高劑量維他命D不會改善血糖指標


  【24drs.com】一篇新研究認為,高劑量維他命D補充品看來並不會改善前期糖尿病患者、或採用飲食療法之第二型糖尿病患者的任何血糖指標。
  
  這些研究結果來自線上發表於1月19日糖尿病照護期刊,瑞典斯德哥爾摩Karolinska研究院分子醫學與外科部、內分泌與糖尿病小組、博士生Henrik Wagner等人進行的8週小型隨機試驗。
  
  雖然以前的觀察型研究顯示,血清維他命D值低和第二型糖尿病或代謝症候群之間有相對一致的關聯,有關維他命D補充品的潛在效益則是各有不同。
  
  目前的這篇研究脫穎而出是因為,研究者校正了血清25(OH)D值的季節性變化,並使用一種高血糖箝制技術黃金標準方法估計胰島素分泌和胰島素敏感性。
  
  Wagner醫師等人結論指出,根據研究結果,維他命D治療對於血糖耐受異常者的葡萄糖穩態並無影響。
  
  不過,麻塞諸塞州波士頓Tufts醫學中心內分泌糖尿病與新陳代謝科醫學教授Anastassios G Pittas醫師指出,這項研究有幾個缺陷,樣本數少、時間短、安慰劑組的結果是意料之外的改善。Pittas醫師指出,至少一年以上的較長時間、且有每日維他命D3劑量的研究,才會有比較多資訊。
  
  Wagner等人進行的這篇研究的研究對象,是44名前期糖尿病(根據口服葡萄糖耐受性試驗,有空腹血糖異常、葡萄糖耐受異常、或兩種皆有者)、或非藥物治療的第二型糖尿病患者(n = 12人),他們被隨機指定接受每週一次的30,000 IU維他命D3或安慰劑共8週。
  
  這兩組研究對象在開始時的季節性校正25(OH)D值為43 nmol/L,第8週時,維他命D補充組的25(OH)D值加倍(+42 nmol/L),安慰劑組則是沒有改變(+0 nmol/L)。
  
  至於初級終點,第一階段的血清胰島素分泌與開始時的相對變化,維他命D組傾向增加,安慰劑組則是顯著增加,兩組之間沒有差異(P = .45)。
  
  第二階段的胰島素分泌或胰島素敏感性,不論是單組內或兩組之間比較,都沒有改變。兩組的第一階段處置指數都增加,兩組之間沒有差異。第二階段處置指數顯示,維他命D組傾向增加(P = .06),但是與安慰劑組相比並無顯著差異(P = .95)。
  
  除了維他命D組的脂肪量百分比微幅增加、非脂肪的重量有相對幅度的降低,兩組之間有顯著差異,其他身體組成方面則是沒有改變。
  
  維他命D組的平均HbA1c值小幅降低(0.1%, P = .06),但是與安慰劑組相比並無顯著差異(P = .84),其他血糖測量參數則是沒有任何改變。
  
  維他命D組的副甲狀腺素(PTH)也降低(28 ng/L),且傾向有顯著意義 (P = .07),安慰劑組的三酸甘油脂則是接近達到顯著程度的降低,與維他命D治療組相比為顯著改變(P = 0.02),兩組的膽固醇和LDL都略為降低,且兩組之間沒有差異。
  
  針對25(OH)D值在開始時最低者和增加最多者進行次組分析顯示,這些結果並未改變。
  
  與安慰劑組相比,維他命D治療組並無高鈣血症或其他不良影響。
  
  Pittas醫師表示,雖然這篇研究衡量結果的方法是穩健的,不過,結果是中性的並不奇怪,因為這項研究有一些限制。
  
  例如,研究對象人數很少,所以這篇研究不會有適當強度,此外,維他命D值需要8-12週或更久才達到平穩,而且可能要更長時間才能看到對葡萄糖耐受度的影響,因此,8週的研究期間並不適當。
  
  Pittas醫師指出,重要的是,安慰劑組處置指數的改善與安慰劑組的處置指數應惡化的事實不一致,與前期糖尿病的自然史一致。
  
  不過,Pittas醫師同意作者的結論,目前沒有足夠資料支持使用維他命D來預防糖尿病。
  
  他建議醫師將患者轉介到現有的試驗,最大型的、國家健康研究院支持的多中心維他命D與第二型糖尿病(D2d)臨床試驗,探討維他命D補充品是否可以降低發生第二型糖尿病之風險;Pittas醫師是D2d這項試驗的主要研究者。
  
  資料來源:http://www.24drs.com/
  
  Native link:High-Dose Vitamin D Doesn't Improve Glycemic Parameters

High-Dose Vitamin D Doesn't Improve Glycemic Parameters

Medscape Medical News

High-dose vitamin D supplementation does not appear to improve any measure of glucose metabolism in patients with prediabetes or diet-treated type 2 diabetes, a new study suggests.

