This can happen because of past surgeries that changed the intestinal shape like gastric bypass and bowel resections, diverticula or small pouches in the intestine and intestinal kinking or narrowing from chronic inflammation or scar tissue
Shin MS, Shin HS, Ahn YB, Kim HD
Science 376 , 11921202 (2022)
doi: 10.1007/s11051-015-3084-4 233
Vitamin D deficiency correlates with worsened neuroinflammation and cognitive deficits in patients with TBI [115]
However, at the same time it is also regarded as a conditionally essential because although it can be made in sufficient quantities under normal circumstances, modern stressful lifestyle , exposure to free radicals or toxins, sicknesses , and other factors greatly increase the demand for this vital amino acid