Peripheral neuropathy in the feet is most commonly triggered by prolonged high blood sugar, but dozens of other causes exist, from vitamin deficiencies to medication side effects to physical nerve compression. In roughly 25% to 46% of cases, no clear cause is ever identified, and that percentage climbs with age. Understanding the full range of triggers can help you and your doctor narrow down what’s behind your symptoms.
High Blood Sugar and Nerve Damage
Diabetes is the single most common identifiable cause of foot neuropathy. When blood sugar stays elevated over months or years, it sets off a chain of metabolic changes that directly injure nerve fibers. Excess glucose fuels the production of harmful byproducts, including a reactive compound called methylglyoxal, which alters the ion channels on pain-sensing nerve endings. This is one reason diabetic neuropathy often starts with burning, tingling, or abnormal pain sensitivity in the toes and soles.
High blood sugar also generates oxidative stress, producing molecules that damage nerve cell DNA and provoke chronic inflammation. On top of that, diabetes injures small blood vessels, reducing the oxygen and nutrient supply that nerves depend on. Nerves in the feet are the most vulnerable because they sit at the end of the body’s longest nerve fibers, where even small reductions in blood flow add up. The damage typically creeps upward from the toes in a “stocking” pattern over time.
What many people don’t realize is that pre-diabetes can trigger neuropathy before a formal diabetes diagnosis. When doctors investigate cases that initially seem to have no explanation, impaired glucose tolerance turns out to be a hidden contributor in a significant number of them.
Vitamin and Nutritional Deficiencies
Vitamin B12 plays a central role in maintaining the protective myelin sheath around nerve fibers. When B12 drops too low, that insulation breaks down, leading to numbness, tingling, and weakness that often starts in the feet. The clinical cutoff for B12 deficiency is set at a level of 148 pmol/L, but research published in Neurology found that nerve conduction and cognitive function don’t reach optimal levels until B12 is around 390 to 410 pmol/L, nearly three times higher than the official deficiency threshold. Low B12 is especially common in older adults, with levels below 260 pmol/L considered highly prevalent in that group.
Other nutritional gaps matter too. Thiamine (vitamin B1) is essential for peripheral nerve health, and deficiency causes a condition historically known as beriberi. Folate, vitamin E, and copper deficiencies can all contribute. People who’ve had gastric bypass surgery, those on long-term acid-reducing medications, and strict vegans are at higher risk for these shortfalls.
Alcohol’s Double Hit on Nerves
Heavy, long-term alcohol use damages foot nerves through two separate mechanisms that compound each other. Ethanol and its breakdown product, acetaldehyde, are directly toxic to nerve fibers. Animal studies show that alcohol disrupts the internal transport system within nerve cells and damages structural components of neurons in the spinal cord.
At the same time, people who drink heavily tend to absorb fewer essential nutrients from food. Thiamine deficiency is particularly common because alcohol impairs both intestinal absorption and the liver’s ability to store it. The result is a combination of direct poisoning and nutritional starvation that accelerates nerve damage. Pure alcoholic neuropathy and thiamine-deficiency neuropathy are technically distinguishable conditions, but in practice, most heavy drinkers experience both simultaneously.
Medications That Cause Nerve Damage
Certain prescription drugs can trigger neuropathy as a side effect, sometimes permanently. Chemotherapy is the most well-known culprit. According to Memorial Sloan Kettering Cancer Center, the drug classes most likely to cause nerve damage are taxanes, vinca alkaloids, and platinum-based agents. The resulting neuropathy often begins during treatment and can persist for months or years after chemotherapy ends.
Beyond cancer drugs, several other medication categories carry neuropathy risk. Some antibiotics (particularly a class called fluoroquinolones), certain seizure medications, and high-dose B6 supplements can all damage peripheral nerves. Antiretroviral drugs used to treat HIV have also been linked to foot neuropathy. If your symptoms started shortly after beginning a new medication, that timing is worth discussing with your prescriber.
