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Effect of month of birth on the risk of suicide

  • Emad Salib (a1) and Mario Cortina-Borja (a2)

Month of birth as a suicide risk factor has not been adequately explored. The findings of published studies are contradictory and inconclusive.


To examine the association between suicide and month of birth using suicide data for a 22-year period in England and Wales. The sample size of 26915 suicides greatly exceeds all previous studies.


We analysed all suicides (ICD-9 codes E950-959) and deaths from undetermined injury (E980-989) reported between 1979 and 2001 in England and Wales for persons born between 1955 and 1966, using Poisson and negative binomial generalised linear models with seasonal components.


Birthrates of people who later kill themselves show disproportionate excess for April, May and June compared with the other months. Overall, we found an increase of 17% in the risk of suicide for people born in the peak month (spring -early summer) compared with those born in the trough month (autumn-early winter); this risk increase was larger for women (29.6%) than for men (13.7%).


The ‘month of birth’ factor in suicide can be interpreted in terms of the foetal origins hypothesis. Our findings might have implications for our understanding of the multifaceted aetiology of suicide and may eventually offer new strategies for research and prevention.

Corresponding author
Dr E. Salib, 5 Boroughs Partnership Trust, Stewart Assessment Unit, Peasley Cross Hospital, St Helens, Merseyside WA9 3DA, UK. Fax: +44 (0)1744 458461; e-mail:
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Asberg, M. (1997) Neurotransmitters and suicidal behaviour. The evidence from cerebrospinal fluid studies. Annals of the New York Academy of Sciences, 836, 158181.
Barker, D. (1998) Mothers, Babies and Health in Later Life. Edinburgh: Churchill Livingstone.
Bradbury, T. N. & Miller, G. A. (1985) Season of birth in schizophrenia: a review of evidence, methodology, and aetiology. Psychological Bulletin, 98, 569594.
Brenner, A. V., Linet, M. S., Shapiro, W. R., et al (2004) Season of birth and risk of brain tumours in adults. Neurology, 63, 276281.
Cameron, A. C. & Trivedi, P. K. (1998) Regression Analysis of Count Data. Cambridge: Cambridge University Press.
Castrogiovanni, P., Iapichino, S., Pacchierotti, C., et al (1998) Season of birth in psychiatry: a review. Neuropsychobiology, 37, 175181.
Chotai, J. & Asberg, M. (1999) Variations in CSF monoamine metabolites according to the season of birth. Neuropsychobiology, 249, 5762.
Chotai, J., Salander, R. & Jacobsson, L. (1999) Season of birth associated with age and method of suicide. Archives of Suicide Research, 5, 245254.
Department of Health (1999) Safer Services; National Confidential Inquiry into Suicide and Homicide by People with Mental Illness. London: Department of Health.
Doblhammer, G. & Vaupel, J. W. (2001) Lifespan depends on month of birth. Proceedings of the National Academy of Sciences of the USA, 98, 29342939.
Edwards, J. H. (1961) The recognition and estimation of cyclic trends. Annals of Human Genetics, 25, 8387.
Huntington, E. (1938) Season of Birth: Its Relation to Human Abilities. New York: Wiley.
Kettl, P. A., Collins, T., Sredy, M., et al (1997) Seasonal differences in suicide in birth rate in Alaska Natives compared to other populations. American Indian and Alaska Native Mental Health Research, 8, 110.
