There are numerous herbs and shrubs included in the term basil, which collectively belong to the genus Ocimum L. (Lamiaceae). The name basil comes from the Greek basileus or “king.” Common basil (Ocimum basilicum L.) leaves have had culinary importance for centuries. More than 20 cultivars have been identified with designations that include Napoletano, Reunion, Genovese, sweet, oriental, Mexican, anise, and purple basils, to name a few. This herb is cultivated widely in Asia, Africa, South America, and the Mediterranean. In foods, dried and fresh basil leaves season tomato dishes, vegetables, fish, meat, soups, salads, and pizza. The essential oils and aromatic extracts from Ocimum varieties are also important components of dental products, pharmaceuticals, cosmetics, and flavoring agents.1–4
Basil plants can differ substantially in genotype and chemical profiles, although they may present similar morphologies. Generally, basil essential oils can be grouped into several chemotypes, each characterized by their most prevalent phytochemicals. Such a group classification is monoterpenoids (eg, linalool, camphor), phenylpropanoids (eg, eugenol, methyleugenol, estragole, and methyl cinnamates), and sesquiterpenoids (eg, β-caryophyllene, α-bergamotene).5–8 Phenolic profiles also have been reported.9,10 The variation in essential oil composition depends on region and conditions of cultivation,11,12 species and cultivar,13–15 season of growth,11,16 age or position of leaves selected,17,18 harvesting procedures,19,20 light exposure,11,21,22 and methods of extraction.23–26
Information about typical human intakes and bioavailability of basil is limited. A Food Frequency Questionnaire completed by Norwegian adults determined intake of fresh and dried basil to be approximately 2.2 g/mo.27 To determine metabolites from basil, volunteers consumed 5 mL of a brewed basil beverage prepared from 500 g basil.28 Estragole, trans-anethole, and para-anisaldehyde levels were then determined in plasma and urine after consumption. The estragole concentration in plasma samples at 8 hours following consumption was 324.7 μg/mL or 60% of the initial amounts absorbed. Likewise, urine concentration of estragole at 9 hours was 59% of the initial dose administered.
An Ocimum plant of note is holy basil, composed of Ocimum tenuiflorum (previously Ocimum sanctum) and sometimes Ocimum gratissimum species, also known as Tulsi in India and Nepal, where it is used in Ayurvedic and other traditional medicine systems. In South America, the term altavaca refers to Ocimum used in traditional medicines. Purported health benefits for Tulsi and other Ocimum species include relief of stress and treatment of respiratory, gastrointestinal, and kidney ailments, as well as blood disorders and skin and eye diseases, to name a few.3,4,29 The present report is intended to provide a brief summary of the potential health benefits of basil as identified from published scientific investigations involving humans and to identify areas for additional research.
METHODS
A search of the PubMed database identified more than 100 relevant reports published prior to 2017. Search terms included Ocimum, basil, altavaca, and Tulsi. 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 human studies varied considerably, all published human investigations identified were included in this discussion, so that the totality and diversity of information can be evaluated, and issues for future research can be identified.
Human Studies
As a component of Ayurvedic medicine for several millenia, Tulsi was extensively studied in humans, especially in India. A recent comprehensive review29 of human trials systematically evaluated the efficacy of Tulsi in the treatment of metabolic disorders, in modulation of the immune system, and in improving neurocognition. For this published review, the term Tulsi included both the O tenuiflorum (O sanctum) and O gratissimum species. The current, brief summary highlights select findings on topics covered by this comprehensive review and also adds newer information not included for these Tulsi topics. In addition, biological actions in humans of other Ocimum species are presented in the current summary.
Metabolic Disorders
Seventeen Tulsi trials, conducted between 1964 and 2016, were selected for the referenced, critical review publication.29 The study populations numbered between 3 and 100. The form of Tulsi leaves administered varied considerably (whole plant, powdered leaves, juice, and water and ethanol extracts), as did the dose (300 mg/d to 6 g/d) and frequency. Taken together, these studies observed significant decreases in fasting and postprandial blood glucose, improved lipid profiles, and lower blood pressure in diabetic and obese participants. Those trials with longer duration of intervention (12–13 weeks) tended to report more substantial beneficial changes. Where measured, hemoglobin A1C (HbA1c) and body mass index (BMI) of obese participants were reduced. Only 1 randomized, double-blind, placebo-controlled trial was among the studies evaluated, and this trial observed an improvement in lipid profiles for 6 of 22 participants. No adverse events were reported in any trial.
