Watermelon may cut blood pressure — and nudge blood sugar up

Fruit-based approaches to heart health attract plenty of claims but relatively little pooled trial evidence, and watermelon is a good example. It has been studied for effects on blood pressure, cholesterol and other cardiovascular risk factors in a scatter of small randomised trials, with no clear consensus emerging. Cardiovascular risk factors such as systolic blood pressure and LDL cholesterol are among the most consequential numbers in preventive health. This meta-analysis set out to establish what the randomised evidence, taken together, actually says about watermelon and these markers.

The authors searched the Cochrane Library, ISI Web of Science, PubMed and Scopus up to March 2022 for randomised controlled trials of watermelon supplementation. From 8962 identified studies, 9 RCTs qualified for the final analysis. A random-effects model computed weighted mean differences across a wide panel of outcomes — blood pressure, heart rate, lipids, fasting blood sugar, insulin, BMI, body fat, arginine and the inflammatory marker CRP — with standard methods applied to examine publication bias, sensitivity and heterogeneity.

Watermelon consumption significantly decreased systolic blood pressure, total cholesterol and LDL cholesterol across the pooled trials. Less conveniently, it also led to a significant increase in fasting blood sugar. A long list of other outcomes did not change significantly: diastolic blood pressure, heart rate, BMI, body fat, and serum levels of arginine, insulin and CRP were all unmoved. The authors describe the blood-pressure finding as promising evidence of an antihypertensive effect, while explicitly urging caution on the remaining outcomes given the thinness of the human evidence.

This is a rare attempt to pool the randomised watermelon literature, and it lands with a genuinely mixed verdict: favourable movement in blood pressure and two lipid measures, an unfavourable shift in fasting glucose, and mostly null results elsewhere. That blend complicates any simple 'watermelon is heart-healthy' message. The authors call for further RCTs with longer follow-ups and larger sample sizes before firm conclusions are drawn, and the fasting blood sugar signal in particular deserves clarification in future work.

For anyone interested in food-first ways of supporting cardiovascular health, this analysis offers a cautiously encouraging signal for watermelon on systolic blood pressure, total cholesterol and LDL. The accompanying rise in fasting blood sugar is worth knowing about, particularly for readers who watch their glucose numbers. Neither finding is definitive: only 9 trials contributed, and the authors themselves flag the results as needing confirmation. This is a reason to see watermelon's cardiovascular story as promising but unfinished, not settled.