Limonene is a compound naturally found in all citrus fruits, which may be used to prevent cancer, boost your metabolism, relieve heartburn, and reduce stress and anxiety without the side effects of prescription drugs. Keep reading to learn about the surprising health benefits of limonene.
What is Limonene?
Limonene is found in the oils of many citrus fruits, including lemon, orange, mandarin, lime, and grapefruit [R].
Limonene is added to numerous foods, drinks, perfumes, soaps, and chewing gum as a flavor and fragrance enhancer [R].
Mechanisms of Action
- Limonene prevents the growth of cancer cells by inhibiting G proteins that are involved in cell signaling pathways that induce cell growth, such as p21ras. Limonene inhibits posttranslational addition of hydrophobic groups to the G protein peptide precursor, which is necessary for the proteins to mature and function properly [R].
- Limonene suppresses the expression of genes that produce MMPs, proteins that break down the extracellular matrix. Limonene also increased antioxidant, inducible iNOS, COX‑2, and ERK expression levels in rats, contributing to its antioxidant and anti-inflammatory effects [R].
- Limonene increases the ability of docetaxel to induce apoptosis in prostate cancer cells. More reactive oxygen species are produced in the cancer cells, while the amount of glutathione, an antioxidant that inhibits tumor growth, is significantly reduced. The activity of caspase, an enzyme involved in triggering apoptosis, is also increased [R].
- Limonene reduces TNF-α and inhibits TNF-α-induced NF-κB translocation, reducing inflammation [R, R].
- Limonene and the product of its breakdown, perillyl alcohol (POH), can both help prevent the HPA axis from being overstimulated, which reduces stress [R].
- The essential oil of Citrus aurantium exhibits anti-anxiety activity through interaction with serotonin receptors. Limonene interacts with 5-HT1A receptors to reduce anxiety, but the exact mechanism is still unknown [R].
- Limonene reduces breast cancer growth by inhibiting the expression of cyclin D1 and IL-6. Cyclin D1 speeds up the progression of a cell through the cell cycle, allowing cancer cells to proliferate faster. Since cyclin D1 is overexpressed in many breast cancers, the ability of limonene to reduce the expression of cyclin D1 suggests that limonene could help slow down breast cancer growth [R].
- In stomach cancer cells, limonene decreased BCL2 and increased p53, inhibiting the spread of cancer [R].
Health Benefits of Limonene
1) Limonene Is an Anti-Cancer
Limonene has antioxidant properties, allowing it to counteract the effects of free radicals, which damage DNA and lead to cancer [R, R]. As an antioxidant, limonene can prevent cell damage and reduce the risk of cancer.
In an animal study, orange oil with limonene reduced the growth of liver tumors, while it increased the growth of, and new connections between, normal cells [R].
Limonene also caused dose-dependent cell death in human stomach cancer cells [R].
In a pilot trial in patients with advanced cancer, limonene reduced the size of lymph nodes in a female breast cancer patient [R].
In another study of 43 women with breast cancer, limonene administered before surgery decreased cyclin D1, a protein that stimulates the growth of cancer cells [R].
Moreover, lemon extract prevented pancreatic and intestinal damage in mice caused by the chemotherapy drug cyclophosphamide (Cytoxan) [R].
In a study of 32 cancer patients, one patient with breast cancer and three with colorectal cancer were given limonene, which slowed tumor growth. However, side effects like nausea, vomiting, and diarrhea prevented them from taking high doses of limonene [R].
2) Limonene May Boost the Immune System
Healthy mice treated with limonene produced significantly more antibodies when exposed to foreign antigens and stimulated immune cells in the pancreas and intestines [R].
In mice with lymphoma, limonene improved survival, increased their ability to fight bacterial infections, and reduced hypersensitivity to foreign compounds, which can ultimately reduce allergic reactions [R].
3) Limonene May Reduce Stress, Anxiety, and Depression
Basil essential oil, which contains limonene, showed anti-anxiety and sedative effects in mice. However, due to the presence of other compounds in the oil, these effects may not be due to limonene alone [R].
While bitter orange essential oil (also contains limonene) has anti-anxiety and sedative effects, limonene extract failed to show the same effects. This may be due to the interaction of limonene with other compounds [R].
Another study showed that essential oil of Brazilian Peppertree (S. terebinthifolius) and compounds present in this oil, including limonene and α-phellandrene, decreased sensitivity to pain and depression [R].
Mice that inhaled limonene showed significantly reduced anxiety levels. Limonene is also highly volatile, which means that it easily evaporates into a gas, making it ideal for inhaled aromatherapy [R].
4) Limonene Can Help Relieve Pain
In rats, limonene reduced pain (induced by physical stresses) and sensitivity to pain [R].
Limonene reduced widespread pain in the bones and muscles of mice, likely by acting on nerves [R].
