To the Editor: Although a great deal of information exists on the association between month of birth and risk of cancer death,1–3 no data are available from Siberia where a harsh climate might be expected to amplify associations reported from more temperate zones. The aim of this study was to find out whether there is a seasonal correlation between month of birth and death from lung cancer, which is currently one of the most common causes of death in Siberia. All death certificates for people who died during the period 1971–1978 in the city of Novosibirsk, southwestern Siberia, were reviewed for any mention of lung cancer. The following information was collected on all decedents: age, sex, region and month of birth, and month of death. A total of 376 male decedents of Siberian origin were included in the analysis. For computing the expected values, data on month-of-birth distribution of sex- and age-matched general population were obtained from the 1989 census data for Novosibirsk. The periodic regression (cosinor) analysis, analysis of variance (ANOVA), and goodness-of-fit statistics were applied. When observed/expected death ratios were graphed by date of birth, the data demonstrated a near-sinusoidal distribution with an evident peak in August–September (Fig. 1). This seasonal pattern differs significantly from that expected when evaluated by Walter and Elwood's method4 (P = 0.035, amplitude = 18.4%, θ = 257°). The best-fitting cosine function with a period of 12 months for the observed/expected ratio is characterized by an amplitude of 18.7% and a 260° acrophase corresponding to mid-September.FIGURE 1.: Variations in age at death (year) and observed/expected ratio (%) for number of deaths by month of birth for men who died of lung cancer in Novosibirsk city, 1971–1978. The smoothed lines are cosine curves, the straight line corresponds to the mean values.The age at death as a function of month of birth also displays a marked seasonal pattern (Hewitt's test,5P = 0.013; ANOVA, P = 0.01). Overall, according to the cosine function (amplitude, 1.45 years; acrophase, 73°), peak is displaced by approximately 180° compared with the incidence curve such that men who were born in March die 2.9 years older than their September-born counterparts. Although there are clear sinusoidally modeled associations with birth month, no evident relationship is found between month of death and either the death rate or age at death from lung cancer. The seasonal pattern for age at death is also confirmed in a sample of 54 decedents of both sexes in Mirny, a small town in western Yakutia (62°30′N, 112°37′E), which has a large temperature differential (46.9°C) between January and July. Ages at death by quarter of birth are as follows (year, mean ± standard deviation): February—April, 53.6 ± 8.4; May—July, 56.7 ± 8.5; August—October, 45.4 ± 8.0; and November—January, 57.5 ± 8.6. This pattern is similar to that seen in Novosibirsk with a substantially earlier age at death among those born in late summer and autumn. No periodic association is found for a number of other death causes, including pulmonary tuberculosis, obstructive lung disease, stomach cancer, ischemic heart disease, and stroke. There is also no evident birth month periodicity for Novosibirsk women dying of lung cancer. The association reported here between birth month and lung cancer deaths in Novosibirsk men is striking but is not limited to that disorder. Our previous work has shown a strong seasonal relationship between birth month and age at death from myocardial infarction in Novosibirsk; however, in contrast to findings in the present study, men born in autumn died at a significantly older age than did those born in the spring.6 The patterns between birth month and death from certain disorders seen in this and other studies remain incompletely explained. Perhaps men born before the onset of a harsh Siberian winter have intrauterine or postbirth environmental experiences that make them susceptible to lung cancer at an earlier age. ACKNOWLEDGMENTS I sincerely thank Lawrence Frisch from Northeastern Ohio Universities College of Medicine for his helpful comments. Vladimir N. Melnikov Siberian Independent Institute Novosibirsk State University Novosibirsk, Russia [email protected]