Kristoffersen, S. & Hartveit, F. (2000) Is a woman's date of birth related to her risk of developing breast cancer? Oncology Reports, 7, 245247.
Langagergaard, V., Norgard, B. & Mellernkjaer, L. (2003) Seasonal variations in month of birth and diagnosis in children and adolescents with Hodgkin disease and non-Hodgkin lymphoma. Journal of Pediatric Hematology/Oncology, 25, 534538.
Lawlor, D. A., Davey Smith, G., Mitchell, R., et al (2004) Temperature at birth, coronary heartdisease, and insulin resistance: cross sectional analysis of the British women's heart and health study. Heart, 90, 381388.
Lester, D. (1995) The concentration of neurotransmitter metabolites in the cerebrospinal fluid of suicidal individuals: a meta-analysis. Pharmacopsychiatry, 28, 4550.
Maes, M., De Meyer, F., Thompson, P., et al (1994) Synchronised annual rhythm in violent suicide rate, ambient temperature and light-dark span. Acta Psychiatrica Scandinavica, 90, 191196.
Mann, J. J. & Malone, K. M. (1997) Cerebrospinal fluid amines and higher-lethality suicide attempts in depressed in-patients. Biological Psychiatry, 41, 162171.
Mortensen, P. B., Pedersen, C. B., Westergaard, T., et al (1999) Effects of family history and place and season of birth on the risk of schizophrenia. New England Journal of Medicine, 340, 603608.
Nordstrom, P., Samuelsson, M., Asberg, M., et al (1994) CSF 5-HIAA predicts suicide risk after attempted suicide. Suicide and Life-Threatening Behaviour, 24, 19.
O'Keane, V. & Scott, J. (2005) From obstetric complications' to a maternal-foetal origin hypothesis of mood disorder. British Journal of Psychiatry, 186, 367378.
Parkes, A. S. (1976) Patterns of Genderuality and Reproduction. Oxford: Oxford University Press.
Petridou, E., Papadopulos, F., Frangakis, C., et al (2002) Brief report: a role of sunshine in the triggering of suicide. Epidemiology, 13, 106109.
Pokorny, A. D. (1960) Characteristics of 44 patients who subsequently committed suicide. Archives of General Psychiatry, 3, 314323.
Prener, A. & Carstensen, B. (1990) Month of birth and testicular cancer risk in Denmark. American Journal of Epidemiology, 131, 1519.
R Development Core Team (2004) R: A Language and Environment for Statistical Computing. Vienna: R Foundation for Statistical Computing.
Salib, E. (2002) Month of birth and suicide: an exploratory study. International Journal of Psychiatry in Clinical Practice, 6, 3944.
Salib, E. & Gray, N. (1997) Weather conditions and fatal self-harm in North Cheshire 1989–1993. British Journal of Psychiatry, 171, 473477.
Sorenson, H. T., Pedersen, L., Olsen, J., et al (2001a) Seasonal variations in month of birth and diagnosis of early childhood acute lymphoblastic leukaemia. JAMA, 285, 168169.
Sorensen, H. H., Pedersen, L., Norgard, B., et al (2001b) Does month of birth affect risk of Crohn's disease in childhood and adolescence? BMJ, 323, 907.
Torrey, E. F., Miller, J., Rawlings, R., et al (2000) Seasonal birth patterns of neurological disorders. Neuroepidemiology 86, 10701077.
Venables, W. N. & Ripley, B. D. (1998) Modern Applied Statistics with S-Plus 2nd edn. New York: Springer.
World Health Organization (1977) Manual of the International Statistical Classification of Diseases, Injuries and Causes of Death (9th revision) (ICD-9). Geneva: WHO.
Yip, P., Chao, A. & Chiu, C. (2000) Seasonal variations in suicide: diminished or vanished: experience from England and Wales, 1982–1996. British Journal of Psychiatry, 177, 366369.
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Effect of month of birth on the risk of suicide

