A paper titled "Dietary salt intake predicts future development of metabolic syndrome in the general population" by Takase et al., looked at the relationship between excessive salt consumption and the likelihood of developing metabolic syndrome. It claimed that high salt intake is a key risk factor for hypertension and can contribute to the onset of metabolic syndrome.
The term "metabolic syndrome" is frequently mentioned in the paper, defined according to Japanese diagnostic criteria. Individuals are diagnosed with metabolic syndrome based on high waist circumference, high triglyceride levels, low high-density lipoprotein cholesterol (HDL-C) levels, elevated blood pressure, and high fasting blood glucose levels.
The study was conducted in a cross-sectional and prospective manner, involving participants from a medical checkup program at the Department of Internal Medicine, Enshu Hospital, Hamamatsu, Japan. The study excluded individuals with a history of cardiovascular disease and those with incomplete data, leaving 13,886 participants for analysis. Baseline salt intake was estimated using 24-hour urinary sodium excretion from collected urine samples.
The results suggested that individuals with higher salt intake had a higher risk of developing metabolic syndrome during the follow-up period. However, there were large differences between individuals who went on to develop metabolic syndrome and those who didn't. Many of these, including the key factors that define metabolic syndrome (waist circumference, HDL-C levels, and blood pressure) were not adjusted for. This completely undermined the study's conclusions.
The paper acknowledged limitations, but it missed the most significant limitation – characteristics that literally defined the subject of interest (metabolic syndrome) were very different and were not adjusted for.