In May 2019 researchers from Canada published their review of the medical scientific literature to identify and assess specific biomarkers in 25 herbs and spices, namely anise, basil, black pepper, caraway, chili pepper, cinnamon, clove, cumin, curcumin, dill, fennel, fenugreek, ginger, lemongrass, marjoram, nutmeg, oregano, parsley, peppermint and spearmint, rosemary, saffron, sage, tarragon, and thyme. The researchers stated that herbs and spices have been used for medicinal purposes since ancient times due to both known and presumed health benefits. They have been shown to have antioxidant, anti-microbial, and anti-inflammatory properties and may in addition reduce the risk of developing chronic diseases, eg cardiovascular disease, neurodegenerative conditions, chronic inflammation, arthritis, cancer, obesity and diabetes type 2. In addition, the use of many herbs and spices tends to reduce the use of salt which has additional cardiovascular health benefits.
It appears that most of the positive health effects of herbs and spices is due to their phytochemical content, particularly polyphenols or polyphenol breakdown products, which target specific receptors or enzymes involved in various anti-inflammatory pathways or immune responses. Herbs and spices, especially in their dried form, contain high levels of polyphenols and other phytochemicals, especially phenolic acids and flavonoids. Compared to other polyphenol-rich foods, eg broccoli or dark chocolate, herbs and spices generally contain somewhat higher levels of polyphenols. For example, oregano has 935 mg/100 g (fresh) and 6367 mg/100 g (dried), rosemary 1082 mg/100 g (fresh) and 2518 mg/100 g (dried)], thyme 1173 mg/100 g (fresh) and. 1815 mg/100 g (dried)], and parsley 89 mg/100 g (fresh) and 1584 mg/100 g (dried). In addition, cloves have 16,047 mg/100 g, cinnamon 9700 mg/100 g, and turmeric 2117 mg/100 g (all fresh weight). In contrast, dark chocolate contains 1860 mg/100 g, while raw blackcurrants contain 821 mg/100 g and broccoli just 199 mg/100 g (both fresh weight).
The average dietary intake of common herbs and spices varies considerably around the world, eg Europeans consume an estimated 0.5 g/person per day, Australians and New Zealanders between 1.3–1.9 g/day, residents of Africa 1.8 g/day, individuals in the Middle East and Eastern Asia 3 g/day whilst those in India, South Africa and Latin America tend to consume an average of 4 g/day. In India, turmeric consumption alone has been estimated to be 1.5 g/person per day. However, whilst the consumption of herbs and spices is generally higher in countries like India, Mexico, Peru, China, and Thailand, herb and spice intake has been increasing in many European and in the USA due to changing food habits and a growing preference for ethnic or spicy food.
A review of the literature revealed that a total of 49 studies met the inclusion criteria and these were included in the review. However, only 17 of the herbs and spices had published, peer-reviewed studies which described potential biomarkers of intake. These were turmeric and curcumin (18 studies), peppermint (6 studies), thyme (4 studies), ginger, Capsicum and parsley (3 studies each), anise and saffron (2 studies each) and cinnamon, fennel, nutmeg, oregano, marjoram, rosemary and sage (1 study each), whilst one study looked at basil, tarragon and fennel together. No studies on biomarker intake were found for black pepper, caraway, clove, cumin, dill, fenugreek, lemongrass, and spearmint. In many studies, the herb or spice of interest was administrated in the form of a capsule or extract and very few studies were performed with actual foods.
Of the 25 herbs and spices included in this review, 21/25 (84%) had at least one published study supporting an anti-inflammatory finding, with the herbs or spices most often identified being thyme, oregano, rosemary, sage, basil, mint, turmeric, dill, parsley, cinnamon, clove, nutmeg, lemon grass, ginger, chili pepper, fenugreek, and pepper. In addition many herbs and spices have been found to have antibacterial, antiviral and antifungal properties, which is one of the reasons why herbs and spices are so frequently used as preservative agents in food. The antimicrobial properties have been attributed to their oils, eg thyme oil has been shown to be particularly active against Aeromonas hydrophila, a pathogen widely found in the environment, domestic animals and food, whilst oils found in thyme, oregano, mint, cinnamon, and cloves have been found to possess strong antibacterial properties against several food-borne bacteria and fungi.
