本帖最後由 goodcat1111 於 2009-4-30 14:54 編輯
作者：Roxanne Nelson
出處：WebMD醫學新聞
April 15, 2009 — 越來越多研究認為維他命D對癌症病患有幫助。此外，實驗室、生態與流行病學研究都有一些證據顯示維他命D值越高，大腸癌、乳癌、子宮內膜癌、前列腺癌風險越低。
不過，雖然證據看來是有趣的，4月6日臨床腫瘤期刊的線上版編輯評論中，論及腫瘤醫師如何將此資訊運用道臨床實務。編輯者、Samuel Lunenfeld研究中心、多倫多Mount Sinai醫院與Princess Margaret 醫院的Pamela J. Goodwin醫師，提供一些有關病患是否需要服用維他命D補充品的建議給腫瘤醫師。她強調她的建議是暫時性的。
她在編輯評論中指出，因為有進行中以及計畫中的研究，許多待解的問題將獲得解答，腫瘤醫師將可以獲得一些明確建議。
【乳癌病患的值偏低】
Goodwin醫師解釋，對維他命D的興趣急速增加。與維他命D有關的發表文獻總數從1990年到2008年11月呈倍數增加，與癌症和維他命D有關的文章幾乎3倍，與乳癌和維他命D有關的增加更達6倍之多。
在同一期的期刊中，有一篇報告指出，在開始時，74%有乳癌的停經前婦女接受輔助化學治療，且維他命D不足者參與1年的 zoledronate介入。補充一年的維他命D3 (400 IU)之後，研究者發現，不到15%的白人和西班牙婦女達到30 ng/mL以上的充足程度，而黑人婦女都沒有達到。
作者寫道，停經前婦女的飲食維他命D建議只有每天200 IU ，我們的研究認為每天400 IU對於乳癌病患、甚至維持骨骼健康都仍顯不足，對於有意義的抗癌效果也偏低。他們也指出，除了確認適當劑量之外，維他命D補充品對於存活的效果仍然未知。
主要作者、紐約市哥倫比亞大學流行病學醫學助理教授Dawn L. Hershman醫師向Medscape Oncology表示，問題是本研究未探討不同劑量。除了改善骨骼健康之外，沒有人知道是否有任何健康好處。
Goodwin醫師指出，這些結果與最近的另一篇研究類似，該研究發現四分之三乳癌存活者的維他命D不足(Am J Clin Nutr. 2008;88:133-139)。研究作者認為，醫師應對乳癌病患監控維他命D狀態。
Goodwin醫師還指出，其團隊進行的一篇研究(J Clin Oncol. 2008;26[15s]:511)，有相同比率的乳癌病患沒有適當的數值。如同Medscape Oncology所報導的，該研究顯示，婦女在診斷時的維他命D值相當低者，相較於維他命D正常者，比較可能發生末期疾病，94%可能發生轉移，73%可能死亡。
【難以選擇一個適當劑量】
她寫道，雖然缺乏高度證據力，但維他命D對癌症風險或結果有一些效果在生物學上看來是有理的。腫瘤醫師現在必須決定如何建議病患，不過，在選擇適當補充劑量上有一些問題。
Goodwin醫師解釋，維他命D攝取與血中濃度之間的不可預期關係，使得難以建議一個標準補充劑量。即使對於特定界限值有一些意見相左，多數專家認為，最能代表維他命D值的25-OHD血中濃度值為75nmol/L (30ng/mL)可視為維他命D足夠。
她指出，維他命D中毒與高鈣血症有關，導致一些併發症，如腎結石與骨質脫鈣，但是有關高維他命D值與非鈣相關結果的資訊缺乏，急需這方面的研究。
【最重要的是不要有傷害】
因為缺乏資料，腫瘤醫師該如何對病患提出建議？Goodwin醫師提供一些建議，但也提及她的建議只是暫時性的。根據年紀，現有的維他命D建議量是每天200-600 IU。因為有足夠證據顯示這些劑量的維他命D與降低死亡率和改善骨骼健康有關，醫師可以依此作為開始劑量。
不過，如研究所指出的，許多癌症病患在這些劑量下仍然不足，需要更高的補充量。Goodwin醫師表示，腫瘤醫師須將目標訂在適當維他命D值的好處，但也須注意「不要造成傷害」這個最高原則。不是任意追高劑量，她建議測量血中的25-OHD值，作為確認病患是否從維他命補充獲利的指標，確保達到的數值是有利的。
Hershman醫師同意。她表示，因為指引建議的劑量偏低，是可以增加，對於未達到正常範圍的病患進行檢查也是合理的。
這些建議增加了利益而降低了傷害風險。Goodwin醫師寫道，維他命D補充品對於癌症病患或許有別於一般人的相關特定利益或傷害，但這些利益和傷害的事實還無定論，因此，腫瘤醫師對於個別病患的建議需謹慎以對。
Goodwin醫師宣告沒有相關財務關係。
J Clin Oncol. 印刷前於2009年4月6日線上發表。
Guidelines Needed for Optimal Vitamin D Supplementation in Cancer Patients
By Roxanne Nelson
Medscape Medical News
April 15, 2009 — A growing amount of research suggests that vitamin?D may be beneficial to cancer patients. In addition, laboratory, ecologic, and epidemiologic studies have shown some evidence that higher levels of vitamin?D might lower the risk for colon, breast, endometrial, and prostate cancers.
