Vitamin B1 (thiamine) plays a central role in how your body processes glucose, and people with diabetes are far more likely to be deficient in it. Research suggests that correcting this deficiency and supplementing with higher doses may help protect against some of the most common complications of diabetes, particularly nerve damage, kidney damage, and blood vessel injury. However, B1 supplementation does not appear to lower blood sugar levels on its own.
Why People With Diabetes Run Low on B1
Both type 1 and type 2 diabetes dramatically increase how fast your kidneys flush thiamine out of your body. A study measuring renal clearance found that people with type 1 diabetes cleared thiamine 24 times faster than healthy volunteers, and people with type 2 diabetes cleared it 16 times faster. The result: plasma thiamine levels were roughly 75% lower in both groups compared to people without diabetes.
This isn’t a matter of not eating enough B1. The deficiency is driven by the kidneys dumping it at an abnormal rate, likely triggered by high blood sugar itself. That means even people with diabetes who eat a balanced diet can still be significantly depleted. Because standard blood tests don’t routinely check thiamine levels, this widespread deficiency often goes undetected.
How B1 Protects Against Sugar-Related Damage
Thiamine is a required helper molecule for several enzymes that process glucose inside your cells. When glucose enters a cell, thiamine-dependent enzymes channel it through normal energy-producing pathways. Without enough thiamine, excess glucose gets shunted into four damaging side pathways that injure blood vessels and nerves. These pathways produce harmful compounds including sorbitol, advanced glycation end products (AGEs), and inflammatory signaling molecules.
AGEs are particularly destructive. They form when sugar molecules bond to proteins, creating stiff, dysfunctional structures that accumulate in blood vessel walls, kidneys, eyes, and nerves. Thiamine’s active form has been shown to block AGE formation more effectively than aminoguanidine, a pharmaceutical compound specifically designed for that purpose. By keeping glucose flowing through normal metabolic channels, thiamine essentially reduces the raw material available for these damaging reactions.
High-dose thiamine has also been shown in lab and animal studies to reduce the activity of a key enzyme in the sorbitol pathway, lower oxidative stress, and decrease abnormal protein modifications linked to diabetic heart damage.
Effects on Blood Sugar Levels
If you’re hoping B1 will bring your blood sugar numbers down, the evidence is disappointing. A systematic review and meta-analysis of clinical trials found no benefit of thiamine supplementation on blood sugar control at doses ranging from 100 to 900 mg per day for up to three months. This held true for both standard thiamine and benfotiamine, a more absorbable form.
There is an interesting historical footnote: a 1948 report from a British medical officer in India described reduced blood sugar and less sugar in the urine among diabetic patients given 50 mg of thiamine by injection daily for 10 to 14 days. Those patients also needed less insulin. But this hasn’t been replicated in modern controlled trials. The current evidence points to B1’s value being in complication prevention rather than glucose lowering.
Kidney Protection
One of the more promising findings comes from a randomized, double-blind, placebo-controlled pilot study in people with type 2 diabetes and early kidney damage. Participants who took high-dose thiamine for three months had a significant reduction in the amount of albumin leaking into their urine, a key marker of diabetic kidney disease. Urinary albumin excretion dropped by a median of 17.7 mg per 24 hours compared to baseline, and was significantly lower than in the placebo group at the end of treatment.
This matters because microalbuminuria (small amounts of protein in urine) is one of the earliest warning signs that diabetes is starting to damage the kidneys. If confirmed in larger trials, thiamine could offer a simple, low-risk way to slow progression at this critical early stage.
Nerve Damage and Neuropathy
Diabetic neuropathy, the tingling, numbness, and pain that often starts in the feet, is the complication most commonly associated with B vitamin therapy. The results here are mixed but not without hope.
A pilot trial using benfotiamine at 600 mg per day (later reduced to 300 mg) over six months found a reduction in neuropathy symptoms as measured by a standardized screening questionnaire. However, improvements in physical examination scores, quality of life, and pain did not reach statistical significance. One short-term trial over 12 weeks showed that benfotiamine combined with vitamins B6 and B12 may improve nerve conduction velocity, the speed at which electrical signals travel through nerves.
On the other hand, a 24-month trial in people with type 1 diabetes found no difference in nerve conduction between benfotiamine (300 mg per day) and placebo. The overall picture is that B1 supplementation may ease some neuropathy symptoms, but strong evidence that it reverses or halts nerve damage is still lacking.
Eye and Blood Vessel Damage
Animal studies have shown that benfotiamine can prevent experimental diabetic retinopathy by blocking the same three damaging glucose pathways it interrupts elsewhere in the body. This is a compelling finding, but human clinical trials specifically testing B1 for diabetic eye disease have not yet been completed. For now, the eye protection evidence remains preclinical.
Standard Thiamine vs. Benfotiamine
Not all forms of B1 are absorbed equally. Standard thiamine (thiamine hydrochloride) is water-soluble and depends on specific transport proteins to cross from your intestine into your bloodstream. These transporters can only move so much at a time, which puts a ceiling on how much you absorb from a single dose.
Benfotiamine is a synthetic derivative that gets around this bottleneck. In the intestine, it’s converted to a fat-friendly form that passes freely through cell membranes without waiting for transporters. The result is plasma thiamine levels at least five times higher than you’d get from the same dose of regular thiamine. Most clinical trials studying diabetic complications have used benfotiamine for this reason, though some positive results (like the kidney study) used standard thiamine at high doses.
Doses Used in Research
The recommended daily intake of thiamine for adults is only about 1.1 to 1.2 mg. Clinical trials in diabetes have used dramatically higher amounts. Studies with standard thiamine typically used 100 to 300 mg per day. Benfotiamine trials ranged from 120 to 900 mg per day, with many using 300 to 600 mg daily.
Thiamine is water-soluble, meaning your body excretes whatever it doesn’t use rather than storing it. No toxic effects from high doses have been reported in the research literature, and it does not accumulate in the body. This favorable safety profile is one reason researchers have been interested in it as a low-risk intervention, though it also means the pharmaceutical industry has little financial incentive to fund the large-scale trials that would be needed to establish firm treatment guidelines.
What the Evidence Adds Up To
Vitamin B1 is not a blood sugar treatment. It won’t replace your diabetes medications or bring your A1C down. What it may do is help protect the organs and tissues that high blood sugar damages over time, particularly the kidneys, nerves, and blood vessels. The biological rationale is strong: people with diabetes are severely depleted, the enzyme pathways that depend on thiamine are directly involved in glucose-related tissue damage, and early clinical trials show measurable benefits for kidney function and neuropathy symptoms.
The main limitation is scale. Most human trials have been small pilot studies or short in duration. The results are encouraging but not yet definitive enough to make B1 supplementation a standard part of diabetes care. Given its safety profile and low cost, it’s a reasonable option to discuss with your care team, especially if you have early signs of kidney involvement or neuropathy.