Anise is a seed spice which comes from a flowering plant belonging to the family Apiaceae. It has a distinctive licorice flavor and aroma which comes from anethole, and which is also found in fennel, basil and tarragon. Anethole occurs naturally in high concentrations in volatile oils such as anise oil (80–90%), star anise oil (over 90%), and fennel oil (80%). In Mediterranean countries, the popularity of alcoholic and non-alcoholic anise-flavored beverages has led to a much greater consumption of trans-anethole. Anethole is also used in medicines as an expectorant, for coughs and an antispasmodic for treating gastrointestinal tract illnesses.
One study measured the blood level of anethole after the intake of alcoholic anise-based beverages. The individual consumed the alcoholic drink ouzo over three different days under controlled conditions and showed rapid resorption of the anethole as well as rapid elimination. An anethole level above the detection level of 3.6 ng/ml serum was detected for 3 hours after the drinking of 120 ml of Helenas ouzo, for 3 h after drinking 200 ml of regular ouzo, and for 7 hours after drinking 360 ml of regular ouzo. The study also looked at the blood collected from 50 motor vehicle drivers who claimed to have consumed drinks containing anethole (ouzo, raki and the German aniseed liqueur “Küstennebel”). In these individuals, 10 out of 50 blood samples had anethole levels of between 5.4 and 17.6 ng/ml. Of these, eight were connected with ouzo consumption, one with raki consumption and one with “Kustennebel” consumption. It was therefore , concluded that anethole can be reliably detected in blood/serum samples after consumption of spirits containing anethole.
The chili pepper comes from plants from the genus Capsicum. Mild or sweet peppers contain similar constituents as Capsicum but with little or no pungent components. Chili peppers are used as food colourants, flavouring agents, as repellants, and a source of pain relief. The compounds responsible for the “hot” taste of chili peppers are called capsaicinoids, with capsaicin being the best known. It is commonly used in both food and medicine, but its strong taste limits the quantity that can be used. Capsicum contains up to 1.5% (by weight) of capsaicin, dihydrocapsaicin, and compounds. Other constituents found in chili peppers are carotenoids, vitamins A, C, and small amounts of volatile oils with more than 125 known components. Another class of capsaicin-like compounds found in chili peppers and non-pungent chili peppers are the capsinoids. Capsinoids have an estimated “hot taste threshold” that is about 1/1000 that of capsaicin making it possible to use capsinoids in food applications without the intense heat effect found in capsaicins. The beneficial effects of capsaicin and capsinoids include anticancer, anti-inflammatory and analgesic effects.
One study found that capsaicin was detected in blood plasma 10 minutes after the ingestion of 5 g of capsaicin derived from chili pepper. It was also rapidly metabolized, ie not detectable in the blood after 90 minutes.
Paprika is a ground spice made from the red, air-dried fruits of the larger and sweeter varieties of the plant Capsicum annuum, which are also called bell peppers or sweet peppers. Paprika can also be modified with the addition of more pungent chili peppers and cayenne pepper. Paprika spices can range from mild to hot, depending on the variety of the source plant. The flavour also varies from country to country although almost all plants grown produce the sweet variety. The red, orange, or yellow colour of paprika is due to its content of carotenoids. The intense colour of paprika makes it an ideal and natural food colourant for many dishes.
One study measured paprika carotenoids in five individuals who had been supplemented with paprika for 4 weeks. The results showed that several carotenoids such as lutein, zeaxanthin, β-cryptoxanthin (also found in vegetables such as carrots and tomatoes) were detectable in the individuals. However, the authors also detected other carotenoids which were specific to paprika, eg cryptocapsin, capsanthin, capsorubin (only found in paprika and lily pollen), cucurbitaxanthin A (only found in paprika and pumpkins) and finally capsanthone. Paprika carotenoids, particularly capsanthin and capsorubin, have been reported to have strong antioxidant properties.
Cinnamon comes from the inner bark of the Cinnamomum tree species, although only a few of the species are grown commercially for spice. The flavour of cinnamon is due to an aromatic essential oil that is mainly composed of cinnamaldehyde (up to 90%) although there are at least 80 other compounds, including various coumarins, which contribute to its overall flavour and aroma. It is widely used as a condiment and for flavouring and is widely known for its anti-diabetic and glucose lowering effects. In addition, coumarin is frequently used in perfumes.
Cinnamaldehyde is quickly metabolized to cinnamic acid, which makes it unusable as a cinnamon biomarker. On the other hand, coumarin has been deemed to be a potentially useful biomarker for cinnamon.
