Thursday September 1 2011
We cannot tell if yoghurt eases human depression
Bacteria found in yoghurt could stave off depression, according to the Daily Mail. The newspaper says that “good” bacteria found in the dairy product have the potential to alter brain chemistry and may help in the treatment of anxiety and depression-related disorders.
The news is based on a laboratory study that looked at the effects of feeding mice a type of “probiotic” bacteria called Lactobacillus rhamnosus. Probiotic bacteria are those that are thought to confer benefits to health, rather than being harmful. They are often found in fermented cultures such as yoghurt.
The study found that mice that were regularly fed the bacteria for a period of 28 days experienced certain chemical changes within the brain that were not seen in mice not fed lactobacillus. In particular, treated mice showed changes in the way their brains handled a chemical called GABA, which is involved in regulating many physiological and psychological processes. The mice fed the bacteria also had lower levels of a stress-related hormone called corticosterone and less anxiety and depression-like behaviour.
This type of early animal research does not show that probiotic yoghurts can help to treat depression in humans. Further testing is needed before they could be considered as a potential treatment for anxiety or depression. Anyone who thinks they may be suffering from a stress-related disorder is advised to see their GP.
Where did the story come from?
The study was carried out by researchers from St Joseph’s Healthcare and McMaster University, Canada and University College Cork, Ireland. Funding was provided by various organisations including Abbott Nutrition, a nutritional products company.
The study was published in the peer-reviewed journal, Proceedings of the National Academy of Sciences (PNAS) in the US.
The Daily Mail’s story perhaps overstated the positive results of the study, although it did mention that it was carried out in mice.
What kind of research was this?
The researchers say there is an increasing body of indirect evidence supporting a connection between bacteria living in the human gut and the functioning of the central nervous system (CNS). They say there is also some clinical evidence that probiotic bacteria can alleviate stress and improve mood and anxiety symptoms in patients with conditions such as irritable bowel syndrome. One type of probiotic bacteria, Lactobacillus rhamnosus, has also been found to have an effect on the immune system.
However, it is unknown whether the improvements in stress levels seen in previous research are due to actions such as the bacteria improving the functioning of the digestive system or if bacteria can actually directly affect the functions of the brain. In particular, say the researchers, it is uncertain if they can have a direct effect on neurotransmitter receptors in the CNS. Neurotransmitters are the chemicals that transmit messages between neurons (brain cells). Their receptors are molecules found on the surface of cells that pick up the chemical signals sent from other cells.
One major neurotransmitter called GABA is significantly involved in regulating many physiological and psychological processes, and alterations in the functioning of GABA receptors are implicated in the development of anxiety and depression. Anxiety and depression are also known often to accompany bowel disorders.
This was a controlled laboratory study in mice that looked at whether regularly feeding mice with the L rhamnosus bacteria had any effect on GABA receptor activity in the brain, on anxiety and depression-related behaviour and on the stress response.
What did the research involve?
The researchers used 36 adult male mice, divided into two groups. Mice in the control group were fed a broth without bacteria, while mice in the treatment group were fed a broth containing L rhamnosus. This procedure was carried out for a period of 28 days, between 8 and 9am each morning.
Towards the end of the treatment the animals underwent a series of behavioural tests designed to evaluate anxiety and depression in animals. For example, the behaviour of the mice in a maze, in an open space and in water was examined. Researchers also measured levels of the hormone corticosterone, which is considered to be a marker for stress.
The researchers then ran experiments looking at the role of the vagus nerve. The vagus nerve is a major nerve that carries information between the brain and many organs of the body, including organs in the gut. To find out if the nerve played a role in bringing about the possible effects of the bacteria they severed the vagus nerve of some of the mice. If mice no longer appeared to be less stressed when fed lactobacillus then it would support the idea that there is a neurological mechanism behind the effect of the bacteria.
The researchers later examined the brain tissue of the mice, using special chemical procedures to detect levels of GABA receptor functioning.
What were the basic results?
- The researchers found that in the behavioural tests, the mice fed L rhamnosus behaved in ways that suggested they were less stressed. For example, in the maze treated mice behaved in a way that suggested they had less anxiety, while in water (the forced swim test), treated mice spent significantly less time immobile (indicating lower levels of depression). The results of the behavioural tests did not always reach significance, however.
- Levels of stress-induced corticosterone levels were significantly lower in the treated mice than the control group.
- Levels of GABA receptor expression were different in the treated mice. The expression of certain receptors was found to be higher in certain parts of the brain (such as the cortical regions and the hippocampus) while other receptor expressions were lower.
- The behavioural and neurochemical effects seen in mice fed the broth were not found in mice who were fed the broth but had had their vagus nerve removed.
How did the researchers interpret the results?
The researchers say the findings highlight the important role of bacteria in communications between the gut and the brain, and suggest that probiotic bacteria may in future provide a useful therapeutic measure to be used alongside existing treatments for stress-related disorders such as anxiety and depression.
They conclude that the vagus nerve is the major communication pathway between the gut exposed to the bacteria and the brain.
This early laboratory study is of interest because it appears to show that mice treated with L rhamnosus bacteria undergo chemical changes within the brain. However, it does not show that probiotic bacteria or yoghurt can ease symptoms of stress-related disorders in humans. In the longer term there is the possibility that it could lead to the development of new treatments.
The following factors limit the implications of these findings in humans:
- The study was carried out in mice. The physiology of mice is clearly different from that of humans and they may react differently to probiotic bacteria.
- It is not clear how the amounts of bacteria fed to the mice would relate to the amounts of bacteria that are provided by probiotic yoghurts.
- The behavioural changes found in the treated mice fed the bacteria did not always reach significance.
- It is not clear if the neurochemical changes found in the treated mice were related to the behavioural changes found in the tests.
There are already effective treatments for anxiety and depression, both drug-based and psychotherapeutic. It is important for anyone with these disorders to get help and treatment.