Vitamin D deficiency and vitamin D insufficiency are associated with increased risk for painful diabetic neuropathy, according to study results published in Diabetes/Metabolism Research and Reviews.

Previous studies have reported an association between vitamin D deficiency and painless diabetic neuropathy. Additional studies have suggested a potential association between vitamin D deficiency and painful diabetic neuropathy.

The goal of the current study was to compare 25-hydroxyvitamin D (25[OH]D) levels in patients with painful diabetic neuropathy, compared with those with painless diabetes neuropathy.

The study sample enrolled 43 randomly selected patients with type 1 diabetes, including 20 subjects with painless neuropathy and 23 participants with painful neuropathy. In addition, 14 age-, sex-, and ethnicity matched non-diabetic healthy controls were included.


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All study participants underwent a comprehensive assessment to determine the severity of painful neuropathy, neurologic deficit, quantitative sensory testing (QST), electrophysiology, intra-epidermal nerve fiber density (IENFD) and corneal confocal microscopy, as well as measurement of serum 25(OH)D.

Patients with painful diabetic neuropathy had significantly higher neuropathy symptom profile score, compared to patients with painless diabetic neuropathy and controls. There were no differences for QST parameters, intra-epidermal nerve fiber density, and corneal confocal microscopy between patients with painful vs. painless diabetic neuropathy. Patients with painful diabetic neuropathy had more significant symptoms of diabetic neuropathy, such as hyperalgesia, allodynia, paraesthesia and numbness.

Mean serum 25(OH)D levels were 24.0±14.1 ng/mL in patients with painful diabetic neuropathy, 34.6±15.0 ng/mL in those with painless diabetic neuropathy and 34.1±8.6 ng/mL in controls. Vitamin D deficiency (<20 ng/mL) was associated with a 10-fold increased risk for painful diabetic neuropathy (odds ratio [OR], 9.8; 95% CI, 2.2-76.4; P=.003) and vitamin D insufficiency (<30 ng/mL) was associated with more than a 4-fold increased risk (OR, 4.4; 95 CI, 1.1-19.8; P=.03).

The study had several limitations, including the small sample size, no data on sunlight exposure or daily activity, and lack of a control group of patients with diabetes without neuropathy.

“We demonstrate a relationship between vitamin D deficiency and painful diabetic neuropathy. 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,” wrote the researchers.

Reference

Alam U, Petropoulos IN, Ponirakis G, et al. Vitamin D deficiency is associated with painful diabetic neuropathy [published online  June 7, 2020]. Diabetes Metab Res Rev. doi:10.1002/dmrr.3361