A common food additive found in many products, including frozen meat, crackers and fried foods, could weaken the human immune system against flu, which accounts for 290,000-650,000 deaths globally every year, say researchers.

Besides increasing the severity of flu symptoms, the study found exposure to the compound — tert-butylhydroquinone (tBHQ) — could reduce effectiveness of flu vaccine through its effects on T cells, a vital component of the immune system.

During the study, mice fed tBHQ-spiked diet were slower to activate both helper T cells and killer T cells, causing slower clearance of the virus.

“Our studies showed mice on a tBHQ diet had a weakened immune response to influenza (flu) infection,” said Robert Freeborn, postdoctoral candidate at the Michigan State University.

“In our mouse model, tBHQ suppressed function of helper and killer T cells. It led to more severe symptoms during a subsequent influenza infection,” Freeborn said.

When the mice were re-infected with a different but related strain of influenza, those on the tBHQ diet had a longer illness and lost more weight. This suggests that tBHQ impaired the “memory response” that typically primes the immune system to fight a second infection, Freeborn said.

tBHQ is an additive used to prevent spoilage, with a maximum allowed concentration of 200 parts per million in food products.

Since tBHQ is not always listed on ingredient labels, the best way to limit tBHQ exposure is to be conscious about food choices. A low-fat diet and less consumption of processed snacks will help reduce tBHQ consumption, he suggested.

Annual flu shot significantly reduces the length and severity of the illness and prevents influenza infection.

The study will be presented at the American Society for Pharmacology and Experimental Therapeutics annual meeting in Orlando.