||Vitamin D is a curious molecule. While humans do get some vitamin D from their diet, most of it is synthesized in the body, so it does not fit the definition of a vitamin-a molecule that must come from the diet. Vitamin D synthesis is initiated by the UVB (290-320 nm) portion of ultraviolet radiation (UVR), and UVA (320-400 nm) breaks it down. UVA and UVB have different properties, with UVA able to be transmitted through glass and plastics. UVB is blocked out by these materials, and is partially attenuated by the atmosphere depending on how much it has to pass through, varying most drastically by latitude and season (1). UVR also increases 15% with each 900 m (2,952 ft) increase in altitude (2). Recent studies have shown that the UVA exposure within the cockpit of a commercial airplane at a cruising altitude of 9,144 m (30,000 ft) is two times higher than at ground level (3). The average airline worker spends 75 hours a month flying, exposing them to conditions that theoretically increase their risk for vitamin D deficiency (4). It is known that airline workers have a higher prevalence of some health conditions (5), and that vitamin D regulates the expression of at least 900 genes in the human genome, many of which correspond to these conditions (6). My experiments tested how the environment of commercial flights affects the biochemistry of vitamin D precursors. I used UV spectrophotometry to analyze a solution of 7-dehydrocholesterol (7-DHC), a precursor to vitamin D found in the skin, before and after exposures to UVA, UVB, and flights. The light absorption properties changed post-exposure in all cases involving UVR. Different conditions, however, led to different changes. The differences in light absorption are due to a change in chemical structure in the solution, which provides further evidence that the in-flight environment could lead to chemical changes contributing to vitamin D deficiency in humans.