There are several causes of genetic variations in health for middle-aged adults. One significant cause is a person’s lifestyle. Lifestyle is considered an environmental factor, meaning that it is dependent on characteristics unique to where and how a person lives his life. Lifestyle is a cause of genetic mutations seen frequently in middle-aged adults because it takes several years for the effects of a person's lifestyle to make an impact on his or her health. For example, a person who smokes for several decades might experience genetic mutations in middle-age that lead to cellular proliferation and cancer.
A second cause of genetic variation in this age group is mutation. Mutations are changes in DNA that introduce new alleles and thus create diversity and variation. A lot of times, these mutations happen with no direct cause.
Finally, one of the main causes of genetic variation in middle-aged adults is inheritance. Genes are passed on from people’s parents, and a lot of the inherited traits that make a person unique are not prominent until a person is an adult. In addition, sometimes mutations are inherited that are problematic but do not become an issue until a person is in middle-age. For example, a person may have inherited the gene for esophageal cancer but not become aware of it until he is in his forties or fifties.