Numbness and tingling in various parts of the body can be linked to the deficiency if vitamin D in one's diet. Also, multiple sclerosis has Vitamin D deficiency as one of its risk factors. How exactly are they related? MS is an autoimmune disorder. What exact role does Vitamin D deficiency play in here?
I don't believe this is known mechanistically to any great degree. Mayo Clinic has an easily understandable post about this.
In summary, the evidence for a relationship is that vitamin D levels correlate with occurrence of MS (high vitamin D intake is associated with less occurrence of MS in individuals; populations further from the equator have less vitamin D and more MS) and that vitamin D in individual MS patients can influence their symptoms and disease progression. Knowledge of those relationships does not require any mechanistic understanding.
The review by Sintzel et al (2018) is another source for these general epidemiological associations and evidence for a possible causal relationship of low vitamin D in MS. Mechanistically, however, they only mention general relationships between vitamin D and the immune system, not any known specific mechanism of the involvement with MS. Autoimmune disease is somewhat notoriously complicated, so I don't find this particularly surprising. The review they cite, Mora et al 2008, takes a more general look at the relationships between vitamin D and immune function, which are highly multifaceted and involve both up- and down-regulation of different cell types involved in different aspects of immune function.
Mora, J. R., Iwata, M., & Von Andrian, U. H. (2008). Vitamin effects on the immune system: vitamins A and D take centre stage. Nature Reviews Immunology, 8(9), 685-698.
Sintzel, M. B., Rametta, M., & Reder, A. T. (2018). Vitamin D and multiple sclerosis: a comprehensive review. Neurology and therapy, 7(1), 59-85.