Long-Term Benfotiamine Treatment Fails to Improve Diabetic Polyneuropathy: Insights from the BOND Randomized Controlled Trial

Introduction: The Rationale for Benfotiamine in Diabetic Neuropathy

Diabetic sensorimotor polyneuropathy (DSPN) remains one of the most prevalent and debilitating complications of diabetes mellitus, affecting nearly half of all patients during their lifetime. The pathophysiology of DSPN is multifactorial, driven primarily by chronic hyperglycemia leading to oxidative stress, advanced glycation end-product (AGE) formation, and the activation of the polyol and hexosamine pathways. Among the proposed therapeutic interventions, benfotiamine—a lipid-soluble derivative of thiamine (vitamin B1)—has garnered significant interest.

Benfotiamine acts as a potent activator of the enzyme transketolase. This activation facilitates the shunting of glycolytic intermediates into the pentose phosphate pathway, thereby potentially reducing the accumulation of toxic metabolites that cause microvascular and neuronal damage. While short-term studies have previously suggested symptomatic benefits, the long-term clinical efficacy of benfotiamine on nerve morphology and neurophysiology has remained a subject of intense debate. The BOND study (Benfotiamine treatment over 12 months on morphometric, neurophysiological and clinical measures in type 2 diabetes patients with symptomatic polyneuropathy) was designed to provide a definitive, evidence-based assessment of this intervention over a one-year period.

Highlights of the BOND Study

– The study found no significant difference between benfotiamine and placebo in the primary endpoint of corneal nerve fiber length (CNFL) after 12 months of treatment.
– Despite a robust increase in blood thiamine analytes, secondary outcomes including nerve conduction studies, skin biopsy results, and cardiovascular autonomic function tests showed no clinical improvement.
– Benfotiamine was well-tolerated with a safety profile comparable to placebo, confirming its feasibility for long-term use, even if its efficacy in this specific cohort was limited.
– A non-significant trend toward improvement in the Neuropathy Symptom Score (NSS) was observed, suggesting a possible but unconfirmed symptomatic benefit.

Study Design and Methodology

This monocentric, phase II, randomized, double-blind, placebo-controlled parallel-group trial was conducted to evaluate the efficacy and safety of high-dose benfotiamine. The study enrolled 57 participants with type 2 diabetes and mild-to-moderate symptomatic DSPN. Participants were randomized in a 1:1 ratio to receive either benfotiamine 300 mg twice daily or a matching placebo for 12 months.

Primary and Secondary Endpoints

The primary endpoint was the change in corneal nerve fiber length (CNFL) from baseline to 12 months, measured via corneal confocal microscopy (CCM). CCM is a non-invasive, high-resolution imaging technique that has emerged as a sensitive biomarker for small fiber damage and repair in diabetic neuropathy.

The secondary endpoints were exhaustive, covering multiple facets of neuropathy:
1. Morphometric measures: Three additional CCM parameters and four parameters from skin biopsies (intraepidermal nerve fiber density).
2. Functional measures: 13 nerve conduction study parameters, six quantitative sensory testing (QST) parameters, and five sudomotor function tests.
3. Autonomic function: 17 indices of cardiovascular autonomic function.
4. Clinical assessment: 15 clinical scores for neuropathic symptoms and signs.
5. Patient-reported outcomes: 13 instruments measuring health-related quality of life and depression.
6. Pharmacokinetics: Measurement of six thiamine analytes in the blood to ensure adherence and biological activity.

Key Findings: No Superiority Over Placebo

The results of the BOND study indicate that the hypothesized regenerative effects of benfotiamine did not translate into measurable clinical or morphometric improvements over 12 months.

Morphometric and Neurophysiological Outcomes

The primary analysis revealed that the change in CNFL from baseline to 12 months did not differ significantly between the benfotiamine and placebo groups. Similarly, the secondary morphometric outcomes derived from skin biopsies and other CCM parameters showed no divergent trends. Nerve conduction studies, which measure large-fiber function, and quantitative sensory testing, which assesses small-fiber function, also failed to demonstrate any significant treatment effect.

