Diabetic peripheral neuropathy (DPN) is a common complication of type 2 diabetes, affecting up to 50% of patients and often resulting in foot and hand muscle weakness, balance disturbance, and neuropathic pain. The pain is often severe and leads to depression, anxiety, sleep disorders, and reduced quality of life. Diabetic neuropathy involves both small and large nerve fibers. The small fibers include C-fibers associated with electric shock or burning symptoms, while large fiber impairments affect balance.
According to a recent position statement from the American Diabetes Association, there is no compelling evidence that supports the efficacy of glycemic control or lifestyle management in the treatment of neuropathic pain, which leaves only pharmaceutical interventions, such as pregabalin, duloxetine, or tapentadol.
Vitamin D deficiency is now known to be prevalent in patients with type 2 diabetes, particularly those with symptoms of DPN, and studies have shown that low serum vitamin D levels are an independent predictor of DPN development. Would supplementation of vitamin D, therefore, improve pain in these patients?
In a randomized, placebo-controlled study of patients with DPN and low vitamin D levels, Sari and colleagues examined the effects of vitamin D replacement therapy on neuropathic pain and balance. They based their study on research that showed vitamin D-associated improvements in axon regeneration and myelination following nerve injury,as well as increases in nerve growth factor synthesis and prevention of neuronal degeneration.
Other studies have looked at the reduction of neuropathic pain following vitamin D supplementation, but this was the first investigation of the effect of vitamin D on balance disturbances in patients with DPN, possibly through a beneficial effect on the central nervous system and muscle tissue.
In their study, Sari and colleagues administered a one-time injection of 300,000 IU vitamin D in a liquid formulation to patients with low levels of circulating 25-hydroxyvitamin D (25(OH)-D) (