BMI较高则骨折风险降低


  【24drs.com】根据发表于美国骨质研究协会2011年会的研究,较高的身体质量指数(BMI)可以让妇女对抗骨折风险;不过,和骨密度(BMD)有所关联。
  
  根据分析了超过25国、超过300,000名妇女、27篇前瞻式人口基础世代的研究显示,85%的骨折发生在那些并不肥胖者;肥胖的定义为BMI值30kg/m2以上,各世代的肥胖率为18%。
  
  研究对象的平均年纪为67岁,74,394名妇女有股骨颈双能量X光吸收测量资料,追踪期间的骨折事件是根据自我报告或由X光确认。
  
  瑞典Gothenburg大学Sahlgrenska Academy骨骼研究中心研究员Helena Johansson医师报告指出,整体追踪期间为140万人-年,有18,336例骨质疏松骨折,包括4,509例髋骨骨折。
  
  研究人员发现,肱骨/手肘骨折风险随BMI值增加,骨质疏松性骨折与髋骨骨折风险随BMI值增加而降低;平均而言,BMI值18.5-25.0 kg/m2的妇女,每100人-年有超过2.5例骨折,BMI值35到40 kg/m2者的骨折少于0.5,BMI值40 kg/m2以上者的骨折率几乎为0。
  
  BMI值35或40 kg/m2者的骨质疏松性骨折风险比(HR),和BMI值26 kg/m2者相比分别是0.89 (95%信心区间[CI]0.84-0.93)和0.83 (95% CI,0.77-0.90);不过,当校正BMD时,相对应的HRs分别是1.14 (95% CI,1.06-1.23)和1.23 (95% CI,1.10-1.39)。
  
  研究结果也显示,较高BMI(40 kg/m2)之妇女的髋骨骨折HR只有0.75 (95% CI,0.67-0.85);至于BMI值26 kg/m2者,HR为0.64 (95% CI,0.53-0.78),不过,当校正BMD时,相对应的HRs分别是1.09 (95% CI,0.91-1.30)和1.14 (95% CI,0.86-1.50)。
  
  Johansson医师指出,虽然一般认为低BMI与骨折风险较大有关,越来越高的肥胖比率也增加了骨折风险改变的考量。
  
  她解释,年长者有较低的BMI,相当低的BMI是骨折的强力风险因素,最近,曾有肥胖和骨折风险的争论,因为BMI值越来越高,这个议题越显重要,有许多研究认为,肥胖可能是骨折的风险因素。
  
  Johansson医师表示,这次的研究结果有点意料之外。因为之前研究BMI时发现,某种程度的BMD [例如肥胖者]会是髋骨骨折的风险因素,只不过影响不显著,但是对于骨质疏松骨折则无关。
  
  现在,我们有越来越多肥胖病患,因此,有比较高的统计强度来检视这些影响。
  
  Johansson医师解释,如果校正其它风险因素如之前的骨折后,这些研究结果证明为真,则可以更新FRAX这个由世界卫生组织发展用来评估骨折风险的工具。
  
  另外,临床影响是,或许可据以建议维持BMI值小于30 kg/m2 ,以避免骨折风险。
  
  多伦多大学药学院的Suzanne M. Cadarette博士表示,研究结果指出了骨折风险的潜在因素。
  
  共同主持该段会议的Cadarette博士表示,或许不单单只是BMI的影响,必须讨论体重、脂肪类型、肥胖者的BMD测量误差、骨折机转,重点是美国人为何会越来越肥胖。这是重要的议题,值得后续研究。
  
  资料来源: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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