Garlic’s Cancer-Fighting Potential
Researchers have developed a urine test that can simultaneously measure the extent of a potential carcinogenic process and an indicator of consumption of garlic in humans.
In a small pilot study, evidence suggests that people eat more garlic, the lower the levels of potential carcinogenic process.
Research is on the body of all the processes associated with nitrogen-containing compounds, scientists say. These processes include nitrosation, or conversion of certain substances in food or contaminated water into carcinogens.
“What we sought was to develop a method that could measure in the urine of two different compounds, one related to cancer risk, and the other, indicating the level of garlic consumption,” said Earl Harrison, Dean Distinguished Professor of Nutrition Human Rights in the state of Ohio, a researcher in the global report from Ohio State University Cancer Center and lead author of the study.
“Our results showed that those were inversely related to each other – which means that again we had the marker for the consumption of garlic, unless the mark is the risk of cancer.”
Ultimately, scientists hope to find that a nutritional intervention could be a way to stop the process that develops these carcinogens. This process started more often by exposure to substances called nitrates in certain processed meats or high-heat food preparation practices, or water contaminated by industrial or agricultural runoff.
About 20 percent of nitrates consumed are converted into nitrites. A cascade of events may make these compounds called nitrosamines, and many but not all, of the nitrosamines are linked to cancer.
Vegetables also contain nitrates, but previous research has suggested that vitamin C in vegetables reduces the risk that the nitrates are converted into something toxic. The researchers suspected that nutrients in garlic might have similar effects of antioxidants such as vitamin C.
The study is published in a recent issue of the journal Analytical Biochemistry.
The investigation began with the study in humans based on the small at Penn State University. There the researchers involved fed a diet lacking in any one week nitrate or garlic. Then gave participants a dose of sodium nitrate – a formulation that would not be toxic, but to display a marker in the urine of potentially toxic process.
The groups were treated with capsules containing different levels of garlic: 1, 3 or 5 grams of fresh garlic, or 3 grams of aged garlic extract. Another group received 500 mg of ascorbic acid or vitamin C. Both the formula and nitrate treatments were given for seven days. Urine samples were collected from participants every other day for seven days.
The research team then went to Harrison and his colleagues, who explored the methods required for a precise quantification of biomarkers in urine for use in both the garlic and the presence of nitrosoproline, the indicator that nitrosation occurred.
Harrison Group developed a urine test using a method called gas chromatography-mass spectrometry.
Gas chromatography separates the different components of a mixture to detect specific substances, and has been used previously to quantify nitrosoproline. The addition of mass spectrometry for the analysis helped determine the chemical structure of molecules in the sample – in this case, the presence of a specific compound that is released into the urine after eating garlic.
When the test was used on urine samples from the pilot study of garlic, which showed that participants who had taken garlic had a marker for nitrosation concentration than those not taking garlic. Although the differences were minor, consumption of 5 grams of garlic per day was associated with the lowest level of the marker for potential carcinogens. A single clove of garlic usually weighs between 1 and 5 grams.
Vitamin C has a similar effect in reducing the mark for nitrosation.
Harrison, also a researcher at the Center for Advanced Functional Foods Research and Entrepreneurship at the Ohio Agricultural Research and Development Center, noted that previous research has suggested that garlic plants and other sulfur-containing compounds offer a variety of potential health benefits. Many questions remain about exactly what those benefits are and exactly how the garlic as a nutritional intervention.
“The exact mechanism by which garlic and other compounds that affect nitrosation is under investigation in depth, but it is unclear at this time,” he said.
“What this research suggests, however, is that garlic may play a role in inhibiting the formation of these nitrogen-based substances. This pilot study was very small, so it is possible that the more you have garlic, the better.
“So if you like garlic and likes garlic containing foods, and leave as much as you want. There is no indication that’s going to hurt, and it may help you.”
The research was supported by grants from the National Institutes of Health and Interinstitutional Cooperation Agreement between NCI and the U.S. Department of Agriculture.
Harrison, co-authored the study with former colleagues from the U.S. Department of Agriculture Human Nutrition Research Center in Beltsville, Maryland, including Keary Cope, a postdoctoral fellow, and Rebecca Seifried, a student, and Harold Siefried, John Milner and Penny Kris-Etherton. Harold Seifried and Milner are in Group Nutritional Sciences Research Division of the National Cancer Institute Cancer Prevention. Kris-Etherton and Milner made the study of human nutrition as faculty members at Penn State University.
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