Effect of Splenda and Stevia on HgbA1c
Neither Splenda (sucralose) nor stevia significantly affect HgbA1c levels in adults with diabetes when used as sweeteners in typical dietary amounts. 1, 2
Evidence from Clinical Trials
Stevia's Effect on HgbA1c
The highest quality evidence comes from randomized controlled trials directly comparing these sweeteners:
A double-blind RCT in type 2 diabetics found no significant differences in HbA1c between stevia extract (2% in tea, three times daily) and sucralose (Splenda) after 8 weeks of use. 1
A 3-month randomized, double-blind, placebo-controlled trial in both type 1 and type 2 diabetics showed that stevioside (250mg three times daily) produced no significant changes in HbA1c compared to baseline or placebo. 2
A 2024 meta-analysis of 12 RCTs (871 participants) found no significant difference in HbA1c between steviol glycosides and controls (MD = 0.01%, 95% CI -0.12% to 0.13%). 3
Fasting Blood Glucose Effects
While HbA1c remains unchanged, there is some evidence for modest effects on fasting glucose:
The same 2024 meta-analysis found a small but significant reduction in fasting blood glucose with stevia (MD = -4.10 mg/dL, 95% CI -6.55 to -1.65), though this did not translate to HbA1c changes. 3
This fasting glucose benefit was most apparent in participants ≤50 years old, those without diabetes or hypertension at baseline, and overweight/obese adults. 3
Clinical Interpretation
Why No HbA1c Impact Despite Some Glucose Effects
HbA1c reflects average glycemia over 2-3 months, so small acute effects on fasting glucose may not be sufficient to meaningfully change this integrated measure. 4
The doses used as sweeteners in typical dietary consumption are far lower than the pharmacological doses (250mg+ three times daily) tested in most trials, making clinically significant effects even less likely. 2
Important Caveats About HbA1c Measurement
When interpreting HbA1c in patients using these sweeteners, be aware of factors that actually do affect HbA1c accuracy:
Vitamins C and E are reported to falsely lower HbA1c results, possibly by inhibiting glycation of hemoglobin. 4
Any condition that shortens RBC survival or decreases mean RBC age produces falsely low HbA1c results regardless of the assay method used. 4
Iron deficiency anemia prolongs erythrocyte lifespan and causes falsely elevated HbA1c levels. 4
Bottom Line for Clinical Practice
Use stevia or Splenda interchangeably as sugar substitutes without concern for differential effects on HbA1c. 1 Neither sweetener requires adjustment of diabetes medications or monitoring frequency based on their use alone. 1, 2 Any changes in HbA1c observed in patients using these sweeteners should prompt evaluation for other causes rather than attribution to the sweetener itself. 4