Could an additive in your food be messing with the immune process that helps you fight off the flu after receiving the influenza vaccine?
Although the seasonal influenza vaccine remains an important tool in the prevention of flu transmission, and can mitigate the virus’ harsh symptoms if it is contracted, the illness still causes thousands of hospitalizations and deaths every year in the US. Vaccinated individuals are less likely to contract the flu, but it does happen. Now, a team of investigators at Michigan State University in East Lansing say they’ve discovered one possible reason for a loss of vaccine efficacy — a common food additive called Tert-butylhydroquinone, or tBHQ.
TBHQ is added to a variety of foods, including crackers, chips, cooking oils, and frozen meats and fish, to extend freshness. According to Cheryl Rockwell, PhD, an associate professor in pharmacology and toxicology and leader of the study team, it may not even be included on the list of ingredients even though chances are high that you consume it. “Nearly everyone who lives in industrialized countries has tBHQ in their diet,” Rockwell told Contagion®. “It is used to stabilize oils and fats in numerous food types that are commonly found at the grocery store.” But in mouse studies recently conducted by Rockwell and her team, tBHQ had a significant impact on the activation of T cells responsible for fighting off the flu.
According to Robert Freeborn, a fourth-year graduate student who also led the study, previous studies the team conducted demonstrated that tBHQ negatively impacted CD4 T cell activation. To test their theory that tBHQ impairs the T cell response to the flu, mice were funneled into 2 groups: 1 group was fed a substance containing tBHQ, and the other was fed a substance without tBHQ. Two weeks later, both groups were given a dose of influenza. The group receiving tBHQ had notable delays in T cell activation and lower levels of viral clearance. The team also discovered, after infecting the mice with an additional (different) strain of flu virus, that the tBHQ group took twice as long—6 days versus 3–to begin recovering from this second bout of flu. “This suggests that tBHQ impaired the memory response to infection with related strains of influenza virus, which would be expected to correlate with reduced vaccination efficacy,” Freeborn wrote in a recent summary of the study’s findings that he presented at the 2019 Experimental Biology meeting.
As far as how much tBHQ is needed to tamp down immune activation, the answer is: not much. “Our study shows that a low dose of tBHQ (0.0014%) hinders the immune response to influenza infection,” Rockwell said. “This concentration is equivalent to what is found in certain human and animal foods.” In his presentation, Freeborn noted that although the allowable daily intake of tBHQ is 0.7 mg/kg/day, estimates using sample diets indicate that people could be eating as much as 7.7 mg/kg/day, or 1,100% of the recommended amount.
The exact mechanism by which tBHQ impacts T cells is not yet known. “Our in vitro studies suggest that activation of a protein called Nrf2 may play a role in how these effects occur,” Rockwell said. “But subsequent studies are needed to determine this.” No further clinical studies on the effect of tBHQ and flu are planned at the moment, although Rockwell and her team are continuing to study tBHQ’s effect on human immune cells. One of her past studies found a correlation between tBHQ and human allergies, and tBHQ also has been controversial for its possible role as a cancer-causing agent.