In a separate study of a different Ocimum species, seeds of Ocimum canum (or O americanum L.), also known as hairy basil, were given to non–insulin-dependent (n = 14) and insulin-dependent (n = 2) Thai patients with diabetes.30 Thirty grams of dried seeds was consumed after meals in divided doses for 1 month. Compared with baseline values, the blood glucose concentration curves determined from the oral glucose tolerance test were significantly suppressed after 1 month of treatment. These seeds provided approximately 24 g/d dietary fiber, which the authors suggested contributed to the lowering of postprandial glucose levels and long-term improvement in glucose tolerance in both the non–insulin-dependent and insulin-dependent patients with diabetes.
In another trial31 with O canum, effects on body composition and metabolic parameters in obese and overweight subjects were examined. Obese patients (n = 5) were instructed to decrease total energy intake to achieve 20%, 30%, and 50% of total caloric intake as protein, fat, and carbohydrate, respectively. After 4 weeks, individuals were provided basil seed extract (4 g/d swollen in water) for 12 weeks. Compared with baseline values, there were significant but small decreases of 2.3% and 2.4% for weight and BMI, respectively. No changes in serum lipid and blood glucose levels and in body fat were observed. No adverse effects were detected, and hematologic, renal, and electrolyte parameters were normal.
The high-fiber seeds of O basilicum were also investigated for effects on anthropometric measures in patients with nonalcoholic fatty liver.32 For this randomized, parallel, single-blind trial, patients (n = 18) consumed 10 g/d of seeds for 12 weeks. Compared with controls, no significant effect of seed consumption was seen for BMI, percent body fat, and lean body mass. The authors attributed this lack of effect to the lower dose of seeds given to the subjects.
Neurocognition
Four clinical trials evaluating the effect of Tulsi on neurocognition were selected for the published systematic review.29 Two of the 4 trials were randomized, double-blind, placebo-controlled designs. The form of Tulsi provided included ethanolic extracts, whole plant, or leaves, and doses varied from 300 mg/d to 6 g/d. All trials were similar in outcomes, observing some degree of positive changes, with benefits that included reduced stress, anxiety, sexual problems, and depression, as well as enhanced working memory and cognitive attention. No adverse events were reported.
A separate inhalation trial examined the impacts of basil (O basilicum) or peppermint essential oils on mental work.33 Adult volunteers were evaluated, in a single experimental run, for changes in sensory perception and mental work following use of inhalers loaded with the essential oils. For basil, there was a positive association between inhalation of the essential oil and mental work, which was accompanied by a significant increase in fingertip skin temperature and an increase in magnitude of β waves of the brain. The authors suggested that these responses for basil demonstrated this fragrance’s capacity to trigger neurophysiologic stimuli and elevate the alert state, findings consistent with those reported by others.34
Immunomodulation and Inflammation
For this topic, 5 clinical trials were selected for the critical review.29 Doses of ethanolic or aqueous extracts of Tulsi leaves varied from 300 mg/d to 10 g/d, and durations of intervention were shorter (1–4 weeks). Beneficial immune responses included increased natural killer and T-helper cells in healthy adults and improved immune response to viral infections. Patients with asthma reported enhanced vital capacity and relief from asthmatic symptoms. Only 1 randomized, double-blind, placebo-controlled study was among the 5 trials evaluated, and it found higher circulating levels of select cytokines and interferons among the 22 subjects. The studies reported no adverse events.
Oral Health and Healing
Seven human studies evaluated basil for its effects on oral cavity health in patients in India and Brazil. For 1 investigation,35 the teeth and gums of 50 adult patients were treated with an extract of O basilicum (250 mg/d) for 3 weeks. Before and after treatment, plaque and soft matter in the gingival area were quantitated (referred to as a plaque index), as were changes in purulent discharges and gingival bleeding and reports of adverse effects. A significant 12% reduction in the plaque index was reported after 3 weeks, compared with the initial scores. The authors also observed a significant treatment-associated reduction in the populations of several oral bacteria, and in 80% of the patients, there was a substantial improvement in gingival bleeding and purulent discharge. No adverse effects were noted.
