We read with great interest the article by Shalom et al entitled “Sacral nerve stimulation reduces elevated urinary nerve growth factor levels in women with symptomatic detrusor overactivity.” The authors suggest that detrusor overactivity patients had significantly higher urinary nerve growth factor (NGF) at baseline than healthy control subjects. However, we think that some points should be discussed.

NGF, a small secreted protein has an important role for growth, maintenance, and survival of neurons. In this study, the authors assessed NGF in a poorly defined study group. The authors should state whether the patients have any neuropsychiatric diseases or cardiometabolic diseases. It is known that neuropsychiatric diseases such as epilepsy, depression, schizophrenia, migraine, primary headache, eating disorders, or cardiometabolic diseases such as atherosclerosis, metabolic syndrome, and type 2 diabetes mellitus affect NGF levels.

The authors note the control group was age-matched (±5 years) with the study group, but the baseline demographics table shows a difference of approximately 14 years, which is statistically significant. Another statistically significant difference between the 2 groups is a body mass index of 6 units. Previous studies show that obesity itself is a cause of higher NGF levels. Older age is also shown as a NGF-affecting factor. Therefore, the control group selection seems unsuitable and likely could have caused an incorrect assessment.

When we consider the mean age of the control group, participants could have been using vitamin D analogues to prevent postmenopausal osteoporosis. Vitamin D analogues probably affect NGF levels. Other supplements such as zinc, vitamin A, vitamin B12, omega 3 fatty acid, or herbal medicines and some drugs such as glucocorticoids, estrogen, acetyl-L-carnitine, antipsychotics should be noted. If participants were taking these, then NGF factors may be affected.

In conclusion, the explanation of these concerns certainly will provide clearer information for the readers.