Sagi-Schwartz et al.(1) studied the longevity of Israeli Holocaust survivors in comparison to non-exposed counterparts, and against all odds disclosed a significantly lower mortality hazard in the survivors. So far, only three smaller sized studies in mortality rates (2-4) compared mortality rates in Holocaust survivors and comparison groups and all three found no differences after following the cohorts for 7 years (2), 10 years (4) or 21-40 years after the end of WWII (3). Two hypotheses were offered by Sagi-Schwartz et al. (1) to explain this unexpected finding: differential mortality during the Holocaust and "Posttraumatic Growth" associated with protective factors in the survivors or in their environment after World War II (WWII).
The study, focusing on a unique population, is well done and well-presented. However, we would like to add some insights that might affect the interpretation of the study's results.
All study participants were born between 1919 and 1935 in Poland, and their exposure status was determined by a proxy variable - the year of immigration to Israel (between 1945 and 1950='exposed'; before 1939='non-exposed'). The authors state that they focused on immigrants from Poland because this is the largest community of survivors immigrating to Israel after 1945. Indeed, the Jewish population in pre–WWII Europe included more than 8,500,000 individuals, with more than 3,000,000 living in Poland alone (5). However, the Molotov–Ribbentrop Pact (August 1939) caused a total of 1,200,000 Polish Jews to become Soviet citizens after the Nazi occupation of Poland in September 1939. In addition, up to 300,000 Polish Jews moved into the Soviet parts of Poland between September 1939 and February 1940. Some returned to Poland after a short stay, some found themselves under Nazi occupation following the German invasion of the former Soviet Union (fSU) in June 1941(5) but many others stayed in the fSU throughout WWII. These subjects may have been less likely to immigrate to Israel before 1950 and thus are not represented in the study population. It is plausible to assume that not all of them would have survived WWII in Poland, an assumption which further emphasize the selectiveness of the exposed study participants. This misclassification may have been differential and should have been discussed.
Furthermore, in 1956 through 1960, the reformist Polish President Gomulka let around 45,000 Polish Jews to immigrate to Israel, in the first legal immigration wave from communist Poland to the State of Israel following WWII (6). These immigrants included Polish Jews who fled to the fSU during the War years and Polish Jews who survived the Nazi occupation. Still, since the authors have chosen the year of 1950 as an end point for the study based on census data, these subjects were not represented in the study population which may have caused a selection bias. According to the Israeli Central Bureau of Statistics (ICBS), 85% of Holocaust survivors immigrated to Israel before 1960 (including those immigrating between 1950 and 1960) and only 15% immigrated to Israel between 1960 and 1989 (7).
The authors argue that "one may similarly pose the hypothesis that the stronger persons who survived the Holocaust chose to stay in Europe or leave Europe to the USA (as many did ) and that only the weaker had no choice but to go to Israel….However, the data show otherwise". It should be noted that based on several reports, currently the world's largest community of Holocaust survivors resides in Israel, not Europe or the US, and counts approximately 225,000 subjects (8, 9).
Last but not least, several reports indicate that in elderly Israeli WWII survivors, war-related experiences are apparently associated not only with mental morbidity and PTSD, but also with several adverse health outcomes, such as osteoporosis (10), hip fractures (11), higher pain levels (12), fibromyalgia (13), chronic functional gastrointestinal symptoms (14) and higher incidence of malignancies (15). These observations support the initial hypothesis of Sagi-Schwartz et al. that it is plausible to expect that Holocaust survivors have a higher risk of dying younger. The methodological issues raised by us might have impact the study results and in order to cautiously interpret them, should have been addressed by the authors.

Lital Keinan-Boker, MD, PhD
Neomi Vin-Raviv, Phd


References

1. Sagi-Schwartz A, Bakermans-Kranenburg MJ, Linn S, van Ijzendoorn MH. Against All Odds: Genocidal Trauma Is Associated with Longer Life-Expectancy of the Survivors. PLoS ONE. 2013;8(7):e69179.
2. Stesssman J, Cohen A, Hammerman-Rozenberg R, Bursztyn M, Azoulay D, Maaravi Y, et al. Holocaust Survivors in Old Age: The Jerusalem Longitudinal Study. Journal of the American Geriatrics Society. 2008;56(3):470-7.
3. Williams RL, Medalie JH, Zyzanski SJ, Flocke SA, Yaari S, Goldbourt U. Long term mortality of NAZI concentration camp survivors. Journal of Clinical Epidemiology. 1993 6//;46(6):573-5.
4. Collins C, Burazeri G, Gofin J, Kark J. Health Status and Mortality in Holocaust Survivors Living in Jerusalem 40–50 Years Later. J Trauma Stress. 2004 2004/10/01;17(5):403-11.
5. Dawidowich L. The War against the Jews 1933 – 1945. Zmora Bitan:Tel Aviv, Israel; 1982 [In Hebrow]


6. Medoff R, Waxman CI. The A to Z of Zionism. Maryland USA: Scarecro Press; 2008.
7. Yeshula V. Compensations and other payments HOLOCAUST survivors in Israel are entitled for . A report presented in the Knesset [Israeli Parliament].May 2001.
8. Ukeles Associates, Inc. An estimate of the current distribution of Jewish victims of Nazi persecution International Commission on Holocaust Era Insurance Claims; New York;2003.
9. DellaPergola S. Review of relevant demographic information on world Jewry International Commission on Holocaust Era Insurance Claims; Jerusalem, Israel;2003.
10. Marcus EL, Menczel J. Higher prevalence of osteoporosis among female Holocaust survivors. Osteoporosis International. 2007;18(11):1501-6.
11. Foldes A, Brodsky J, Bentur N. Long-term effects of poor environmental conditions during early life: increased prevalence of hip fractures among Holocaust survivors, 50 Years Later. J Bone Miner Res. 2003;18:S53-S.
12. Yaari A, Eisenberg E, Adler R, Birkhan J. Chronic Pain in Holocaust Survivors. Journal of Pain and Symptom Management. 1999;17(3):181-7.
13. Ablin J, Cohen H, Eisinger M, Buskila D. Holocaust survivors: the pain behind the agony. Increased prevalence of fibromyalgia among Holocaust survivors. Clinical and experimental rheumatology. 2010;28(6 suppl 63):S51-6.
14. Stermer E, Bar H, Levy N. Chronic functional gastrointestinal symptoms in Holocaust survivors. The American journal of gastroenterology. 1991;86(4):417-22.
15. Keinan-Boker L, Vin-Raviv N, Liphshitz I, Linn S, Barchana M. Cancer incidence in Israeli Jewish survivors of World War II. JNCI : Journal of the National Cancer Institute. 2009;101(21):1489-500.