In India, a randomized, crossover, Latin square–designed study evaluated schoolchildren (n = 45) for the efficacy of 0.2% chlorhexidine, Listerine, and 4% Tulsi extract mouth rinses in reducing salivary Streptococcus mutans levels.36 All 3 rinses significantly decreased salivary S mutans levels, with mean reductions for chlorhexidine, Listerine, and Tulsi of 53%, 45%, and 43%, respectively, compared with baseline values. The only adverse effect of the Tulsi rinse was a bitter taste, which the authors attributed to the higher 4% concentration chosen. Two other studies also evaluated the oral health benefits of holy basil (O sanctum). A triple-blind, randomized, parallel-design, controlled trial (30-day duration) among medical student volunteers examined the strength of a 4% ethanolic extract of Tulsi (prepared from dried, powdered leaves), 0.12% chlorhexidine, and saline (n = 36/group) in decreasing plaque and gingival inflammation.37 Both holy basil and chlorhexidine treatments significantly decreased supragingival plaque and gingivitis, compared with saline controls, and no significant difference in efficacy was observed between the 2 treatment groups. Similarly, in a single-blind, randomized, parallel-design study,38 a 4-day treatment with a water extract of holy basil was found to significantly suppress plaque regrowth among 30 adult volunteers, compared with water controls, and showed similar clinical efficacy to 0.2% chlorhexidine.
Using O gratissimum samples, a randomized, parallel, double-blind trial39 evaluated the effectiveness of a mouth rinse containing an extract of this basil species in inhibiting de novo development of dental plaque and gingival inflammation, compared with a rinse containing 0.12% chlorhexidine digluconate (CLX). Following tooth polishing to remove existing plaque, subjects (n = 10/group) brushed teeth and rinsed with one of the formulations (3 times per day) for 3 months. Compared with controls (no antiseptic agents) at 90 days, the plaque index for basil and CLX rinses significantly decreased by 43% and 64%, respectively. The gingival bleeding index also significantly decreased by 63% and 77% for the basil and CLX groups, respectively, compared with controls. Taken together, these results indicate similar efficacy of basil and CLX groups, and no adverse effects were recorded for those using the basil rinse. In a later clinical study by the same research group,40 a crossover, double-blind trial design was used to evaluate the effectiveness of mouth rinses of this basil and CLX on plaque regrowth in the absence of tooth brushing. Dental plaque remnants were removed from subjects (n = 15), who then rinsed twice daily with control, basil (10% vol/vol essential oil) and CLX (0.12%) formulations for 3 days, while abstaining from mechanical cleaning of teeth. Compared with controls, both basil and CLX rinses significantly inhibited de novo plaque growth, but the efficacy of the CLX rinse was significantly better than that of the basil rinse.
For a clinical trial in India,41 individuals with jaw (mandibular) fractures (n = 9) consumed 2.5 g of an alcoholic extract of Tulsi (O sanctum) leaves (4 times per day) during the period of jaw immobilization and healing (4–6 weeks). Compared with placebo controls (starch powder, n = 9), subjects given Tulsi extract showed a significant 32% reduction in time of immobilization. Comparable evidence of complete clinical healing among the 2 groups was demonstrated radiologically and by identical bite force tensile strength results. No adverse effects were reported.
