In our quest to explore the role of nutrition in the restoration of human and environmental health, we sought out an expert on chili peppers, Dr. Ivette Guzman, to set us straight on the healing powers of “heat.” Dr. Guzman is a research scientist at New Mexico State University.
Chili Basics
As one of the first domesticated crops dating as far back as 10,000 BCE, chili peppers—also known as chile, chilli, peppers, and capsicum—are an extremely valuable and popular vegetable and spice crop from South America. Indigenous populations likely first cultivated chilies for their antibacterial properties[1].
Members of the Solanaceae family and the Capsicum genus, there are thirty-two identified chili species, only five of which have been domesticated: (C. annuum, C. baccatum, C. chinense, C. frutescens, and C. pubescens)[2].
Altogether, there are an estimated 4,000 different chili pepper types worldwide, and each variety is unique in both flavor and level of heat[3].
Indigenous populations likely first cultivated chilies for their antibacterial properties.
Nutritional Powerhouses
Chili peppers produce medicinal and nutritional compounds important to humans, including vitamins C and E and folate[4]. Among the most important of the biologically active compounds in peppers are capsaicinoids and carotenoids. Capsaicinoids have no color and are alkaloids that bind to heat and pain receptors in humans, while carotenoids are colorful pigments known for being strong antioxidants and providers of Vitamin A[5].
The Spicy Capsaicinoids
The purpose of capsaicinoids in peppers is to discourage the consumption of the spicy fruits by mammals, in order to protect the plant’s seeds. Despite this fact, peppers play an important role in the world’s cuisines and in human health.
The fruit morphology of peppers, or the forms and structures of peppers, includes the colored fruit wall of the pepper and the colorless placenta membrane that holds onto the seeds.
Contrary to popular belief, the seeds are not the location of the spicy capsaicinoids. It is the colorless placenta, in fact, that contains vesicles, or fluid-filled sacs that resemble blisters, which produce and store capsaicinoids.
In 2015, Bosland et al. discovered a novel mutation that increases the heat level of peppers by "augmenting the number of capsaicinoid-filled blisters on the fruit wall" in addition to those normally found within the placenta.
How Capsaicinoids Work Inside Us
Chili peppers make twenty-two distinct capsaicinoids and each one is able to bind to human sensory pain neurons, thus accounting for the heat sensations that chilies are known for[6]. Capsaicin is the predominant capsaicinoid found in chilies, with the remaining twenty-one found in minor amounts[5].
Researchers have discovered that capsaicin acts by binding to a transient receptor potential vanilloid receptor (TRPV). TRPVs are responsible for thermal reactions in the body and are located on nociceptor neurons that are found in almost all parts of our anatomy.
Nociceptor neurons alert the brain to threatening stimuli[5]. As a result, capsaicin induces “hot” pain-like sensations in the body. Repeated doses of capsaicin initially induce pain in humans, followed by analgesia, or the inability to feel pain.
The Healing Powers of Heat
Due to the prevalence of capsaicin in Capsicum species, most capsaicinoid pharmacological studies have focused on capsaicin. Capsaicin is now used orally or as an intradermal and topical application to treat pain. Reports indicate that topical application of eight percent capsaicin produces desensitization, decreasing pain for twelve weeks, and oral capsaicin can be used to treat cough by reducing inflammation of the airways[5].
Capsaicin has also been shown to aid in regulating pro-inflammation in the gastrointestinal tract. It can help patients suffering from stomach pain associated with gastric acid, irritable bowel syndrome, or irritable bladder [5]. In addition, capsaicin may be anti-inflammatory in salivary gland cells and suppress inflammation associated with bile duct cancer, making capsaicin a potential anti-tumor compound. In addition, capsaicin’s anti-inflammatory response in the gastric epithelial cells extends to reducing inflammation generated from H. pylori infections, a common cause of ulcers[5].
It was previously thought that spicy food caused ulcers, however, these results prove the opposite, and could potentially help patients suffering from bacteria-induced ulcers. As with all such studies, it is important to note that the capsaicin dosage was crucial in evaluating its efficacy.
It was previously thought that spicy food caused ulcers, however, recent test results prove the opposite, that spicy food could potentially help patients suffering from bacteria-induced ulcers.
And What About the Carotenoids?
Carotenoids are pigments that are produced in ripening chili peppers. They do not have a flavor, nor are they spicy; however, they are extremely valuable anti-oxidants, some of which are pro-Vitamin A[7].
The important chili carotenoids are two orange carotenoids, beta-carotene and beta-cryptoxanthin, and two yellow carotenoids, lutein and zeaxanthin. Beta-carotene and beta-cryptoxanthin are converted to Vitamin A in the human gut, while lutein and zeaxanthin are absorbed and form the macular pigment designated to protect our eyes’ ocular nerve from harmful blue light oxidation[8].
In general, dark red chili peppers contain high amounts of carotenoids, but could still be void of the pro-Vitamin A, lutein and zeaxanthin. Although we know that colored fruits are good for us, color is still not a good indicator of what type of carotenoids are in the fruits[9]. Even so, we know that consuming spicy and colorful chili peppers is better than limiting consumption to non-spicy, colorful fruits, based on another study[10] where higher amounts of beta-carotene were absorbed by rats being fed beta-carotene and capsaicin together.
