Effects of Watermelon on Blood Pressure

Prehypertension is a condition in which the blood pressure of an individual is just above the normal limit, but not high enough to diagnose the person as hypertensive. This study evaluated the utility of watermelon extracts in preventing the progression of prehypertension to hypertension. The researchers measured blood pressure in the aorta, as it is more representative of the load on the heart, than blood pressure measured in the arm. Along with aortic pressure, they also measured a few other parameters that are indirect measures of the stress on the heart. “In conclusion, we found that six weeks of watermelon supplementation improved aortic hemodynamics in middle-aged adults with prehypertension.”

Nitric oxide synthesized from the inner lining of blood vessels produces relaxation of blood vessels. Thus, it reduces the blood pressure. An amino acid L-arginine is necessary for the production of nitric oxide. L-arginine can be synthesized from another amino acid, L-citrulline. Watermelon is rich in L-citrulline and L-arginine. Many earlier experiments conducted on both humans and animals have shown that consumption of watermelon reduces blood pressure in both prehypertensive and hypertensive individuals. However, these experiments measured blood pressure in the arm only. Therefore, researchers of the present study aimed to evaluate the effect of watermelon consumption on aortic blood pressure. They also measured the augmentation index (pulse wave reflection) and femoral pulse wave velocity, which are better indicators of cardiovascular risk.

* The study included nine participants (five women and four men) aged around 55 years. All of them had marginally high blood pressure. Data regarding their dietary habits, physical activity, and body mass index were collected.
* Baseline measurements of aortic and arm blood pressure, augmentation index, and femoral pulse wave velocity were noted.
* The participants were divided into two groups. Test group received watermelon extracts, containing 1.35 g of L-citrulline and 0.65 g of L-arginine, twice every day. The control subjects also received a sweet drink not containing watermelon. This intervention was carried out for six weeks, after which a washout phase was observed.
* At the end of six weeks, aortic and arm blood pressure, augmentation index, and femoral pulse wave velocity were again measured in both the groups and were then compared.

* No side effects of watermelon consumption were observed during the study.
* Dietary habits, body mass index, and physical activity were almost similar between the participants in both the groups. Baseline parameters of aortic and arm blood pressure, augmentation index, and femoral pulse wave velocity were also similar.
* At the end of the intervention, significant improvement in blood pressure parameters was observed in the test group. Compared to the control group, those who consumed watermelon had their blood pressure in the arm reduced by 8 mm of Hg, aortic pressure reduced by 7 mm of Hg, and augmentation index reduced by six percent. No significant change was observed in femoral pulse wave velocity.

Shortcomings/Next steps
The sample size of this experiment (9) was too small for the findings to be generalized. Further larger clinical trials are necessary to confirm these findings. In this study, the levels of L-arginine and nitric oxide in blood were not measured. Such measurements would prove that L-citrulline present in watermelon is actually responsible for the reduction of blood pressure.

This pilot study indicates that six weeks of watermelon supplementation containing natural L-citrulline and L-arginine, reduced blood pressure measured in the arm and the aorta. It also improved the augmentation index in middle-aged individuals with prehypertension. Reduction in blood pressure reduces the load on the heart and prevents the progression of coronary heart disease. For hypertensive patients, watermelon extracts may be given in addition to their usual drugs. By using this adjunctive therapy, further rise in blood pressure and subsequent complications of hypertension can be prevented. Some studies on rats have shown that supplementation of L-arginine produces higher level of nitric oxide in blood. According to the researchers of present study, similar changes may occur even in humans upon consumption of watermelon.

For More Information:
Effects of Watermelon Supplementation on Aortic Blood Pressure in Individuals with Prehypertension
Publication Journal: American Journal of Hypertension, July 2010
By Arturo Figueroa; Marcos A Sanchez-Gonzalez
From the Florida State University, Tallahassee, Florida

*FYI Living Lab Reports Are Summaries of the Original Research.

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