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   Gut Feeling? Probiotics May Ease Anxiety and Depression   
      
      
      
   by Rachael Rettner, Senior Writer   
   Date: 24 December 2014 Time: 09:01 AM ET   
        
   A woman looks at her yogurt cup.   
   The plethora of microbes living in the human gut not only affect people's   
   physical health, they may also influence mental health, according to a growing   
   body of research.   
   Recent studies in animals show that changes in the gut bacteria community   
   appear to make mice less anxious, and also affect levels of the stress hormone   
   cortisol.   
   In humans, there is some very early evidence of a link between gut bacteria   
   and mental health. A new study from England found that supplements that boost   
   "good" bacteria in the gut (called "prebiotics") may alter the way people   
   process emotional    
   information, suggesting that changes in gut bacteria may have anti-anxiety   
   effects.   
      
   Scientists are now interested in studying whether probiotics (strains of good   
   bacteria) or prebiotics (carbohydrates that serve as food for those bacteria)   
   could be used to treat anxiety or depression, or if the substances improve   
   patients' response to    
   psychiatric drugs, said study author Philip Burnet, a researcher in the   
   University of Oxford's department of psychiatry. [5 Ways Gut Bacteria Affect   
   Your Health]   
   But experts caution that the idea that taking a probiotic or a prebiotic could   
   improve mental health in humans is still an unproven hypothesis that needs to   
   be investigated with further research.   
   "It's becoming a very interesting question in the field," said Dr. Roger   
   McIntyre, a professor of psychiatry and pharmacology at the University of   
   Toronto. "The animal data looks really interesting, and looks very suggestive,   
   [but] we're still waiting    
   for that convincing human study," McIntyre said.   
   Could bacteria reduce anxiety?   
   In the new study from England, 45 healthypeople ages 18 to 45 took either a   
   prebiotic or a placebo, every day for three weeks. At the end of the study,   
   they completed several computer tests to assess how they processed emotional   
   information, such as    
   negative and positive words.   
   During one computer test, people who took the prebiotic paid less attention to   
   negative information, and more attention to positive information, compared   
   with people who took a placebo. A similar effect has been seen in people who   
   take drugs for    
   depression or anxiety, and the finding suggests that the people in the   
   prebiotic group had "less anxiety about negative or threatening stimuli,"   
   Burnet said.   
   The study also found that people who took the prebiotics had lower levels of   
   cortisol in their saliva when they woke up in the morning, compared with   
   people who took a placebo. High cortisol levels have been linked with stress,   
   anxiety and depression,    
   Burnet said. The study was published in the Dec. 3 issue of the journal   
   Psychopharmacology, and was funded in part by Clasado Research Services, which   
   makes prebiotics.   
   The researchers said they did not find any change in the study participants'   
   self-rated levels of stress and anxiety. This may have been because the   
   participants did not take the prebiotic long enough to have an effect, or   
   because they already had fairly    
   low levels of stress and anxiety to begin with, Burnet said.   
   However, a 2011 study from France found that people who took probiotics for 30   
   days did have reduced levels of psychological distress. Because this is just   
   one study, its findings need to be confirmed in future research.   
   In a 2013 study, UCLA researchers gave women milk with or without probiotics,   
   and then scanned their brains while they viewed photos of people with   
   emotional facial expressions. Those who took the probiotics had less activity   
   in their brains in areas    
   involved in processing emotions, compared with those who did not take the   
   probiotic.   
   Behind the link   
   Researchers aren't sure exactly how changes in gut bacteria might affect the   
   brain. Some researchers suspect that the vagus nerve -- which conveys sensory   
   information from the gut to the brain -- plays a role. Gut bacteria may also   
   affect the immune    
   system, which could, in turn, influence the brain, Burnet said.   
   A recent study by McIntyre and colleagues found that giving people the   
   antibiotic minocycline reduced symptoms of depression. However, because the   
   study did not analyze participants' gut microbes, it's not known whether the   
   effect on depression was due    
   to changes in gut bacteria, or a different mechanism, McIntyre said. The study   
   has not yet been published.   
   McIntyre said future studies are needed to better understand whether gut   
   microbes play a role in psychiatric disorders, like depression and anxiety,   
   and which bacteria species are important.   
   Follow Rachael Rettner @RachaelRettner. Follow Live Science @livescience,   
   Facebook & Google+. Original article on Live Science.   
      
      
      
      
      
   http://m.livescience.com/49248-gut-bacteria-mental-health.html   
      
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