Coumarin has a pleasant spicy odour of fresh hay or vanilla. It has been found in a number of bedding plants, eg sweet woodruff, oxlip amongst others, but none of these plants are usually used as edible foods so therefore the main source of coumarin in the diet is cinnamon. Coumarin is a well-known liver toxin (based on animal studies). However, different species of cinnamon have different levels of coumarin, eg C. cassia cinnamon contains up to 1% coumarin, whereas C. verum contains only trace levels. C. cassia cinnamon, as it is cheaper, is used in many commercially available food products and therefore these products have high levels of coumarin. It is notable that German Christmas cookies (which contain considerable amounts of C. cassia cinnamon) have a coumarin content which often exceeds the maximum tolerable dose intake of 0.1 mg/kg body weight).
Fennel, basil and tarragon
Whilst fennel, basil and tarragon are three very distinct herbs, they share a number of common chemicals and therefore they tend to be grouped together in food intake studies.
Fennel is a seed and bulb spice, as well as a leaf herb, that is derived from Foeniculum vulgare. Fennel is a highly aromatic and flavourful herb/spice and is one of the main ingredients of absinthe. The distinctive licorice flavour and aroma from fennel comes from anethole. Other compounds found in fennel include estragole, fenchone, 1,8-cineole (eucalyptol), and p-allylphenol. In addition to its use in culinary uses, fennel has long been used as a medicinal herb to treat gastrointestinal illnesses and upper respiratory tract infections as well as to increase milk production in breastfeeding mothers through the consumption of fennel tea.
Basil (Ocimum basilicum) is a culinary herb which is prominently featured in Italian dishes as well as in many Southeast Asian cuisines. Depending on the species, the leaves can have a similar taste to anise. Thai basil is also a condiment in the Vietnamese noodle soup. Basil has been used traditionally as a medicinal herb in the treatment of headaches, coughs, diarrhoea, constipation, warts, worms, and kidney disorders.
Tarragon (Artemisia dracunculus), also known as estragon, is a perennial herb belonging to the Asteraceae family. Two well-described “cultivars” (Russian and French) are widely used. Studies have shown that tarragon has antibacterial, antifungal, and antiplatelet activity as well as anti-inflammatory, hepatoprotective, antihyperglycemic, and antioxidant activity.
Two studies have assessed the potential biomarkers of fennel (alone) or fennel, tarragon, and basil intake. One study looked at the levels of estragole in humans consuming fennel tea. However, no levels for this compound could be reported or correlated with fennel dosage. Estragole, which is also found in tarragon, basil and anise, is rapidly metabolized to 1′-hydroxyestragole and quickly excreted. However, in the second study trans-anethole, estragole, and para-anisaldehyde (three major components of fennel, basil and tarragon) were found in both blood plasma and urine after the consumption of either 15 ml of fennel extract, 15 ml of tarragon extract or 15 ml of brewed basil.
Ginger is a member of the turmeric family (the Zingiberaceae family). Ginger is widely used as a culinary additive as well as being a popular medicine. Its flavour and aroma comes from its volatile oils (approximately 1-3% of the weight of fresh ginger) and non-volatile pungent oleoresins. A variety of active components have been identified including zingerone, gingerols (6, 8, and 10-gingerols), and shogaols (6, 8, and 10-shogaols). Gingerols (especially 6-gingerol) are the main substances found in the fresh ginger rhizome whereas the quantity of shogaols are significantly increased in dried ginger. It has also been noted that zingerone is produced from gingerols during drying. In addition to ginger’s well-known use as a treatment for nausea, many components in ginger have been found to have anti-inflammatory, antibacterial, antipyretic, antilipidaemic properties as well as reducing the risk of cancer or progression of cancer.
A total of three studies have been reported. Two studies showed that despite 6, 8-, and 10-gingerols and 6-shogaol being absorbed after oral ginger extract dosing and were detectable, no free 6-gingerol was found in blood plasma despite it being the most abundant component of ginger extracts (2.64%). In comparison, although 6-shogaol makes up 2.25% and 10-gingerol only accounts for 1.22% of most ginger extracts, 6-shogaol and 10-gingerol were readily detected in blood plasma. However, further studies showed very short half-lives for these four compounds and therefore no accumulation was observed for 6-, 8-, and 10-gingerols and 6-shogaol in either blood plasma or colon tissues even after multiple daily dosing. A third biomarker intake study focused on the metabolism of shogaol and the results showed that it was possible to detect all the major thiol-conjugated metabolites of shogaol in human urine. Further studies are required to confirm whether they are also seen with actual ginger-based food intake.
