It is important to note that selected patients were a relatively healthy, homogenous population with good blood pressure control and an already low urinary sodium excretion. Very few were active smokers and many took regular exercise. All RAAS antagonists and diuretic agents were stopped for an 8 week run in and blood pressure was controlled with alternative agents. At week 0, Olmesartan was then commenced, and at 8 weeks, subjects were randomised to control or intensive education groups.
The primary endpoint was the decrement in albuminuria by week 16 and was reached in the intensive salt reduction group. They demonstrated a significant reduction in albuminuria (278 mg/d to 178 mg/d) compared to the conventional therapy group (258 mg/d to 231 mg/d). There was a greater reduction in urinary sodium excretion in the intensive education group than the conventional group, but no change in blood pressure or renal function. In subgroup analyses, the authors examined those that received a reduction of > 25% of their dietary salt and those who did not, irrespective of treatment group. Notably, only 60% of those who achieved this reduction came from the intensive group.
Overall this is an interesting, well-performed study which successfully demonstrates that lower salt excretion correlates with lower albuminuria. This occurred despite no effect on BP in a cohort with already excellent BP control. It may be better to interpret this as a “proof of concept” that salt restriction in humans could influence albuminuria. For clinical practice however, there are issues around the generalizability of these findings to everyday patients, given this was a highly selected, compliant group of patients. Also, as we know in the nephrology community from previous trials, an improvement in a relatively soft endpoint like albuminuria will not necessarily translate into improvements in renal/cardiovascular events or mortality.
Check out the full text of the paper, our complete post and discussion over at the CJASN eJC website.
Authored by Eoin O’Sullivan & Paul Phelan