People who suffer migraines are more likely to have bacteria that turn nitrates (NO3-) to nitrites (NO2-) and nitric oxide in their mouths. The association does not prove that the bacteria cause the headaches, but the strength of the correlation does suggest some connection.
"There is this idea out there that certain foods trigger migraines – chocolate, wine, and especially foods containing nitrates," said Antonio Gonzalez of the University of California, San Diego, in a statement. "We thought that perhaps there was a connection between someone's microbiome and what they were eating."
While human cells cannot turn nitrate to nitrite, many bacteria can. This nitrite can then be converted into nitric oxide, which may improve blood flow.
Gut microbes are increasingly being linked to many aspects of our health. Gonzalez tested the genome of the microbes present in the intestines of 1,996 people, but also looked at those from 172 individuals' mouths. Both groups had responded to surveys about whether they suffered from migraines.
Gonzalez found no major differences in the microbial species inhabiting the bodies of so-called “migraineurs” from those who are migraine-free, but the examination of specific genes proved more fruitful.
Recent work has suggested that nitrate-reducing organisms in the gut may be more important than previously recognized, but fecal samples providing information on participants' gut bacteria revealed only small, although statistically significant, differences between the migraineurs and non-migraineurs. The gap was much larger for the oral microbes, however. Nitrate-reducing genes were almost 100 times as common in bacteria from the mouths of people who reported suffering migraines than those who were migraine-free. Genes for reducing nitrites and nitric oxide showed similar discrepancies.
Besides being found in foods as diverse as leafy vegetables and cured meats, nitrates are a big part of cardiac medications, with headaches as a common side-effect. These can manifest as either mild to medium pain within an hour of nitrate consumption or more severe migraines three to six hours later. The swift-onset headaches, at least, appear to be associated with nitric oxide (NO), which causes veins to dilate.
Gonzalez published the findings in mSystems, a new peer-reviewed journal, but one launched by the American Society for Microbiology, unlike many of the less credible newly founded journals.
The research did not explore how some people come to have hundreds of times more nitrate-reducing bacteria in their mouths than others, nor the frequency of nitrate-heavy foods as a trigger, compared to all the other causes of migraines.
Even if mouth microbes are proven to be the culprit, eradicating them may prove problematic. The conversion of nitrates to nitric oxide is thought to benefit cardiac health, the reason nitrates are included in heart medications in the first place. Nevertheless, it may be possible for those not at risk of heart disease to judiciously reduce the concentrations of relevant bacteria.
One day, Gonzales hopes that "we will have a magical probiotic mouthwash for everyone that helps your cardiovascular health without giving you migraines." For the moment, however, he recommends that those prone to migraines change their diet.
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