When someone stops using tobacco and nicotine products, it can take more than two weeks for the blood level of cotinine to drop to the level that a non-tobacco user would have and several weeks more for the urine level to decrease to a very low concentration.
Pre-school children require 10-13 hours a day. School-age children require 9-11 hours a day. Teenagers need about 8.5-9.5 hours on average. Most adults need 7 to 9 hours a night for the best amount of sleep, although some people may need as few as 6 hours or as many as 10 hours of sleep each day. Women in the first 3 months of pregnancy often need several more hours of sleep than usual.
Sleeping at a time that is in sync with this rhythm is important for healthy sleep. Sleep needs change over a person's lifetime. Children and adolescents need more sleep than adults. Interestingly, older adults need about the same amount of sleep as younger adults -- seven to nine hours of sleep per night. Unfortunately, many older adults often get less sleep than they need. One reason is that they often have more trouble falling asleep. A study of adults over 65 found that 13 percent of men and 36 percent of women take more than 30 minutes to fall asleep.