The groups most likely to develop B12-related hair and skin changes are the same ones at risk for deficiency generally: vegans and vegetarians, adults over 50, people on long-term metformin or proton pump inhibitors, anyone who's had bariatric surgery, and people on GLP-1 protocols whose reduced appetite has significantly lowered their overall nutrient intake for an extended period
10.1016/S0074-7742(04)59012-8 Int
10.1016/j.ecoenv.2018.06.070 25 GuderleyH.LapointeD.BdardM.DutilJ
Physical exercise as a modulator of vascular pathology and thrombin generation to improve outcomes after traumatic brain injury
(ref) Chang CH, Tsai WC, Hsu YH, Pang JH
Smoking, high cholesterol, or lack of physical activity can narrow blood vessels, slowing nutrient flow to the lower limbs