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Hi SuEs.  Well, the enzyme that performs the forward reaction, DHCR7, is technically capable of preforming the reverse reaction (http://enzyme.expasy.org/EC/1.3.1.21), but not under physiological conditions where [NADPH] out numbers [NADP+] by at least 100:1 (http://www.biochemj.org/content/115/4/609).  There is literature on the downregulation of DHCR7 in response to high levels of cholesterol, leading to increased vitamin D production (http://www.jbc.org/content/291/16/8363.full.pdf), but I also can't find anything about biological reactions that convert cholesterol back into 7DHC.  
[[User:AlexanderPico|AlexanderPico]] 22:34, 25 May 2017 (UTC)