Michaelsson K, Holmberg L, Ljunghall S, Mallmin H, Persson P G, Wolk A
Department of Orthopaedics, Central Hospital, 721 89 Vasteras, Sweden. The Study Group of the Multiple Risk Survey on Swedish Women for eating Assessment (MRS SWEA).
Int J Epidemiol. 1996 Apr;25(2):403-10. doi: 10.1093/ije/25.2.403.
Dietary factors are presumed to have influence on bone mass and hence fracture susceptibility. Most information in this respect is based on retrospective assessment of previous dietary habits. In a population-based case-control study nested within a cohort, we collected dietary information both before and after a first hip fracture. Thus it was possible to study reported changes in dietary habits, intentional as well as unintentional, among hip fracture patients after a first hip fracture and to compare postfracture with prefracture dietary information.
More than 65 000 women born 1914-1948 in two counties in central Sweden completed a food frequency questionnaire regarding their usual current dietary habits, before attending a mammographic screening between the years 1987 and 1990. Subsequently 123 of them sustained a first hip fracture and were defined as cases in the present study. For every case, one control, individually matched by age and county of residence, was selected from the cohort. A second identical food frequency questionnaire was mailed to both cases and controls on average 2 years after the hip fracture event. In total 98 case/control pairs could be included in the analysis. The association between diet and hip fracture was evaluated and the results from the two dietary assessments were contrasted. Women who themselves claimed that they had not changed their diet in recent years were analysed separately.
The hip fracture cases, compared with the controls, had reduced their reported dietary intake of dairy products after the fracture. Apparently this was not intentional since this effect was more pronounced among those cases who claimed that their diet was unchanged. The changes were most apparent among the younger cases with a more recent hip fracture and with a body mass index above the median. Half of the cases, more than twice the frequency in controls, who were initially classified as having high intake of dairy products were classified as having low intake (<800 mg calcium/day) after the hip fracture. This also lowered, in fact reversed, the relative risk estimates of hip fracture both for intake of dairy products and calcium. Crude odds ratios of highest quartile of intake versus lowest, changed from 3.0 to 0.6 for dairy products and from 2.6 to 0.9 for calcium. No other foods or nutrients displayed such notable differences between the two surveys.
We conclude that the use of current and retrospective dietary information after a hip fracture can lead to a differential misclassification in dietary studies and to biased estimates of hip fracture risk as compared with prospectively collected dietary information.
饮食因素被认为会影响骨量，进而影响骨折易感性。这方面的大多数信息基于对既往饮食习惯的回顾性评估。在一项基于队列的人群病例对照研究中，我们收集了首次髋部骨折前后的饮食信息。因此，有可能研究髋部骨折患者首次髋部骨折后报告的饮食习惯变化，包括有意和无意的变化，并将骨折后的饮食信息与骨折前的进行比较。
瑞典中部两个县1914年至1948年出生的65000多名女性在1987年至1990年间参加乳房X光筛查前，完成了一份关于她们当前日常饮食习惯的食物频率问卷。随后，其中123人发生了首次髋部骨折，并被定义为本研究中的病例。对于每个病例，从队列中选择一名年龄和居住县相匹配的对照。在髋部骨折事件平均2年后，向病例和对照邮寄第二份相同的食物频率问卷。总共98对病例/对照可纳入分析。评估饮食与髋部骨折之间的关联，并对比两次饮食评估的结果。对那些自称近年来饮食没有改变的女性进行单独分析。
与对照组相比，髋部骨折病例在骨折后报告的乳制品摄入量减少。显然这并非有意为之，因为这种影响在那些声称饮食未改变的病例中更为明显。这些变化在较年轻的病例中最为明显，这些病例近期发生髋部骨折且体重指数高于中位数。最初被归类为高乳制品摄入量的病例中，有一半在髋部骨折后被归类为低摄入量（<800毫克钙/天）频率是对照组的两倍多。这实际上也降低了，甚至逆转了，乳制品和钙摄入量的髋部骨折相对风险估计值。摄入量最高四分位数与最低四分位数的粗比值比，乳制品从3.0变为0.6，钙从2.6变为0.9。两次调查之间没有其他食物或营养素显示出如此显著的差异。
我们得出结论，与前瞻性收集的饮食信息相比，使用髋部骨折后的当前和回顾性饮食信息可能导致饮食研究中的差异错误分类，并导致髋部骨折风险的偏差估计。
