Elderberry and the "Cytokine Storm" Myth: What the 2020 Concern Actually Was

In the spring of 2020, a widely-circulated claim warned that elderberry supplements could cause a "cytokine storm" in patients with COVID-19. The claim spread through wellness blogs, social media, and several news outlets, and many people abruptly stopped taking elderberry. The underlying scientific basis was much weaker than the warning implied — and the warning conflated specific in vitro signals with a clinical reality that hasn't been demonstrated.

The actual evidence behind the concern

The cytokine-storm claim traced primarily to a single in vitro study showing that elderberry extract increased TNF-α and several inflammatory cytokines in cell culture [1]. In vitro cytokine modulation is reported for many phytochemicals — green tea, turmeric, mushroom extracts — and is generally considered evidence of immunomodulatory activity, not of clinical pro-inflammatory harm. The 2020 viral message extrapolated cell-culture findings to a severe COVID-19 phenotype, a leap that the original investigators did not make.

What "cytokine storm" actually means

Cytokine release syndrome (sometimes called cytokine storm) is a specific clinical syndrome characterised by extreme systemic inflammatory response — markedly elevated IL-6, IL-1, TNF-α, and ferritin, leading to multi-organ failure. It is treated with IL-6 inhibitors (tocilizumab) and immunomodulators. Causing it requires more than mild upregulation of cytokine mRNA in a cell culture dish [2]. No clinical case series has linked elderberry to cytokine release syndrome, and no controlled trial of elderberry in COVID-19 has reported worsened outcomes.

What elderberry trials actually show

The largest body of evidence is in influenza, where small RCTs have reported shorter symptom duration with elderberry syrup or extract [3]. A 2019 meta-analysis of four RCTs in 180 participants found a modest reduction in upper respiratory symptom severity and duration with elderberry [4]. Effect sizes are small and trials are short. There is no clinical evidence that elderberry worsens any respiratory illness, including COVID-19.

The mechanism that gave rise to the concern

Elderberry phenolics, particularly cyanidin glycosides, do upregulate macrophage cytokine production in vitro. This is the same kind of immunomodulatory pattern seen with many polyphenol-rich foods, and it is the proposed basis for the antiviral effect — increasing innate immune response to clear viral infection. Translating that to harm in a clinical inflammatory condition requires evidence that has not been generated. The reasoning that links the in vitro cytokine signal to the COVID-19 cytokine storm is plausible-sounding but speculative.

What is actually true about elderberry safety

Raw, unripe elderberries contain cyanogenic glycosides and lectins that cause GI upset; commercially processed elderberry products are heated to inactivate these compounds and are safe at recommended doses [5]. The clinically observed adverse events from commercial elderberry are uncommon and mild. There are no documented serious adverse events from properly prepared elderberry in clinical trials.

The lesson, not the resolution

The COVID-19 elderberry scare is a case study in the gap between mechanistic in vitro plausibility and clinical risk. Many supplements have hypothetical immunomodulatory effects; very few of them produce demonstrable clinical harm in real patients. People with serious infections should consult clinicians about all medications and supplements, not because elderberry is dangerous, but because clinical care should not be guided by social-media-amplified speculation. For routine cold and flu use in otherwise healthy adults, elderberry has modest clinical evidence supporting symptom reduction and a benign safety profile.

What to do during active illness

The reasonable clinical position is: continuing routine elderberry use during a mild upper respiratory illness is not contraindicated. Stopping it during a severe inflammatory illness in hospital is sensible — not because of cytokine-storm risk, but because of the general principle that non-essential supplements with poorly-characterised pharmacokinetics are best paused in the ICU setting. The 2020 advisory itself has not been repeated by mainstream medical bodies and is now considered an over-interpretation of the in vitro data.