  • Emad Salib (a1) and Mario Cortina-Borja (a2)
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Re: The effects of month of birth and geographical latitude on risk of suicide and related disorders

Emad Salib, Honorary Senior Lecturer
09 March 2007

We are grateful to Piet Hein Jongbloet for introducing us to this fascinating area of biological research. Jongbloet, who has a most impressive record in this field for more than 30 years, provides an alternative explanation of our findings about the effect of month of birthon suicide, which is based on ‘oocyte origins’ hypothesis as opposed to the maternal foetal origin hypothesis. />
According to the oocyte hypthesis, the intricate interplay between nonoptimal oocyte maturation and genes results in a subtle but complex pathogenesis of the foetal nervous system .. This occurs in well-timed menstrual cycles, but more so in instances of distorted hormonal tuning, not only in deprived socioeconomic conditions but also at the extremes of maternal reproductive life, among endocrinologically unbalanced mothers, after very short pregnancy intervals, during the seasonal transitions of the "ovulatory" seasons, etc (Jongbloet 2001). A similar broad spectrum ofmale-biased developmental anomalies—low birth weight and length, small stature at school age or adulthood, morbidity, and mortality—is present inall these circumstances (Jongbloet (1985).

To illustrate the oocyte hypothesis in practical terms; mothers withlow socioeconomic status are known to suffer from more menstrual disorders, low standards of nutrition, and abnormal body mass index (Power & Matthews 1997). They also are more likely to be smokers or drug users (Pierrce et al 1989) and to employ less safe methods of contraception, resulting in more unplanned and unwanted pregnancies, particularly at the extremes of maternal reproductive age and during the postpartum restoration of the ovulatory pattern, ie, after very short interpregnancy intervals. They are likely to have non optimal oocyte maturation, thus rendering the offspring vulnerable to low birth weight and certain psychiatric disorders. However, we are not clear as to how this hypothesis actually differs from the maternal foetal origin hypothesis used to explain our findings (Salib & Cortina Borja 2006).

The geographic latitude effect in incidence rate of suicide in England and Wales and elsewhere is assumed by Jongbloet to be a consequence of the stronger seasonal ovulatory pattern the further away from the Equator, just as in animals, and, in turn, stronger transitional stages between the ovulatory seasons and, thus, more poor quality oocytes,The only way to accept or reject this concept is by demonstrating the sameincrease of suicide incidence rate—and of other disease entities or behaviour of complex origin.

Emad Salib Honorary Senior Lecturer, Liverpool UniversityPeasley Cross Hospital, St Helens WA9

Mario Cortina-Borja Centre for Paediatric Epidemiology and BiostatisticsInstitute of Child Health, University College London


Jongbloet PH. (1985) The ageing of gamete in relation to birth control failures and Down syndrome. Eur J Pediatr. 1985; 144: 343–347

Jongbloet PH, (2001) Zielhuis GA, Groenewoud HMM, Pasker-de Jong PCM.The secular trends in male: female ratio at birth in postwar industrialized countries. Env Health Perspect. 2001; 109: 749–752.

Pierrce JP, Fiore MC, Novotny TE, et al. (1989) Trends in cigarette smoking in the United States. JAMA. 1989; 61: 56–60.

Power C, Matthews S. (1997) Origins of health inequalities in a national population sample. Lancet. 1997; 350: 1584–1589.

Salib E., Cortina-Borja M (2006) Effect of month of birth on risk of suicide. British Journal of Psychiatry, 188, 416-422 ... More

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Month of birth in relation to suicide

Jayanti Chotai, MD, PhD, Assoc Professor
19 May 2006

In their interesting and thorough article, Salib & Cortina-Borja (2006) find that persons born during the spring-summer season of April, May and June were significantly more likely to commit suicide compared to those born during other months. They find a peak for the birth month May and a trough for October.

However, they misreport our earlier results in this field when they state in the introduction that ”Chotai et al (1999) reported that people born in winter in Sweden were significantly more likely than those with other birth seasons to have used hanging as a suicide method.” They further misreport other earlier findings of ours when they state in the discussion that ”However, winter variations in serotonin reported by Chotai & Åsberg (1999) are inconsistent with the findings of this study, essentially the opposite of the Swedish findings.”

Contrary to these statements of Salib & Cortina-Borja (2006), ourearlier findings are in fact similar to and consistent with their results.In Chotai et al (1999), we clearly show and state that those who preferredhanging rather than poisoning or petrol gases were significantly more likely born during February to April. In Chotai & Åsberg (1999) we clearly show and state that those born during February to April had significanly lower 5-HIAA (5-hydroindoleacetic acid).

We have also published cosinor analyses of our data (Chotai & Adolfsson, 2002), where we found that the minimum of the month-of-birth curve for 5-HIAA was obtained for the birth month April (t-min 3.4 in Table 1 of that paper, where the interval 3-4 depicts April), and the maximum was obtained for October (t-max 9.4). We also report there that the maximum of the month-of-birth curve for preferring hanging was for March-April and the minimum was for September-October.

Low serotonin turnover has been implicated as a risk factor for suicidal behaviour, particularly with violent or lethal methods of suicide, as discussed by Salib & Cortina-Borja (2006). Thus our findings are in line with those of Salib & Cortina-Borja (2006) regarding suicidality, since we obtained a peak for the birth month April comparable to their peak for May, and our findings are consistent with theirs since we found a trough for 5-HIAA for the birth month April.