Skin Health
A single-blind study42 of male volunteers (n = 11) was conducted evaluating a facial skin cream formulation containing 3% concentrated ethanol extract of basil leaves and flowers, compared with the base formulation without basil. Subjects applied the 2 creams at night on separate cheeks for 12 weeks. Biophysical measurements of skin smoothness, moisture, and wrinkle prevalence were determined. Compared with the base cream, the formulation with basil significantly enhanced moisture content, decreased roughness, and suppressed wrinkling. No harmful effects were noted. Dermatology outpatients in India were randomly assigned to control (n = 26) and treatment (n = 25) groups in a single-blind controlled study.43 The control group was administered a standard treatment for acne consisting of oral tetracycline (500 mg, 2 times per day) and a facial sulfur lotion (2 times per day), and the treatment group members were instructed to manually crush fresh O basilicum leaves, smear the resulting juice on the facial acne lesions, and leave this covering overnight until washing with mild soap the next morning. Both groups continued these protocols for 8 weeks. The responses of the acne lesions (comedones, papules, pustules, and cysts) to treatment indicated that the basil treatment was just as effective as the standard acne drug. A randomized, placebo-controlled clinical trial evaluated a series of 16 O gratissimum–containing formulations (n = 7/formulation) on management of acnes vulgaris in university students in Nigeria.44,45 Test samples were prepared from 1 of 4 doses of O gratissimum essential oil along with 1 of 4 base blends and applied to the face topically (2 times per day) for 4 weeks. Compared with the lesion counts prior to the study, at 4 weeks the essential oil preparations, especially at the higher doses, were significantly more efficacious than a reference drug product (10% benzoyl peroxide lotion) in reducing the number of papules and pustules. Adverse effects were reported to be minimal, with some higher doses producing skin irritation.
Safety
As reported in numerous human trials, adverse effects of Tulsi appear to be minimal. This, along with its long history of use in Ayurvedic medicine, suggests that it has no oral toxicity at the doses used.1 Toxicological experiments in animals of the essential oil and of alcoholic extracts demonstrated no toxic effects of oral administration up to the highest doses tested.46,47 Some reports led to a concern that excessive consumption of cultivars with high contents of estragole could be problematic,48,49 but adverse effects are unlikely at typical levels of human consumption.28 There are reports suggesting dietary Tulsi can affect the reproductive behavior of male rats and rabbits,50,51 although the relevance of the doses examined to human intakes is not known.
CONCLUSIONS
Portions of the basil plant, especially the leaves, and its extracts demonstrated health benefits in a variety of clinical settings (Table). All the species tested, O tenuiflorum/O sanctum, O basilicum, and O canum, showed some level of benefit, with the magnitude of change depending on the end point examined and the experimental methods. The benefits identified include improving glucose homeostasis and lipid profiles for patients with diabetes, strengthening of the immune system, alleviating stress and anxiety, and enhancing memory. Oral and skin health and healing were reported. Comparisons of beneficial effects among Ocimum species exhibiting different chemotypes are difficult to make at this point. The number of clinical trials evaluating specific health issues vary greatly among species. Only 2 studies were reported for O canum in which inconsistent responses of postprandial glucose levels to basil administration were noted. Similarly, only 4 reports indicated benefits for O basilicum in mental performance, treatment of acne, and tooth health, with no effect seen for BMI and percent body fat. In contrast, at least 34 clinical trials have been conducted for Tulsi (O sanctum, O tenuiflorum, O gratissimum) in which benefits were observed toward metabolic disorders, mental and immune health, gingival inflammation and tooth decay, and skin health. Valid comparisons of health benefits among these species await more reports of trials using species other than those in Tulsi.
TABLE: Reports Some of the Purported Benefits of Ocimum Species From Human Studies
Despite no adverse events being detected at the doses and durations of basil evaluated in these human investigations, any adverse effects from long-term intake of basil and its extracts need to be carefully documented. Although there is encouragement to include basil in the diet to improve management of diabetes and the metabolic syndrome,52 several issues need to be more thoroughly addressed when assessing all these purported health benefits. As Jamshidi and Cohen29 have pointed out, only a minority of the published studies can be considered high-quality, and approximately only 13% of the trials incorporated a double-blind approach. The methodological concerns, as well as the widespread lack of details about the basil cultivars, dosage form, and chemical composition of the test samples, suggest that there are still insufficient data to support specific recommendations for use. Additional studies are needed with larger subject populations, longer periods of intervention, and better characterization of the effective forms and the active dietary doses of basil. Studies should report chemical composition of samples, and, in any trials using basil for adjunct or complementary treatments, data on interactions with commonly prescribed drugs should be provided.29
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