Does salt cause metabolic syndrome?

Executive summary

* A paper called "Dietary salt intake predicts future development of metabolic syndrome in the general population" has been published by a Japanese team. The word predicts implies causation, which cannot be established in epidemiological studies.

* The study used the Japanese diagnostic criteria for metabolic syndrome. These include waist circumference, blood pressure, fasting glucose and some blood lipid markers.

* The researchers assumed from the outset that salt was a risk factor for hypertension and hypertension was one of the attributes of metabolic syndrome, so they assumed what they set out to prove.

* There were two types of population studies involved in this paper. Both found that people with metabolic syndrome were entirely different to those without. Many factors were vastly different: BMI, waist circumference, blood pressure, diabetes etc. Despite these, the authors want us to believe that salt intake is the predictor of metabolic syndrome.

* The key differences – those that literally define metabolic syndrome (waist circumference, blood pressure, blood glucose levels, HDL-C) – were not adjusted for.