Joshy Grace, Korda Rosemary J, Bauman Adrian, Van Der Ploeg Hidde P, Chey Tien, Banks Emily
National Centre for Epidemiology and Population Health, The Australian National University, Canberra, Australia.
National Centre for Epidemiology and Population Health, The Australian National University, Canberra, Australia ; Australian Centre for Economic Research on Health, The Australian National University, Canberra, Australia.
PLoS One. 2014 Feb 12;9(2):e88641. doi: 10.1371/journal.pone.0088641. eCollection 2014.
Findings regarding the association between overweight and all-cause mortality range from significantly lower to higher risk, compared with body-mass-index (BMI) within the "normal" range.
We examined empirically potential methodological explanations for these apparently conflicting results using questionnaire and linked mortality data from 246,314 individuals aged ≥45 years in the Australian 45 and Up Study (11,127 deaths; median follow-up 3.9 years). Hazard ratios (HR) for all-cause mortality associated with BMI were modelled according to different methods of accounting for illness at baseline, finer versus broader gradations of BMI and choice of reference group, adjusting for potential confounders.
In analyses using the broad World Health Organization (WHO) categories, the all-cause mortality HR was significantly lower in the overweight category (25.0-29.99 kg/m²), than the normal weight (18.5-24.99 kg/m²) category. However, in analyses accounting for baseline illness, which excluded those with pre-existing illness at baseline, ever-smokers and the first 2 years of follow up, absolute age-standardised mortality rates varied up to two-fold between finer BMI categories within the WHO normal weight category; rates were lowest at 22.5-24.99 kg/m² and mortality HRs increased steadily for BMI above (p(trend)<0.02) and below (p(trend)<0.003) this reference category. Hence, the breadth of the BMI categories used and whether or not baseline illness is accounted for explain the apparent discrepancies between reported BMI-mortality associations.
Using fine BMI categories and the category with the lowest absolute rates as the reference group and accounting for the potential confounding effects of baseline illness is likely to yield the most reliable risk estimates for establishing the independent relationship of BMI to all-cause mortality. These results and those of other studies indicate that a BMI of 22.5-24.99 kg/m², not the broad "overweight" category of 25-29.99 kg/m², was associated with the most favourable mortality risk.
与“正常”范围内的体重指数（BMI）相比，超重与全因死亡率之间的关联研究结果从显著降低到风险升高不等。
我们利用澳大利亚45岁及以上研究中246,314名年龄≥45岁个体的问卷调查和关联死亡率数据（11,127例死亡；中位随访3.9年），实证研究了这些明显相互矛盾结果的潜在方法学解释。根据基线时疾病的不同核算方法、BMI的更精细与更宽泛分级以及参照组的选择，对与BMI相关的全因死亡率风险比（HR）进行建模，并对潜在混杂因素进行调整。
在使用世界卫生组织（WHO）宽泛分类的分析中，超重类别（25.0 - 29.99 kg/m²）的全因死亡率HR显著低于正常体重类别（18.5 - 24.99 kg/m²）。然而，在考虑基线疾病的分析中，排除了基线时已有疾病者、既往吸烟者以及随访的前两年，WHO正常体重类别中更精细的BMI类别之间的绝对年龄标准化死亡率相差高达两倍；在22.5 - 24.99 kg/m²时死亡率最低，且高于（p趋势<0.02）和低于（p趋势<0.003）该参照类别的BMI对应的死亡率HR稳步上升。因此，所使用的BMI类别广度以及是否考虑基线疾病解释了所报告的BMI与死亡率关联之间的明显差异。
使用精细的BMI类别以及绝对死亡率最低的类别作为参照组，并考虑基线疾病的潜在混杂效应，可能会得出最可靠的风险估计值，以确定BMI与全因死亡率之间的独立关系。这些结果以及其他研究结果表明，与最有利死亡率风险相关的BMI是22.5 - 24.99 kg/m²，而非25 - 29.99 kg/m²这个宽泛的“超重”类别。
