 Once
drawing up horoscopes was a routine part of a physician's
job. Astrology has long since been consigned to the outer
realms of quackery — even homeopaths consider it
a pseudoscience. But it might still be worthwhile to bear
in mind a patient's month of birth, according to a study
published in the December 7 issue of the British Medical
Journal. The research suggests that there's a link
between a baby's month of birth and the chance of their
developing multiple sclerosis (MS) later in life.
It's been known for some time that
the environment contributes in some way to MS, since
there's a well-established correlation between high
geographical latitude of birth and MS prevalence. However,
the latest findings are the first to demonstrate that
events or the environment in the first days of life,
and possibly even before birth, have an impact on MS
prevalence.
UNSUNNY
DISPOSITIONS
What that impact might be remains a mystery, according
to Dr George C Ebers, a neurologist at England's Oxford
University, who led the Canadian collaborative Study
Group in this research. "It may be something to do with
sunlight or vitamin D exposure in pregnancy. That would
be a testable hypothesis, one that we have started researching.
Sunlight influences a variety of different cycles and
hormones — for example, the pineal gland, melatonin,
as well as temperature responses."
Canadians, Swedes, Danes and Scots
born in November are significantly less likely to develop
multiple sclerosis than people born in other months.
Canadians made up the largest group of subjects in the
study, with a statistically robust 17,874 Canadian MS
patients participating. Of these, 8.5% fewer than expected
were born in the month of November, far beyond the possibility
of random variation.
In addition, when the 44,045 MS
patients participating in all four countries were pooled
for analysis, those born in May were significantly more
likely than others to develop the disease as adults.
Overall, the researchers concluded, people born in these
countries in May are 13% more likely to develop MS than
those born in November.
Oddly, there was no steady rise
and fall throughout the year — almost all of the
variation was confined to these two months. The effect
was most significant in Scots, who have the world's
highest rates of MS. It was also especially significant
in those who have a family history of the disease.
UPSIDE
DOWN UNDER
It's been shown before that season of birth can influence
later health. Germany's Max Planck Institute for Demographic
Research has found that in the Northern hemisphere,
people born in autumn outlive those born in spring.
Revealingly, the pattern is reversed in Australia, where
March-May babies live longest. It's been speculated
that people born in cold weather tend to build up fat
more easily, and are more subject to cardiovascular
disease.
But the phenomenon goes way beyond
fat. It was first demonstrated more than 70 years ago
that schizophrenia is more common in winter births,
a finding that has been frequently replicated. More
recently, depressive symptoms were found to be most
common in Australians born between September and November.
Some researchers have suggested that the phenomenon
corresponds to flu season in the crucial second trimester
of pregnancy, when the foundations of the nervous system
are laid.
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