Weight gain and fat accumulation in both middle and older age raise the risk of diabetes, according to a prospective cohort study reported in the June 23/30 issue of JAMA.

The links between overweight and diabetes, and between central adiposity and diabetes, are well known in younger adults but have not been fully explored in older adults, said Mary L. Biggs, Ph.D., of the University of Washington School of Public Health and Community Medicine, Seattle, and her associates.

They examined these associations using data on 4,193 subjects participating in the Cardiovascular Health Study, a prospective, longitudinal cohort study of people aged 65 years and older living in four communities in North Carolina, Maryland, Pennsylvania, and California. The subjects were enrolled beginning in 1989 and followed annually for a median of 12 years.

The mean age at baseline was 73 years; 59% of the subjects were women, and 10% were African American.

Changes in the participants’ weight, body mass index, fat mass, waist circumference, waist-to-hip ratio, and waist-to-height ratio were documented from baseline onward, at ages 65 and older. The subjects also were asked to report body composition measures from when they were age 50, so that their BMI at age 50 could be calculated.

During follow-up, 339 subjects developed diabetes.

Measures of overall and of central adiposity both at both middle age (50 years) and older age (at least 65 years) were significantly associated with the risk of developing diabetes in men and women. Subjects in the highest category of adiposity had a two- to sixfold greater risk of incident diabetes than did those in the lowest category.

Similarly, the risk of diabetes rose monotonically with the amount of weight gained between age 50 and baseline. “Compared with participants whose weight remained stable [during that interval], those who gained 9 kg or more between the age of 50 years and study entry had an approximately threefold greater risk of developing diabetes during follow-up,” Dr. Biggs and her colleagues said (JAMA 2010;303:2504-12).

“Participants who were obese (BMI greater than or equal to 30) at 50 years of age and who experienced the most weight gain (greater than 9 kg) between the age of 50 years and study entry had five times the risk of developing diabetes, compared with weight-stable participants with normal BMI (less than 25) at 50 years of age,” they added.

Subjects in the highest categories of both BMI and waist circumference were more than four times as likely to develop diabetes as were subjects in the lowest categories of those measures.

The increased risk associated with adiposity appeared to wane as subjects aged, but even among participants aged 75 and older, those in the highest category of BMI still had double the risk of developing diabetes, compared with those in the lowest category of BMI.

The reason that diabetes risk declines somewhat after age 75 is not known. It is possible that anthropomorphic measures may not adequately quantify body fat at that age because of age-related changes in body composition, such as decreased muscle mass and decreased height.

“A second possibility is that regional fat distribution is more important in the etiology of diabetes than absolute fat mass,” the researchers wrote. Another reason may be that the pathology of diabetes in older adults differs from that in younger adults. Or it simply may be that people more susceptible to adiposity-related death do not survive into old age, resulting in selective survival of fitter people, Dr. Biggs and her colleagues said.

The investigators were somewhat surprised to note that the risk of diabetes did not decline in subjects who lost weight during follow-up. Again, the reason is not yet known.

“Older adults may lose proportionately more muscle mass with weight loss than younger ones, decreasing the accuracy of weight loss as a surrogate for loss of adipose tissue in older adults. Furthermore, the loss of skeletal muscle mass may decrease insulin sensitivity, negating the benefit derived from fat loss,” they noted.

However, clinicians should note that the relation between weight loss and diabetes risk in older adults is complex, and “our results do not preclude the possibility that voluntary weight loss reduces the risk of diabetes in older adults,” they added.

This study was supported by the U.S. National Heart, Lung, and Blood Institute, the U.S. National Institute on Aging, the University of Pittsburgh Claude D. Pepper Older Americans Independence Center, and the U.S. National Institute of Neurological Disorders and Stroke. No financial conflicts of interest were reported.

