Scented geraniums offer many ornamental and aromatic pleasures. They also contain compounds that may benefit human health. One particular compound, geraniol, has slowed the growth of cancerous tumors in both human cell cultures and animals.
A source of essential oils used in the perfume and fragrance industries, scented geraniums (Pelargonium spp.) are unusual because their scent comes from their leaves rather than their flowers. Varieties of scented geraniums include mint, apple, pine, lemon, nutmeg, and rose. In the sixteenth century, European explorers found scented geraniums growing wild in South Africa and took them back to their homeland, where the plants became very popular. The French discovered that oil from rose-scented geraniums (P. radens x P. capitatum) could substitute for the more expensive attar of roses (top-quality rose petal extract) in making perfume.
Geraniol, one of the principal components of rose geranium oil, has a sweet, mildly floral aroma, according to the University of Delaware’s Arthur Tucker, Ph.D., an expert on essential oils and an Herbs for Health adviser. Geraniol belongs to a large class of plant chemicals known as isoprenoids, compounds that are concentrated in essential oils; they include chemicals such as menthol and vitamin E.
A steady intake of various isoprenoids is believed to be one reason that diets high in fruits and vegetables decrease the risk of cancer and cardiovascular disease. Some isoprenoids, including geraniol, also help detoxify the liver and moderately lower blood-cholesterol levels.
Preventive care may not be the only benefit of isoprenoids. In recent studies, isoprenoids have suppressed the growth of aggressive cancers in human cell cultures. And a review of animal studies shows that geraniol inhibits tumor growth when given in controlled amounts in the animals’ food. In one study, liver cancer didn’t grow when rats received either 400 micromoles of geraniol in their daily diet or 45 micromoles of geranoic acid through daily injections. In both groups, some rats survived–tumor-free.
In two other experiments, researchers tested to see whether isoprenoids could be used to treat pancreatic cancer, which is usually unresponsive to chemotherapy. (The five-year survival rate is only 4 percent.) Researchers transplanted pancreatic tumors into groups of fifteen hamsters. In the first experiment, hamsters were fed a diet containing geraniol, farnesol (an isoprenoid found in lemon grass and cumin), or perillyl alcohol for one week before the transplant and for twenty-five days after. Tumor growth in the hamsters fed geraniol or farnesol at 20 g per kg of body weight stopped completely. But 50 percent of the hamsters fed perillyl alcohol at 40 g per kilogram of body weight developed tumors, and 20 g doses were ineffective.
In the second experiment, hamsters were fed geraniol and farnesol only when the researchers could feel the tumors (this helps them track size). Both isoprenoids completely inhibited tumor growth. The doses used in these two experiments were higher than levels found in foods or medicinal plants, yet weren’t toxic to the animals, so these compounds may be safe for human chemotherapy as well. More research is under way.
Self-treatment of cancer is not recommended, but the following information may be useful to your health-care provider: Aromatic isoprenoids such as geraniol are volatile and not very soluble in water, so essential oils and alcohol tinctures of fresh herbs are the best sources of these phytochemicals. Hot-water infusions of fresh herbs and, to a lesser extent, dried herbs will extract some of the essential oils, but cold water will not.
C. Leigh Broadhurst holds a doctorate in geochemistry and is a nutrition consultant in Clovery, Maryland. James Duke spent thirty years working for the U.S. Department of Agriculture and is a member of the Herbs for Health Editorial Advisory Board.
Additional reading
Burke K. D., et al. “Inhibition of pancreatic cancer growth by the dietary isoprenoids farnesol and geraniol.” Lipids 1997, 32:151-156.
Elson C. E., and S. Yu. “The chemoprevention of cancer by mevalonate-derived constituents of fruits and vegetables.” Journal of Nutrition 1994, 124:607-614.
He L., et al. “Isoprenoids suppress the growth of murine B16 melanomas in vitro and in vivo.” Journal of Nutrition 1997, 127:668-674.
