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agate
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Location: Oregon
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 Posted: Mon Dec 24, 2012 7:20 pm Post subject: (Abst.) Birth month as latitude-dependent risk factor/Norway |
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From PubMed, December 22, 2012:
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Mult Scler. 2012 Dec 20.
Month of birth as a latitude-dependent risk factor for multiple sclerosis in Norway
Grytten N, Torkildsen O, Aarseth JH, Benjaminsen E, Celius EG, Dahl OP, Holmøy T, Løken-Amsrud K, Midgard R, Myhr KM, Risberg G, Vatne A, Kampman MT.
Norwegian Multiple Sclerosis Competence Centre, Department of Neurology, Haukeland University Hospital, Bergen, Norway.
OBJECTIVE:
We aimed to determine if the risk of multiple sclerosis (MS) is associated with month of birth in Norway and to explore a possible latitudinal gradient.
METHODS:
All patients with MS born between 1930 and 1979 registered in the Norwegian MS Registry or ascertained in Norwegian prevalence studies were included (n = 6649). The latitude gradient was divided in Southern, Middle and Northern Norway, according to the estimated regional yearly mean vitamin D effective UV dose.
RESULTS:
Risk of MS was 11% higher for those born in April (p = 0.045), and 5% higher for those born in May (p = 0.229), 5% lower for those born in November (p = 0.302) and 12% lower for those born in February (p = 0.053) compared with the corresponding population, unaffected mothers and siblings.
In Southern Norway the odds ratio of MS births in April and May was 1.05 (0.98 - 1.24), in Middle Norway 1.11 (0.97 - 1.27) and in Northern Norway 1.28 (1.0 - 1.63) compared with the other months.
CONCLUSIONS:
This study confirms previous reports of increased MS births in spring and decreased MS births in the winter months. This could support the role of decreased sunlight exposure during pregnancy and vitamin D deficiency in prenatal life in MS.
PMID:23257620 |
The abstract can be seen here. |
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agate
Site Admin
Joined: 17 May 2006
Posts: 5694
Location: Oregon
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| Posted: Sat Jun 08, 2013 9:08 am Post subject: (Abst.) Birth-month theory questioned |
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Another view of the birth-month theory--from PubMed, June 8, 2013:
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Ann Neurol. 2013 Jun 6.
Confounding underlies the apparent 'month of birth' effect in multiple sclerosis
Fiddes B, Wason J, Kemppinen A, Ban M, Compston A, Sawcer S.
University of Cambridge, Department of Clinical Neurosciences, Addenbrooke's, Hospital, Hills Road, Cambridge, CB2 0QQ, UK.
OBJECTIVE:
Several groups have reported apparent association between month of birth and multiple sclerosis. We sought to test the extent to which such studies might be confounded by extraneous variables such as year and place of birth.
METHODS:
Using national birth statistics from two continents, we assessed the evidence for seasonal variations in birth rate and tested the extent to which these are subject to regional and temporal variation. We then established the age and regional origin distribution for a typical multiple sclerosis case collection and determined the false positive rate expected when comparing such a collection with birth rates estimated by averaging population specific national statistics.
RESULTS:
We confirm that seasonality in birth rate is ubiquitous and subject to highly significant regional and temporal variations. In the context of this variation we show that birth rates observed in typical case collections are highly likely to deviate significantly from those obtained by the simple un-weighted averaging of national statistics. The significant correlations between birth rates and both place (latitude) and time (year of birth) that characterise the general population, indicate that the apparent seasonal patterns for month of birth suggested to be specific for multiple sclerosis (increased in the spring and reduced in the winter) are expected by chance alone.
INTERPRETATION:
In the absence of adequate control for confounding factors, such as year and place of birth, our analyses indicate that the previous claims for association of multiple sclerosis with month of birth are probably false positives. |
The abstract can be seen here. |
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agate
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Location: Oregon
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| Posted: Mon Jun 24, 2013 7:33 am Post subject: Another summary of the Fiddes/Wason study |
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The second article above has been summarized in the MS International Federation newsletter for June 18, 2013:
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Confounding underlies the apparent month of birth effect in MS
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This study group reviewed the evidence that month of birth varies significantly with geographical location and over time in the population and considered the implication of this variation for case-control studies considering month of birth as a risk factor for the development of MS. They assessed the evidence for seasonal variations in birth rate and tested the extent to which these are subject to regional and temporal variation using national birth statistics from two continents.
From this they then established the age and regional origin distribution for a typical MS case collection. They then determined the false positive rate expected when comparing such a collection with birth rates estimated by averaging population specific national statistics.
They found that seasonality in birth rate is ubiquitous and subject to highly significant regional and temporal variations. Birth rates seen in typical case collections are highly likely to deviate from those obtained by the simple un-weighted averaging of national statistics. The apparent seasonal patterns for month of birth suggested to be specific for MS (increased in the spring and reduced in the winter) are probably false positives due to the absence of adequate control for confounding factors, like year and place of birth.
These observations serve as a reminder that risk factors that are easy to determine and seemingly homogenous, like date of birth, may yet be heterogenous within the general population and therefore generate false positive signals if cases and controls are not adequately matched.
Authors: Fiddes B, Wason J
Source: Ann Neurol. 2013 Jun 6 |
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