Nutmeg is a fragrant spice coming from the seed of an evergreen tree belonging to the Myristicaceae family. The nutmeg essential oil is obtained by steam distillation of ground nutmeg and typically contains sabinene (21.4%), 4-terpineol (13.9%), and myristicin (13.6%), as well as safrole, elimicin, terpineol, α-pinene d-camphene, limonene, linalool, and isoeugeunol. It is widely used in the perfumery and pharmaceutical industries. Psychotropic effects have been noted following the ingestion of large doses of nutmeg.
Only one study was found for the evaluation of nutmeg ingestion. In this study, an individual ingested the powder derived from 5 nutmeg seeds. A urine sample identified the following metabolites, O-demethyl elemicin, O-demethyl dihydroxy elemicin, demethylenyl myristicin, dihydroxy myristicin, and demethylenyl safrole but neither amphetamine derivatives nor the main nutmeg ingredients could be detected in the urine.
Myristicin is a natural organic sumstance found not only in nutmeg oil, but also, to a lesser extent, in carrots, parsley, celery, dill, parsnip, and black pepper. The amount of myristicin in nutmeg and mace is very high, with 13,000 mg/kg being found in nutmeg and 27,000 mg/kg in mace. However, it is much less in dill and parsley, with 1200 mg/kg being found in dill and 727 mg/kg in parsley. It is also very low in celery at 0.33 mg/kg, carrots at 0.16 mg/kg and parsnip at 0.002 mg/kg. Elemicin has been identified as being an essential oil of carrots, parsley, elemi oil, banana, anise, and oregano although nutmeg appears to be the major contributor of elemicin intake. In addition, safrole is a major constituent (85%) of the aromatic oil of sassafras root bark (Sassaras albidum). However, it is also a minor component or trace subastance found in mace, nutmeg, cinnamon, black pepper, cocoa, anise, and a number of other spices.
Oregano, marjoram, rosemary and thyme
Oregano, marjoram, rosemary, and thyme are culinary herbs derived from members of the Lamiaceae plant family, which also includes basil, mint, sage, lavender, and others.
Oregano (Origanum vulgare) is a herb. The marjoram plant is related to oregano and has a similar flavour. The compounds which contribute to the flavour of oregano are carvacrol, thymol, limonene, pinene, ocimene, and caryophyllene. Oregano also contains polyphenols, including caffeic, p-coumaric, and rosmarinic acid, which have antioxidant activity and prevents lipid peroxidation. It is used in Mediterranean cuisine, the Philippines, and Latin America, especially in Argentina.
Rosemary (Rosmarinus officinalis) contains a number of phytochemicals, including rosmarinic acid, camphor, caffeic acid, ursolic acid, betulinic acid, carnosic acid, and carnosol. Major essential oils found in rosemary oil are borneol (26.5%), α-terpinene (15.6%), and α-pinene (12.7%). The leaves are used as a flavoring agent in a variety of foods in traditional Mediterranean cuisine.
Thyme (Thymus vulgaris) has been used in folk medicine since the times of the ancient Egyptians, Greeks, and Romans. The essential oils of common thyme contain 20–58% thymol and p-cymene (15–28%), linalool (0.7–6.5%), γ-terpinene (4–10%), carvacrol (1–4%), myrcene (1–3%), 1,8-cineole (0.8%), and borneol (0.7–1.7%). Thymol is the compound that provides the distinct flavor of thyme. It is also found in oregano and is used as one of the many additives in cigarettes. Thyme is often added to meat, fish, and food products for flavour, aroma and food preservation and also used as a herbal medicine.
Oregano, rosemary, thyme, along with sage and mint share several polyphenols and essential oils which include caffeic acid, chlorogenic acid, ferulic acid, p-coumaric acid, p-hydroxybenzoic acid, protocatechuic acid, and rosmarinic acid. Some of the essential oils that are common to many herbs in the Laminaceae family are thymol (thyme, oregano, marjoram), carvacrol (thyme, oregano, marjoram), carnosic acid (rosemary and sage), carnosol (rosemary and sage), and rosmanol (rosemary and sage).
The three herbs are well known for their beneficial health properties, eg carnosic acid found in rosemary and sage appear to have an anti-obesity effect (including body weight and lipid-lowering effects), whilst thymol and carvacrol (oregano, thyme), carnosic acid, carnosol, rosmanol, (rosemary, sage), and epirosmanol (rosemary) have been shown to prevent lipid peroxidation and to have anti-inflammatory properties. In addition thymol, carvacrol, carnosol, rosmanol, and caffeic acid which are found in other herbs from the Laminaceae family have also been shown to have antimicrobial activity.
