Examination of data for upper level purposes A number of approaches were taken to examine the data for the purposes of considering whether it would be possible to set a UL for sodium. The difference in dose of sodium between the high and low arms of the studies varied greatly, and so the impact on blood pressure would also be expected to vary among the studies assuming that there is a dose-response relationship between sodium intake and blood pressure. The meta-analysis done above does not take this into account but compares all low sodium arms to all high sodium arms. To remove confounding between studies to testing of different dose ranges, the change in SBP was re-expressed per 500mg increment in the difference in Na excretion between the high and low Na group in each study. The range in effect size was examined. The simple and weighted average differences in SBP, SBP per 500mg decrease in Na and difference in Na for the groups defined by the moving dichotomous cutpoints of the low sodium group were graphed. This allowed inspection for patterns (converging or diverging lines) which might indicate that the effect was increasing with increasing excretion (i.e. a UL) or that effect was decreasing (e.g. had reached a threshold of effect, this is not a UL). The graphs were created for all studies and for the largest subgroup, hypertensives, who also show a larger response than do normotensives. 2.3.4 Examination of data for SDT purposes For SDT purposes, data was considered on the range of 24-hour Na excretion in which a relationship between decrease in sodium intake and decrease in SBP could be observed. The issue of a dose response relationship was considered. The proximity of the lower end of observed data to the upper end of the AI range was another consideration, bearing in mind that at least 50% of population intakes should be above the AI. The overall meta-analysis result is dependent of the relative proportions of normotensive and hypertensives in the studies is not the same as in the Australian and New Zealand populations. Hence the overall meta-analysis result cannot be interpreted as the difference in
Examination of data for upper level purposes A number of approaches were taken to examine the data for the purposes of considering whether it would be possible to set a UL for sodium. The difference in dose of sodium between the high and low arms of the studies varied greatly, and so the impact on blood pressure would also be expected to vary among the studies assuming that there is a dose-response relationship between sodium intake and blood pressure. The meta-analysis done above does not take this into account but compares all low sodium arms to all high sodium arms. To remove confounding between studies to testing of different dose ranges, the change in SBP was re-expressed per 500mg increment in the difference in Na excretion between the high and low Na group in each study. The range in effect size was examined. The simple and weighted average differences in SBP, SBP per 500mg decrease in Na and difference in Na for the groups defined by the moving dichotomous cutpoints of the low sodium group were graphed. This allowed inspection for patterns (converging or diverging lines) which might indicate that the effect was increasing with increasing excretion (i.e. a UL) or that effect was decreasing (e.g. had reached a threshold of effect, this is not a UL). The graphs were created for all studies and for the largest subgroup, hypertensives, who also show a larger response than do normotensives. 2.3.4 Examination of data for SDT purposes For SDT purposes, data was considered on the range of 24-hour Na excretion in which a relationship between decrease in sodium intake and decrease in SBP could be observed. The issue of a dose response relationship was considered. The proximity of the lower end of observed data to the upper end of the AI range was another consideration, bearing in mind that at least 50% of population intakes should be above the AI. The overall meta-analysis result is dependent of the relative proportions of normotensive and hypertensives in the studies is not the same as in the Australian and New Zealand populations. Hence the overall meta-analysis result cannot be interpreted as the difference in
Sodium%20Supporting%20Document%202%20%20Statistical%20Analyses.docx