A daily dose of 1500 mg L-citrulline [structural formula shown here] rids half of the men who have a mild erection problem of this complaint. Urologists at the University of Foggia draw this conclusion from a study in which 24 men with an average age of 56 participated.

High blood pressure, reduced insulin sensitivity and deteriorating cholesterol balance can all in the long term lead to a stiffening of the blood vessels in the male penis. As a result, the penis can lose its ability to have an erection. Doctors usually deal with this problem by prescribing phosphodiesterase type-5 inhibitors, such as sildenafil.

Phosphodiesterase type-5 converts cyclic guanosine monophosphate [cGMP] into inactive guanosine monophosphate. Cyclic guanosine monophosphate makes blood vessels more supple, and helps create and maintain an erection.

Lots of men prefer not to take medicines like Viagra or Cialis. They're also expensive and sometimes have unpleasant side effects such as headache. That's why the Italians wondered whether they'd be able to help some men by using L-citrulline. L-Citrulline is a precursor of L-arginine, which in turn is a nitrogen monoxide [NO] donor.

If the NO concentration is high, then the enzyme guanylate cyclase converts the compound guanosine triphosphate into the erection enhancing cyclic guanosine monophosphate. So NO donors boost the production of cyclic guanosine monophosphate, while PDE-5 inhibitors inhibit its breakdown. Different mechanism, same effect. At least, that's what you'd expect.

Experiments in which men with erection problems were given L-arginine have not had very encouraging results. L-Arginine does not stay in the body for long, researchers believe. Some supplements manufacturers have tried to solve this problem by adding plant-based substances to boost the effect of arginine, but the Italians decided to try using L-citrulline. They gave their subjects a placebo for a month first, and then two doses of 750 g L-citrulline every day for a month.

At the start of the experiment the men's Erection Hardness Score was 3. They were able to have sex but their erection was not optimal.

As a result of L-citrulline supplementation, half of the men managed an Erection Hardness Score of 4. At the end of the experiment even the men for whom it didn't help still asked for a PDE-5 inhibitor. There were no side effects [AEs]. The researchers suspect that longer-term supplementation may have better results. An increased NO level in blood vessels can activate the hormone VEGF. VEGF stimulates the formation of new blood vessels. "Although less effective than PDE-5 inhibitors, at least in the short term, L-citrulline supplementation proved to be safe and was psychologically well accepted by patients", the doctors write. "Its role as an alternative and less expensive (less than 15 euro per month) treatment for mild to moderate erectile dysfunction, particularly for patients psychologically fearing PDE-5 inhibitors, deserves additional research."

Source:

Urology. 2011 Jan; 77(1): 119-22.

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