Pass the (iodized) salt: Iodine deficiency drives frailty risk in people with diabetes

By Priyanjana Pramanik, MSc.Reviewed by Susha Cheriyedath, M.Sc.Mar 26 2025

A five-year study in Shanghai reveals that using iodized salt could help prevent frailty in older adults with diabetes—particularly those with underactive thyroids.

Study: Association of iodized salt intake with the risk of physical frailty in patients with type 2 diabetes. Image Credit: Rufiyana Nikitushkina / Shutterstock

In a recent study published in The Journal of Nutrition, Health and Aging, researchers investigated whether urinary iodine concentrations (UIC) and the consumption of iodized salt were linked to frailty in individuals with type 2 diabetes. Their findings indicate the importance of maintaining adequate levels of iodine intake, primarily through iodized salt, for reducing the risk of frailty when living with diabetes, especially among those with thyroid dysfunctions.

Background

The prevalence of diabetes is increasing rapidly worldwide; in 2021, it affected 537 million adults, a number expected to rise to 783 million by 2045. As physiological functions decline, individuals may suffer from frailty, a condition that disproportionately affects people with diabetes, with an estimated prevalence of 50%. Frailty raises the danger of mortality, hospitalization, heart disease, and disability among diabetic populations, but it can be reversible.

People with type 2 diabetes also have lower UIC than healthy individuals; prior studies suggest that lower UIC levels have been linked to higher diabetes risk and could worsen health outcomes in people with the condition. Low UIC has been implicated in high cholesterol levels, blood pressure, and blood sugar.

Iodine is critical for the production of thyroid hormones and the regulation of growth and metabolism functions, but as many as two billion people around the world are iodine deficient despite intensive salt iodization efforts.

While previous research has established that thyroid dysfunction, especially hypothyroidism, increases frailty risk among older individuals, how these two conditions interact in people with diabetes has not been studied.

About the Study

In this study, the research team investigated how frailty among an urban population was influenced by UIC and iodized salt intake, also assessing whether these relationships were moderated by thyroid functioning, measured by thyroxine (FT4) and thyroid-stimulating hormone (TSH) levels.

They utilized data from a cohort study on metabolic conditions conducted in Shanghai, China, which followed 957 individuals with type 2 diabetes across 11 communities between 2018 and 2023, with 850 individuals providing complete data.

Their iodine intake was measured by asking about the type of salt they consumed (non-iodized, mixed, or iodized) and by measuring urinary iodine concentration (UIC) levels in morning urine samples using a mass spectrometer.

People were considered frail if they exhibited three or more of five signs associated with frailty, namely slow walking speed, weak measured grip strength, low level of physical activity, exhaustion, and weight loss.

Other clinical tests and questionnaires were used to collect medical history (including thyroid disorders, diabetic kidney disease, cardiovascular disease, dyslipidemia, and hypertension), physical measurements (including blood pressure and body mass index or BMI), demographic data (including lifestyle, education, sex, and age), and blood markers (including for diabetes, vitamin D, kidney function, cholesterol, and thyroid hormones).

Statistical comparisons were used to compare frail and non-frail groups of individuals, while regression models including subgroup analyses were run to examine the relative risks of frailty across different iodine levels.

Findings

The participants in the study were 65.6 years old and had been diagnosed with diabetes for approximately 9.1 years on average. Their mean UIC level was 139.7 μg/L, with 50.5% reporting the use of non-iodized salt, 21.9% using both iodized and non-iodized salt, and 27.6% using iodized salt.

Over five years, 12.9% or 111 individuals showed at least three signs of frailty. On average, frail patients consumed more non-iodized salt, had a higher BMI, and were older. They also had lower UIC levels, though this difference was not statistically significant (p=0.230).

Compared to those who used iodized salt, individuals who did not have a 9% higher risk of frailty, while a lower UIC was associated with a 10% higher risk. When analyzed by UIC tertiles, low UIC levels were linked to higher frailty risk, but there was no significant dose-response trend or non-linear relationship observed in restricted cubic spline models.

Notably, slow walking speed was the only frailty component significantly tied to iodine status: specifically, consuming non-iodized salt was associated with a 32% increased risk of having a slow walking speed, while a lower UIC was associated with a 26% increased risk. Other components of frailty—low grip strength, weight loss, fatigue, and low physical activity—showed no significant associations.

Older individuals and women were at a higher risk of frailty if they had low UICs and consumed non-iodized salt; however, this association was not statistically significant. People with high TSH and low FT4 levels—indicators of hypothyroidism—showed stronger associations between iodine deficiency and frailty, despite no baseline increase in frailty risk.

Conclusions

While China has implemented a universal salt iodization program since 1996, concerns remain. People with diabetes in this study had lower median UIC levels than the general population of the country. They were also more likely to consume non-iodized salt, potentially due to concerns about thyroid disease risk, as diabetes is associated with higher rates of thyroid disorders.

Iodized salt remains the most effective and affordable method for preventing iodine deficiency, even in urban coastal areas. Findings suggest that iodized salt use may help reduce the risk of frailty, especially in patients with high TSH or low FT4 levels. Despite some limitations of the study, including the possibility of reverse causality (though researchers adjusted for baseline physical activity to partially address this) and a lack of generalizability to other regions, these results underscore the importance of maintaining an adequate intake of iodine, particularly for individuals with thyroid dysfunction.