Elderberry syrup is a natural immune booster, and it seems like everyone, from health enthusiasts to celebrities like Gisele Bündchen, is raving about its benefits.

But what exactly is elderberry syrup?

Elderberries are small, dark purple berries that grow on the elderberry tree, and they have been used for centuries as a natural remedy for colds, flu, and other respiratory ailments. The berries are rich in antioxidants and vitamins, making them a powerful immune booster.

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To make elderberry syrup, the berries are cooked down and then strained to create a concentrated liquid that can be taken by the spoonful or added to drinks. Some people mix elderberry syrup with honey and other ingredients to create a tasty and nutritious tonic.

Bündchen loves to add Gaia Herbs‘ Black Elderberry Syrup to her smoothies. “The elderberry syrup is something I’ve been taking for 20 years. Elderberries are a great immune booster,” she told People.

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She regularly gives it to her children to prevent colds. “When I lived in Boston ... that was my little secret weapon. So anytime [we] start getting a cold, I would just get all of us at the house just a big spoon of elderberry syrup in the morning before the kids went to school,” she says of the two children she shares with Tom Brady, son Benjamin Rein, 14, and daughter Vivian Lake. “It really helped them not get sick.”

So, what are the benefits of elderberry syrup?

Studies have shown that elderberries contain compounds that can help to reduce inflammation, boost the immune system, and even fight off viruses like the flu. Some people also use elderberry syrup to help with allergies, sinus infections, and other respiratory issues.

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Choosing a high-quality product from a reputable source is important if you’re interested in trying elderberry syrup. You can also make your elderberry syrup at home using dried elderberries and other natural ingredients.