If you have ever eaten ripe elderberries or made elderberry jam, syrup, or wine, then you will be familiar with their sharp, tart, yet refreshing taste. According to tradition, these dark, purple berries can fortify a person’s immune system. New evidence suggests this is correct — and research explain how.

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Elderberries really do have antiviral properties, and a new study explains why.

Sambucus nigra, the black elder, is a common shrub spread widely across regions of Europe and North America.

Traditionally, people use both the elder’s flowers and its fruit to make seasonal drinks or jam.

In late spring or early summer, many people collect elderflowers to make flavorsome cordials, while the elderberry harvest occurs in late summer or early autumn when the fruit is ripe.

The harvesting time is important because uncooked, unripe elderberries can be toxic. Historically, individuals have reported cases of elderberry poisoning, which may have been due to too early harvesting or improper preparation.

For instance, the Centers for Disease Control and Prevention (CDC) recorded the case of no fewer than 11 people who fell sick after having drunk elderberry juice from the same batch.

The report explains that the shrub’s “fresh leaves, flowers, bark, young buds, and roots contain a bitter alkaloid and also a glucoside that, under certain conditions, can produce hydrocyanic acid,” which is a type of cyanide.

Nevertheless, elderberry drinks and desserts have remained a familiar culinary staple in many communities. Moreover, some people believe that elderberries can help fortify a person’s immune system and guard against disease.

According to a new study that researchers from the University of Sydney in Australia conducted, elderberries really do have antiviral properties, and they can fight a virus once an infection has already occurred.

In a study paper that appears in the Journal of Functional Foods, the investigators report that substances present in elderberries can stop an influenza virus from entering and replicating in human cells.

“What our study has shown is that the common elderberry has a potent direct antiviral effect against the flu virus,” says one of the study’s co-authors, Golnoosh Torabian, Ph.D.

“It inhibits the early stages of an infection by blocking key viral proteins responsible for both the viral attachment and entry into the host cells,” the scientist continues.

In their study, the researchers examined the effect of commercially farmed elderberries that they processed into a serum. This the investigators administered to cells at multiple different stages of the influenza cycle, including before infection with a flu virus and during infection.

The scientists found that the phytochemicals — the natural, plant-derived substances that the elderberry serum contained — had a “mild inhibitory effect” when the flu virus was just about to infect a cell.

However, once a cell already contained infection, the same chemicals were significantly effective in stopping the virus from propagating.

“This observation was quite surprising and rather significant because blocking the viral cycle at several stages has a higher chance of inhibiting the viral infection,” says co-author Peter Valtchev, Ph.D.

Moreover, the researchers explain that applying the elderberry solution also boosted the cells’ own reaction against the attacking virus.

In addition to that, we identified that the elderberry solution also stimulated the cells to release certain cytokines, which are chemical messengers that the immune system uses for communication between different cell types to coordinate a more efficient response against the invading pathogen.”

Prof. Fariba Deghani

The researchers explain that the antiviral properties of elderberries are due to the anthocyanidins — plant pigments — it contains. According to other research, anthocyanidins also have an antioxidant effect, meaning that they can protect cells from becoming damaged.