But although the "evidence is intriguing," an editorial published online April 6 in the Journal of Clinical Oncology speculates about how oncologists should disseminate this information in clinical practice. Editorialist Pamela J. Goodwin, MD, from the Samuel Lunenfeld Research Institute, Mount Sinai Hospital and Princess Margaret Hospital, in Toronto, Ontario, offers some suggestions to oncologists who are being asked to advise their patients about whether they should take vitamin?D supplements. She emphasizes that her suggestions are of an interim nature.
"As results of ongoing and planned research become available, many unanswered questions will be resolved, and more definitive recommendations that can be embraced by oncologists will be forthcoming," she notes in her editorial.
Low Levels Noted in Breast Cancer Patients
Interest in vitamin?D has risen exponentially, Dr. Goodwin explains. The total number of published studies relating to vitamin?D more than doubled from 1990 to November 2008, articles relating to cancer and vitamin?D nearly tripled, and those specifically relating to breast cancer and vitamin?D increased almost 6-fold.
The editorial was prompted by a report, published in the same issue of the Journal, that, at baseline, 74% of premenopausal women with breast cancer who received adjuvant chemotherapy and participated in a 1-year zoledronate intervention were vitamin?D deficient. After 1 year of vitamin?D3 supplementation (400?IU), the investigators found that sufficient levels, defined as 30?ng/mL or greater, were achieved by less than 15% of the white and Hispanic women and by none of the black women.
"Although the recommended dietary allowance of vitamin?D in premenopausal women is only 200?IU daily, our study suggests that a dose of 400?IU daily is inadequate in breast cancer patients, even to maintain skeletal health, and is probably too low for meaningful anticancer effects," the authors write. They also note that, in addition to determining optimal dosing, the effect of vitamin?D supplementation on survival is still unknown.
"The problem is that the study did not look at different doses," lead author Dawn L. Hershman, MD, MS, assistant professor of medicine and epidemiology at Columbia University, in New York City, told Medscape Oncology. "No one knows if repleation will have any health benefits at this point, other than improving bone health."
These results, Dr. Goodwin points out, are similar to those of another recent study, which found that about three quarters of breast cancer survivors had insufficient levels of vitamin?D (Am J Clin Nutr. 2008;88:133-139). The study authors suggest that clinicians consider monitoring vitamin?D status in breast cancer patients.
Dr. Goodwin also notes that in a study conducted by her team (J Clin Oncol. 2008;26[15s]:511), the same proportion of patients with breast cancer had inadequate levels. As reported by Medscape Oncology, the study showed that women with very low levels of vitamin?D at diagnosis were more likely to have aggressive disease, 94% more likely to develop metastases, and 73% more likely to die than those with normal levels of vitamin?D at diagnosis.
Difficulty Selecting an Optimal Dose
Although there is a lack of high-level evidence, it is biologically plausible that vitamin?D can have an effect on cancer risk or outcome, she writes. Oncologists must now decide how to advise patients, but selecting an optimal dose for supplementation can be problematic.
Dr. Goodwin explains that the "unpredictable relationship between vitamin?D intake and blood levels" makes it difficult to recommend a standard dose for supplementation. Even though there are some minor disagreements about specific cut points, most experts suggest that a blood level of 25-OHD, considered to be the best marker of vitamin?D status, of approximately 75?nmol/L (30?ng/mL) is required for vitamin?D sufficiency.
Hypervitaminosis D has been associated with hypercalcemia and resulting complications, including renal stones and bone demineralization, she notes, but information regarding the effects of high levels of vitamin?D on noncalcium-related outcomes "is lacking and is urgently needed."
Above All, Do No Harm
Given this lack of information, what should oncologists recommend to their patients? Dr. Goodwin offers suggestions, but warns that her advice should be viewed as interim. Depending on age, current recommendations for vitamin?D range from 200 to 600?IU per day. Given that there is sufficient evidence that vitamin?D supplementation at these doses is associated with reduced mortality and improved bone health, clinicians should feel comfortable using them as a starting point.
However, as studies have indicated, many cancer patients will remain deficient at these levels, and higher supplementation might be needed. Oncologists, says Dr. Goodwin, should aim to achieve the benefits of adequate vitamin?D levels, but they should also be guided by the principle, "above all, do no harm." Rather than just endorsing an arbitrary higher dose, she recommends measurement of blood levels of 25-OHD as the most prudent approach to determine which patients might benefit from supplementation, as well as ensuring that the levels reached are advantageous.
Dr. Hershman agrees. "Since the recommended guidelines are low, and are likely to be increased soon, it is not unreasonable to check levels and replete patients that are deficient to the normal range," she said.
These recommendations increase the potential for benefit while reducing the risk for harm. "There may be specific benefits and harms associated with vitamin?D supplementation in cancer patients that are not present in the general population, despite the fact that these benefits and harms have not been conclusively demonstrated," Dr. Goodwin writes. "As a result, oncologists making recommendations to individual patients should take a cautious approach."
Dr. Goodwin has disclosed no relevant financial relationships.
J Clin Oncol. Published online before print April 6, 2009. |
|
