The use of the GRADE dose–response gradient domain in nutrition evidence syntheses varies considerably

OBJECTIVES: This study aimed to identify and describe the use of the Grading of Recommendations Assessment, Development and Evaluation (GRADE) dose-response gradient domain to upgrade the certainty of evidence (CoE) in nutrition systematic reviews (SRs). STUDY DESIGN AND SETTING: We searched for SRs of observational studies of nutrition topics that used GRADE and upgraded the CoE of at least one outcome for a dose-response gradient or reported reasons for not upgrading. RESULTS: Within eligible SRs (21/281), 123 of 371 outcomes were upgraded for a dose-response gradient. For 118 outcomes, the authors conducted linear dose-response analyses, and for 106 outcomes, the authors conducted nonlinear dose-response analyses. From these, 107 outcomes showed a statistically significant (P < 0.05) association in the linear dose-response model, and for 28 outcomes, the test for nonlinearity was statistically significant. The CoE for 0.8% of all outcomes was rated as high, 47.2% as moderate, 43.9% as low, and 8.1% as very low. Fifty-five percent of outcomes that were upgraded for a dose-response gradient were already downgraded for at least one domain. This is contrary to GRADE guidance. CONCLUSION: The approach for rating up the CoE for dose-response relationship is not consistent in nutrition reviews, likely because of a lack of clear guidance for when and how to do it. Therefore, more comprehensive GRADE guidance is necessary to enhance the correct use and comparability of dose-response upgrading.