One of the most painful potential consequences of diabetes is peripheral neuropathy — nerve damage in your extremities (arms, legs, hands and feet) caused by elevated blood glucose levels. Neuropathic pain is widespread in people with diabetes, but until recently, treatment options have been very limited and often not targeted to this specific condition. Furthermore, some potential treatments, like anti-seizure drugs or antidepressants, carry significant risks or side effects.
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The past few weeks have seen two promising new treatments for diabetic neuropathy make headlines. First, a study presented at the virtual Scientific Sessions of the American Diabetes Association showed that high-frequency spinal cord stimulation — in which a small device is implanted under the skin near the spine, and emits pulses to reduce pain signals to the brain — is an effective treatment for neuropathic pain.
Next, the U.S. Food and Drug Administration (FDA) approved a pain-relief patch for diabetic neuropathy that delivers prescription-strength capsaicin (a compound derived from chili peppers) directly to the affected area. This patch is applied in your doctor’s office and can remain effective for up to three months.
But there may be a cheap, widely available pill that can help reduce neuropathic pain in some people with diabetes, according to the results of a recent study: vitamin D supplements, in people who lack enough of this vitamin in their blood. The study, published in the journal Diabetes/Metabolism Research and Reviews, looked at 43 people with type 1 diabetes who had neuropathy that was either painless (20 people) or painful (23 people), along with 14 people without diabetes or neuropathy as a control group. Researchers took a variety of measurements in all participants to try to find factors that might be associated with neuropathic pain.
Among the factors and measurements the researchers looked at were age, body-mass index (BMI, a measure of body weight that takes height into account), HbA1c (a measure of long-term blood glucose control), blood lipid levels (cholesterol and triglycerides), and blood vitamin D levels. They found that vitamin D levels were significantly lower, overall, in participants with painful neuropathy (an average of 24.0 ng/ml) than in those with painless neuropathy (34.6 ng/ml) or in the control group (34.1 ng/ml). Participants with a vitamin D level below 20 ng/ml — the threshold for deficiency — were 9.8 times more likely to have painful neuropathy than other participants. Those with a vitamin D level below 30 ng/ml — the threshold for insufficiency — were 4.4 times as likely to have painful neuropathy.
These dramatic results suggest that vitamin D may play an important role in how diabetic neuropathy develops in the body, or at least how it is perceived. While this study didn’t look at the effect of taking vitamin D supplements on neuropathic pain, it references past research that has done so. This research has shown that taking vitamin D can dramatically reduce pain, numbness and weakness in people with diabetic neuropathy, including a 50% reduction in pain scores in one study.
More research is needed to find out whether taking vitamin D supplements can help relieve neuropathic pain even in people with adequate vitamin D levels, and whether there is an upper limit past which increasing blood levels of this vitamin stops having any effect on pain relief. It could also be useful to study how, exactly, vitamin D helps relieve neuropathic pain. So far, studies suggest that the vitamin may help limit demyelination — loss of the protective layer on the outside of nerve cells — and help nerve fibers regenerate.
Limitations of the current study, the researchers note, include its small size, absence of measuring sunlight exposure or physical activity, and lack of a comparison group with diabetes but without any neuropathy. A major strength, though, is the detailed measurements researchers took in many areas to ensure that these factors weren’t responsible for differences in neuropathic pain.
“We demonstrate a relationship between vitamin D deficiency and painful diabetic neuropathy,” the researchers emphasize. “A well‐constructed clinical trial of vitamin D in painful diabetic neuropathy is required to assess the effectiveness of a potentially simple treatment with no obvious side effects.”