriaria L.,” “sumac,” “sumach,” and “sumaq.” Full reports of English-language publications and English-language abstracts of foreign-language articles from peer-reviewed journals were the primary sources of information. Although the quality of identified studies varied considerably, all relevant, published investigations were included in this overview so that the totality and diversity of information can be described, and issues for future research can be identified. Additional information was gleaned from bibliographies within these sources. Studies of sumac as a component within multi-ingredient preparations were not included in this overview.
EFFECTS OF R. CORIARIA IN HUMANS
The Table summarizes the effects of intake of sumac powder on risk factors associated with type 2 diabetes mellitus, dyslipidemia, obesity, hypertension, and nonalcoholic fatty liver disease. Considered together, the trials are characterized by small sample sizes (generally ≤40), and notable variability in duration of treatments (1–3 months) and doses administered (1–6 g). Because of the inconsistency and heterogeneity in health outcomes from sumac powder intake in these few studies, no clear pattern of beneficial effects on cardiometabolic risk factors is apparent. Specifically, regarding blood glucose homeostasis, 5 of 7 studies reported no effect after sumac intake, whereas 4 of 5 trials observed a decrease in measures of insulin resistance. Two of 3 trials observed a sumac-associated reduction in glycosylated hemoglobin (HbA1C) levels, and in 3 of 4 trials, serum insulin concentrations decreased. In light of these inconsistencies, 3 meta-analyses examined the effects of sumac administration on these cardiometabolic risk factors. Two of the meta-analyses reached contrasting conclusions for some of the variables examined. For the report of Ghafouri et al,22 9 trials were included in the analyses and it was determined that sumac intake significantly lowered fasting blood glucose and insulin resistance. However, no significant influence of sumac on these variables was determined in the meta-analysis of 6 trials conducted by Mohit et al.23 For both reports, no effect of sumac consumption on HbA1C was detected. The reasons for these different conclusions are not clear, although the qualities of the trials selected for the 2 evaluations and the different statistical methodologies used in each may partly explain the disparities. In the study by Ghafouri et al22 and in a third meta-analysis by Akbari-Fakhrabadi et al,24 no effects of sumac intake on levels of total cholesterol, triglycerides, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol were found. Moreover, one analysis showed no significant influence of sumac on body mass index, systolic blood pressure, and diastolic blood pressure.22
Effect of R. coriaria
Powder on Cardiometabolic Risk Factors in Humans
||3 g/d (n = 22), control (n = 19); 3 mo
↓SI, ↓HOMA-IR, ↓FBG, ↓HbA1C, ↓ApoB, ↑ApoA-1
|↓MDA, ↓CRP, ↓TAC, ↑PON1
|3 g/d (n = 10), control (n = 10); 10 wk, ♀ only
NE: FBG, BMI, WHR
|6 g/d + yogurt (n = 30), control: yogurt (n = 28); 3 mo
NE: FBG, HbA1C, HOMA-IR, SI, PPBG, ß-cell function
||1 g/d (n = 34), control (n = 36); 6 wk
NE: TC, LDL, TG, FBG, DBP, SBP, ApoB
|NE: ALT, AST, ALP, GGT, creatinine
|1 g/d (n = 30), control (n = 30); 4 wk
||▲↓BMI, ↓BW, ↓TC, ↓SBP, ↓DBP, ↑brachial FMD
NE: TG, HDL, LDL, FBG
|1 g/d + 20-mg/d lovastatin (n = 86), control: 20-mg/d lovastatin (n = 86); 3 mo
|1.5 g/d (n = 36), control (n = 36); 1 mo, adolescents only
↓TC, ↓LDL, ↓TG
||1 g/d (n = 25), control (n = 24); 6 wk both with low-fat/low-carb diet
↓BW, ↓BMI, ↓SI, ↓HOMA-IR
|3 g/d (n = 31), control (n = 31); 12 wk, both + cal-restr diet, ♀ only
↓BW, ↓BMI, ↓body fat, ↓visceral fat
NE: CRP, IL-6, TNF-α, depression
||1 g/d + 25-mg/d captopril (n = 39), control: 25-mg/d captopril (n = 44); 8 wk
||2 g/d (n = 40), control (n = 40); 12 wk
↓TC, ↓LDL, ↓TG, ↑HDL, ↓BW, ↓SBP, ↓steatosis
NE: DBP, BMI
|2 g/d (n = 40), control (n = 40); 12 wk both + low-cal diet
↓FBG, ↓HbA1C, ↓SI, ↓HOMA-IR, ↑QUICKI, ↓fibrosis
|↓ALT, ↓AST, ↓CRP, ↓MDA
Abbreviations: ALP, alkaline phosphatase; ALT, alanine aminotransferase; Apo-A1, apolipoprotein-A1; Apo-B, apolipoprotein-B; AST, aspartate aminotransferase; BMI, body mass index; BW, body weight; cal-restr, calorie-restricted; CRP, C-reactive protein; DBP, diastolic blood pressure; FBG, fasting blood glucose; FMD, flow-mediated dilation; GGT, gamma-glutamyl transferase; HbA1C, glycosylated hemoglobin; HDL, serum high-density lipoprotein cholesterol; HOMA-IR, homeostatic model assessment for insulin resistance; IL-6, interleukin-6; LDL, serum low-density lipoprotein cholesterol; MDA, malondialdehyde; NAFLD; nonalcoholic fatty liver disease; NE, no statistically significant effect; PON1, paraoxonase 1; PPBG, postprandial blood glucose; QUICKI, quantitative insulin-sensitivity check index; SI, serum insulin; SBP, systolic blood pressure; TAC, serum total antioxidant capacity; TC, serum total cholesterol; TG, serum triglycerides; TNF-α, tumor necrosis factor-α; T2DM, type 2 diabetes mellitus; WHR, waist-height ratio.
