The Health Benefits of D-Limonene

D-limonene is a compound sourced from the peel of citrus fruits, including include oranges, mandarins, limes, and grapefruit. It takes its name from the lemon and is often used as a flavoring agent in foods. D-limonene differs from a less common type of limonene known as L-limonene, which is found in mint oil.

Sold as a dietary supplement, D-limonene is said to offer a variety of health benefits, in part because of its ability to dissolve fats, including cholesterol. Proponents believe that D-limonene can not only aid in weight loss but treat or prevent certain diseases, including cancer.

Alternative practitioners have long touted the benefits of D-limonene, claiming that it not only burns fat but reduces inflammation and kills disease-causing germs. Many of these beliefs are culled from its use in industry, where D-limonene is commonly used to make hand sanitizers, perfumes, botanical pesticides, and chemical solvents.

Among some of the conditions that D-limonene is believed to prevent or treat are:

• Bronchitis
• Cancer
• Diabetes
• Gallstones
• Gastroesophageal reflux disease (GERD)
• Heartburn
• High cholesterol
• Inflammatory bowel disease (IBD)
• Metabolic syndrome
• Obesity
• Peptic ulcers

To date, there is little solid evidence that D-limonene can treat any medical condition. With that said, a number of preliminary studies have hinted at benefits that may warrant further investigation.

There is some evidence that D-limonene can promote weight loss by lowering blood sugar and lipids associated with metabolic syndrome. A 2013 study in the European Journal of Pharmacology reported that obese mice fed a high-diet diet supplemented with D-limonene experienced decreases in blood glucose, total cholesterol, and "bad" LDL cholesterol as well as increases in "good" HDL cholesterol.

These findings suggest that D-limonene may be useful in preventing or treating metabolic syndrome, although it is unclear what dose would be needed to achieve such benefit in humans. Further research is needed.

D-limonene may help reduce the risk of peptic ulcers and other inflammatory gastrointestinal diseases, suggests a 2009 study published in the Chemico-Biological Interactions. According to the researchers, high concentrations of D-limonene in the essential oil of bitter orange (C. aurantium) served to protect the lining of the stomach of lab rats fed high-doses of alcohol and nonsteroidal anti-inflammatory drugs (NSAIDs).

Contrary to popular belief, it did so not by suppressing stomach acid but by increasing the production of gastric mucus.

Despite the positive findings, it is unclear if D-limonene did so on its own or if some other component in the essential oil contributed. Further research is needed.

Alternative practitioners have long touted the anticancer properties of D-limonene. The effect of is attributed to a substance known as perillic acid, which is released into the bloodstream when D-limonene is broken down by the body.

A number of test-tube studies have reported that D-limonene applied to cancer cells can trigger apoptosis (programmed cell death). This is considered significant given that apoptosis—a naturally occurring event that allows old cells to be replaced by new cells—does not occur with cancer cells. This effect was seen in recent studies involving colon cancer, skin cancer, and other common malignancies.

It remains unclear whether taking D-limonene by mouth might render the same benefit. A 2013 study in Cancer Prevention Research aimed to evaluate this effect by providing 43 women with breast cancer with 2 grams of D-limonene daily for two to six weeks.

At the end of the study period, a biopsy of breast tissue showed high concentrations of D-limonene but little of the perillic acid needed to arrest cancer growth. Further research is needed to determine whether higher doses or longer treatment may help improve these results.

Widely used as a food flavoring, D-limonene is generally considered safe and has been used for up to a year in clinical research without incidence. Common side effects include stomach upset and reflux.

D-limonene may cause irritation if applied to the skin. This includes citrus essential oils that are characteristically high in D-limonene. To reduce irritation, always mix essential oils with a carrier oil (such as avocado oil or sweet almond oil) if you intend to use it for massage purposes.

The safety of D-limonene has not been established in children, pregnant women, or nursing mother. As a precaution, always speak with your doctor before using D-limonene or any other supplement if you are pregnant or breastfeeding. As the benefits of D-limonene in children is unknown, it is best to play it safe and avoid the supplement altogether.

D-limonene is broken down by many of the same liver enzymes—called cytochrome P450 (CYP450)—that other drugs use for metabolization. Because of this, D-limonene may increase or decrease the concentration of certain drugs as they compete for the same enzyme.

Possible drug-drug interactions include:

• Anticoagulants like Coumadin (warfarin)
• Anticonvulsants like Tegretol (carbamazepine)
• Antifungal drugs like Nizoral (ketoconazole)
• Anti-hypertensive medications like Cozaar (losartan)
• Antipsychotic drugs like Orap (pimozide)
• Atypical antidepressants like nefazodone
• Benzodiazepine tranquilizers like Halcion (triazolam)
• H2 blockers like Tagamet (cimetidine)
• Macrolide antibiotics like clarithromycin and telithromycin
• Nonsteroid anti-inflammatory drugs (NSAIDs) like Advil (ibuprofen) and Voltaren (diclofenac)
• Proton pump inhibitors like Prilosec (omeprazole)

Many of these interactions can be mitigated by separating the doses by two to four hours. Others may require a dose adjustment or substitution.

To avoid interactions, always advise your doctor about any medications you are taking, whether they are prescription, over-the-counter, nutritional, herbal, or recreational.

D-limonene supplements are most often sold in soft gel capsules and are easily sourced online or in stores specializing in dietary supplements.

As a rule of thumb, never exceed the dose on the product label. There is no evidence that higher doses confer to improved health benefits.

Most D-limonene soft gels can be stored safely at room temperature. You can also keep them in the refrigerator if there is a risk of heat exposure. Never use a supplement past its expiration date, and dispose of any soft gels that are either leaking, discolored, or misshapen.

Because dietary supplements are not strictly regulated in the United States, it can be difficult to tell which brands are good and which are not.

One way to do so is to choose brands that have been tested by an independent certifying body like the U.S. Pharmacopeia (USP), NSF International, or ConsumerLab.

Always check the product label for ingredients you may be sensitive to, including preservatives and gluten. If you are strictly vegetarian or vegan, opt for soft gels made with vegetable-based gelatin rather than animal-based gelatins made from beef or pork cartilage.