BMI較高則骨折風險降低


  【24drs.com】根據發表於美國骨質研究協會2011年會的研究,較高的身體質量指數(BMI)可以讓婦女對抗骨折風險;不過,和骨密度(BMD)有所關聯。
  
  根據分析了超過25國、超過300,000名婦女、27篇前瞻式人口基礎世代的研究顯示,85%的骨折發生在那些並不肥胖者;肥胖的定義為BMI值30kg/m2以上,各世代的肥胖率為18%。
  
  研究對象的平均年紀為67歲,74,394名婦女有股骨頸雙能量X光吸收測量資料,追蹤期間的骨折事件是根據自我報告或由X光確認。
  
  瑞典Gothenburg大學Sahlgrenska Academy骨骼研究中心研究員Helena Johansson醫師報告指出,整體追蹤期間為140萬人-年,有18,336例骨質疏鬆骨折,包括4,509例髖骨骨折。
  
  研究人員發現,肱骨/手肘骨折風險隨BMI值增加,骨質疏鬆性骨折與髖骨骨折風險隨BMI值增加而降低;平均而言,BMI值18.5-25.0 kg/m2的婦女,每100人-年有超過2.5例骨折,BMI值35到40 kg/m2者的骨折少於0.5,BMI值40 kg/m2以上者的骨折率幾乎為0。
  
  BMI值35或40 kg/m2者的骨質疏鬆性骨折風險比(HR),和BMI值26 kg/m2者相比分別是0.89 (95%信心區間[CI]0.84-0.93)和0.83 (95% CI,0.77-0.90);不過,當校正BMD時,相對應的HRs分別是1.14 (95% CI,1.06-1.23)和1.23 (95% CI,1.10-1.39)。
  
  研究結果也顯示,較高BMI(40 kg/m2)之婦女的髖骨骨折HR只有0.75 (95% CI,0.67-0.85);至於BMI值26 kg/m2者,HR為0.64 (95% CI,0.53-0.78),不過,當校正BMD時,相對應的HRs分別是1.09 (95% CI,0.91-1.30)和1.14 (95% CI,0.86-1.50)。
  
  Johansson醫師指出,雖然一般認為低BMI與骨折風險較大有關,越來越高的肥胖比率也增加了骨折風險改變的考量。
  
  她解釋,年長者有較低的BMI,相當低的BMI是骨折的強力風險因素,最近,曾有肥胖和骨折風險的爭論,因為BMI值越來越高,這個議題越顯重要,有許多研究認為,肥胖可能是骨折的風險因素。
  
  Johansson醫師表示,這次的研究結果有點意料之外。因為之前研究BMI時發現,某種程度的BMD [例如肥胖者]會是髖骨骨折的風險因素,只不過影響不顯著,但是對於骨質疏鬆骨折則無關。
  
  現在,我們有越來越多肥胖病患,因此,有比較高的統計強度來檢視這些影響。
  
  Johansson醫師解釋,如果校正其他風險因素如之前的骨折後,這些研究結果證明為真,則可以更新FRAX這個由世界衛生組織發展用來評估骨折風險的工具。
  
  另外,臨床影響是,或許可據以建議維持BMI值小於30 kg/m2 ,以避免骨折風險。
  
  多倫多大學藥學院的Suzanne M. Cadarette博士表示,研究結果指出了骨折風險的潛在因素。
  
  共同主持該段會議的Cadarette博士表示,或許不單單只是BMI的影響,必須討論體重、脂肪類型、肥胖者的BMD測量誤差、骨折機轉,重點是美國人為何會越來越肥胖。這是重要的議題,值得後續研究。
  
  資料來源:http://www.24drs.com/professional/list/content.asp?x_idno=6633&x_classno=0&x_chkdelpoint=Y
  

Higher BMI Reduces Fracture Risk

By Nancy A. Melville
Medscape Medical News

October 20, 2011 (San Diego, California) — Having a high body mass index (BMI) appears to provide protection against fractures in women; however, bone mineral density (BMD) tends to mediate the effect, according to research presented here at the American Society for Bone and Mineral Research 2011 Annual Meeting.

