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Geoge Davey Smith and Andrew Phillips raise some issues concerning methods used in correcting for regression dilution in Intersalt but offer no judgment on the crucial issue of the strength and importance of the relation of dietary salt to blood pressure. To assess this matter properly, in the context of Intersalt findings, three judgments must be made: firstly, on the aetiological significance of the salt-blood pressure relation; secondly, on the probable underestimate of the size of this relation in Intersalt analyses of individuals; and thirdly, on the soundness of Intersalt's updated estimates “revisiting” the strength of this relation, both from its within population and its cross population analyses.1 Davey Smith and Phillips deal not at all with the first and second of these points, and only partially and inconsistently with the third. Much of their commentary deals with generalities, not with specifics of the salt-blood pressure relation and Intersalt results. As a consequence, their commentary neither sheds light on the substantive matter nor contributes positively to public policy. Davey Smith and Phillips state that corrections for regression dilution and other biases “could as well be applied to spurious associations as to causal ones…. Judgment has to be applied to decide if an association is causal.” They make no such judgment on the salt-blood pressure relation, the subject of their commentary. In fact, the totality of the evidence—the only sound basis for judgment on this matter—supports the conclusion that this association is causal. The significant independent findings on the sodium-blood pressure relation in Intersalt's within population and cross population analyses1 are components of that total evidence. Independent expert groups, national and international, have repeatedly concluded that the extensive, concordant, strong data from all disciplines—clinical investigation, randomised controlled trials, animal experimentation, epidemiological research …

Objectives: To assess further the relation in Intersalt of 24 hour urinary sodium to blood pressure of individuals and populations, and the difference in blood pressure from young adulthood into middle age. Design: Standardised cross sectional study within and across populations. Setting: 52 population samples in 32 countries. Subjects: 10 074 men and women aged 20-59. Main outcome measures: Association of sodium and blood pressure from within population and cross population multiple linear regression analyses with multivariate correction for regression dilution bias. Relation of sample median daily urinary sodium excretion to difference in blood pressure with age. Results: In within population analyses (n=10 074), individual 24 hour urinary sodium excretion higher by 100 mmol (for example, 170 v 70 mmol) was associated with systolic/diastolic blood pressure higher on average by 3/0 to 6/3 mm Hg (with and without body mass in analyses). Associations were larger at ages 40-59. In cross population analyses (n=52), sample median 24 hour sodium excretion higher by 100 mmol was associated with median systolic/diastolic pressure higher on average by 5-7/2-4 mm Hg, and estimated mean difference in systolic/diastolic pressure at age 55 compared with age 25 greater by 10-11/6 mm Hg. Conclusions: The strong, positive association of urinary sodium with systolic pressure of individuals concurs with Intersalt cross population findings and results of other studies. Higher urinary sodium is also associated with substantially greater differences in blood pressure in middle age compared with young adulthood. These results support recommendations for reduction of high salt intake in populations for prevention and control of adverse blood pressure levels. Key messages The within population findings were previously underestimated because of incomplete correction for the regression dilution problem Revised estimates of the within population association of sodium to blood pressure in Intersalt are concordant with the cross population findings for 52 samples Estimates of the effect of median sodium excretion higher by 100 mmol/day over a 30 year period (age 55 minus age 25) were a greater difference of 10-11 mm Hg in systolic blood pressure and 6 mm Hg in diastolic blood pressure These results lend further support to recommendations for mass reduction of high salt intake for the prevention and control of adverse blood pressure levels and high blood pressure in populations

Objectives-To assess the relation between alcohol intake and blood pressure in men and women and in men at younger and older ages; to examine the influence of amount and pattern of alcohol consumption, as well as of acute effects, taking into account body mass index, smoking, and urinary sodium and potassium excretion. Design-Subjects reported alcohol consumption for each of seven days before standardised blood pressure measurement, and whether they had consumed any alcohol in the 24 hours before measurement. Setting-50 centres worldwide. Subjects-4844 men and 4837 women aged 20-59. Main outcome measures-Effect of alcohol on blood pressure estimated by taking a weighted average of regression coefficients from centres. Acute effect assessed by examining mean differences in blood pressure of non-drinkers and of heavy drinkers who had and had not consumed alcohol in the 24 hours before measurement. Effect of pattern of consumption assessed by examining mean in blood pressure of non-drinkers with drinkers (i) whose intake was concentrated in fewer days or who were drinking more frequently, and (ii) whose alcohol intake varied little over the seven days or varied more substantially, as indicated by the standard deviation of daily consumption Results-Of the 48 centres in which some people reported consuming at least 300 ml/week of alcohol, 35 had positive regression coefficients linking heavy alcohol consumption to blood pressure. Overall, alcohol consumption was associated with blood pressure, significantly-at the highest intake. After: account was taken of key confounders, men who drank 300-499 ml alcohol/week had systolic/diastolic blood pressure on average 2.7/1.6 mm Hg higher than non-drinkers, and men who drank greater than or equal to 500 ml alcohol/week had pressures of 4.6/3.0 mm Hg higher. For women, heavy drinkers (greater than or equal to 300 ml/week) had blood pressures higher by 3.9/3.1 mm Hg than non-drinkers. Heavy drinking and blood pressure were strongly associated in both sexes, and in men at both younger (20-39 years) and older (40-59 years) ages. In men who were heavy drinkers, episodic drinkers (those with great variation in daily alcohol consumption) had greater differences in blood pressure compared with non-drinkers than did regular drinkers of relatively constant amounts. Conclusion-The significant relation of heavy drinking (3-4 or more drinks/day) to blood pressure, observed in both men and women, and in younger and older men, was independent of and added to the effect on blood pressure of body mass index and urinary excretion of sodium and potassium. The findings indicate the usefulness of targeting those at high risk as well as the general population to reduce the adverse effects of alcohol on blood pressure.

The Salt Institute continues to misrepresent the findings of Intersalt (and other studies) on salt and blood pressure, and the availability of Intersalt data. It not only incorrectly attempts to discredit the Intersalt finding that average population salt intake is positively related to slope of blood pressure with age1; it also ignores or misrepresents two other important results—the positive relations between sodium excretion of individuals and their blood pressure (found in over 10 000 adults), and the positive association of average population sodium intake with average blood pressure and prevalence of hypertension across the 52 populations in the Intersalt study. The institute's statement that “the primary Intersalt hypotheses were largely negative” is incorrect. The Salt Institute was clearly not happy with the implications of the original Intersalt findings on salt intake and blood pressure slope with age—an additional 9 mm Hg higher systolic blood pressure over 30 years (for example, from age 25 to 55) for an additional 100 mmol population sodium intake. It therefore requested that the Intersalt group perform several additional analyses on the slope of blood pressure with age, using statistical methods suggested by the institute. These were done, and all analyses again showed a significant relation of average population salt intake (as assessed by average 24 hour urinary sodium excretion) and population blood pressure slope with age.2 The analyses included those that had controlled for pressure in young adults (ages 20-29). Findings were similar to the original results: the higher the population salt intake, the greater the upward slope of blood pressure with age—for all 52 population samples and also when the four low sodium samples were excluded (fig 1). These findings were made …