Sex Differences and Radiation Effects

There are disproportionate age and sex differences in the aftermath of exposure to ionizing radiation. The young are, by far, the most radiosensitive as reflected in a greater risk of a variety of diseases later in life compared to adults exposed to the same dose. Less frequently recognized, however, is that fact that females are more at risk than males–given exposure to the same dose of ionizing radiation. In particular, girls exhibit a substantially higher risk of solid cancer incidence and mortality and, indeed, are the most vulnerable segment of the population in the atomic age.

The National Academy of Sciences report Biological Effects of Ionizing Radiation (BEIR), first issued in 1956, is the most up-to-date and comprehensive summary of the relevant science. The survivors of the atomic bombing of Hiroshima and Nagasaki, Japan are a key component of the analysis as are data derived from workers exposed to ionizing radiation in occupational settings and the existing medical sciences literature. As the research continues to amass, the disproportionate risk for females in relation to solid cancer incidence and mortality continues to be revised upwards, as documented in successive BEIR reports.

Figure 1 highlights the lifetime risk of solid cancer mortality from acute exposure to one-tenth of one gray, delineated by age and sex. The data refer to the number of excess deaths per 100,000 persons exposed. A gray is a measure of absorbed ionizing radiation. BEIR VII defines “low dose” as anything less than one-tenth of a gray. The dose depicted in Figure 1, in turn, is the cut-off point in this regard.

Infant boys encountering one-tenth of one gray illustrate three times the lifetime risk of cancer mortality than a male aged 30-50 exposed to the same dose. An infant girl exposed to ionizing radiation has an estimated lifetime risk of solid cancer mortality over five times higher than a male aged 30-50 when exposed. Clearly, children exhibit a greater risk of developing cancer later in life than adults encountering the same level of ionizing radiation. However, girls under ten years of age have a significantly higher risk of solid cancer mortality over their lifetime than boys under ten. The steepness of the curve for females under ten years compared to males is indicative of their radiosensitivity. But females–exposed at any age–have an elevated lifetime risk of solid cancer mortality compared to males.

To be young and/or female in the atomic era is to confront an unequal risk of solid cancer incidence and mortality due to exposure to ionizing radiation.

The sex-specific differences outlined in Figure 1 are, in part, due to the induction of breast cancer. And, again, age is significant in this regard. Girls exposed to ionizing radiation in childhood or at puberty are especially at risk of developing breast cancer later in life. This is thought to be particularly pronounced when girls are subject to such multiplicative processes in childhood or at puberty.

Indeed, breast cancer is the canary within the coal mine that is modernity. It is a biophysical cue highlighting the disproportionalities of “progress.” It is indicative of not simply exposure to ionizing radiation but synthetic chemicals, including herbicides and pesticides. Nuclear technology and the agro-chemical industrial complex are profitable, hegemonic industries. The unintended costs they generate are, in crucial ways, borne socially and individually in a strikingly sex-specific manner. But female radiosensitivity is also expressed in a higher risk of lung, bladder, and thyroid cancer, as well. Across all ages depicted in Figure 1, females have roughly twice the mortality risk of lung cancer due to exposure to one-tenth of one gray of ionizing radiation.

These are enduring biological facts, but how they are given meaning, particularly in constructing standards for the use of nuclear technology, is predicated on social and political negotiation and contestation. And in this regard, the most vulnerable in society have historically been excluded from participating in such debate. Indeed, the atomic-industrial complex in the United States has often been reticent to acknowledge disproportionate effects–despite incremental empirical evidence of their validity.