A plausible nutritional mechanism needs confirmation in controlled outcomes. The GROW trial directly evaluated whether oral glutathione improved growth in a selected cystic fibrosis population. Primary study
Trial and result
GROW was a multicenter, randomized, double-blind, placebo-controlled study of oral reduced glutathione in pancreatic-insufficient children with cystic fibrosis aged two to ten years. Its primary endpoint was the change in weight-for-age z-score over 24 weeks. Fifty-eight participants completed the study. The reported between-group estimate was minus 0.08, with a 95 percent confidence interval from minus 0.22 to 0.06 and P=.25. Secondary anthropometric and inflammatory comparisons also did not show significant differences. Primary trial abstract.
Registration: NCT03020719.
Our appraisal: keep the negative result in the evidence base
A study should not disappear from a summary because it fails to support a proposed benefit. Its estimate and uncertainty help determine which effect sizes remain plausible and whether further research is justified.
Weight-for-age z-score is not a raw kilogram change or a percentile-point change. The scale standardizes weight against a reference distribution. Reporting the metric accurately is necessary when comparing studies that use different growth outcomes.
The completion count should not automatically be labeled the randomized count. Participant flow, treatment discontinuation, and the analysis population need separate reporting. Missing measurements can affect interpretation even in a randomized study.
This population boundary also matters: pancreatic insufficiency, age, background nutritional care, and disease severity define the question addressed. A null result here does not prove that every glutathione formulation has no effect in every setting. Equally, evidence from another setting should not override this trial's direct result.
Before release, inspect the protocol, adherence, missing-data handling, and adverse-event table. In particular, tolerability claims should account for treatment discontinuation rather than relying only on an overall favorable description. This trial did not establish oral glutathione as a growth-improving adjunct for the children studied.
Frequently asked questions
Was GROW placebo-controlled?
Yes.
Was the main endpoint adult height?
No; it was childhood weight-for-age change.
Did the primary comparison show a significant benefit?
No.
Are z-scores and percentile points interchangeable?
No.
Does the completion count necessarily equal enrollment?
No.
Does this settle every glutathione question?
No.
What should a balanced summary retain?
The null finding, uncertainty, selected population, and treatment-discontinuation details.