Common food additive linked to increased susceptibility to influenza

09 Apr 2019 --- Regular consumption of the ubiquitous food additive tert-butylhydroquinone (tBHQ) may suppress immune responses to the flu virus. This is according to research from the American Society for Pharmacology and Experimental Therapeutics (ASPET). The tBHQ additive is used to extend shelf life, prevent rancidity and inhibit discoloration in food-grade products – but offers no health benefits. The study also found that tBHQ exposure could reduce the effectiveness of the influenza vaccine through its effects on T cells, a vital defense mechanism of the immune system.

The researchers say the connection may help explain why seasonal influenza continues to pose a major health threat globally, as an estimated 290,000-650,000 people die from flu-related respiratory problems each year. As T cells are involved in the immune response to a variety of diseases, it is suggested that tBHQ could also play a role in precipitating other types of infectious diseases.

When asked about the impact of tBHQ on the health of patients with immunodeficiencies, like HIV, lead researcher Robert Freeborn told NutritionInsight, “In the case of HIV, it is possible that tBHQ could impair the immune system and lead to opportunistic infections. However, this is completely speculation at this point.”

It is unclear how much tBHQ people are exposed to. However, researchers cited estimates based on model diets, which suggest that some US consumers eat almost double the recommended amount of tBHQ suggested by the Joint FAO/WHO Expert Committee on Food Additives. Moreover, people in other parts of the world may consume up to 11 times the recommended amount, they say. 

”It can be hard to know if you are consuming tBHQ, as it is not always listed on ingredient labels,” says Freeborn, adding that this is often the case when tBHQ is used in food preparation, such as in the oil used for frying. “The best way to limit tBHQ exposure is to be cognizant about food choices. Since tBHQ is largely used to stabilize fats, a low-fat diet and cutting down on processed snacks will help reduce tBHQ consumption.”

Study found that tBHQ suppresses T cells
Levels of tBHQ exposure in Freeborn’s studies fall within estimates of human exposure. The allowed concentration of tBHQ is 200 parts per million in food products. In the study, mice were fed tBHQ at a dose of 1.2 mg per kg each day (the daily average per animal). The mice were allowed to eat freely and the food was weighed daily to determine tBHQ exposure.

“Our studies showed that mice on a tBHQ diet had a weakened immune response to influenza infection,” says Freeborn. “In our mouse model, tBHQ suppressed the function of two types of T cells, helper and killer T cells. Ultimately, this led to more severe symptoms during a subsequent influenza infection.”

Helper T cells direct other parts of the immune system and help coordinate an appropriate response to the influenza virus, while killer T cells hunt down infected cells and clear them from the body. The researchers found that mice eating a tBHQ-spiked diet were slower to activate both helper T cells and killer T cells, resulting in slower clearance of the virus.

“Right now, my leading hypothesis is that tBHQ causes these effects by upregulating some proteins which are known to suppress the immune system,” explains Freeborn. 

“Expression of these proteins, CTLA-4 and IL-10, was upregulated in two different models we use in the lab. However, more work is necessary to determine if upregulation of these suppressive proteins is indeed causative for the effects of tBHQ during influenza infection.”

Moreover, when the mice were later re-infected with a different but related strain of influenza, those on the tBHQ diet experienced a prolonged 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 says. Since the memory response is central to how vaccines work, impairment of this function could potentially reduce the efficacy of the flu vaccine.

Freeborn emphasized that getting a yearly flu shot remains the best way to prevent influenza infection. While it is possible to contract the flu after receiving the vaccine, being vaccinated has been shown to significantly reduce the length and severity of the illness.

Building on their studies conducted in mice, the researchers plan to use human blood samples to further investigate how tBHQ affects T cell activity. 

Freeborn will present the research at the American Society for Pharmacology and Experimental Therapeutics annual meeting during the 2019 Experimental Biology meeting, held on April 6-9, 2019, in Orlando, Florida.

By Benjamin Ferrer