Vitamine
D tegen Multiple Sclerose.*
Uit een bevolkingsonderzoek onder 7 miljoen Amerikanen blijkt dat voldoende vitamine D de kans op Multiple Sclerose sterk doet dalen. Mensen met de hoogste bloedwaarde aan vitamine D hadden 62% minder kans op het ontstaan van de ziekte dan zij met de laagste bloedwaarden. Deze studie bevestigt de conclusies van eerdere onderzoeken waarin vitamine D het immuunsysteem deed versterken en auto-immuunreacties deed afnemen.
The
Risk Of Multiple Sclerosis May Be Decreased By High Levels Of Vitamin D In The
Body
The
possibility that vitamin D could help protect people from developing multiple
sclerosis (MS) has been posited by researchers in recent decades, but evidence
to support that link has been scant. In the first large-scale, prospective study
to investigate the relationship between vitamin D levels and MS, researchers at
the Harvard School of Public Health (HSPH) have found an association between
higher levels of vitamin D in the body and a lower risk of MS. The study appears
in the Journal of the American Medical Association.
"If confirmed, this finding suggests that many cases of MS could be
prevented by increasing vitamin D levels. Although these levels could be
increased by taking supplements, before any recommendation is made it is
important to establish whether we are seeing a true causal association or
whether vitamin D levels are only a marker of MS risk," said Alberto
Ascherio, senior author of the study and associate professor of nutrition and
epidemiology at HSPH.
MS is a chronic degenerative disease of the central nervous system. It affects
some 350,000 people in the U.S. and 2 million worldwide, and occurs most
commonly in young adults. Women, who are affected more than men, have a lifetime
risk of about 1 in 200 in the U.S. Vitamin D is a hormone manufactured naturally
in the body, and its levels can be increased with exposure to sunlight,
consumption of foods rich in vitamin D, such as fatty fish, and by taking
supplements.
The researchers, led by Ascherio, worked in collaboration with colleagues in the
U.S. Army and Navy to determine whether vitamin D levels measured in healthy
young adults predict their future risk of developing MS. The investigation
relied on a study population of more than 7 million individuals, whose serum
samples are stored in the Department of Defense Serum Repository. Between 1992
and 2004, 257 U.S. Army and Navy personnel with at least two serum samples
stored in the repository were diagnosed with MS. A control group, consisting of
participants who did not develop MS, was randomly selected from the study
population. Serum samples were analyzed for levels of 25-hydroxyvitamin D, a
good indicator of vitamin D availability to tissues, and individuals were
divided into five groups of equal size according to their average levels.
Because vitamin D levels are strongly influenced by skin color, separate
analyses were conducted among whites, blacks, and Hispanics.
The results showed that, among whites, MS risk declined with increasing vitamin
D levels--the risk was 62% lower among individuals in the top fifth of vitamin D
concentration (corresponding approximately to levels above 100 nmol/L or 40 ng/mL)
than among those in the bottom fifth (approximately below 63 nmol/L or 25 ng/mL).
The association was strongest among individuals who were younger than 20 when
they first entered the study. No significant association was found among blacks
and Hispanics, possibly because of a smaller sample size and the lower levels of
vitamin D found in those groups. The average age of onset of MS cases was 28.5
years old; there was no significant difference in the results between men and
women.
"The results of this study converge with a growing body of experimental
evidence supporting the importance of vitamin D in regulating the immune system
and suppressing autoimmune reactions, which are thought by most experts to play
a key role in the development of MS," said Ascherio. Kassandra Munger,
first author and a doctoral candidate in nutrition at HSPH, added, "The
amount of vitamin D that is needed to reach levels associated with MS protection
is largely considered safe, and in fact higher vitamin D levels could be
beneficial to prevent osteoporosis and other chronic diseases."
The researchers note that there could be other possible explanations for the
protective role of vitamin D. For example, it’s possible that exposure to
UV light from the sun--the major determinant of serum levels of
25-hydroxyvitamin D--could protect people in other ways than increased vitamin D
production.
The authors suggest further studies exploring how vitamin D may protect
individuals from developing MS. "Although the results of this study are
quite encouraging, reasonable certainty of a protective effect of vitamin D
supplements requires direct experimental evidence in a large trial. Meanwhile,
we are planning to expand our study to obtain more accurate data on the
importance of age and of the vitamin D levels that need to be achieved for
optimal protection," said Ascherio.
###
The work was supported
by grants from the National Institute of Neurological Disease and Stroke and by
a pilot grant from the National Multiple Sclerosis Society.
Harvard School of Public Health is dedicated to advancing the public's health
through learning, discovery, and communication. More than 300 faculty members
are engaged in teaching and training the 900-plus student body in a broad
spectrum of disciplines crucial to the health and well being of individuals and
populations around the world. Programs and projects range from the molecular
biology of AIDS vaccines to the epidemiology of cancer; from risk analysis to
violence prevention; from maternal and children's health to quality of care
measurement; from health care management to international health and human
rights.
(Jan. 2007) (Opm. Meer over Vitamine D en voedingsbronnen van vitamine D.)