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Probiotics attenuate inflammation-associated sickness behaviors.

The gut-brain axis, a bidirectional signaling pathway between the gastrointestinal tract and the nervous system, plays critical roles in human health. Key elements of this pathway are the tens of trillions of microbes that comprise the intestinal microbiota. Findings from a 2015 study suggest that probiotics attenuate inflammation-associated sickness behaviors.

Probiotics are typically defined as live microorganisms that, when consumed in sufficient amounts, confer a health benefit on the consumer. They contain a variety of microorganisms, but Lactobacillus and Bifidobacterium bacteria are among the most common. Probiotics can be found in yogurt, kefir, kimchi, and other fermented foods and are widely available as dietary supplements.

Sickness behaviors are adaptive behavioral changes that occur during infection or chronic inflammatory disorders and may include lethargy, depressed mood, appetite loss, sleepiness, pain, or confusion. Evidence suggests that tumor necrosis factor-alpha (TNF-alpha), a pro-inflammatory cytokine produced by immune cells, activates microglia (the brain’s resident immune cells) and recruits white blood cells to the brain, driving the development of inflammation-associated sickness behaviors.

The investigators used a model of liver inflammation in mice to study the effects of a probiotic on inflammation-associated sickness behavior. Mice with this form of liver inflammation typically have high levels of pro-inflammatory cytokines and exhibit distinct sickness behaviors. They fed the mice either a probiotic or a placebo and then they studied the animals' behavior. They also measured TNF-alpha levels in the animals' blood and the number of activated immune cells in the animals' brains.

They found that although the probiotic did not reduce the severity of liver inflammation in the mice, it did reduce sickness behaviors better than the placebo. Mice that received the probiotics also had lower TNF-alpha levels and fewer activated immune cells in their brains compared to mice that received a placebo.

These findings suggest that probiotics attenuate inflammation-associated sickness behaviors in mice, likely via modulation of the gut-brain axis. Learn about factors to consider when choosing a probiotic supplement in this clip featuring Dr. Jed Fahey.

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