Lemons, especially their peels, are an excellent source of terpenes such as d-limonene. The term terpene probably conjures up images of cleaning solvents, but while naturally occurring terpenes are actually used as alternative to synthetic terpenes in many natural cleaning products, the primary health benefits of terpenes revolve around some impressive anticancer effects – both in prevention and possibly treatment.

Background Data:
D-limonene and related terpenes have shown considerable benefits in animal studies against a wide number of cancers. Preliminary studies in humans are also showing promising results. For example, six individuals with advanced cancers were able to halt the progression of their cancer for periods of time ranging from six to twelve months while taking d-limonene.

New Data:
In a study conducted at the University of Arizona Cancer Center 43 women with newly diagnosed operable breast cancer electing to undergo lumpectomy (surgical excision) were given 2 grams of limonene daily for two to six weeks before surgery. Blood and breast tissue were collected to determine the level of d-limonene and its metabolites as well as changes in systemic and tissue biomarkers of breast cancer risk or carcinogenesis.

Results showed that d-limonene was found to preferentially concentrate in the breast tissue, reaching high tissue concentration (average = 41.3 μg/g tissue), whereas the major active circulating metabolite, perillic acid, did not concentrate in the breast tissue.

Results also showed that d-limonene supplementation resulted in a 22% reduction in the expression of tumor markers. Specifically, d-limonene reduced the expression of breast tumor cyclin D1.

Cyclin D1 is one of the frequently overexpressed proteins and one of the commonly amplified genes in breast cancer. The gene that leads to cyclin D1 formation is an estrogen-responsive gene. The overexpression of cyclin D1 occurs in more than half of invasive breast cancers. Recent evidence also shows that cyclin D1 interferes with the anti-cancer effect of tamoxifen in estrogen receptor-positive breast cancers – potentially accounting for treatment failure with tamoxifen therapy.

The benefits seen with d-limonene in this study should be followed up in women with breast cancer who are expressing cyclin D1.

D-limonene is available as a dietary supplement, but it is easily obtained from the diet. In lemons the highest content of limonene is found in the peel and white spongy inner parts. A typical average-sized lemon has about 300 mg of d-limonene.

My feeling is that the best way to take advantage of the health benefits of lemons and achieve adequate d-limonene intake is by juicing them. But, since lemon juice is usually too sour on its own, I recommend mixing it with other juices. Fortunately, adding ½ or 1 whole lemon (complete with peel) is an excellent addition to just about any fresh fruit or vegetable juice including green vegetable juices.

If you are going to juice whole lemons, be sure to choose organic versions. If you can’t find organic lemons, soak or spray non-organic ones with a biodegradable wash, then rinse.

Other dietary sources of terpenes are other citrus fruits, berries, cherries, and volatile herbs such as peppermint, basil, thyme, and rosemary.

Miller JA, Lang JE, Ley M, et al. Human breast tissue disposition and bioactivity of limonene in women with early-stage breast cancer. Cancer Prev Res (Phila). 2013 Jun;6(6):577-84.

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