In another epidemiological study (Chotai & Salander Renberg, 2002), we report that the season of birth associations with the suicide methods were found in those without a history of psychiatric contacts, butnot in those with. We have argued that season of birth associations for suicide methods are likely to be mediated to a large extent by a suicidality trait independently of specific major psychiatric disorders, with serotonin as the likely underlying neurotransmitter.

In our studies, the season of birth variation was found for hanging as the suicide method, but not for other methods often denoted as violent together with hanging, for example firearms or drowning. Hanging is a moreuniversal method of suicide, and gender differences in the proportion of hanging are much lower than for the other methods. In this light, it wouldbe of interest to analyse the data of Salib & Cortina-Borja (2006) specifically regarding whether there is a month of birth variation in suicide by hanging.


Chotai J, Adolfsson R (2002) Converging evidence suggests that monoamine neurotransmitter turnover in human adults is associated with their season of birth. European Archives of Psychiatry and Clinical Neuroscience 252, 130-134.

Chotai J, Åsberg M (1999) Variations in CSF monoamine metabolites according to the season of birth. Neuropsychobiology 39, 57-62.

Chotai J, Salander Renberg E, Jacobsson L (1999) Season of birth associated with the age and method of suicide. Archives of Suicide Research 5(4), 245-254.

Chotai J, Salander Renberg E (2002) Season of birth variations in suicide methods in relation to any history of psychiatric contacts supportan independent suicidality trait. Journal of Affective Disorders 69, 69-81.

Salib E, Cortina-Borja M (2006) Effect of month of birth on the risk of suicide. British Journal of Psychiatry 188, 416-422.
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Conflict of interest: None Declared

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Season of birth effects and developmental vitamin D

John J McGrath, Psychiatrist
19 May 2006

Dear Sir,The paper by Salib and Cortina-Borja contributes further evidence demonstrating that seasonally-fluctuating early-life exposures influence asurprisingly diverse range of adult health outcomes. However, the questionfor the research community is no longer “Does season of birth influence health outcomes?” We have known the answer to this question for decades. We must avoid falling into the trap of ‘circular epidemiology’, where oft-replicated ecological findings fail to move from ecological to analytical studies (Kuller, 1999).

The task for the research community can be summarized in three steps.Firstly, specific candidate exposures need to be proposed. Secondly, the biological plausibility of these candidates with respect to particular health outcomes needs to be examined, mostly in animal models (e.g. does prenatal exposure to a certain biological agent alter brain development ina fashion that is relevant to depression and/or suicide). Thirdly, the candidate exposure needs to be directly measured in analytical studies that link individual-level exposure with the health outcome.

Salib and Cortina-Borja propose developmental candidates such as melatonin, serotonin and cortisol. Our group has focused on vitamin D as acandidate exposure underpinning risk of schizophrenia (maternal, and thus fetal, vitamin D levels fluctuate across the seasons). The readers may be interested to learn that there is now robust evidence from animal experiments (rats) demonstrating that developmental vitamin D deficiency is associated with altered adult brain outcomes (e.g. increased ventricles, altered neurotrophin levels, altered behaviour) (Becker, Eyles, McGrath, et al, 2005; Burne, Becker, Brown, et al, 2004; Feron, Burne, Brown, et al, 2005; Kesby, Burne, McGrath, et al, in press).

Researchers interested in season-of-birth effects might like to include developmental vitamin D as a biologically-plausible, seasonally-fluctuating candidate exposure.

John McGrathDarryl EylesThomas Burne

Becker, A., Eyles, D. W., McGrath, J. J., et al (2005) Transient prenatal vitamin D deficiency is associated with subtle alterations in learning and memory functions in adult rats. Behav Brain Res, 161, 306-312.Burne, T. H., Becker, A., Brown, J., et al (2004) Transient prenatal Vitamin D deficiency is associated with hyperlocomotion in adult rats. Behav Brain Res, 154, 549-555.Feron, F., Burne, T. H., Brown, J., et al (2005) Developmental Vitamin D3 deficiency alters the adult rat brain. Brain Res Bull, 65, 141-148.Kesby, J., Burne, T. H., McGrath, J. J., et al (in press) Developmental vitamin D deficiency is associated with MK 801-induced hyperlocomotion in the adult rat: an informative animal model of schizophrenia. Biological Psychiatry.Kuller, L. H. (1999) Circular epidemiology. Am J Epidemiol., 150, 897-903.
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Effect of Month of Birth on the Risk of Suicide. Role of Mood Variation.

