Vitamine D tegen
kanker.*
Twee
nieuwe studies over Vitamine D en kanker laten zien dat deze vitamine de kans op
borstkanker met 50% kan doen afnemen en de kans op darmkanker wel met 75% kan
doen afnemen. Deze studies zijn meta-analyses van verschillende eerdere studies
waardoor de resultaten veel nauwkeuriger zijn.
De
borstkankerstudie: Vrouwen werden ingedeeld in verschillende groepen naar gelang
hun bloedwaarde vitamine D, de laagste groep met 13 ng/ml en de hoogste met 52
ng/ml. Duidelijk was dat vrouwen in de laagste groep de meeste kans hadden op
het krijgen van borstkanker. Naarmate de bloedwaarden stegen verminderde ook de
kans op het krijgen van borstkanker. Zo hadden de vrouwen in de hoogste groep
wel 50% minder kans.
Ook
bij de darmkankerstudie werden er verschillende groepen gemaakt. Nu blijkt dat
een bloedwaarde van 34 ng/ml vitamine D de kans op darmkanker met 50% doet
afnemen en een bloedwaarde van 46 ng/ml die kans met 75% doet afnemen.
Om
een bloedwaarde van ca. 50 ng/ml te bereiken dient men toch iedere dag wel 50
mcg vitamine D binnen te krijgen. Dan zal behalve een kwartier per dag in de zon
en een voeding rijk aan vitamine D ook wel een supplement nodig zijn.
Vitamin D For Cancer
Prevention
Two
new vitamin D studies using a sophisticated form of analysis called
meta-analysis, in which data from multiple reports is combined, have revealed
new prescriptions for possibly preventing up to half of the cases of breast cancer
and two-thirds of the cases of colorectal cancer in the United States. The work
was conducted by a core team of cancer prevention specialists at the Moores
Cancer Center at University of California, San Diego (UCSD), and colleagues from
both coasts.
The breast cancer study, published online in the current issue of the Journal
of Steroid Biochemistry and Molecular Biology, pooled dose-response data
from two earlier studies - the Harvard Nurses Health Study and the St. George's
Hospital Study - and found that individuals with the highest blood levels of
25-hydroxyvitamin D, or 25(OH)D, had the lowest risk of breast cancer.
The researchers divided the 1,760 records of individuals in the two studies into
five equal groups, from the lowest blood levels of 25(OH)D (less than 13
nanograms per milliliter, or 13 ng/ml) to the highest (approximately 52 ng/ml).
The data also included whether or not the individual had developed cancer.
"The data were very clear, showing that individuals in the group with the
lowest blood levels had the highest rates of breast cancer, and the breast
cancer rates dropped as the blood levels of 25-hydroxyvitamin D increased,"
said study co-author Cedric Garland, Dr.P.H. "The serum level associated
with a 50 percent reduction in risk could be maintained by taking 2,000
international units of vitamin D3 daily plus, when the weather permits, spending
10 to 15 minutes a day in the sun."
The colorectal cancer study, published online February 6 in the American
Journal of Preventive Medicine, is a meta-analysis of five studies that
explored the association of blood levels of 25(OH)D with risk of colon cancer.
All of the studies involved blood collected and tested for 25 (OH)D levels from
healthy volunteer donors who were then followed for up to 25 years for
development of colorectal cancer.
As with the breast cancer study, the dose-response data on a total of 1,448
individuals were put into order by serum 25(OH)D level and then divided into
five equal groups, from the lowest blood levels to the highest.
"Through this meta-analysis we found that raising the serum level of
25-hydroxyvitamin D to 34 ng/ml would reduce the incidence rates of colorectal
cancer by half," said co-author Edward D. Gorham, Ph.D. "We project a
two-thirds reduction in incidence with serum levels of 46ng/ml, which
corresponds to a daily intake of 2,000 IU of vitamin D3. This would be best
achieved with a combination of diet, supplements and 10 to 15 minutes per day in
the sun."
Vitamin D3 is available through diet, supplements and exposure of the skin to
sunlight, or ultraviolet B (UVB). In the paper, the researchers underscored the
importance of limiting sun exposure such that the skin does not change color
(tan) or burn. For a typical fair-skinned Caucasian individual, adequate vitamin
D could be photosynthesized safely by spending 10 to 15 minutes in the noontime
sun on a clear day with 50 percent of skin area exposed to the sun. Darker
skinned individuals may require more time in the sun, such as 25 minutes. For
people with photosensitivity disorders, or anyone with a personal or family
history of nonmelanoma skin cancer, any amount of extra sun exposure would be
inadvisable.
The meta-analysis on colorectal cancer includes data from the Women's Health
Initiative, which had shown in 2006 that a low dose of vitamin D did not protect
against colorectal cancer within seven years of follow-up. However, the
researchers wrote, the meta-analysis indicates that a higher dose may reduce its
incidence.
"Meta-analysis is an important tool for revealing trends that may not be
apparent in a single study," said co-author Sharif B. Mohr, M.P.H.
"Pooling of independent but similar studies increases precision, and
therefore the confidence level of the findings."
###
The authors recommend further research to study individuals for the effect of
vitamin D from sunlight, diet and supplements on the risk of cancer.
Co-authors on both the breast cancer and colorectal meta-analysis papers are
Edward D. Gorham, MPH, Ph.D., Cedric F. Garland, Dr.P.H.; Frank C. Garland, Ph.D.;
Sharif B. Mohr, MPH; William B. Grant, Ph.D; Martin Lipkin, M.D.; Harold L.
Newmark, ScD; Edward Giovannucci, M.D., ScD; and Michael F. Holick, M.D., Ph.D.
Co-author on the colorectal meta-analysis paper only was Melissa Wei, B.S.
Authors' institutional affiliations are UCSD Department of Family and Preventive
Medicine and Moores UCSD Cancer Center (Gorham, Garland, Garland); Naval Health
Research Center, San Diego (Gorham, F.C. Garland, Mohr); SUNARC-Sunlight,
Nutrition and Health Research Center, San Francisco (Grant); Strang Cancer
Prevention Center of Rockefeller University, New York, NY (Lipkin); Rutgers--The
State University of New Jersey and Cancer Institute of New Jersey (Newmark);
Harvard Schools of Public Health and Medicine (Giovannucci, Wei); and Boston
University School of Medicine (Holick). Funding for this research was provided
by a Congressional allocation to the Hollings Cancer Center of the Medical
University of South Carolina through the Department of the Navy. (Febr. 2007) (Opm.
Meer over vitamine D in de voeding.)