An analysis of four studies which looked at the biomarkers for these four herbs (thyme, marjoram, oregano, rosemary) suggest that carvacrol can be considered a specific biomarker of both thyme and oregano intake. A further study looking at biomarkers for marjoram found mainly polyphenol compounds in the urine of 6 healthy individuals who had taken a single dose of marjoram extract. These polyphenols are also found in many other plant foods and beverages such as tea, wine, coffee, cereals, cocoa, and in vegetables and fruits, so cannot be considered specific biomarkers for these herbs. Whilst rosmarinic acid is a very specific polyphenol for this family (Laminaceae), no rosamarinic acid could be detected in humans after consumption due to its rapid metabolism. With regard to essential oils, thymol and thymol sulfate in blood plasma and urine and thymol glucuronides in urine appear to be plausible biomarkers of thyme intake. However, these compounds are also present in oregano.
Parsley (Petroselinum crispum) is a herb belonging to the Apiaceae family. It is a source of several flavonoids, especially luteolin and apigenin. The major essential oil found in parsley leaves is 1,3,8-p-menthatriene, but other components are also present in lesser amounts including myristicin and limonene, among others. Apigenin has been associated with anti-inflammatory activities and has also been identified as a potential cancer chemopreventive agent.
Research studies have shown that there is a strong correlation between parsley consumption and urinary apigenin excretion. Ingestion of apigenin-rich foods, like parsley, has led to elevated levels of apigenin in blood plasma and red blood cells, although it was barely detectable (ie close to the limit of detection). Apigenin is a flavone which is also found in other vegetables from the same family (Apiacea), such as celery, parsnip, carrots, and fennel so cannot be considered a specific biomarker for this herb.
Peppermint and spearmint are herbs that belong to the Laminacea family. Spearmint (Mentha spicata) is believed to be the oldest of the mints. Peppermint (Mentha piperita), however, is a hybrid mint being a cross between watermint and spearmint. The active constituents of spearmint include spearmint oil, various flavonoids (diosmin, diosmetin), phenolic acids, and lignans. The most abundant compound in spearmint oil is carvone, which gives spearmint its distinctive smell. Spearmint oil also contains significant amounts of limonene, dihydrocarvone, and 1,8-cineol. Unlike peppermint oil, spearmint oil contains minimal amounts of menthol and menthone. However, peppermint has a high menthol content (41%), along with menthone (23%), and other essential oils such as menthyl acetate (4%), 1,8-cineole (5%), limonene (3%), menthofuran (4%), and β-caryophyllene (2%). Peppermint also contains terpenoids and flavonoids such as eriocitrin, hesperidin, and kaempferol 7-O-rutinoside. Peppermint leaves are often used alone or with other herbs in herbal teas, ice cream, confectionery, chewing gum, toothpastes and shampoos. Menthol is the primary source of the cooling sensation that follows the application of peppermint oil on the skin.
Six studies were identified which looked at the administration of peppermint oil although no studies were found that assessed spearmint. All six peppermint studies assessed the effect of menthol following peppermint oil administration. The main goal of these studies was to find a way to delay the absorption and increase the effectiveness in treating spastic colon and irritable bowel syndrome. As menthol is fat-soluble it is rapidly absorbed from the small intestine when taken orally, which makes it particularly useful for targeting disorders of the intestine. Further studies have looked at menthol metabolism and it has been seen that approximately, 70% of the administered menthol and its metabolites are excreted in urine, the amount fluctuating independently of the dose.
While menthol is highly abundant in peppermint (40%), it can also be found in sunflower petals (essential oils), tarragon (0.1%), basil, and thyme (traces). However, due to the high menthol content in peppermint compared to the other two herbs and given that sunflower petals are not an edible food, menthol can be considered a specific marker of peppermint. Given that menthol glucuronide is also detectable in urine, this compound could also be a suitable biomarker of peppermint intake, particularly after capsular oral administration.