There is no consistent evidence from these trials to illuminate potential mechanisms responsible for observed changes in blood glucose and lipid regulation. The divergent conclusions from the meta-analyses support this conclusion.
In rodent models of diabetes and dyslipidemia, dietary sumac powder and oral dosing with aqueous and alcoholic extracts were assessed.24–35 In general, some improvements in measures of blood glucose homeostasis and lipid profiles were observed. Potential mechanisms were essentially limited to enhanced antioxidant defenses, inhibition of α-glucosidase, maltase and sucrase activities, and suppression of production of proinflammatory mediators.25,35
A number of issues need to be addressed in future human trials to better understand any potential health benefits.22,24 Well-designed, larger randomized controlled trials evaluating the effects of multiple doses of sumac for extended durations of intervention on clearly defined and relevant outcomes in subjects sharing more homogeneous health conditions are needed. This is particularly important for measurement of HbA1C levels, for example, for which 2 to 3 months of treatment are necessary to obtain values that accurately reflect sumac-induced changes in glycosylated hemoglobin levels. An issue often overlooked is the need to report the composition of the sumac sample administered in sufficient detail so that trial methodologies and outcomes can be better compared and contrasted. Furthermore, after administration of sumac samples to trial subjects, the reporting of subsequent blood concentrations of select sumac phytochemicals would allow for assessment of relative sumac bioavailability, information that is important for interpretation of outcomes among diverse trials. Measuring sumac-induced alterations in hypothesized biochemical mediators can provide insights into potential mechanistic processes underlying main outcomes. Finally, recruitment of subjects from different regions would expand application and relevance of the findings to a larger geographical area.
Systematic assessments of the safe use of R. coriaria by humans are limited. When adverse effects are reported, the published clinical trials did not detect significant clinical or laboratory adverse events at the doses and durations of treatments evaluated. Sumac is not included in the list of spices considered generally recognized as safe, although it is listed among those plants from which tannins or hydrolysable gallotannins, direct food substances that are affirmed as generally recognized as safe, can be extracted (21CFR§184.1097; https://www.govinfo.gov/app/details/CFR-2021-title21-vol3/CFR-2021-title21-vol3-sec184-1097). From animal studies, sumac was determined not to be carcinogenic or genotoxic36,37 and can be DNA protective.38 Safety studies in rodents administering high doses of various extracts showed minimal acute toxicity.39 Sumac was noted in preclinical experiments to modify circulating levels of estrogen, testosterone, follicle-stimulating hormone, and luteinizing hormone,33,40,41 although the significance of this for humans is unknown. A case study of allergic reactions upon contact with sumac was reported, and systemic contact dermatitis was detected in Korea for those ingesting a commercially produced rhus (boiled chicken fed with a Rhus verniciflua–supplemented diet) as a health food or folk medicine.42,43
A number of sumac-containing products and supplements are available online. The bulk quantities sold recommend different culinary uses. Capsules containing sumac powder or extracts vary in daily intakes suggested from no dosing guidance to recommending 500 mg/d to 1350 mg/d or 6 capsules/d containing an undefined amount of sumac. Liquid extracts are available that may suggest use at levels of 1 mL/d to 90 drops/d. A hydroalcoholic extract of sumac leaves is sold for purposes of mouth rinsing only. There also is a recipe for making a sumac beverage from mashed sumac berries steeped in water for a day. The specific type and chemical composition of sumac extracts often are not specified. Sumac products may not identify from which variety of Rhus the material is prepared, although a few noted use of R. glabra, smooth sumac, and staghorn sumac, in addition to R. coriaria. Care is warranted when consuming sumac extracts at much higher levels than typical amounts used as a spice in culinary applications or in traditional beverages, until more information about efficacy and safety is available from high-quality human trials. In addition, in light of human studies indicating a possible effect of sumac intake on cardiometabolic risk factors, care is warranted for those considering taking sumac supplements along with medications to control blood glucose and cholesterol levels.
There is preliminary but limited and inconsistent evidence that sumac extracts may modify blood glucose and lipid homeostasis, blood pressure, and body weight in humans. Additional well-defined interventional trials are required before any evidence-based recommendations can be made regarding sumac and health.
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