The Dirt on Depression

(From the "humans are crazy" and "truth is stranger than fiction" departments...)

Want to be happy?  Try eating dirt... or at least dirty plants.

Seriously.

From an article in Discover magazine, "Is Dirt The New Prozac?":

The results so far suggest that simply inhaling M. vaccae—you get a dose just by taking a walk in the wild or rooting around in the garden—could help elicit a jolly state of mind. “You can also ingest mycobacteria either through water sources or through eating plants—lettuce that you pick from the garden, or carrots,” Lowry says.

Graham Rook, an immunologist at University College London and a coauthor of the paper, adds that depression itself may be in part an inflammatory disorder. By triggering the production of immune cells that curb the inflammatory reaction typical of allergies, M. vaccae may ease that inflammation and hence depression. Therapy with M. vaccae—or with drugs based on the bacterium’s molecular components—might someday be used to treat depression. “It’s not clear to me whether the way ahead will be drugs that circumvent the use of these bugs,” Rook says, “or whether it will be easier to say, ‘The hell with it, let’s use the bugs.’”

Given the way the industry works, we'll probably either see drugs, or somebody will patent the bacteria.  But that's sort of secondary.  The real point is that to the extent our current environment doesn't match our ancestral one, there are likely to be "bugs", no pun intended.

(The original study: “Identification of an Immune-Responsive Mesolimbocortical Serotonergic System: Potential Role in Regulation of Emotional Behavior,” by Christopher Lowry et al., published online on March 28 in Neuroscience.)

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Maybe this is why Japan has such a high suicide rate? They always take their shoes off when they go inside, lowering the soil bacteria count inside the home.

Japanese suicide rate while high isn't an outlier. It's just 10% higher than in Belgium, and nobody ever talks about causes of suicide among Belgians. There are even countries like Lithuania with suicide rate 60% higher than Japan.

Very interesting that China is the only country (that I noticed) where women have a higher suicide rate than men. In the Slavic countries men kill themselves ~5 times more often.

São Tomé and Príncipe too, but it's probably small sample effect.

But Chinese data surprises me - I would have guessed that skewed gender ratio would work to advantage of women, but the result is the opposite, so it must be something else going on.

Or are men just less competent at that? Googling says they make more suicide attempts:

Suicide has become one of the greatest health concerns worldwide. Statistics show that annually, an estimated total of 1 million people commit suicide, and the number of failed suicide attempts is more than 10 times the figure.

[...]

In terms of suicide attempts, rural areas outnumber urban areasand males outnumber females. The young and the old stand at the forefront, Zhang Zhou added.

I've read that, in the U.S., women make more suicide attempts than men, but are more likely to survive them, because men tend to use more lethal methods. (Women are less likely to try to kill themselves using a gun, for example.)

According to that article and some others most suicide attempts in China are unplanned and involve self-poisoning. Perhaps men having larger bodies are less likely to succeed.

So I wonder how much cross-country variability is about variability in suicide attempt rates, and how much due to different techniques used.

For some reason, European countries speaking Finno-Ugric langauges have high suicide rates:

It doesn't seem so, Estonia has a lot lower rate than nearby Latvia, Lithuania, Russia, and Belarus.

Hungary has slightly lower rate than its Slavic neighbour Slovenia. Its other neighbours Croatia and Serbia and Montenegro have fairy high rates too.

Finland has higher suicide rate than Sweden and Norway, but much lower than its other neighbour Russia, and comparable with nearby Estonia.

These facts are pretty good counter-evidence for the theory that there's some special Finno-Ugric - suicide connection.

These facts are pretty good counter-evidence for the theory that there's some special Finno-Ugric - suicide connection.

A single tear rolls down the cheek of Benjamin Whorf's ghost.

This experiment extended a theoretical framework of depression, elegantly demonstrating a plausible mechanism to explain a link between immune function and emotional outcomes that had previously been observed in humans.

It does NOT provide a good reason to eat dirty salad. I'm not a microbiologist, but from personal experience I can state that salmonella has a negative impact on mood.

I once thought I had mono for a whole decade - turns out I was just short on M. vaccae.

I hadn't seen that about depression before, but that many chronic diseases are caused by yet undiscovered infectious agents has been around for a while. There is a good, very readable survey of the idea "Plague Time" by Paul Ewald written in 2000 and 2002 (http://www.amazon.com/Plague-Time-Germ-Theory-Disease/dp/0385721846/ref=sr_1_1?ie=UTF8&s=books&qid=1247684918&sr=8-1). The idea has been around for decades, but received a new boost when peptic ulcers were shown to be bacterial.

I hadn't seen that about depression before, but that many chronic diseases are caused by yet undiscovered infectious agents has been around for a while.

You've completely reversed the idea of the article: this is an infectious agent that cures a chronic disease (depression), rather than causing one. And it's an interesting explanation for why "getting out in nature" might help people be less depressed, besides a change of pace and some sunshine.

Maybe, but "may be in part an inflammatory disorder" suggests that it may be caused by bacterial agents. Ewald made the same point about arterial plaques may be caused by bacteria and that aspirin's effect at reducing heart attacks may be from its anti-inflammatory effects.

That peptic ulcers are most commonly caused by bacteria triggers an absolute denial macro in some people, I've noticed. I was fascinated when I learned that helicobacter pylor was found to be the primary cause of stomach ulcers, but it really seems to put some people off. I've had a conversation like this more than once:

"I'm so stressed at work I'm going to get an ulcer."

"Did you know that most stomach ulcers are actually caused by bacterial infection?"

"Stress causes ulcers."

"No, really; not too long ago a certain bacteria was shown to cause the majority of peptic ulcers."

"Well stress makes you more susceptible to the infection then."

"That could be, but I don't know how much evidence there is for that..."

"My grandfather had ulcers; they were caused by stress."

"I'm just saying the majority of stomach ulcers aren't..."

"But some are caused by stress."

"I think they're correlated, but maybe the people who have ulcers are more under more stress because their stomach is bleeding?"

"I don't think that's very likely."

sigh...

Huh. So apparently some people actually still believe that -- I had always taken “so stressed I'm going to get an ulcer” to be just a figure of speech.

I haven't read the book, but the Atlantic had a series with Ewald & Greg Cochran on "New Germ Theory".