Saffron is among the world’s most costly spices and comes from the dried flower stigma of Crocus sativus. Saffron contains more than 150 volatile compounds, with safranal being the major compound at 70%. Saffron also has a number of other active compounds many of which are carotenoids, including zeaxanthin, lycopene, and various α- and β-carotenes. However, the golden yellow-orange color of saffron is primarily the result of the carotenoid α-crocin, a glycosyl ester of crocetin. Picrocrocin has also been found in saffron spice ranging from 0.8 to 26.6% on a dry basis. In addition, saffron also contains riboflavin (56 to 138 μg/g) which is the highest reported for any food, and thiamine (0.7 to 4 μ g/g) which is within the range of values reported for many vegetables.Saffron is mainly used as a seasoning and colouring agent in food. Saffron extracts and tinctures have been used as antispasmodic agents, gingival sedatives, nerve sedatives, expectorants, stimulants and aphrodisiacs.
One study was identified which looked at saffron compounds in the blood plasma of four healthy individuals following a single dose of saffron tea. Crocetin was found to be rapidly absorbed, being detected in the circulation 2 hours after administration and remains present for up to 24 hours. A separate study using purified crocetin, which had been extracted from Gardenia jasminoides fruit, showed a strong dose-dependent absorption profile into the bloodstream of 10 healthy adult subjects. However, as Gardenia jasminoides is not considered a common edible food, crocetin can be considered a specific biomarker of saffron in blood plasma.
Sage or Salvia officinalis is a herb belonging to the Lamiaceae family. The major components present in sage are α-thujone (12–19%), viridiflorol (10–19%), 1,8-cineole (9–16%), camphor (5–15%), manool (6–13%), β-caryophyllene (3–9%), α-humulene (2–9%), and β-thujone (5–6%). The major phenolic compounds found in sage include rosmarinic acid, caffeic acid, carnosol, and carnosic acid. All of these polyphenols are also present in rosemary, thyme and oregano. Sage is used as a seasoning and flavouring in many different foods including sausages and stuffing. It has also been used in traditional medicine for the treatment of seizures, ulcers, gout, rheumatism, inflammation, dizziness, tremors, paralysis, diarrhea, and hyperglycemia.
Only one study has been performed on sage which involved a single female individual who ingested sage tea. The compounds identified in plasma and urine were 1,8-cineole as well as a number of its derivatives. 1,8-cineole is also known as eucalyptol, and is a major component of essential oils from Eucalyptus polybractea. It is also present in numerous spices, such as rosemary, sage, basil, and laurel. 1,8-cineole is also used in pharmaceutical preparations to treat coughs, muscular pain, neurosis, rheumatism, asthma, and kidney stones.
Although 1,8-cineole is detectable in urine after sage intake, it is also found in several other herbs. Therefore, 1,8-cineole and its derivates cannot be considered to be specific for sage intake. In addition, its rapid metabolism makes it a poor biomarker.
Turmeric (Curcuma longa) is a rhizomatous spice belonging to the ginger family, Zingiberaceae. The most notable phytochemical compounds include curcuminoids, such as curcumin (diferuloylmethane), demethoxycurcumin and bisdemethoxycurcumin. The oils of turmeric contain more than 40 identifiable compounds, with the main constituents being α-turmerone (30–32%), aromatic-turmerone (17–26%), and β-turmerone (15–18%). Turmeric is a key ingredient in many Asian dishes and is used mainly as a colouring agent. Turmeric has antioxidant, anti-inflammatory, and anti-tumor properties, but recent studies have demonstrated that curcumin may be able to treat immune deficiencies, improve cardiovascular health, treat depression, combat Alzheimer’s disease, and treat diabetes, arthritis and inflammatory bowel disease.
Curcumin has been shown to have a very low oral bioavailability, which is primarily due to its poor solubility, low absorption, rapid metabolism, and systemic elimination. As a result, most ingested curcumin is excreted through the feces unmetabolized. The small portion that is absorbed is extensively converted to its water-soluble metabolites, glucuronides, and sulfates. Due to curcumin’s poor absorption, poor bioavailability, and fast excretion, several studies have looked at different ways of administering curcumin to increase its bioavailability. Formulated curcumin, curcumin biotransformation products, and curcuminoids can be detected in plasma and in faeces, but due to the fact that curcumin was administered in a formulated preparation, these biomarkers cannot be considered robust biomarkers of turmeric/curcumin consumption.
The researchers concluded that following their review it is clear that further research is required to assess the use of herbs and spices.
Vázquez-Fresno R et al. Herbs and Spices- Biomarkers of Intake Based on Human Intervention Studies – A Systematic Review. Genes Nutr. 2019 May 22;14:18. eCollection 2019.