Make the most of your day and a healthy relationship to nighttime comes naturally. This doesn't mean the harder you work in the day, the better you sleep (but that's often true when you're healthy) but rather having fun and eating well are just as important or else you will greet the darkness with dissatisfaction and restlessness.
A riboflavin (vitamin B₂) deficiency will make it very hard to sleep at appropriate times.
• Miyamoto, Yasuhide, and Aziz Sancar. Vitamin B2-based blue-light photoreceptors in the retinohypothalamic tract as the photoactive pigments for setting the circadian clock in mammals. Proceedings of the National Academy of Sciences 95.11 (1998): 6097-6102.
☞ https://doi.org/10.1073/pnas.95.11.6097
As will either a diet high in polyunsaturated fatty acids (PUFA) or having tissues loaded down with PUFA from a long history of eating them, because PUFA works to destroy riboflavin with UV light.
• Cardoso, Daniel R., et al. Riboflavin-photosensitized oxidation is enhanced by conjugation in unsaturated lipids. Journal of agricultural and food chemistry 61.9 (2013): 2268-2275.
☞ https://doi.org/10.1021/jf305280x