Can Bacteria (Probiotics) Make You Happier?

For most of us, how we feel varies from day to day. On a good day you may feel happy or confident, and on a bad day you may be depressed or anxious. As it turns out, mood can have serious effects; in fact, negative mood can increase the risk of heart attack or stroke in people with cardiac conditions. As we age, it’s common for mood to decline, especially after age 80. Aging is also associated with increased rates of depression, a state of prolonged negative mood and sadness. So, how can we improve our mood and feel happier as we age?

Many factors contribute to mood—including signals from our bodies and the environment—and scientists are very interested in this topic. One hot area of research is the “gut-brain axis,” a communication pathway that sends signals between the intestines and the brain, and the influence of the microbiome—the population of bacteria that inhabit the intestines. Each of us has a variety of healthy bacteria that live in the gut and help with many aspects of digestion and nutrient uptake. As we age, the composition of the microbiome changes, and scientists now think this change may contribute to age-related declines in health.

So, can “fixing” the microbiome improve mood? Well, one way to alter the microbiome is to eat or take probiotics (healthy bacteria like those found in yogurt). Traditionally, probiotics have been marketed as a supplement intended to improve digestive health or boost immune function. But new research suggests that probiotics may have a number of other effects on the body—one of which might be improving mood.

A number of studies in mice and other animals suggest that probiotics may reduce anxiety and depression. In fact, a daily dose of probiotics has been shown to reduce depression symptoms in rats that had heart attacks or experienced stress. Probiotics also decrease anxiety and stress in mice. Based on these findings, researchers have started to test the effects of probiotics on mood in people. So far, only a few studies have been done, but they are promising. For example, one recent study found that 30 days of daily probiotic use improved mood in healthy adults.

So, What About Aging…?
Other evidence suggests that probiotics may also improve mood in older adults. In one study, researchers examined the effects of probiotics on 124 subjects aged 48 to 79. For 20 days, the subjects drank a daily dose of either plain milk or milk containing probiotics. Throughout the experiment, the researchers asked subjects to describe their mood. Subjects who said they were happy before the experiment did not report an increase in happiness, but subjects who said they were depressed experienced a positive change in mood after 20 days of the probiotics. The most common improvements were on measures of clearheadedness, confidence and general happiness (vs. sadness). Interestingly, although the researchers anticipated that these changes might be associated with improvements in gastrointestinal function (another effect of probiotics), this was not the case in most subjects.

Probiotics just might have the potential to combat the increased rates of depression we see in older adults. However, only a few studies really support this idea. There is not yet enough evidence to determine exactly how much of a probiotic—and which kind you need—to change the microbiome “just right.” The studies discussed here focused on the bacterial strains lactobacillus and bifidobacterium, but there are many more probiotic bacteria available as supplements—and food products such as yogurt contain combinations of bacteria. Scientists do believe that lactobacillus and bifidobacterium are important probiotics, but more research is needed to determine if a combination of bacteria may be beneficial. Therefore, while the evidence suggests that daily use of probiotics may have a positive effect on mood, more research is needed, and for now we can’t recommend probiotics as a sure thing.

Contributing authors: Lauren Cuevas, Thomas Moehlman, and Jamie Richey

(Feature image: Each of us has a variety of healthy bacteria that live in the gut and help with many aspects of digestion and nutrient uptake. As we age, the composition of the microbiome changes, and scientists now think this change may contribute to age-related declines in health. Image by Dawn Hudson, publicdomainpictures.net)

Tom LaRocca

Tom LaRocca, Ph.D., is a research associate and instructor in the Department of Integrative Physiology at the University of Colorado Boulder.