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Definition: "An ergogenic aid is any substance or phenomenon that enhances performance "
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04.05.2011 |
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Men with cat-litter disease are manlier
About half of all men have cysts in their brains, heart and muscles that contain the single-celled parasite Toxoplasma gondii. The most likely origin of the parasite? Cats' droppings. According to parasitologists at Charles University in Prague, men who are infected with the parasite have higher testosterone levels.
Toxoplasma gondii starts its life cycle in a rat. In many rats the parasites live in cysts, where they do little harm – until they are eaten by a cat. Toxoplasma gondii can reproduce sexually in cats' intestines. Traces of the pathogen leave the cats' body through the excreta, and then find their way into humans' bodies, via the mouth. Common activities involved are gardening or cleaning a cat's litter tray. Another source is eating infected pork. Pork that has not been properly cooked may contain the parasite. That's not such a surprise, given that pigs are known to eat whatever comes their way: dead rats, living mice, cats that don't move fast enough, anything.
The Czechs suspect that the encapsulated organisms influence the hosts' behaviour, one mechanism contributing to this being via the male sex hormone testosterone. In 2008 they published a study in which they had measured the testosterone concentration in the saliva of 174 female and 91 male students. They then examined blood samples from the students to see whether they were infected with Toxoplasma gondii. The figure below shows that infected men had more testosterone in their saliva, but infected women had less.
Normally speaking, the human male's testosterone level is highest early in the morning and then declines throughout the rest of the day. This is the pattern recorded in the non-infected men [white circles], but it occurs less in the infected men [black circles].
According to the Czechs, the relationship between Toxoplasma gondii and testosterone is so strong that you can tell from the men's faces whether they are infected or not. The Czechs did an experiment: they showed women photos of 89 male students, of whom 18 were infected. [Neuro Endocrinol Lett. 2007 Apr; 28(2): 110-4.] The women described the faces of the infected men as 'more manly' and 'more dominant'.
It is not clear whether men can actually boost their testosterone levels by deliberately infecting themselves with Toxoplasma gondii. The Czechs will soon publish the results of an experiment in which they infected mice with Toxoplasma gondii. [Exp Parasitol. 2011 Mar 30. [Epub ahead of print].] In these animals the testosterone levels actually went down.
Maybe Toxoplasma gondii only raises the testosterone level after a delay. Or maybe the infection actually made the mice too ill to be able to produce much of the hormone, suggest the Czechs. They don't discount the possibility that infection doesn't raise testosterone levels at all, but that men with high testosterone levels are more easily infected. High testosterone production does partially deactivate the immune system.
Toxoplasma gondi infection is in no way healthy. Some studies have shown that infection by this parasite raises the chance of developing schizophrenia. [Schizophr Bull. 2007 May; 33(3): 741-4.] [Acta Psychiatr Scand. 2006 Jul; 114(1): 40-8.] [Schizophr Bull. 2007 May; 33(3): 782-8.] What's more, infected people are more often involved in traffic accidents. [BMC Infect Dis. 2009 May 26; 9:72.] [Forensic Sci Int. 2006 Nov 10; 163(1-2): 34-7.] The parasite probably delays reaction time.
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