Scientists, including one of Indian origin, have found that people who suffer from migraines harbour significantly more microbes in their mouths which have with the ability to modify nitrates.
"There is this idea out there that certain foods trigger migraines - chocolate, wine and especially foods containing nitrates," said Antonio Gonzalez, from University of California, San Diego in the US.
"We thought that perhaps there are connections between what people are eating, their microbiomes and their experiences with migraines," said Gonzalez.
Nitrates, found in foods such as processed meats and green leafy vegetables and in certain medicines, can be reduced to nitrites by bacteria found in the mouth.
When circulating in the blood, these nitrites can then be converted to nitric oxide under certain conditions.
Nitric oxide can aid cardiovascular health by improving blood flow and reducing blood pressure.
However, roughly four in five cardiac patients who take nitrate-containing drugs for chest pain or congestive heart failure report severe headaches as a side effect.
Using publicly available data from the American Gut Project, a crowdfunded citizen science effort managed by Gonzalez and colleagues sequenced bacteria found in 172 oral samples and 1,996 fecal samples from healthy participants.
The participants had previously filled out surveys indicating whether they suffered from migraines.
The bacterial gene sequencing found that bacterial species were found in different abundances between people who get migraines (migraineurs) and non-migraineurs.
In terms of bacterial community composition, the team did not find huge differences in either fecal or oral samples from migraineurs compared to non-migraineurs.
Researchers, including Naseer Sangwan from the University of Chicago, then used a bioinformatic tool to analyse which genes were likely to be present in the two different sets of samples, given the bacterial species present.
In fecal samples, they found a slight but statistically significant increase in the abundance of genes that encode nitrate, nitrite and nitric oxide-related enzymes in migraineurs.
In oral samples, these genes were significantly more abundant in migraineurs.
The study was published in the journal mSystems.