Nutrition Column – Garlic May Repel Pests as Well as People

Garlic, a common staple found in countless kitchens and recipes worldwide, long has been considered a special food – not just for the unique flavor it imparts, but also for its medicinal value. Botanically known as Allium sativum, garlic is a bulb crop found in the family of onions, chives and shallots. It is thought to have originated in Central Asia, and its use as a condiment and for medicinal purposes predates written history. During World War II, British physicians treated battle wounds with garlic preparations when antibiotics were scarce.  

Most of its therapeutic value, as well as its flavor and odor, can be attributed to sulfur compounds contained within the garlic clove. One such compound is the amino acid, alliin. Once a clove is cut or crushed, alliin is converted to allicin, the main contributor to garlic’s widespread medicinal and antimicrobial benefits. Allicin is a very unstable compound; once in the gastrointestinal tract, it is rapidly converted to other compounds that can be used by the body.

In recent years, garlic has been widely studied for its role in preventing heart disease and cancer, with somewhat mixed results. There is good evidence, however, that garlic possesses antibacterial, antiviral, antifungal, antiprotozoan and insect-repellent properties.

Given the recent surge of the West Nile virus spread by infected mosquitoes, it’s useful to explore the value of garlic as one more method for avoiding mosquito bites. A number of studies have shown that the oil fraction of garlic destroys certain species of mosquito larvae. Garlic sprays (made primarily with garlic extract) are available on the market for use on plants as an alternative botanical pesticide to chemical pesticides. The sulfurs contained within the garlic extract have been shown to be effective against a wide range of insects, including mosquitoes, and the lingering odor can deter mosquitoes from the area for weeks.

It is thought that garlic may be an alternative mosquito repellent for humans as well. In a field study conducted in India, a preparation made of 1 percent garlic oil, petroleum jelly and beeswax that was rubbed on the arms and legs of study subjects was found to be effective in preventing mosquito bites for up to eight hours.

In addition, there is some evidence that heavy consumption of garlic through supplements or well-flavored foods may help ward off mosquitoes. When garlic is eaten and its components are metabolized, compounds are released from the body through the skin and the breath. Although they may not be detectable by others (or may, in the case of garlic breath!), mosquitoes use smell to locate a host. For example, carbon dioxide and lactic acid released from the breath of humans are two known mosquito attractants that can be detected within 40 yards. While it has not been proven through clinical studies, it is thought that the sulfur compounds present on the skin and in the breath after eating garlic may help ward off those pesky mosquitoes.

The bottom line: Mosquito repellents containing DEET are still your best bet for avoiding mosquitoes – but a little garlic breath may also be a good thing. Before deciding to use garlic supplements, it’s important to consider the potential side effects as well as possible benefits. Garlic supplements are not for everyone. For example, they’re not recommended for pregnant or lactating women, for persons on blood thinning medications, for those going into surgery or for those on certain medications such as the anti-HIV drug Saquinavir.

As with any supplement regimen, it’s best to consult with your health-care provider about the efficacy of the supplement for your health care needs.

by Pat Kendall, Ph.D., R.D., Food Science and Human Nutrition Specialist, Colorado State University, Cooperative Extension