A number of structural and microscopic changes occur as the liver ages. (See also Overview of the Liver and Gallbladder for a discussion of normal function of the liver and gallbladder.) For example, the color of the liver changes from lighter to darker brown. Its size and blood flow decrease. However, liver test results generally remain normal.
The ability of the liver to metabolize many substances decreases with aging. Thus, some drugs are not inactivated as quickly in older people as they are in younger people. As a result, a drug dose that would not have side effects in younger people may have dose-related side effects in older people (see Aging and Drugs). Thus, drug dosages often need to be decreased in older people. Also, the liver's ability to withstand stress decreases. Thus, substances that are toxic to the liver can cause more damage in older people than in younger people. Repair of damaged liver cells is also slower in older people.
The production and flow of bile decrease with aging. As a result, gallstones are more likely to form.