Reply to Delanghe et al.: Iron status is not likely to play a key role in the gender survival gap under extreme conditions

Females survive better than males in populations under stressful conditions, such as famines, epidemics, and slavery (1). Delanghe et al. (2) identify a biological mechanism that might partly explain this finding. They emphasize that women generally have smaller body iron stores than men, and therefore are less prone to develop conditions such as scurvy or siderophilic infections. This could be a key survival advantage under extreme mortality situations, when these diseases are likely to be major causes of death. However, we observed the biggest mortality sex difference in infancy, an age when there is no indication of less iron storage in females in high- or low-income contemporary populations (3–6). Kassebaum et al. (6) analyzed changes in the global anemia burden between 1990 and 2010 in 187 countries and found that females had higher prevalence and mean severity of anemia in virtually all regions and throughout adulthood, while male children had higher anemia prevalence than girls, a difference that appears to be almost entirely driven by excess prevalence of mild anemia resulting from hookworm. However, whether similar patterns were present in the extreme populations we studied is unknown.

Another interesting point raised by Delanghe et al. (2) is the role of postmenopause age, when the gender gap in iron status narrows, thus potentially reducing the gender gap in survival. Our analysis (1) shows that older adult ages contributed minimally to the total female advantage in life expectancy. The absolute sex difference, however, in mortality after age 50 did not decrease. In contrast, although the data are affected by noise and fluctuations, the male–female mortality difference generally increased or stayed constant.