Researchers suggest that sodium - which we commonly ingest through salt, or sodium chloride - could increase the risk of type 2 diabetes and latent autoimmune diabetes in adults.
Diabetes is a common condition that affects more than 29 million people in the United States, according to the Centers for Disease Control and Prevention (CDC). Type 2 diabetes accounts for up to 95 percent of all diagnosed cases and is characterized by abnormal levels of blood sugar.
This type of diabetes is most often diagnosed in middle-aged and senior people. Another metabolic condition called latent autoimmune diabetes in adults (LADA) is often misdiagnosed as type 2 diabetes; it also appears later in adulthood.
LADA is a more slowly progressing disease, and it does not initially require insulin treatment.
A new study conducted by Dr. Bahareh Rasouli, of the Institute of Environmental Medicine at the Karolinska Institutet in Stockholm, Sweden - in collaboration with researchers from other Swedish and Finnish institutions - now looks at the impact of sodium intake on the risk of type 2 diabetes and LADA.
Each extra gram of sodium increases risk
Existing research had already suggested that the sodium we usually absorb from our daily intake of salt may significantly increase the risk of developing type 2 diabetes.
The team explains that this may be because sodium impacts insulin resistance, but also because excess salt can lead to hypertension and gaining excess weight. But until now, no studies had looked at the impact of sodium intake on the risk of LADA.
"Given the autoimmune component of LADA," Dr. Rasouli explained to Medical News Today, "we hypothesized that a high-salt diet may accelerate autoimmunity and play a role in the pathogenesis [disease development] of LADA.
"Also," she added, "there are limited data on the association between sodium intake and the risk of type 2 diabetes. Therefore, we aimed to study the risk of LADA and type 2 diabetes in relation to sodium intake."
Dr. Rasouli and colleagues analyzed data from the Epidemiological Study of Risk Factors for LADA and Type 2 Diabetes, which is a large Swedish cohort study.
The team looked at data from 355 people diagnosed with LADA and 1,136 individuals with type 2 diabetes, comparing the results of this analysis with the findings from a healthy group of 1,379 individuals (the controls).
Questionnaires were used to collect information about the participants' daily diets. These data then allowed the team to calculate the daily caloric, nutrient, and sodium intake for each participant.
Dr. Rasouli and colleagues also took into consideration genetic risk factors for diabetes, and the participants were split into "high risk" and "other" categories depending on their genetic profile.
Confounding variables, including age, sex, body mass index (BMI), smoking, physical activity levels, and alcohol intake, were also adjusted for.
The researchers found that each extra gram of sodium (or 2.5 grams of salt) per day was linked to a 43 percent higher risk of type 2 diabetes. For LADA, each extra gram of sodium led to a 73 percent increase in developing the condition.
Participants were also divided into three groups depending on the quantity of their sodium intake. These were "low consumption" (for under 2.4 grams of sodium daily, or up to 6 grams of salt), "medium consumption" (2.4 to 3.15 grams of sodium, or up to 7.9 grams of salt), and "high consumption" (more than 3.15 grams of sodium daily, or more than 7.9 grams of salt).
It was noted that the people who fell within the high consumption category were at a 58 percent higher risk of developing type 2 diabetes than the individuals in the low consumption group.
People with a high genetic risk of diabetes who also had a high daily sodium intake were almost four times as likely to develop LADA than people with a low daily intake of sodium.
Interaction between genetics and diet?
Based on these findings, the researchers "confirm an association between sodium intake and type 2 diabetes." They add that "high sodium intake may be a risk factor for LADA, especially in carriers of high risk HLA [human leukocyte antigen] genotypes." These are people who already carry a significant genetic risk of diabetes.
Dr. Rasouli told us that the study had one major limitation: due to the fact that the research was based on questionnaires, it is possible that the participants may have misremembered relevant details, leading to recall bias. Yet, if anything, this bias may have led to an underestimation of the effects of sodium intake on the risk of type 2 diabetes and LADA.
"The main limitation," Dr. Rasouli suggested, "is the retrospective design that may lead to recall bias. To minimize this potential bias, patients received the questionnaire in close proximity to diagnosis with instructions to report their dietary/lifestyle habits before diagnosis."
"However, the recall bias cannot be ruled out. If this potential recall bias has happened, this would lead us to underestimation of the risk, not overestimation of results," she added.
She also told MNT that further investigation of the interaction between diet and genetic factors in the context of diabetes might reveal further pathways for tackling disease prevention. Dr. Rasouli also revealed an interest in testing the effects of minimizing salt intake on the prevention of these two types of diabetes.
"It is interesting to study the risk of LADA and type 2 diabetes in relation to [the] interaction between dietary salt intake and genetic factors [...] It would also be interesting to investigate in controlled clinical studies whether a reduction in dietary salt intake is beneficial in prevention of type 2 diabetes and autoimmune diabetes."
Dr. Bahareh Rasouli