Gold and colleagues from Harvard's School of Public Health, based their on 5,158 boys and 4,902 girls between the ages of 10 and 18- a third of whom had smoke-who were examined annually between 1974 and 1989.The study found that smoking just five cigarettes a day appeared reduce lung volume slightly , especially for girls.The study also found that girls who smoked five or more cigarettes a day had a one percent slower then usual growth each year of their forced expiratory volume. This is the amount of air that can be blow out of the lungs in second,and it is an important measure of long health.