Substance present in onions may be an ally of cardiovascular health

Despite its unfamiliar name, quercetin can be easily found in the supermarket produce section. Besides appearing in onions, it's also present in bell peppers, asparagus, broccoli, and fruits like apples, grapes, and mangoes. It's also present in other research areas, where it's been investigated for its potential health benefits.

One of the recent studies, carried out by scientists from Poland, was published in May in the scientific journal Nutrients and presents a review of 92 studies, demonstrating mechanisms related to cardiovascular protection.

There's evidence that quercetin helps preserve the endothelium, a cell membrane that lines the inside of blood vessels, and that it contributes to increased production of nitric oxide, a vasodilator. These effects affect vascular elasticity and may help control blood pressure. The article also mentions the substance's impact on cholesterol levels, reducing the risk of atherosclerosis, or the clogging of blood vessels.

Behind these actions, its antioxidant and anti-inflammatory properties stand out. The study shows that quercetin helps neutralize free radicals, molecules that, in excess, cause cellular damage. This action mitigates oxidative stress, preserving arterial cells, among other things.

The anti-inflammatory action also benefits blood vessels. The authors cite mechanisms such as reducing the activity of cytokines and other pro-inflammatory substances.

However, even with so much evidence of protective effects, the review emphasizes that much of the work was conducted on cells, under microscopes, and in animal models. "One of the limitations of the work is the scarcity of large clinical trials with humans," notes nutritionist Júlia Forti Roque of Einstein Hospital Israelita.

Another negative factor, discussed in the text, is quercetin's low bioavailability—that is, its ability to be absorbed and utilized by the human body. "But the substance has promising potential, especially in the context of chronic diseases," the nutritionist opines.

Protective group

Quercetin is a member of the polyphenols, a group with over 8,000 members cataloged to date. "These compounds are classified as secondary metabolites," explains biologist Nicholas Vannuchi, who researches several classes of polyphenols at the laboratory of the Federal University of São Paulo (Unifesp), Baixada Santista campus.

These are substances synthesized by plants to protect them in adverse natural situations. They protect against ultraviolet rays and adverse weather conditions, whether during drought or heavy rain. "They also help combat fungi and pathogens that can harm plants," says Vannuchi.

Unlike other polyphenols, quercetin is not a pigment. "And it's sensitive to heat," the biologist points out. Therefore, the suggestion to reap its benefits is to avoid cooking food or to quickly steam it. "One strategy that optimizes its use is to combine it with sources of healthy fat, such as olive oil or avocado," suggests the Einstein nutritionist.

A guacamole recipe might be a good option, as would a vinaigrette with olive oil. It's also worth using red onions, which have a higher concentration of the substance, especially the layer just below the skin.

Combining it with vitamin C sources, such as citrus fruits, is another trick to get the most out of it. "It's also recommended to spread your intake throughout the day to keep quercetin circulating in your body," says Vannuchi.

Finally, it's always worth emphasizing that there's no point in relying on quercetin if your lifestyle is unhealthy. Cardiovascular protection only occurs when your diet is balanced, with plenty of fruits, vegetables, whole grains, seeds, beans, nuts, and the like. Daily physical activity, good sleep, and stress management also count.

Source: Einstein Agency

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