Molecular and genetic epidemiology actually represent two separate branches of epidemiology. The terms molecular and genetic epidemiology are sometimes used interchangeably, however, because one common application of molecular epidemiology is the use of inherited (vs. acquired) variation in DNA to classify study subjects. As Friis and Sellers (1999) put it well, the distinction between the two fields is that “Molecular epidemiology evaluates the association of variation in known genes with risk of disease, whereas genetic epidemiology includes the identification of unknown genes that influences risk of disease.” In addition, molecular epidemiology also uses molecular markers to link exposures to disease, especially to cancer.

Advances in molecular (or genetic) markers have a great impact on health risk assessment (RA) in that they can be used to flag preclinical effects of exposure. The advantages of using molecular markers or genetic factors in RA may be illustrated with the examples provided by Friis and Sellers. For example, rather than treating all cases of breast cancer as the same disease, an epidemiologist can use tumor markers to identify potentially more heterogeneous subsets. Another example is that we can assess serum levels of micronutrients to obtain more accurate measurements, rather than to rely on the individual’s recall of usual diet to estimate his or her intake of fruits, vegetables, and the like.