|
More persuasive evidence for the environment
comes from the dramatic shifts in cancer risk among migrant populations. In
studies of breast cancer in Asian Americans led by Regina Ziegler we found
that the risks varied by six-fold, being lowest when migrants and all 4
grandparents on the—on the left were born in rural parts of the East and
lived less than 8 years here in the West, and highest when migrants were
born in the West along with at least 3 grandparents. In the last group, the
incidence rates are as high as the rates in the U.S. white population. And
the factors underlying this migrant effect are not entirely clear, but they
appear related at least partly to changing reproductive histories and
endogenous hormones, increases in body weight and height, and dietary
factors. We’re not sure about dietary fat which Alice Whittemore mentioned
this morning, but we have seen a—what appears to be a protective effect of
soy, especially when consumed during the childhood years. |