Causes of less sleep and difficulty sleeping in newborns include the following: First, vitamin D deficiency rickets caused by. If a newborn grows very rapidly and usually has less time in the sun, the newborn will develop vitamin D deficiency. Because vitamin D can be synthesized by itself through sunlight exposure to the skin, a newborn’s low sun exposure will cause a decrease in the level of the synthetic vitamin in the body. A decrease in vitamin D levels will cause a decrease in calcium absorption and hypocalcemia in newborns, which will lead to less sleep and difficulty sleeping. Second, parents do not maintain a good sleep environment caused by. If the newborn is sleeping, the environment inside the home is relatively strong light, or there is a sound chaos, the newborn will sleep less, and difficult to sleep. For this situation, parents should promptly change the sleep environment at home to help newborns sleep.