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."
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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.)

 

 

 

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