Department of Family Medicine and Community Health, University of Minnesota, Minneapolis, Minnesota, USA.
Department of Epidemiology and Environmental Health, School of Public Health and Health Professions, University at Buffalo, The State University of New York, Buffalo, New York, USA.
J Epidemiol Community Health. 2018 Apr;72(4):302-308. doi: 10.1136/jech-2017-209985. Epub 2018 Jan 26.
Frustrated with the onslaught of articles reporting fascination with results that appear paradoxical but are merely due to selection bias, we studied the apparent effect of obesity on diabetes risk in youth who had a test for diabetes. We hypothesised that obese subjects would have lower rates of diabetes than non-obese subjects due to selection bias, and consequently, obesity would appear to lower the risk of diabetes.
Retrospective cohort study of children (4-9 years), pre-teens (10-12 years) and teenagers (13-19 years). Participation was restricted to those who had a test of haemoglobin A1C along with measured height and weight. Body mass index percentile via the Centers for Disease Control and Prevention age and sex standards was calculated and categorised. The main outcome was A1C%, subsequently categorised at the level for diagnosis of diabetes mellitus (≥6.5%).
The sample consisted of 134 (2%) underweight, 1718 (30%) healthy weight, 660 (12%) overweight and 3190 (56%) obese individuals. 16% (n=936) had an A1C≥6.5%. Overall, healthy weight children had 8.2 times the risk of A1C≥6.5% (95% CI 5.3 to 12.7) compared with those in the obese category. The relative risk was 13 in pre-teens (95% CI 8.5 to 20.0) and 3.9 in teenagers (95% CI 3.3 to 4.7).
Healthy weight was associated with a 4-13 times higher relative risk of diabetes mellitus compared with being obese. While apparently shocking, the study's fatal flaw (selection bias) explains the 'paradoxical' finding. Ignoring selection bias can delay advances in medical science.
我们对大量报道令人着迷的结果但实际上仅是由于选择偏倚的文章感到沮丧，因此研究了在进行糖尿病检测的青少年中肥胖对糖尿病风险的明显影响。我们假设由于选择偏倚，肥胖受试者的糖尿病发病率会低于非肥胖受试者，因此肥胖似乎会降低糖尿病的风险。
对儿童（4-9 岁）、青少年前期（10-12 岁）和青少年（13-19 岁）进行回顾性队列研究。参与者仅限于那些同时接受血红蛋白 A1C 检测、身高和体重测量的人。根据疾病控制与预防中心的年龄和性别标准计算并分类体重指数百分位数。主要结局是 A1C%，随后根据糖尿病的诊断水平进行分类（≥6.5%）。
样本包括 134 名（2%）体重不足、1718 名（30%）健康体重、660 名（12%）超重和 3190 名（56%）肥胖个体。16%（n=936）的 A1C≥6.5%。总体而言，与肥胖组相比，健康体重儿童发生 A1C≥6.5%的风险高 8.2 倍（95%CI 5.3 至 12.7）。在青少年前期，相对风险为 13（95%CI 8.5 至 20.0），在青少年中为 3.9（95%CI 3.3 至 4.7）。
与肥胖相比，健康体重与糖尿病的相对风险增加 4-13 倍相关。虽然这看起来令人震惊，但该研究的致命缺陷（选择偏倚）解释了这种“矛盾”的发现。忽略选择偏倚会阻碍医学科学的进步。