Autoimmune and Infectious Causes
When the immune system misfires, it can attack the nerves themselves or the myelin sheath surrounding them. Several autoimmune conditions are known triggers for foot neuropathy:
- Guillain-Barré syndrome: a rapid-onset condition where the immune system attacks peripheral nerves, often starting with weakness and tingling in the feet and legs
- Chronic inflammatory demyelinating polyneuropathy (CIDP): a slower, long-term version of Guillain-Barré that progressively strips myelin from nerve fibers
- Lupus and rheumatoid arthritis: systemic autoimmune diseases that can damage nerves through inflammation of blood vessels (vasculitis) supplying the peripheral nervous system
- Sjögren’s syndrome: primarily known for dry eyes and mouth, but also capable of causing a painful sensory neuropathy
Infections can also trigger or directly cause neuropathy. Shingles can damage the nerves it reactivates along. Lyme disease, hepatitis B and C, and HIV all carry neuropathy risk through different mechanisms, ranging from direct viral invasion of nerve tissue to immune-mediated inflammation. Some cancers cause neuropathy through a phenomenon called paraneoplastic syndrome, where the immune response to a tumor inadvertently attacks nerve tissue.
Heavy Metal and Toxic Exposures
Exposure to certain metals, whether through occupational contact, contaminated water, or other environmental sources, can poison peripheral nerves. Each metal produces a somewhat different pattern of damage:
- Arsenic: Chronic exposure causes a sensorimotor neuropathy alongside skin changes and gastrointestinal symptoms. Acute poisoning can trigger a severe, rapid-onset nerve injury resembling Guillain-Barré syndrome weeks after the initial illness.
- Mercury: Prolonged exposure leads to a sensory neuropathy with balance problems, often accompanied by tremor, personality changes, and kidney issues.
- Thallium: Causes a painful sensorimotor neuropathy that can range from mild tingling to a severe, rapidly progressing illness. Gastrointestinal symptoms and hair loss are telltale signs.
- Lead: Unusually, lead tends to affect motor nerves first, causing weakness in the hands before the feet, though chronic exposure can produce sensory neuropathy.
- Cadmium: Associated with sensory nerve symptoms and has been shown to accumulate in nerve cell clusters along the spine.
Industrial solvents, pesticides, and certain glues can also be neurotoxic with sustained exposure.
Physical Compression and Injury
Not all foot neuropathy is systemic. Sometimes the problem is mechanical pressure on a specific nerve. Tarsal tunnel syndrome occurs when the tibial nerve gets compressed as it passes through a narrow channel on the inner side of the ankle. According to Johns Hopkins Medicine, common causes include flat feet, swelling from an ankle sprain, ganglion cysts, varicose veins, bone spurs, and swollen tendons. Arthritis and diabetes can also contribute by causing inflammation in that area.
Repetitive stress from running, ill-fitting shoes, or prolonged standing can compress smaller nerves in the foot, particularly between the metatarsal bones (a condition called Morton’s neuroma). Traumatic injuries, herniated discs in the lower spine, and surgical complications can also damage the nerves supplying the feet.
When No Cause Is Found
Even after thorough testing, doctors cannot pinpoint a cause in a large proportion of cases. Peripheral neuropathy is labeled idiopathic in 25% to 46% of patients, and in up to 50% of cases, a standard history and physical exam alone won’t reveal the trigger, particularly when symptoms are mild. This is more common in older adults, where age-related changes to nerves, blood vessels, and nutrient absorption may all play small, compounding roles that no single test can isolate.
If you’re in this category, it doesn’t necessarily mean nothing can be done. Doctors typically check for hidden contributors like impaired glucose tolerance, subtle B12 insufficiency (keeping in mind that “normal” B12 levels on a lab report may still be suboptimal for nerve health), thyroid dysfunction, and kidney disease. A nerve conduction study can confirm the presence and severity of neuropathy even when the cause remains uncertain, which helps guide symptom management.