Frequent Addition of Salt to Food Linked to Higher Risk of Chronic Kidney Disease

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A higher self-reported frequency of adding salt to food was significantly associated with an increased risk for chronic kidney disease (CKD), according to findings from a large prospective cohort study published in JAMA Network Open.

Among participants from the UK Biobank who were free of CKD at baseline, compared with those who reported never or rarely adding salt to their food, those who sometimes added extra salt (adjusted hazard ratio [aHR] 1.04, 95% CI 1.00-1.07), those who usually added salt (aHR 1.07, 95% CI 1.02-1.11), and those who always adding salt to their food (aHR 1.11, 95% CI 1.05-1.18) had an increased risk of CKD (P for trend <.001) after researchers adjusted for covariates.

Furthermore, the associations were more pronounced among participants with a higher estimated glomerular filtration rate (eGFR) and lower body mass index (BMI) or exercise level, reported corresponding author Lu Qi, MD, PhD, Department of Epidemiology, School of Public Health and Tropical Medicine, Tulane University, and colleagues.

“These findings support the reduction of adding salt to foods as a potential intervention strategy for CKD prevention,” wrote Qi and coauthors.

Previous research has shown that salt intake is associated with an increased risk of premature mortality, cardiovascular diseases (CVD), and type 2 diabetes, according to investigators.

“However, to our knowledge, no study has explored whether the frequency of adding salt to food is associated with CKD risk in general population in a prospective setting,” stated researchers. For this reason, they conducted the current study of UK Biobank participants aged 37-73 years without CKD at baseline. The cohort included 465 288 individuals (average age 56 years), 54.8% of whom were women.

Researchers noted that due to most of the participants being of European descent, “it is unclear whether our findings could be applied to other populations and, thus, future studies are needed in other populations, particularly in subpopulations with unique dietary habits.”

The main outcome was incident CKD, which was identified via ICD-10 codes. Salt intake was self-reported via a questionnaire where persons were asked if they added salt to food on a 5-point scale: never/rarely, sometimes, usually, always, or prefer not to answer.

According to the study, models were adjusted for age, sex, race and ethnicity, Townsend Deprivation Index, eGFR, BMI, smoking status, alcohol consumption, regular physical activity, diabetes, CVD, hypercholesterolemia, infectious disease, immune disease, and nephrotoxic drugs use at baseline.

FINDINGS

During a median follow-up of 11.8 years, there were 22 031 CKD events documented in the cohort, according to the results.

Researchers observed that compared to participants who reported a lower frequency of adding salt to their food, those with higher self-reported frequency were more likely to have a higher BMI and Townsend Deprivation Index score and a diminished eGFR rate. Also, persons who added salt to food were more likely than those who did not to be current smokers and have diabetes or CVD at baseline.

In addition, after adjusting for eGFR, investigators found that higher self-reported frequency of adding salt to foods was still associated with a higher risk for CKD for participants who reported sometimes adding salt to food (aHR 1.02, 95% CI 0.98-1.05), usually adding salt (aHR 1.05, 95% CI 1.01-1.10), and always adding salt (aHR 1.09, 95% CI 1.03-1.16) compared with those who reported never or rarely adding salt (P for trend=.001).

“Higher self-reported frequency of adding salt to foods was both significantly associated with a higher risk of CKD in participants with eGFR of 90 mL/min/1.73 m² or higher and eGFR greater than or equal to 60 mL/min/1.73 m² and less than 90 mL/min/1.73 m²,” added Qi and colleagues.

“Post hoc analysis or follow-up studies to clinical trials are necessary to validate these findings,” concluded researchers.

Source: Tang R, Kou M, Wang X, et al. Self-reported frequency of adding salt to food and risk of incident chronic kidney disease. JAMA Netw Open. 2023;6(12):e2349930.