Clinical and Quality of Life Measures

Clinical scores, including the Neuropathy Impairment Score (NIS) and various quality of life instruments, remained similar between the two groups throughout the study. Interestingly, the Neuropathy Symptom Score (NSS) showed a slight trend toward improvement in the benfotiamine group compared to placebo (p=0.098), but this did not reach the threshold for statistical significance. This trend might echo previous short-term trials that suggested symptomatic relief, but the BOND study underscores that such changes are not robust when subjected to rigorous, long-term evaluation.

Pharmacokinetics and Safety

One of the strengths of the BOND study was the confirmation of benfotiamine’s biological uptake. Benfotiamine treatment led to a significant increase in all six thiamine analytes measured in the blood (p≤0.003 vs. placebo), confirming that the lack of efficacy was not due to poor absorption or non-adherence. Regarding safety, the treatment was well tolerated. The incidence and severity of adverse events were balanced between the treatment and placebo arms, with no relevant safety signals identified.

Expert Commentary: Interpreting the Neutral Results

The neutral findings of the BOND study are significant for several reasons. First, they challenge the widespread use of benfotiamine as a primary treatment for reversing nerve damage in patients with established DSPN. While the mechanistic basis—activating transketolase to reduce metabolic stress—is scientifically sound, the clinical application may be hindered by several factors.

One consideration is the stage of neuropathy. The BOND study focused on participants with mild-to-moderate symptomatic DSPN. It is possible that by the time symptoms and morphometric changes are measurable, the underlying pathological process is too advanced for metabolic intervention alone to reverse. Furthermore, the 12-month duration, while longer than many previous trials, might still be insufficient to observe significant regeneration of nerve fibers, which is a notoriously slow process.

Another point of discussion is the baseline thiamine status of the participants. Benfotiamine might be more effective in individuals with a subclinical thiamine deficiency, a condition relatively common in diabetic populations due to increased renal clearance. If the study population was thiamine-replete at baseline, the marginal benefit of additional supplementation might be negligible.

Conclusion and Clinical Implications

In conclusion, the BOND study provides high-quality evidence that 12 months of treatment with benfotiamine 300 mg twice daily does not significantly improve corneal nerve morphology, neurophysiological function, or clinical symptoms in patients with type 2 diabetes and symptomatic DSPN. While the safety of the supplement is confirmed, its role as a disease-modifying agent for diabetic neuropathy remains unproven.

For clinicians, these results suggest that while benfotiamine is a safe option, it should not be prioritized over established strategies such as intensive glycemic control and evidence-based pain management. Future research may need to explore whether benfotiamine is more effective in earlier stages of the disease (pre-neuropathy) or when combined with other metabolic interventions.

Funding and Registration

The BOND study was registered with the European Clinical Trials Database (EudraCT 2017-003054-16) and the German Register for Clinical Trials (DRKS00014832). The research was supported by institutional funding and grants dedicated to the study of diabetic complications.

References

1. Ziegler D, Sipola G, Strom A, et al. Effects of benfotiamine treatment over 12 months on morphometric, neurophysiological and clinical measures in type 2 diabetes patients with symptomatic polyneuropathy: a randomized, placebo-controlled, double-blind clinical trial (BOND study). BMJ Open Diabetes Res Care. 2026;14(1):e005773. doi:10.1136/bmjdrc-2025-005773.
2. Hammes HP, Du X, Edelstein D, et al. Benfotiamine blocks three major pathways of hyperglycemic damage and prevents experimental diabetic retinopathy. Nat Med. 2003;9(3):294-299.
3. Stracke H, Gaus W, Achenbach U, et al. Benfotiamine in diabetic polyneuropathy (BENDIT): results of a randomised, double-blind, placebo-controlled clinical study. Exp Clin Endocrinol Diabetes. 2008;116(10):600-605.
4. Malik RA, Tesfaye S, Newrick PG, et al. Corneal confocal microscopy: a non-invasive surrogate of nerve fiber damage and repair in diabetic neuropathy. Diabetologia. 2003;46(5):683-688.