Watermelon sales are on the rise? Why? Because hopeful men have been seduced by media reports proclaiming that watermelon may excite more than their taste buds. I suppose this should come as no great surprise given that it was Texas A&M, a major American university, that put out a press release announcing that "Watermelon May Have Viagra-Effect." News organizations around the world picked up the story, tantalizing their readers with ingenious headlines such as "Watermelon, The New Oyster?" and "Watermelon Could Add Bite to Sex Life." Some even came up with irresponsible, but attention-grabbing banners like "Watermelon Can Duplicate Viagra Effects."
Is there any evidence to support these farfetched claims? No. Did researchers at Texas A&M, or indeed anywhere else, carry out studies to demonstrate that watermelon has any such effect? No. So how did the fanciful headlines come about? Texas A&M carries out extensive research on plant breeding, including that of watermelon. One aim of this research is to investigate the possibility of increasing the naturally occurring amount of an amino acid called citrullin in watermelon. This compound is of scientific interest because once ingested it can be converted into arginine, an amino acid that plays a role in immune system activity, as well as in the dilation of blood vessels.
A press officer at the University, given the task of publicizing this rather mundane research, asked breeder Dr. Bhimu Patil to suggest some interesting items about watermelon to be included in the press release. Patil then speculated about the fruit increasing levels of arginine in the blood, and mentioned that arginine is the source of nitric oxide, which in turn dilates blood vessels and can increase blood flow. He also pointed out that Viagra works by increasing levels of nitric oxide. Presto, the press officer put two and two together and came up with five, and the press release about watermelon increasing libido was born. Pure mythology.
While there is zero evidence about watermelon having any effect on male performance, the notion of citrulline increasing arginine levels is correct. That was clearly shown in a study published in Nutrition, a respected peer-reviewed journal. Twenty-three volunteers were asked to drink either three or six eight-ounce glasses of watermelon juice a day for three weeks and then had their blood tested for arginine. This amount of juice of course corresponds to more watermelon than anyone could reasonably eat. Compared with subjects who drank no watermelon juice, levels of arginine increased by 12-22%. No physiological consequences of this increase were measured in any way. The point of the research was simply to determine the possibility of increasing arginine levels by diet because of the role of this amino acid in improving blood flow.
Arginine first came to the public's attention back in 1992 when its metabolic breakdown product, nitric oxide, was named Molecule of the Year by the prestigious journal, "Science." Inspired by Time magazine's Man of the Year, the editors of Science decided in 1989 that bestow an annual award on a molecule that according to them made the greatest impact that year. Not quite as esteemed as an Oscar, but impressive nevertheless.
Why was nitric oxide accorded this honor? Because researchers had shown that it had the ability of relaxing the muscles in blood vessels and increasing blood flow. This is exactly what is desired when coronary arteries become narrowed by arteriosclerosis. The dilation of blood vessels also leads to lower blood pressure, another plus. In fact, this effect had been noted indirectly during World War I, when munitions workers whose job was to fill artillery shells with nitroglycerin were found to have very low blood pressure. That's because nitroglycerin can break down to form nitric oxide. Today of course nitroglycerine is commonly used in the treatment of angina. But nobody knew until 1987 that nitric oxide was made in the body from arginine. Interest escalated with the subsequent discovery that this molecule also played a role in producing erections. Its ability to enhance blood flow at the right time was of course responsible for this effect. As soon as this observation was made, pharmaceutical companies began to explore methods for increasing nitric oxide levels in the blood. The erection sweepstakes were won by Pfizer with the development of a drug that attacked the problem indirectly. Viagra blocks an enzyme that normally breaks down cyclic guanosine monophosphate (cGMP), the substance that is produced in response to nitric oxide stimulation and is actually responsible for blood vessel dilation.
An obvious question that arises, is why not just take arginine directly as a dietary supplement? Indeed, there is some evidence that arginine taken orally can allow blood vessels to dilate more readily, but at the dosage required, arginine pills have been linked with nausea and gastrointestinal discomfort. Supplying the body with citrulline, which is then converted into arginine, may get around this problem. That's why Texas A&M researchers are interested in breeding watermelon with higher levels of citrulline. But keep in mind that no studies have shown that boosting arginine, either through supplements, or through high-citrulline foods has any significant effect on erectile biology. The only activity that will be stimulated by increasing watermelon intake is urination. A ripe, sweet watermelon can certainly give a boost to the taste buds, but don't expect anything else to be boosted. And as a final note, most of the citrullin in watermelon is found in the rind, not exactly the focus of consumption. That little tidbit escaped the attention of writers who generated silly headlines like "No Wonder Watermelons Grow So Big." But it probably didn't escape the attention of supplement manufacturers with visions of rising profits from the sale of watermelon rind tablets.
Joe Schwarcz, MCIC, is the director of McGill University's Office for Science and Society. He hosts the Dr. Joe Show on Montreal's radio station CJAD and Toronto's CFRB. The broadcast is available at www.CJAD.com.
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|Publication:||Canadian Chemical News|
|Date:||Oct 1, 2008|
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