Strange Salt

A new JAMA study finds a strong correlation: the third of folks who eat the least salt die over three times as often as the third of folks who eat the most salt. Yet other studies almost as big find contrary effects. I find it quite disturbing that such big studies can show such different results; something is very wrong in big diet correlation study land. Details:

Among 3681 participants followed up for a median 7.9 years, [heart attack] deaths decreased across increasing tertiles of 24-hour sodium excretion, from 50 deaths in the low, 24 in the medium, and 10 in the high excretion group (P < .001). … In multivariable-adjusted analyses, this inverse association retained significance (P=.02): the [hazard ratio] in the low tertile was 1.56 (95% CI, 1.02-2.36; P=.04). Baseline sodium excretion predicted neither total mortality (P = .10) [though 118, 64, 37 total deaths for low, medium, high tertiles sure looks significant to RH]. … All hazard ratios were adjusted for study population, sex, and baseline variables: age, body mass index, systolic blood pressure, 24-hour urinary potassium excretion, antihypertensive drug treatment, smoking and drinking alcohol, diabetes, total cholesterol, and educational attainment. …

Our current observations on cardiovascular mortality are consistent with several other reports. The National Health and Nutrition Examination Surveys (NHANES) I and II demonstrated an inverse association of cardiovascular and total mortality with salt intake as assessed from dietary recall with a similar trend in NHANES III. Alderman and colleagues followed up for 3.5 years 2937 patients with mild to moderate hypertension. There was an inverse association between the incidence of myocardial infarction and 24-hour urinary sodium excretion at baseline for the total population and for men, but not women. …

At variance with our current findings, other prospective studies suggested that a high-salt intake may lead to a worse outcome. … Cook and colleagues analyzed the long-term results of dietary sodium restriction on cardiovascular outcomes by combining 10 to 15 years of follow-up of 744 and 2382 participants randomized in the Trials of Hypertension Prevention, phases 1 and 2. Net sodium reductions during the intervention period (from 18 to 48 months) were 44 mmol and 33 mmol per day, respectively. … With adjustments applied for trial, clinical site, race, sex, and age, the [hazard ratios] for intervention vs control were 0.80 (95% CI, 0.51-1.26; P = .34) for total mortality. … In a 19-year follow-up study of 3126 Fins, the multivariable- adjusted [hazard ratios] associated with a 100- mmol increase in 24-hour urinary sodium were 1.26 (95% CI, 1.06-1.50) for total mortality, 1.45 (95% CI, 1.14- 1.84) for CVD, and 1.51 (95% CI, 1.14- 2.00) for coronary heart disease. (more)