"Research shows [migraine] sufferers have higher levels of bacteria involved in processing nitrates, and could explain why some foods appear to act as migraine triggers," The Guardian reports.
Nitrates are found in processed meats, like bacon, as well as some wines and chocolate.
The story is based on a study that used data from the American Gut Project. This is an ongoing project exploring the connections between the human microbiome – the "bacterial ecosystem" inside the body – and health.
Researchers examined the data to see whether the type of bacteria in the mouth and upper throat (the oral cavity) and poo (faecal) samples taken from healthy participants were linked to migraines.
Nitrates from our food are broken down by certain types of bacteria. They are eventually turned into nitric oxide in the bloodstream, which has been associated with headaches.
This research suggests migraine sufferers have higher levels of these bacteria in their oral cavity and therefore higher levels of nitric oxide.
But this is based on samples taken from just six people who suffer from migraines, so it is not reliable.
Faecal samples from 171 migraine sufferers also indicated a slightly higher number of these types of bacteria, but no further details were provided by the researchers.
The researchers hope to develop a "migraine mouthwash" that could remove the bacteria from the oral cavity, but this is currently just an aspiration.
If you have experienced migraines after eating nitrate-rich foods, it's probably a good idea to avoid them in future, delicious as they may be.
Where did the story come from?
The study was carried out by researchers from the University of California San Diego and the University of Chicago. The paper does not acknowledge any sources of funding.
Coverage of the study was generally accurate, although The Guardian, the Daily Mail and The Sun all report gut bacteria could be causing migraines, when the samples of bacteria investigated were actually taken from either faecal samples or the oral cavity. The researchers do not mention samples taken from the gut itself.
Also, none of the papers reported the extremely small number of oral samples taken from people who have migraines, which is not enough for us to have any confidence in the results.
While it's plausible that nitrate-rich food could trigger migraines in people with this type of bacteria, the study did not actually look at this issue directly.
What kind of research was this?
This was a cross-sectional analysis of data from the American Gut Project. The project is one of the world's largest microbiome research projects, exploring the connections between the human microbiome and health.
The study aimed to use this data to explore the link between migraines and bacteria that convert nitrates from food into nitrite and nitric oxide.
As it is a cross-sectional study, it can suggest an association, but cannot prove causation: that the bacteria in the oral cavity and faecal samples directly cause migraines.
What did the research involve?
The researchers used the publicly available data from the American Gut Project to look for a link between bacteria that increase levels of nitric oxide and migraines.
They aimed to see whether bacteria that convert nitrate from food into nitrite and nitric oxide were more abundant in the oral cavity and faecal samples taken from migraine sufferers, compared with non-sufferers.
The researchers examined 172 oral samples and 1,996 faecal samples from healthy participants. Prior to this, participants had completed surveys to say whether they suffered from migraines or not.
They used gene sequencing techniques to categorise what types of bacteria were present in the samples, and their number.
What were the basic results?
Six migraine sufferers had, on average, significantly more bacteria that convert nitrates in their oral cavity than 166 people who did not report suffering from migraines.
The levels were also slightly higher in faecal samples from 171 migraine sufferers, compared with 1,825 people who do not have migraines.
How did the researchers interpret the results?
The researchers concluded that the results "show for the first time a potential link between bacterial nitrate, nitrite, and nitric oxide reducers and migraines, by reporting their higher abundances in the oral cavities of people with migraines than in the oral cavities of those who do not suffer from migraines."
They also suggested that, "Future studies should focus on further characterising the connection between oral bacterial nitrate, nitrite, and nitric oxide reducers and migraines."
This study shows an association between migraines and bacteria that reduce nitrates in faecal samples.
But the small number of oral samples taken from people who suffer from migraines means we don't know if there is an association with the type and number of oral bacteria. With such a small sample, any possible association could be the result of chance.
While it is an interesting hypothesis, further work is needed to more fully explore if such a link exists before we can think about any potential treatments, such as a "migraine mouthwash".
If you suffer from migraines, identifying and avoiding triggers can reduce their frequency. Keeping a diary can be a useful start, recording your activity, sleep, stress levels, and food and drink intake.
Drug treatments are also effective for some people, including triptans, which aims to stop the dilation of blood vessels. Other options include taking non-steroidal anti-inflammatory drugs, such as ibuprofen, and the anti-epilepsy drug, topiramate.