Measuring the “Heat”
Heat intensity, when measured as the total amount of capsaicinoids in a pepper, is generally represented as Scoville Heat Units (SHU), a measurement of heat-level developed by Wilbur Scoville[3]. The hottest chili pepper cultivar, determined by the Chile Pepper Institute, is the Trinidad Moruga Scorpion, surpassing two million SHU. To put that level of heat in context, The SHU for jalapeños ranges from 4,000–50,000, while bell peppers have zero SHU[11]. Heat profiles of peppers that were introduced by Guzman and Bosland[13] in 2017 added to the cultural context of the “burn” within this popular fruit.
Chileheads and The Rest of Us
A report in 2013 by Lillywhite indicated that spicy chili pepper consumption had doubled in the U.S. from 1980 to 2012[11]. Their research also found that the most popular types of peppers were not necessarily the hottest nor the mildest available on the market, indicating that there are other factors, besides heat, that are driving chili pepper consumption; factors such as flavor, nutrition, and availability.
Perhaps the best known, and fastest growing niche of pepper enthusiasm, is populated by the “chileheads,” a grouping of connoisseurs of the “super hot” varieties; peppers with names like bhut jolokia or “ghost chilies.”
Chili Breeding for Nutrition
The genetics of each pepper dictates its nutritional value; therefore, breeders and food scientists are joining forces to improve chili nutrition. A preliminary step in increasing nutritional value is to discover individual peppers with high amounts of desired compounds, followed by cross-breeding to incorporate the traits into more commonly preferred varieties. In 2016, Kantar screened 101 varieties of chili peppers in search of chilies that could be used to breed for higher nutritional content in other chilies[4]. The group measured pro-Vitamin A, Vitamin C and folate.
A similar study was done with capsaicin and SHU amounts in high capsaicin varieties, known as the “super hots”[9]. The goal of these studies was to develop varieties with high nutritional content, like that in NuMex LotaLutein[12]. This cultivar was bred to be rich in lutein which serves to prevent macular degeneration, an eye condition that worsens with age. Chili nutrition research continues to gain attention as scientists learn more about this nutritious, medicinal food crop.
Footnotes
Cichewicz, R.H., and Thorpe, P.A.1996. “The antimicrobial properties of chile peppers (Capsicum species) and their uses in Mayan medicine.” Journal of Ethnopharmacology 52:61–70.
Carrizo García, C., Barfuss, M.H.J, Sehr, E.M., et al. 2016. “Phylogenetic relationships, diversification and expansion of chili peppers (Capsicum, Solanaceae).” Annals of Botany 118:35–51.
Guzman, I. and Bosland, P.W. 2017. “Sensory properties of chile pepper heat — and it’s importance to food quality and cultural preference.” Appetite 117:186–190.
Kantar, M.B., Anderson J.E., and Lucht, S.A., et al. 2016. “Vitamin variation in Capsicum spp. provides opportunities to improve nutritional value of human diets.” PLoS One 11.
Guzman, I. and Bosland, P.W. 2018. “A matter of taste: capsaicinoid diversity in chile peppers and the importance to human food preference.” In Mozsik, Gyula (Ed.), Capsaicin and its Human Therapeutic Development. Rijeka: IntechOpen.
Walpole CS, Wrigglesworth R, Bevan S, Campbell EA, Dray A, James IF, Masdin KJ, Perkins MN, Winter J. Analogues of capsaicin with agonist activity as novel analgesic agents; structure-activity studies. 3. The hydrophobic side-chain ‘‘C-region.’’ J Med Chem. 1993;36:2381–2389.
Guzman, I., Bosland, P. W., and O’Connell, M.A. 2011. “Heat, color and flavor compounds in Capsicum Fruit.” in The Biological Activity of Phytochemicals. Ed. David R. Gang. Springer, New York. 109–126.
Johnson, E.J., Vishwanathan, R., Johnson, M.A., Hausman, D.B., Davey, A., Scott, T.M., Green, R.C., Miller, S.L., Gearing, M., Woodard, J., Nelson, P.T., Chung, H.Y., Schalch, W., Wittwer, J., and Poon, L.W. 2013. “Relationship between serum and brain carotenoids, a-tocopherol, and retinol concentrations and cognitive performance in the oldest old from the Georgia centenarian study.” Journal of Aging Research 2013:951786
Lozada, D.N., Coon, D.L., Guzman, I., Bosland, P.W. 2021. “Heat profiles of ‘superhot’ and New Mexican type chili peppers (Capsicum spp.).” Scientia Horticulturae 283:110088
Veda, S., and Srinivasan, K. 2011. “Influence of dietary spices on the in vivo absorption of ingested β-carotene in experimental rats.” The British Journal of Nutrition 105:1429–1438.
Lillywhite, J.M., Simonsen, J.E., and Uchanski, M.E. 2013. “Spicy pepper consumption and preferences in the United States.” HortTechnology 23:868–876.
Guzman, I., Coon, D., Vargas, K., and Bosland, P.W. 2020. “NuMex LotaLutein, a high-lutein serrano pepper.” HortScience 55:2052–2055.