A chemical widely used in food preservation is implicated in an uptick in recent UK deaths by suicide, with a disproportionately high number of cases among young people and boys/men, finds a comprehensive analysis of available data for the period 2019-24, published in the open access journal BMJ Public Health.
There's now an urgent public health need to review unrestricted access to this source, to avoid further preventable deaths, say the researchers.
Rates of death by suicide have been falling across the UK since the early 1990s. But there is some evidence of a recent uptick in the numbers, coinciding with increasing reports of suicide associated with sodium nitrite poisoning around the world, they explain.
To find out if this form of poisoning is implicated in deaths by suicide in the UK, the researchers retrospectively analysed the details of cases submitted by coroners, forensic pathologists, and police forces between March 2019 and August 2024 to the primary UK laboratory that assesses nitrite and its oxidised metabolite, nitrate, in postmortem samples.
During this period, the laboratory received 274 samples from 201 cases of suspected deliberate or unintentional poisoning from across the UK, Ireland, and Gibraltar.
Most of these cases came from Greater London, South East England, Ireland, and the Midlands, although these figures may reflect coroner awareness rather than true incidence, caution the researchers.
The number of cases rose substantially after 2019, the first year samples were received for nitrite/nitrate assessment.
The final analysis included only the data for which coroners granted permission for use— 82% (164) of the cases received between 2019 and 2024.
The average age of these cases was 28, but ranged from 14–74 for males and 17–82 for females. Nearly three quarters (71%) of all the cases were among younger generations: Gen Z (33%; born 1981-96); and Millennials (38%; born 1997-2012, but listed up to 2005 to account for a separate category of minors, as 4% of cases were among those under the age of 18).
Overall, there were more men (109) than women (52) among the cases. And more than half of the cases in each generation were men, except for the oldest classified generation (Silent, born 1928-45), where the only case was that of a woman.
Levels of nitrite and nitrate found in the blood samples were 100 times higher than would be expected physiologically in 87% of cases, suggesting that swallowing the chemical was intentional, say the researchers.
The researchers highlight some caveats to their findings, including that because nitrite and nitrate analysis isn't routinely mandated for all suspected suicides, it's not clear exactly how many such deaths are caused by this chemical.
"It is therefore likely that the cases included here represent a substantial underestimate of the actual incidence. Secondly, the interval between death and sample receipt varied considerably, introducing the possibility that delays may have affected the accuracy of the biochemical measurements," they say.
Nevertheless, the observed rise in cases among predominantly young people, who tend to be tech savvy, is concerning, they suggest.
"Intentional poisoning has contributed to these recent increases, and at least in the USA, this rise has been partly attributed to the use (and availability) of sodium nitrite," they point out.
"This trend has emerged alongside freely accessible online information detailing how sodium nitrite can be obtained and used, disseminated both under the guise of providing mental health support and for more explicitly harmful purposes," they explain.
Their findings warrant urgent action, they suggest. "Collectively, these findings establish unequivocally that use of sodium nitrite in the UK as a method of suicide is both substantial and concerning," they write.
"Our data provide strong support for the suggestion that the improved digital literacy of younger people enables access to illicit online material promoting suicide practices and lends further support for calls for tighter legislation to prevent availability of such information in online forums," they add.
In the meantime, steps to mitigate the effects of this type of poisoning, such as the provision of an antidote (methylthioninium chloride kits) in ambulances would be "a simple and cost effective timely method to prevent the devastating consequences of ingestion," they point out.
*Lead researcher, Professor Amrita Ahluwalia, comments: "This is an extremely difficult subject to talk about, and we appreciate the impact that this might have on all those affected by suicide.
"What our research shows is deeply upsetting. But it makes clear why urgent steps are needed to regulate access to this chemical and to reduce the spread of harmful information about it online."
