All-trans-retinol-d5 is a supplement that is used to protect the brain from oxidative damage and to help maintain healthy skin. It is an antioxidant that prevents free radicals from damaging cells and helps maintain the structural integrity of cell membranes. All-trans-retinol-d5 can be found in high concentrations in animal tissues, such as liver, lung, kidney, heart, brain, and eye. It can also be found in human urine. The presence of all-trans-retinol-d5 in urine has been correlated with neuroprotective effects. Retinol levels have been shown to be higher in children who are less obese than those who are obese or overweight. All-trans retinol has been shown to inhibit cancer cell proliferation and induce apoptosis by inhibiting protein synthesis at the level of transcription.