Epigenetic Influences on the Descendants of Union Army POWs
The number of adults worldwide who are overweight or obese is rising, with much of the increase driven by developing countries. Famine exposure at early ages is a contributing factor, and it is not clear whether such exposure transmits across generations. In Overweight Grandsons and Grandfathers’ Starvation Exposure (NBER Working Paper 30599), Dora Costa develops novel evidence on this issue by studying the grandchildren of Union Army veterans, some of whom were prisoners of war (POWs).
Data on the grandchildren of Civil War soldiers support the epigenetic hypothesis, namely that paternal health shocks are transmitted only to male-line descendants.
Prior to July 1863, most POWs in the US Civil War were immediately exchanged. For those in this group who survived to 1900, the average time in captivity was 16 days. Between July 1863 and July 1864 prisoner exchanges stopped; survivors’ time in captivity grew to an average of 231 days. After July 1864, exchanges resumed; time in captivity shortened to an average of 125 days. Conditions were poor, with rampant scurvy, diarrhea, and dysentery. Some soldiers returning home weighed less than 100 pounds.
Costa’s data sample consists of 3,048 male-line grandsons and 3,177 female-line grandsons of veterans who were ages 17–24 during the nonexchange period, as well as 1,069 male-line grandsons and 1,069 female-line grandsons of veterans who were age 25 or older during the nonexchange period. All are descendants of white Union Army veterans who survived to 1900. Grandsons’ heights and weights, taken from draft cards, are used to calculate body mass index (BMI). Overweight is defined as having a BMI of 25 or more.
Controlling for veterans’ pre-enlistment and postwar characteristics, ex-POWs in their late 40s and early 50s were 1.8 times more likely to be overweight and on average had a BMI 0.7 higher than their non-POW counterparts.
Costa tests whether the intergenerational transmission of being overweight is epigenetic, meaning that the environmental factors encountered by the POWs affected the way their descendants’ genes work. Epigenetic imprinting is sex specific because the Y chromosome, which carries epigenetic effects, is transmitted only to men. Therefore, the epigenetic hypothesis predicts that paternal health shocks are transmitted to male-line but not female-line grandsons. It also predicts stronger effects of shocks during the grandfathers’ developmental transition ages.
The average BMI of all grandsons was 23.7 and 29 percent were overweight. Male-line grandsons of nonexchange ex-POWs held captive between the ages of 17 and 24 were 6 percent more likely to be overweight, and reported BMIs 0.4 higher than grandsons of non-POWs. Moreover, relative to grandsons of exchanged ex-POWs, grandsons of nonexchange ex-POWs were 8 percent more likely to be overweight and had 0.3 higher BMI. There is no effect on female-line grandsons, suggesting epigenetic imprinting may be the transmission mechanism.
Of those who survived to age 45, overweight grandsons on average lived to age 71.5, compared to 74.4 for grandsons who were not overweight. Among female-line grandsons, the overweight lived on average to age 72, and the nonoverweight to age 74.3. Grandfathers’ POW status is associated only with the longevity of male-line grandsons whose BMI explains about 14 percent of this disparity.
The researchers acknowledge support from the National Institutes of Health under grants P01 AG10120 and R21 AG064460.