A child's place of birth and their mother's exposure to sunlight
during early pregnancy could play an important role in later life
multiple sclerosis risk, according to a new Australian study by the
Murdoch Childrens Research Institute and The Australian National
University.
The study, published online today by the British Medical Journal
(bmj.com), found low maternal sunlight exposure - the main source
of vitamin D - during the first four months of pregnancy increased
the risk of multiple sclerosis in offspring in Australia.
Region of birth was also related to risk, with prevalence of
multiple sclerosis highest in Tasmania and lowest in Queensland,
suggesting exposure to sunlight during childhood and early
adulthood may also be important.
Sunlight exposure levels during early pregnancy were reflected
in a month of birth pattern, with Australian children born in
November and December having a higher risk of developing multiple
sclerosis than those born in May and June. This is consistent with
previous research that found a reciprocal pattern in the northern
hemisphere, where there were more cases of multiple sclerosis in
people born in May and fewer in those born in November.
Study co-author Professor Anne-Louise Ponsonby said the findings
indicated a need to review guidelines for vitamin D supplementation
during pregnancy and childhood to help prevent multiple
sclerosis.
"Low vitamin D levels can affect the development of the central
nervous system or immune system," Professor Ponsonby, of the
Murdoch Childrens Research Institute, said.
"The higher risk of multiple sclerosis for people born in
November and December is consistent with these infants having
experienced lower levels of ultraviolet radiation during the first
trimester."
The study gathered data on the birth month, sex and region of
birth of 1524 multiple sclerosis patients born in Australia between
1920 and 1950.
No association was found between daily ultraviolet radiation
levels at the time of birth or in late pregnancy, and subsequent
risk of multiple sclerosis. However, maternal exposure to low
ultraviolet radiation levels during the first four months of
pregnancy predicted a higher risk of multiple sclerosis. This
effect persisted after adjustment for region of birth and appeared
more important than the month of birth.
Multiple sclerosis is a disease of the central nervous system
that affects an estimated 18,000 people in Australia.