Rotterdam Study authors find no health benefit for cutting salt and "borderline" additional risk
A new Dutch study of 2,896 subjects studied for 5-6 years has concluded that there is no health benefit for healthy subjects to reduce dietary salt. The risk for subjects with cardiovascular disease and diabetes was not reported.
This, the 16th study of the health outcomes of reduced-salt diets, examined the incidence of heart attacks and strokes, cardiovascular mortality and all-cause mortality. Unfortunately, all the studies are observational (this is a case-cohort analysis); a controlled trial is required to address the question. The paper was published in the October issue of the European Journal of Epidemiology.
The research team headed by Diederick E. Grobbee examined a large, high-quality and much-admired database that contains data unavailable to some of the earlier studies. The authors reported:
Urinary sodium was not significantly associated with incident myocardial infarction, incident stroke, or overall mortality. For CVD mortality, however, a borderline significant inverse association was observed (RR = 0.77 (0.60–1.01) per 1-SD, model 3) but the relationship was attenuated after excluding subjects with a history of CVD or hypertension (RR = 0.83 (0.47–1.44) per 1-SD, model 3). In subjects initially free of CVD, the risk of all-cause mortality was also examined across quartiles of 24-h urinary sodium (median values: 45, 87, 125 and 190 mmol, respectively). RR in consecutive quartiles, using the lower quartile as the reference, were 0.80 (0.43–1.49), 0.66 (0.34–1.27) and 0.98 (0.54–1.78), respectively (model 3). In a subgroup analysis of CVD free subjects with a body mass index ≥25 kg/m2, the association of urinary sodium with CVD mortality or all-cause mortality was neither statistically significant (RR = 0.91 (0.44–1.89) and RR = 1.19 (0.86–1.66) per 1-SD, respectively; model 3).
The authors explained the significance:
The absence of a relationship between salt intake and mortality in our study corroborates the findings from the large Scottish Heart Health Study among almost 12,000 middle-aged subjects with 24-h urine samples. Follow-up data of the MRFIT trial neither showed a relationship between dietary sodium intake estimated by 24-h recall and cardiovascular events or mortality. However, other prospective epidemiological studies do suggest that sodium intake is related to morbidity and mortality, although this may be confined to specific subgroups with overweight, hypertension or high salt intake.
This last quote betrays an anti-salt bias since four studies are cited as evidence for a relationship of sodium intake to morbidity and mortality. Yes, four studies found a relationship, but they didn't all find the SAME relationship. In two of those studies, the authors found obese subjects were at addtional risk. But the other two studies found an INVERSE relationship, one in a hypertensive population and the other in the NHANES database of the entire U.S. population (and the authors failed to cite a second NHANES analysis that documented the same conclusion: low-sodium diets increased mortality by 20% in NHANES I and 37% in NHANES II).
The authors also confirmed that it is the balance of electrolytes that seems to be important, though data are scanty.
