We read with great interest, the paper from Givon et al. [1], reporting on the absence of a relationship between an individual’s month of birth and development of multiple sclerosis (MS) in Israel. The authors considered that the relatively stable weather conditions in Israel allow for adequate sun exposure throughout the year. However, it has been suggested that the month in which a person is born and the development of MS might be related through the influence of the mother’s exposure to sunlight during pregnancy, possibly affecting vitamin D metabolism. This theory has been supported by data from several countries with pronounced winters [2,3,4,5,6,7], confirming that more individuals with MS were born at the end of the winter season. In other studies, the season of birth did not seem to interfere with the development of MS later in life, despite severe winters [10].

The present study aimed to assess whether the month of birth might influence the development of MS in a specific geographic region of Brazil. The study was approved by the institutions participating in data collection. Information on the month of birth from 2,030 MS patients was obtained from Brazilian MS units in 15 cities between the latitudes of 18°55′23′′S and 29°43′23′′S. The typical climate of the region within these latitudes is tropical and subtropical, with mild winters and hot summers. A control group of nonneurological patients and employees from different hospital units was created with 2,030 individuals.

The month of birth of MS cases and control individuals is shown in figure 1a and showed no significant differences when compared using χ2 analysis. Similarly, no differences were observed when the data set was divided into the annual seasons (fig. 1b).

Fig. 1
Fig. 1. Month of birth of Brazilian cohort of control and MS patients: number of births recorded in individual months between 1997 and 2012 (a) and distribution of births throughout the annual seasons (b). No significant differences were observed.
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Month of birth of Brazilian cohort of control and MS patients: number of births recorded in individual months between 1997 and 2012 (a) and distribution of births throughout the annual seasons (b). No significant differences were observed.

Fig. 1
Fig. 1. Month of birth of Brazilian cohort of control and MS patients: number of births recorded in individual months between 1997 and 2012 (a) and distribution of births throughout the annual seasons (b). No significant differences were observed.
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Month of birth of Brazilian cohort of control and MS patients: number of births recorded in individual months between 1997 and 2012 (a) and distribution of births throughout the annual seasons (b). No significant differences were observed.

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Our results are similar to those of Givon et al. [1]. Israel and Brazil share similar daylight and temperatures throughout the year. These findings may indeed reinforce the idea that stable weather without severe and dark winters might exclude the seasonal distribution of MS patients born in different periods of the year.

Disclosure Statement

The present study was carried out without financial support from private or governmental grants. The authors have no conflicts of interest to declare regarding this work.

1.
Givon U, Zeilig G, Dolev M, Achiron A: The month of birth and the incidence of multiple sclerosis in the Israeli population. Neuroepidemiology 2012;38:64–68.
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Wiberg M, Templer DI: Season of birth in multiple sclerosis in Sweden: replication of Denmark findings. J Orthomol Med 1994;9:71–74.
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Bharanidharan P: Monthly distribution of multiple sclerosis patients’ births. Int J Biometeorol 1997;40:117–118.
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Willer CJ, Dyment DA, Sadovnick AD, Rothwell PM, Murray CJ, Ebers GC: Timing of birth and risk of multiple sclerosis. BMJ 2005;330:120.
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Staples J, Ponsonby AL, Lim L: Low maternal exposure to ultraviolet radiation in pregnancy, month of birth, and risk of multiple sclerosis in offspring: longitudinal analysis. BMJ 2010;340:c1640.
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Salzer J, Svenningsson A, Sundström P: Season of birth and multiple sclerosis in Sweden. Acta Neurol Scand 2010;122:70–73.
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Bayes HK, Weir CJ, O’Leary C: Timing of birth and risk of multiple sclerosis in the Scottish population. Eur Neur 2010;63:36–40.
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Saastamoinen KP, Auvinen MK, Tienari PJ: Month of birth is associated with multiple sclerosis but not with HLA-DR15 in Finland. Mult Scler 2012;18:563–568.
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© 2012 S. Karger AG, Basel
2012
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