Inhaling limonene reduced pain severity in 63 women (out of 126 women in labor with similar levels of pain) [R].
Limonene as an aromatherapy agent reduced nausea, vomiting, and pain during the first stage of labor in a study (DB-RCT) of 100 pregnant women [R].
5) Limonene Dissolves Gallstones
Limonene, given every other day, dissolved the remaining gallstones after surgical gallstone removal in a pilot trial of three patients. In a fourth patient, limonene was given instead of performing surgery, but this was not successful [R].
In a study of 200 patients, 20-30 mL of a 97% limonene solution dissolved gallstones completely in almost half of the patients [R].
6) Limonene Relieves Heartburn
In a study of 19 people taking heartburn medications, 17 had no heartburn symptoms after taking only limonene daily for two weeks [R].
Another study (DB-RCT) of 13 participants found that, after two weeks, limonene relieved heartburn symptoms in all but one of the patients [R].
7) Limonene May Help with Metabolic Syndrome and Obesity
Metabolic syndrome increases the risk of heart disease, strokes, and type 2 diabetes. This syndrome involves high blood sugar, fat, and cholesterol, insulin resistance, and high blood pressure [R].
In mice fed a high-fat diet, limonene reduced blood pressure, heart rate, and blood sugar and increased levels of antioxidants, lowering the risk of developing nonalcoholic fatty liver disease due to large amounts of fat in the liver [R].
Limonene decreased the size of fat cells, reduced glucose and fat levels in the blood, and decreased the accumulation of fat in the liver of mice fed high-fat diets [R].
In obese mice, limonene lowered blood sugar levels, reduced the amount of low-density lipoprotein (LDL) cholesterol, and raised the level of high-density lipoprotein (HDL) cholesterol in the blood [R].
8) Limonene May Reduce Inflammation in the Gut
In a cell-based study, limonene reduced reactive oxygen species and inflammatory cytokines in human leukemia cells [R].
Moreover, a study of 5 healthy adults showed that limonene increases bowel movements, which can promote regularity in people who struggle with regular bowel habits [R].
9) Limonene May Improve Wound Healing and Skin Repair
Due to its anti-inflammatory effects, limonene applied to the skin of mice reduced damage, inflammation, and rashes [R].
Limonene also increased the production of new cells and blood vessels and improved skin healing after an injury in mice [R].
The blood vessels of diabetics tend to be narrower and harder with poorer circulation than those of non-diabetics, which prolongs wound healing time and inflammation. Limonene applied to the skin of diabetic mice reduced inflammation and wound size and formed new skin, speeding up wound healing [R].
10) Limonene May Protect the Eyes
Oxidative stress is caused by free radicals, which damage cells. Due to its antioxidant properties, limonene protected human eye cells from damage by hydrogen peroxide, which is a natural byproduct of human metabolism [R].
Side Effects of Limonene
While limonene is not toxic in animals even after multiple doses, it caused skin irritation and sensitivity in some cosmetics and scented household products [R].
14 people in a study developed dermatitis (skin inflammation and rashes) after using detergents, hand cleansers, and dish-washing liquids containing limonene. Three individuals exhibited this allergic reaction after using cosmetics with limonene [R]. However, these results cannot be attributed to the effect of limonene alone.
While limonene caused kidney cancer in rats, this should not affect humans since the protein involved in this particular pathway is not present in humans [R].
Based on various studies, limonene is safe in humans as long as it is taken in moderate amounts and for up to a year. Longer studies (2 years) were conducted with mammalian cells and rats with no negative effects [R].
Some users stated that limonene relieved their heartburn, some even more than traditional heartburn medications, such as Nexium and Prilosec. They recommend switching to limonene from proton-pump inhibitors (PPIs), which reduce stomach acid to relieve heartburn but can be harmful after extensive use. The only reported side effect of limonene was orange-flavored burps.
Most of the reviews reported that limonene was effective in relieving heartburn, but some said that it caused nausea, and one review indicated that the limonene gel capsules did not taste good and caused orange taste and burps. In some cases, limonene helped users suffering from bloating, flatulence, and stomach pain, even though it took two weeks of use [R].
Another user mentioned “I take a 500 mg capsule of limonene with my evening meal. Around 45 mins after the meal, I do typically feel a sense of relaxation (that feels cleaner somehow than e.g., the sleepiness you get from say eating a bunch of carbs). I’d vaguely wondered what might be causing it. But I take so many supplements with my evening meal – narrowing down what is causing the relaxation response would be a chore.”
Limonene is naturally found in the rinds of citrus fruits such as grapefruit, lemon, lime, and oranges.
Limonene can be supplemented as an oil, usually in soft gel capsules.
Limonene oil can also be used as aromatherapy or applied externally to the skin.