Findings from the small randomized 8-week trial were published online January 19 in Diabetes Care by PhD student Henrik Wagner, of the endocrinology and diabetes unit, department of molecular medicine and surgery, Karolinska Institute, Stockholm, Sweden, and colleagues.

While prior observational studies have shown a relatively consistent association between low serum vitamin D levels and type 2 diabetes or metabolic syndrome, data have conflicted regarding potential benefits of vitamin D supplementation.

The current study stands out because the investigators adjusted for seasonal changes in serum 25(OH)D levels and used a gold-standard hyperglycemic clamp technique to estimate insulin secretion and insulin sensitivity.

"According to the findings of our study, we see no implication for vitamin D treatment to affect glucose homeostasis in subjects with abnormal glucose tolerance," Dr Wagner and colleagues conclude.

However, Anastassios G Pittas, MD, professor of medicine in the division of endocrinology, diabetes, and metabolism, Tufts Medical Center, Boston, Massachusetts, pointed out several flaws of the study, including small size, short duration, and an unexpected improvement in the placebo group.

"Longer studies of at least 1-year duration or longer with daily doses of vitamin D3 will be more informative," Dr Pittas told Medscape Medical News.

No Effect on Glycemic Parameters

Study subjects were 44 adults with either prediabetes (impaired fasting glucose, impaired glucose tolerance, or both according to an oral glucose tolerance test), or non–drug-treated type 2 diabetes (n = 12). They were randomized to 30,000 IU vitamin D3 once weekly or placebo for 8 weeks.

Season-adjusted 25(OH)D levels were 43 nmol/L in both groups at baseline. At 8 weeks, 25(OH)D level was doubled in the vitamin-D–supplemented group (+42 nmol/L) and remained unchanged in the placebo group (+0 nmol/L).

For the primary end point — relative change from baseline in first-phase serum insulin secretion — there was a tendency to an increase in the vitamin D group and a significant increase in the placebo group, with no difference between the two groups (P = .45).

No changes in second-phase insulin secretion or insulin sensitivity within or between the groups were seen. First-phase disposition index increased in both groups, with no group difference. Second-phase disposition index showed a tendency to increase in the vitamin D group (P = .06), but there was no significant difference compared with placebo (P = .95).

There were no changes in body composition except for a small increase in percent fat mass in the vitamin D group, accompanied by a similar decrease in fat-free mass, with significant differences between groups.

There was a small reduction in median HbA1c in the vitamin D group (0.1%, P = .06), but with no significant difference vs placebo (P = .84). No other glycemic measurements showed any changes.

There was a decrease of parathyroid hormone (PTH) in the vitamin D group (28 ng/L), with a tendency toward significance by group (P = .07). Triglycerides decreased nearly significantly in the placebo group, a significant change vs the vitamin D–treated group (P = 0.02). Cholesterol and LDL decreased slightly in both groups, with no difference between the groups.

Subgroup analyses of those with the lowest basal and greatest increase in 25(OH)D levels did not change these results.

No hypercalcemia or other adverse effects of vitamin D treatment were seen compared with placebo.

Longer, Larger Study Needed?

Dr Pittas told Medscape Medical News that while the study's method to measure the outcome was "robust," nonetheless "it is not surprising that results are neutral because the study has several limitations."

For one, he said, the number of participants was very small, so the study was unlikely to be adequately powered. Moreover, "It takes 8 to 12 weeks or more for vitamin D levels to plateau and probably a bit more before we see an effect on glucose tolerance. Therefore, study duration of 8 weeks is likely inadequate."

And importantly, Dr Pittas pointed out that the improvement in disposition index in the placebo group is "inconsistent with the fact that disposition index should be worse with placebo, consistent with the natural history of prediabetes."

Dr Pittas does, however, agree with the author's conclusion that "at this point, there are not enough data to support the use of vitamin D to prevent diabetes."

He recommended that clinicians refer patients to existing trials, the largest of which is the National Institutes of Health–supported multicenter Vitamin D and Type 2 Diabetes (D2d) clinical trial, which is investigating whether vitamin D supplementation can reduce the risk of developing type 2 diabetes. Dr Pittas is D2d's principal investigator.

The study was supported by grants from the European Federation for the Study of Diabetes, the Swedish Research Council, and the Swedish Diabetes Association. Renapharma contributed to independent monitoring and Merck contributed study medication. The study authors reported no further relevant financial relationships. Dr Pittas is principal investigator of the D2d study, which is funded by the National Institutes of Health and the American Diabetes Association. He has no further relevant financial relationships.

Diabetes Care. Published online January 19, 2016.

    
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