Sunlight
for Children May Help Prevent Multiple Sclerosis
A new study of identical twins suggests that children who
spend more time in the sun have a lower risk for developing multiple sclerosis,
or MS, as adults.
Reported in the medical journal Neurology,
the study shows that evidence is growing that sunlight and/or vitamin D exposure
during childhood may help protect health.
According to the National Multiple
Sclerosis Society, MS is an autoimmune disease of the central nervous
system that currently affects more than 400,000 Americans. More than 2.5
million men and women worldwide suffer from the disorder.
While it is unclear what causes MS, the often-crippling
disease is thought to develop when the body's own immune system begins attacking
a fat and protein-laden substance called myelin that insulates nerve fibers.
Numbness, tingling, loss of coordination and balance, blindness,
fatigue, and even paralysis can ensue, as normal communications between brain
and body progressively collapse.
The majority of MS patients are first diagnosed between
the ages of 20 and 50, and female patients outnumber males two-to-one.
The new study findings echo those of a recent Harvard School
of Public Health study, published in the Journal of
the American Medical Association (JAMA).
Among 140 Caucasian men and women, those with the highest
levels of sunlight-derived vitamin D were 62 percent less likely to have developed
MS than those with the lowest levels.
However, the finding was not replicated in a smaller patient
pool of either African Americans or Hispanics.
In the latest
study, Dr. Thomas Mack’s team assessed
the sun exposure of 79 pairs of identical twins in the US and Canada, in which
at least one twin in each pair had been diagnosed with MS.
Most of the twins were girls, and among those with MS, most
had been diagnosed between the ages of 20 and 40.
Each subject was asked about his or her childhood history
of outdoor activity, as well as that of the twin.
Time spent tanning, going to the beach, and playing team
sports during childhood was also noted. No absolute sun exposure measurements
were recorded.
The authors assessed relative degrees of sun exposure between
twins, based on personal recall.
All participants were also asked to reveal any history of
childhood infections as well as smoking habits.
The result: The twin with MS usually had been exposed to
less sun overall as a child than the twin without the disease, the researchers
find.
They observed, however, that this protective effect was
only apparent among female twins. The lack of evidence among male twins could
simply be a function of the relatively small number of male twins included
in the study, the researchers say.
The degree to which the risk for developing MS was reduced
as a result of increased sun exposure ranged from 25 percent to 57 percent,
depending on the disease-free twin's activities.
For example, the researchers determined that non-MS twins
who had spent more childhood time sun-tanning than their sibling had a nearly
50 percent reduced risk of developing MS as an adult.
It is not clear how sun exposure might protect against the
illness. Ultraviolet rays might trigger a beneficial cellular immune response
directly, or perhaps sunlight helps stave off the disease indirectly, by boosting
vitamin D production.
To better understand
the mystery behind sun exposure and its link to MS risk, the researchers
said future sun-MS studies should be given "high
priority."
"If it's true that sunlight is protective and/or vitamin
D is protective, then there's one group of people who ought to think seriously
about it, and that is young parents who have MS," notes Dr. Mack.
He says the likelihood that a child of a parent with MS
will go on to get MS is 3 percent or 4 percent, and this is many, many times
the likelihood that the average person could get MS.
"So, I think if I was a young parent, and I or my wife had
MS, and I had a child, I would want to take every step I could take to prevent
my child from getting the disease," adds Dr. Mack.
"But," he cautions, "the
problem is, of course, that we know that too much sunlight is the cause of
melanoma. So, that's a dilemma.
We want to give the child some exposure but not too much."
Dr. John Richert, executive vice president for research
and clinical programs at the National Multiple Sclerosis
Society, which co-sponsored the study, says that "we all have to take
note of" the new findings.
"This is one of a series of reports over the last couple
of years that have at least indirectly implicated the role of sun exposure
and vitamin D production with susceptibility to MS," he notes.
"And this builds a stronger and stronger case that sun is
one of the factors that can contribute to the development of MS," says Dr.
Richert.
Dr. Richert observed that MS in general is more common the
farther away from the equator one lives, particularly during childhood, further
supporting the sunlight-MS link.
However, he also agreed that too much sunlight brings its
own risks.
"Certainly, in terms of relative risk - skin cancer that
can develop from sun exposure versus the potentially diminished risk for MS
- we don't have equations to really balance these," stresses Dr. Richert.
"And there's a lot more work that still needs to be done
before any kind of recommendations can be made about sun exposure or vitamin
D intake," he says.
Always consult your physician for more information. |