Copyright (c) 2009 Elsevier Global Medical News. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

据6月23/30日出版的《美国医学会杂志》(JAMA)中报道的一项前瞻性队列研究，中老年人体重增加和脂肪积聚可增加糖尿病风险。

 

西雅图华盛顿大学公共卫生和社区医学院Mary L. Biggs博士及其合作者称，较年轻的成人中超重与糖尿病之间以及向心性肥胖与糖尿病之间的关联已众所周知，但这种关联尚未在较年长者中加以充分探讨。

 

他们利用4,193位参加心血管健康研究(Cardiovascular Health Study)的受试者的数据对上述相关性进行了调查。心血管健康研究为一项前瞻性、纵向队列研究，受试者为65岁及以上、分别居住在北卡罗莱纳州、马里兰州、宾夕法尼亚州及加利福尼亚州4个社区的老年人。受试者在1989年开始入组此研究，之后每年检查1次，中位随访时间为12年。

 

受试者在基线时的平均年龄为73岁；其中59%为女性，10%为非洲裔美国人。

 

从基线开始(年龄≥65岁)，记录受试者的体重、体重指数(BMI)、体脂和腰围、腰/臀比以及腰围/身高比。同时要求受试者从50岁起报告其身体成分测量值，以计算其相应年龄的BMI。

 

在随访过程中，有339例受试者新发糖尿病。

 

无论是中年人(50岁)抑或老年人(至少65岁)，整体肥胖和向心性肥胖的测量值均与糖尿病发病风险有显著相关性，无性别差异。肥胖程度处于最高范围内的受试者其新发糖尿病的风险较处于最低范围内者高2~6倍。

 

同样，糖尿病风险随着50岁至基线时的增重量呈现出单一升高的趋势。Biggs博士及其同事说：“与这段时间体重保持平稳的受试者相比，50岁至参加研究时体重增加不低于9 kg者随访期间发生糖尿病的风险大约增加3倍。” (JAMA 2010;303:2504-12)。

 

他们同时指出：“50岁时肥胖(BMI≥30)的受试者及50岁至参加研究时体重增加最多(≥9kg)的受试者发生糖尿病的风险是50岁时BMI(<25)正常、体重稳定者的5倍。”

 

BMI和腰围均处于最大范围内的受试者其发生糖尿病的风险是处于最低范围内者的4倍以上。

 

随着受试者年龄的增长，肥胖关联的风险增加的趋势减弱，但即使在年龄≥75岁的受试者中，BMI处于最高范围内的受试者其发生糖尿病的风险仍较处于最低范围内者高1倍。

 

75岁以后糖尿病风险有所下降，其原因尚不清楚，很可能是由于年龄相关的身体成分发生变化，如肌肉量减少和身高下降，使拟人指标无法对体脂充分定量。

 

研究者写道：“另一种可能是局部脂肪分布在糖尿病发病机制中比绝对体脂更重要”。Biggs博士及其同事说，另一个原因可能是老年人糖尿病病理学特点不同于较年轻的成人。或者可能只是因为在步入老年后，人们对肥胖相关的死亡更为易感，形成适者生存的状况。

 

研究者略感惊讶地发现，随访过程中体重减轻的受试者糖尿病风险并未降低，其原因尚不清楚。

 

他们指出：“与较年轻的成人相比，老年人随着体重减轻可能会成比例地减少较多的肌肉量，进而降低老年人中以体重减轻代替脂肪组织减少的准确性。此外，骨骼肌量的减少可能会降低胰岛素敏感性，从而抵消脂肪减少所带来的收益。”

 

然而，临床医生应注意的是老年人体重减轻与糖尿病风险之间的关联很复杂，他们说： “我们的研究结果并不排除老年人主动减重以减少糖尿病风险的可能。”

 

该研究得到美国国家心肺血液研究所、美国国家老化研究所、匹兹堡大学Claude D. Pepper 美国老年人独立中心(University of  Pittsburgh Claude D. Pepper Older Americans Independence Center)以及美国国家神经疾病和卒中研究所的资助。作者们无经济利益冲突的报告。

 

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