Is salt in foods a risk factor for type 2 diabetes?

Frequently adding salt to foods increases not only the risk of hypertension but the risk of type 2 diabetes (T2D) as well, as reported in a large study.

Data from the UK Biobank showed that the risk of T2D increased in proportion to the frequency of adding salt to foods (p<0.001 for trend), ranging from 11 percent with “sometimes” (hazard ratio [HR], 1.11, 95 percent confidence interval [CI], 1.06–1.15) to 18 percent with “usually” (HR, 1.18, 95 percent CI, 1.12–1.24) and 28 percent with “always” (HR, 1.28, 95 percent CI, 1.20–1.37) relative to “never” or “rarely.” [Mayo Clin Proc 2023;98:1641-1652]

“This association was independent of lifestyle factors, socioeconomic factors, and other traditional risk factors for T2D. In addition, we found that the association between adding salt to foods and T2D was partly mediated by adiposity measurements [body mass index: 33.8 percent; waist-to-hip ratio: 39.9 percent] and C-reactive protein [8.6 percent],” according to the investigators led by Prof Lu Qi of Tulane University School of Public Health and Tropical Medicine, New Orleans, Louisiana, US.

“The significant mediation effect of body mass index was largely driven by the body fat mass rather than the body fat-free mass,” Qi added.

A good surrogate marker

While Qi acknowledged that sodium intake cannot be quantified from the frequency of adding salt to foods, the latter has been shown to have a graded relationship with levels of objectively measured urinary sodium, indicating that the frequency of adding salt could reflect individual’s long-term salt taste preference. [Eur Heart J 2022;43:2878-2888]

Like previous studies, the present study showed the validity of adding salt to foods as a good marker for long-term sodium intake. A dose-response relationship between higher levels of urinary sodium and a higher risk of T2D emerged on multivariable analysis, with HRs ranging from 1.12 to 1.35 across the quintiles of urinary sodium (p<0.001 for trend).

“Moreover, we also found the frequency of adding salt to foods was significantly related to risks of premature mortality and cardiovascular diseases. Taken together, these results indicate that the frequency of adding salt to foods may be an effective surrogate marker for evaluating the long-term sodium intake,” Qi said. [Eur Heart J 2022;43:2878-2888; J Am Coll Cardiol 2022;80:2157-2167]

Limiting dietary salt

The study included a total of 402,982 UK Biobank participants, with 13,120 incident cases of T2D documented over a median follow-up of 11.9 years. Participants with higher versus lower frequency of adding salt to foods had higher levels of Townsend deprivation index, body mass index, and C-reactive protein. In addition, those with a higher frequency of adding salt to foods were less likely to adhere to a DASH-style diet.

“We already know that limiting salt can reduce the risk of cardiovascular diseases and hypertension, but this study shows for the first time that taking the saltshaker off the table can help prevent T2D as well,” Qi said.

“It’s not a difficult change to make, but it could have a tremendous impact on your health,” he added.

Qi called for additional research to establish the mechanism underlying the potential association between salt intake T2D risk.