Five-month-old babies who do not sleep during the day are mostly considered to be caused by physiological factors, such as sufficient sleep at night or hunger. Secondly, it may also be caused by diseases, such as vitamin D deficiency rickets. 1. Physiological factors: if the baby sleeps too much at night or does not eat during the day has been in a state of hunger, there will be a five-month-old baby does not sleep during the day. 2. Vitamin D deficiency rickets: Vitamin D deficiency rickets is a malfunction of calcium and phosphorus metabolism caused by vitamin D deficiency, and the affected children will show increased neural excitability, such as daytime sleeplessness. Five-month-old babies do not sleep during the day, there may be other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment under the guidance of the doctor.