Angelo Cagnacci, Associate Professor Ob/Gyn
09 May 2006

I read with great interest the article by Salib &Cortina-Boria (1). At the end of their discussion the authors suggest that “the month of birth factor in suicide may reflect individual’s constitutional vulnerability and affective predisposition” . We recently obtained data in support of this hypothesis.

In a multicentric study, by evaluating the psychological status of 2581 Italian women in postmenopause, we showed that anxiety and depression are minimal in women born in Autumn (lowest value November) and peak in women born in Spring (maximal value in March) (2). This seems to reflect quite nicely the seasonal pattern of suicide reported by Salib &Cortina-Boria (1). In our study, data were corrected for the month into which the psychological evaluation was indeed performed.

Mood varies throughout the year, and seasonal rhythms of suicide (3,4), or of events related to low mood, as voluntary abortion, have been reported (4).

Interestingly, these rhythms are similar to the one reported by Salib & Cortina-Boria for the month of birth and risk of suicide(1). It would be interesting to see whether data of this latter study would remain significant when corrected for the seasonal rhythm of suicide. If this is the case, the concordance between the seasonal rhythm of suicide, and the predisposition

to suicide at birth, would suggest that the mechanisms predisposing the newborn to the risk of suicide are operative in the last part of pregnancy, very close to the timing of delivery.

1.Salib, E. & Cortina-Borja, M. (2006) Effect of month of birth on the risk of suicide. British Journal of Psychiatry, 188, 416-422.2.Cagnacci, A., Pansini, F.S., Bacchi-Modena, A., Volpe, A. (2006) The relation of season of birth to severity of menopausal symptoms. Menopause,

13, in press3.Maes, M., Meltzer, H.Y., Suy, E., et al. (1993) Seasonality in severityof depression:relationships to suicide and homicide occurrence. Acta Psychiatrica Scandinavica, 88, 156-161.4.Cagnacci, A. & Volpe, A. (2001) Is voluntary abortion a seasonal disorder of mood? Human Reproduction, 16, 1748-1752.
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Age Specific Data Analysis is Needed

Leonid A. Gavrilov, Ph.D., Scientist
04 May 2006

It may be interesting to reanalyze the data of this new published study for specific age groups (say 20-24, 25-29 and 30-34 years, etc.), tosee whether the month-of-birth effect on suicides still remains to exist. This is an important issue, because the number of people surviving to certain age also depends on the month of birth (Gavrilov & Gavrilova, 1999; 2003; 2004; Gavrilova et al, 2003; Gavrilova & Gavrilov, 2005). Thus the exposure to risk of suicide (denominator numbers) depends on the month of birth in a complex age-specific manner, and these exposure data could not be simply estimated from the seasonality of births.


Gavrilov, L.A. & Gavrilova, N.S. (1999) Season of birth and humanlongevity. Journal of Anti-Aging Medicine, 1999, 2(4): 365-366.

Gavrilov, L.A. & Gavrilova, N.S. (2003) Early-life factors modulating lifespan. In: Rattan, S.I.S. (Ed.).Modulating Aging and Longevity. Kluwer Academic Publishers, Dordrecht, The Netherlands, 27-50.

Gavrilova N.S., Gavrilov L.A., Evdokushkina, et al., (2003) Early-life predictors of human longevity: Analysis of the 19th Century birth cohorts. Annales de Demographie Historique, 2: 177-198.

Gavrilov, L.A. & Gavrilova, N.S. (2004) Early-life programming of aging and longevity: The idea of high initial damage load (the HIDL hypothesis). Annals of the New York Academy of Sciences, 1019, 496-501.

Gavrilova, N.S. & Gavrilov, L.A. (2005) Search for Predictors ofExceptional Human Longevity. In: “Living to 100 and Beyond” Monograph. TheSociety of Actuaries, Schaumburg, Illinois, USA, pp. 1-49. Published online at:
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