Consuming a large amount of nitrites from food additives versus none was associated with a greater risk of developing type 2 diabetes in the NutriNet-Santé study in France, researchers report.
However, a few experts who were not involved with this research question the strength of the findings because of study limitations.
The study involved more than 100,000 adults with a mean age of 43, and 79% were women.
Individuals with the highest intakes of nitrites from food additives (top third) had a 53% higher risk of developing type 2 diabetes during a median follow-up of 7 years compared with those with the lowest intake of this food additive after controlling for intake of sugars, red and processed meats, heme iron, salt, and saturated fatty acids. Consumption of nitrates from food additives was not associated with risk of type 2 diabetes.
“Our findings suggest a direct association between additives-originated nitrites and [type 2 diabetes] risk and corroborate previously suggested associations between total dietary nitrites and [type 2 diabetes],” the researchers report in an article published online in PLoS Medicine.
However, “as this is the first large-scale study finding these associations, these results need to be replicated in other large-scale cohorts,” senior author Mathilde Touvier, PhD, head of the Nutritional Epidemiology Research Team (EREN-CRESS), INSERM, INRAE, Sorbonne Paris Nord University, and lead author Bernard Srour, PhD, PharmD, a scientist at the same institution, said in a joint email to this news organization.
Short-term intervention studies to determine insulin resistance could also be tested, they add.
In the meantime, “this study adds further evidence to the existing strong link between nitrites and colorectal cancer risk, and supports the importance of further regulation of nitrites as food additives and nitrogen fertilizers,” they say.
According to Dr. Touvier and Dr. Srour, the takeaway message for clinicians is the finding that nitrites from food additives are associated with type 2 diabetes, “support existing guidelines recommending [limiting] the consumption of processed meats to prevent chronic diseases. However, the consumption of vegetables should be encouraged as they contain several beneficial compounds and contribute to chronic disease prevention.”
Some experts are skeptical
But three experts who were not involved with the research were skeptical about the conclusions, in comments made to the U.K. Science Media Centre.
“The fundamental weakness of this study is how the food additive intake was assessed,” said Tom Sanders, DSc, PhD, professor emeritus of nutrition and dietetics, King’s College London. “Estimates of intake were based on recalls of dietary intake on two separate occasions at the beginning of the study with no further estimates in the follow-up period of over 7 years,” he noted.
Other limitations include the relatively young age of the cohort and relatively low incidence of new cases of type 2 diabetes (about 1% of the study population over 7 years).
Moreover, the level of nitrite food additive ingestion is much lower than the acceptable daily intake. The findings would need to be replicated with appropriate adjustment for differences in body weight.
Gunter Kuhnle, PhD, professor of nutrition and food science, University of Reading, England, said that “the study does not support the claim in the press release and paper that food additives are responsible for the increased risk.”
He pointed out that “nitrite from additives contributes only about 4%-6% of total nitrite intake in the population, and it is not clear why this should have a stronger impact on risk than nitrite from other sources,” such as nitrate found in food and water.
Duane Mellor, PhD, registered dietitian and senior lecturer, Aston University, Birmingham, England, said: “It could be questioned how accurate estimating intakes of individual additives like sodium nitrite, which was less than 1 mg per day from a record of just 2 days food intake per year, as it assumes people ate the same the other 363 days of the year.”
Moreover, “it is perhaps worth noting that the use of nitrites as an additive is often as sodium nitrite, which is used to cure meats like bacon, which if someone is seeking to reduce their risk of type 2 diabetes would be something people would be encouraged to eat less of [anyway].”
“The best way to reduce your risk of developing type 2 diabetes,” he said, “is to be physically active, maintain a healthy weight for you, and eat a varied diet based on vegetables, pulses, nuts, seeds, and fruit along with wholegrain and moderate intakes of dairy foods and meat (especially processed meats).”