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 Experts
call the hypothesis - that deficiency in pregnant
women and young children is a factor - speculative
by MARTIN MITTELSTAEDT
The growing prevalence of autism is one of the
biggest scientific whodunits in the medical world,
with few clues for its rising incidence.
But a U.S. researcher is advancing a controversial
hypothesis: that autism is related to vitamin
D deficiency during fetal development and early
childhood.
Dr. John Cannell, a psychiatrist and prominent
vitamin D advocate, says flagging levels of the
vitamin in pregnant women and young children could
be the elusive factor explaining the rising rate
of autism.
The evidence for such a link is circumstantial,
and autism experts describe the hypothesis as
speculative. But Dr. Cannell, founder of the Vitamin
D Council, a non-profit advocacy group, says autism
rates have skyrocketed in lockstep with medical
advice given to the public since the late 1980s
to avoid all exposure to bright sunshine.
"If it's true, I can't think of another situation
where medical advice was so damaging to such a
large number of people," says Dr. Cannell,
who practises at Atascadero State Hospital in
California.
The vitamin D link "is an interesting speculation,"
says Dr. Wendy Roberts, a professor of pediatrics
at the University of Toronto and one of Canada's
leading autism experts.
Because the cause of autism is such an enigma,
Dr. Roberts says researchers should investigate
vitamin D, but the public should treat the idea
more cautiously.
"You like to be able to have something that
is firm and clear before you get parents all excited
and doing something and then, once again, being
disappointed," she said.
Although Dr. Cannell is something of a maverick
in research circles, he has credentials. Last
year, he published an important peer-reviewed
paper linking low vitamin D levels to an increased
susceptibility to influenza, based on research
at his hospital.
But for his autism hypothesis, he is now jeopardizing
his chances of publication in a scientific journal
by e-mailing the Vitamin D Council newsletter
outlining the idea to thousands of U.S. autism
activists - a possible violation of the rules
of publication.
Dr. Cannell said he decided to disseminate his
hypothesis now to encourage the public to increase
its sun exposure during the warmer part of the
year.
"If only 10 pregnant women go outside and
sunbathe a little bit, they may be saved a lifetime
of misery," he said.
The idea that vitamin D deficiency may have a
link to autism isn't as farfetched as it once
might have seemed because the deficiency is also
emerging as a possible cause of many diverse illnesses,
ranging from multiple sclerosis to cancer.
Last month, the Canadian Cancer Society recommended
adults start taking the sunshine vitamin to reduce
their risk of cancer.
Autism refers to a spectrum of conditions that
involve repetitive behaviours and difficulty communicating
and interacting socially. Autism manifests itself
in the first few years of life and is thought
to be some kind of neurological disorder affecting
brain function.
One discredited theory is that the mercury-containing
preservative thimerosal once used in childhood
vaccines causes autism. Studies have failed to
find any link.
The cause of autism is further clouded because
some scientists speculate that part of the apparent
increase in incidence - in the United States it
is being diagnosed about 10 times more frequently
now than in the early 1990s - may reflect improved
reporting by doctors more aware of the condition.
The current Canadian estimate is that about 60
children out of every 10,000, or about 1 in 165,
have autism and related conditions. Up until the
1990s, the prevalence was thought to be far lower,
at only 4 or 5 children in 10,000.
If there is a vitamin D link, incidence rates
around the world would probably vary by latitude.
Rates would be lower in equatorial areas, where
sun exposure is higher, than in northern latitudes,
but studies investigating geographical differences
in diagnosis haven't been done.
Dr. Cannell says some of the strongest evidence
vitamin D may have a hand in the disorder is that
the vitamin is converted in the body to a steroid
hormone, which in animal experimentation has been
found to influence brain development. If vitamin
levels are low, whatever brain development it
is linked to will be skewed.
Startling trend
The occurrence of autism spectrum disorders (the
most sever of which is autism) has risen sharply
during recent years.
Rate per 10,000
UNITED STATES
1980s: 4-5
1990s: 30-60
2000A: 67
CANADA
2001B: 60
SOURCES: ENVIRONMENTAL HEALTH PERSPECTIVES
A- CENTRES FOR DISEASE CONTROL
B-CAIRN
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