A study of 27 prospective population-based cohorts representing more than 25 countries showed that, among nearly 300,000 women, 85% of fractures occurred in those who were not obese.

Obesity was defined as having a BMI of 30 kg/m2 or higher, and the obesity rate across the cohorts was 18%.

The average age was 67 years, and dual-emission x-ray absorptiometry measurements at the femoral neck were available for 74,394 of the women. Fractures during follow-up were self-reported or confirmed by radiography.

During the overall follow-up of 1.4 million person-years, there were 18,336 osteoporotic fractures, including 4509 hip fractures, reported lead author Helena Johansson, MD, a research fellow at the Centre for Bone Research at Sahlgrenska Academy, University of Gothenburg, Sweden.

The researchers found that, whereas the risk for humerus/elbow fractures increased with higher BMI, the risk for osteoporotic and hip fracture decreased progressively with increasing increments of BMI.

There were, on average, more than 2.5 fractures per 100 person-years in women with a BMI between 18.5 and 25.0 kg/m2, compared with fewer than 0.5 fractures in those with a BMI of 35 to 40 kg/m2, and nearly 0 fractures for those with a BMI of 40 kg/m2 or higher.

The hazard ratios (HR) for osteoporotic fracture among those with a BMI of 35 or 40 kg/m2, compared with a BMI of 26 kg/m2, were 0.89 (95% confidence interval [CI], 0.84 to 0.93) and 0.83 (95% CI, 0.77 to 0.90), respectively.

When adjusted for BMD, however, the corresponding HRs were 1.14 (95% CI, 1.06 to n1.23) and 1.23 (95% CI, 1.10 to 1.39).

The results also show reductions in HR for hip fracture among women with higher BMIs — for a BMI of 40 kg/m2, HR was 0.75 (95% CI, 0.67 to 0.85); for a BMI of 26 kg/m2, HR was 0.64 (95% CI, 0.53 to 0.78). However, when adjusted for BMD, the corresponding HRs were 1.09 (95% CI, 0.91 to 1.30) and 1.14 (95% CI, 0.86 to 1.50).

Altrhough a low BMI has traditionally been associated with a greater risk for fracture, the rapidly growing obesity rate has raised concern about a possible shift in fracture risk, noted Dr. Johansson.

"Elderly people have lower BMIs, and a very low BMI is a strong risk factor for fracture," she explained. "Lately, there has been a debate about obesity and risk of fracture. Since the BMI is getting higher and higher in the world, this is getting more important. Several studies suggest that obesity also might be a risk factor for fracture."

Dr. Johansson said the findings are somewhat unexpected.

"I was partly surprised because we have previously studied BMI and found that for a given BMD [in obese people], there could be a risk factor for hip fracture, even if this effect was not significant, but not for osteoporotic fracture," she said.

"Now we have more patients and a higher proportion of obese persons, and therefore higher statistical power to be able to detect the effects."

The findings, if demonstrated to be true when adjusted for other risk factors, such as previous fracture, could represent a pertinent update for FRAX, a tool developed by the World Health Organization to evaluate fracture risk, Dr. Johansson explained.

"Another clinical implication is that perhaps the advice about keeping BMI below 30 kg/m2 is also valid in the area of fracture risk."

Suzanne M. Cadarette, PhD, from the Leslie Dan Faculty of Pharmacy, University of Toronto, Ontario, Canada, said the findings shed light on potential factors in fracture risk.

"Perhaps the answer is not as simple as BMI," said Dr. Cadarette, who comoderated the session. "There was discussion of body weight, type of fat, BMD measurement error among obese, the mechanism of fracture, and the importance of how the American population is increasingly obese."

"The issue is important, and it would be good to investigate further," she added.

Dr. Johansson and Dr. Cadarette have disclosed no relevant financial relationships.

American Society for Bone and Mineral Research (ASBMR) 2011 Annual Meeting: Abstract 1036. Presented September 17, 2011.

    
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