There is little change in lung capacity through most of middle adulthood. however, at about the age of 55, the proteins in tissue become less elastic. this change, combined with a gradual stiffening of connective tissues in the chest wall, decreases the lungs' capacity to shuttle oxygen from the air people breathe to the blood in their veins. The lung capacity of individuals who are smokers drops precipitously in middle age, but if the individuals quit smoking their lung capacity improves, although not to the level of individuals who have never smoked. Recent research also has found that low cognitive ability in early adulthood is linked to reduced lung functioning in middle age.