Many patients suffering from chronic pain have low or ultra low vitamin D3 levels. Vitamin D3 is a very important vitamin, we quote Harrison’s principles of internal medicine about its physiological functions:
The biologic effects of this vitamin are mediated by vitamin D receptors, which are found in most tissues, thus potentially expanding vitamin D actions on nearly all cell systems and organs (e.g., immune cells, brain, breast, colon, and prostate) as well as exerting classic endocrine effects on calcium metabolism and bone health. Vitamin D is thought to be important for maintaining normal function of many nonskeletal tissues such as muscle (including heart muscle), immune function, and inflammation as well as cell proliferation and differentiation. Studies have shown that it may be useful as adjunctive treatment for tuberculosis, psoriasis, and multiple sclerosis or for the prevention of certain cancers. Vitamin D insufficiency may increase the risk of Type 1 diabetes mellitus, cardiovascular disease (insulin resistance, hypertension, or low-grade inflammation), or brain dysfunction (e.g., depression).
Especially the role of vitamin D in low grade inflammation helps to understand its synergy with palmitoylethanolamide in chronic pain disorders.