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Vitamine D en borstkanker*
Uit een Canadese studie blijkt dat vrouwen met lage bloedwaarden vitamine D op het moment van het vaststellen van borstkanker veel meer risico lopen op uitzaaiingen en een veel grotere kans hebben om dood te gaan aan de ziekte. 512 vrouwen met een gemiddelde leeftijd van 40-60 jaar deden aan de studie mee en werden gemiddeld 14 jaar gevolgd. Slechts 123 vrouwen (24%) bleken voldoende bloedwaarden vitamine D te hebben. De kans op overleven zonder uitzaaiingen was liefst 94% minder in de groep vrouwen met de laagste vitamine D waarden. In het algemeen gaven lage bloedwaarden vitamine D een 73% lagere overlevingskans, alhoewel dit verband er bij niet hormoongevoelige borstkanker niet leek te zijn. De gemeten bloedwaarden vitamine D in de zomer bleken slechts weinig meer te zijn dan in de zomer.
Breast Cancer Spread And Poorer Survival Linked To Vitamin D
Research from Canada suggests that women with breast cancer who were low in Vitamin D at the time of their diagnosis had a higher risk of the cancer spreading and poorer survival rates compared with women who had adequate levels of Vitamin D.
The study was presented at the 44th Annual Meeting of the American Society of Clinical Oncology (ASCO) by lead investigator Dr Pamela Goodwin of Mount Sinai Hospital in Toronto, and colleagues.
The ASCO meeting was held in Chicago from 30th May to 3rd June 2008. An abstract of the study is also due to be published as a supplement to the Journal of Clinical Oncology.
For the study, Goodwin and colleagues examined diagnostic records of new breast cancer cases and the results of dietary questionnaires from 512 women aged around 40 to 60 years, who were enrolled at three University of Toronto hospitals from 1989 to 1995 and who were followed until 2006.
The women also gave blood samples when they were diagnosed; these had been kept at 80 degrees C and the researchers used radioimmunoassay to assess the Vitamin D levels at time of diagnosis.
The results showed that:
· 288 women had T1 tumours, 164 of them had T2 tumours, and 24 had T3/T4 tumours (the higher the T number, the larger and more invasive the tumour).
· 356 of the tumours were N0 (no lymph nodes involved) and 342 were estrogen receptor (ER) positive.
· 73 tumours were grade 1, while 202 were grade 2 and 173 were grade 3 (higher grade means tumour cells are less "normal" and more likely to grow and spread).
· 199 women received adjuvant chemotherapy (treatment given after the primary treatment) and 200 received tamoxifen.
· The cancer spread in 22.7 per cent (116) of the women and 20.7 per cent (106) of them died during a median follow up of 11.6 years.
· Only 24 per cent (123) of the women had adequate leves of Vitamin D in their blood samples.
· Low Vitamin D levels were linked to a reasonable degree (p<0.03) to being premenopausal, having a high BMI (body mass index), high insulin and high tumour grade.
· Low Vitamin D levels were more strongly linked (p<0.02) to low dietary intake of retinol, Vitamin E, grains and alcohol.
· Vitamin D levels were slightly lower for blood samples given in winter (October to March) than in Summer (April to September).
· Distant disease-free survival (DDFS), ie surviving without cancer spread, was a significant 94 per cent worse in women with deficient Vitamin D levels compared with women with adequate Vitamin D levels.
· Overall survival was 73 per cent worse in women who were deficient in Vitamin D.
· The link between DDFS and Vitamin D was independent of age, BMI, insulin, tumour stage (T and N), ER and tumour grade.
· The link between overall survival and Vitamin D did, however, depend on tumour grade.
· In the case of ER negative breast cancers, there appeared to be no link between Vitamin D levels and overall survival.
The researchers concluded that:
"Vit D deficiency is common at BC [breast cancer] diagnosis and is associated with poor prognosis."
Goodwin told the press that this was:
"The first time that vitamin D has been linked to breast cancer progression," according to a report in the Los Angeles Times.
The results have been described as "provocative" by experts not involved in the study, which was sponsored by the National Breast Cancer Institute. One told the Times that there was some evidence that certain drugs for breast cancer are "activated" by vitamin D.
Vitamin D is known to regulate many aspects of cellular growth and differentiation. Previous research has linked Vitamin D deficiency with increased risk of breast cancer, but this is the first study to examine the prognostic effect of Vitamin D on a group of women who already had breast cancer.
Because this was a prospective study, as opposed to say a randomized clinical trial, it would be wrong to conclude from these findings that Vitamin D levels directly impacts cancer spread and survival rates, and therefore women should not use these results as a reason to start taking Vitamin D supplements to treat their breast cancer.
"Frequency of vitamin D (Vit D) deficiency at breast cancer (BC) diagnosis and association with risk of distant recurrence and death in a prospective cohort study of T1-3, N0-1, M0 BC."
P. J. Goodwin, M. Ennis, K. I. Pritchard, J. Koo, N. Hood.
J Clin Oncol 26: 2008 (abstr 511)
Source: ASCO, LA Times, National Cancer Institute. (Juni 2008)