Chakri Naruebodindra Medical Institute, Faculty of Medicine Ramathibodi Hospital, Mahidol University, Samut Prakan, Thailand.
Division of Geriatric Medicine, Dalhousie University & Nova Scotia Health, Halifax, Nova Scotia, Canada.
BMC Med. 2022 Oct 24;20(1):404. doi: 10.1186/s12916-022-02596-7.
Parallel to growth of aging and obese populations, the prevalence of metabolic diseases is rising. How body mass index (BMI) relates to frailty and mortality across frailty levels is controversial. We examined the associations of high BMI with frailty and mortality and explored the effects of percent body fat on these associations.
We included 29,937 participants aged ≥50 years from the 2001-2006 National Health and Nutrition Examination Survey (NHANES) cohorts (N=6062; 53.7% females) and from wave 1 (2004) of Survey of Health, Ageing and Retirement in Europe (SHARE) (N=23,875; 54% females). BMI levels were categorized as: normal: 18.5-24.9 kg/m, overweight: 25.0-29.9, obese grade 1: 30.0-34.9, and obese grade 2 or 3: >35.0. A frailty index (FI) was constructed excluding nutrition-related items: 36 items for NHANES and 57 items for SHARE. We categorized the FI using 0.1-point increments: FI ≤ 0.1 (non-frail), 0.1 < FI ≤ 0.2 (very mildly frail), 0.2 < FI ≤ 0.3 (mildly frail), and FI > 0.3 (moderately/severely frail). Percent body fat was measured using DXA for NHANES participants. All-cause mortality data were obtained until 2015 for NHANES and 2017 for SHARE to estimate 10-year mortality risk. All analyses were adjusted for age, sex, educational, marital, employment, and smoking statuses.
Mean age of participants was 63.3±10.2 years for NHANES and 65.0±10.0 years for SHARE. In both cohorts, BMI levels ≥25 kg/m were associated with higher frailty, compared to normal BMI. In SHARE, having a BMI level greater than 35 kg/m increased mortality risk in participants with FI≤0.1 (HR 1.31, 95%CI 1.02-1.69). Overweight participants with FI scores >0.3 were at lower risk for mortality compared to normal BMI [NHANES (0.79, 0.64-0.96); SHARE (0.71, 0.63-0.80)]. Higher percent body fat was associated with higher frailty. Percent body fat significantly mediated the relationship between BMI levels and frailty but did not mediate the relationship between BMI levels and mortality risk.
Being overweight or obese is associated with higher frailty levels. In this study, we found that being overweight is a protective factor of mortality in moderately/severely frail people and obesity grade 1 may be protective for mortality for people with at least a mild level of frailty. In contrast, obesity grades 2 and 3 may be associated with higher mortality risk in non-frail people. The relationship between BMI and frailty is partially explained by body fat.
随着老龄化和肥胖人群的增长，代谢性疾病的患病率也在上升。身体质量指数（BMI）与虚弱和死亡率之间的关系在虚弱水平上存在争议。我们研究了高 BMI 与虚弱和死亡率的关系，并探讨了体脂百分比对这些关系的影响。
我们纳入了来自 2001-2006 年国家健康和营养检查调查（NHANES）队列的 29937 名年龄≥50 岁的参与者（NHANES，N=6062；女性占 53.7%）和来自欧洲健康、衰老和退休调查（SHARE）第 1 波（2004 年）的参与者（SHARE，N=23875；女性占 54%）。BMI 水平分为：正常：18.5-24.9kg/m2；超重：25.0-29.9kg/m2；肥胖 1 级：30.0-34.9kg/m2；肥胖 2 级或 3 级：>35.0kg/m2。构建了一个不包括营养相关项目的虚弱指数（FI）：NHANES 为 36 项，SHARE 为 57 项。我们使用 0.1 点增量对 FI 进行分类：FI≤0.1（非虚弱）；0.1<FI≤0.2（非常轻度虚弱）；0.2<FI≤0.3（轻度虚弱）；FI>0.3（中度/重度虚弱）。NHANES 参与者使用 DXA 测量体脂百分比。NHANES 获得了所有原因的死亡率数据，直到 2015 年，SHARE 获得了直到 2017 年的死亡率数据，以估计 10 年的死亡率风险。所有分析均调整了年龄、性别、教育、婚姻、就业和吸烟状况。
NHANES 参与者的平均年龄为 63.3±10.2 岁，SHARE 为 65.0±10.0 岁。在两个队列中，与正常 BMI 相比，BMI 水平≥25kg/m2 与更高的虚弱程度相关。在 SHARE 中，FI≤0.1 的参与者中，BMI 水平大于 35kg/m2 会增加死亡率风险（HR 1.31，95%CI 1.02-1.69）。FI 评分>0.3 的超重参与者与正常 BMI 相比，死亡率风险较低[NHANES（0.79，0.64-0.96）；SHARE（0.71，0.63-0.80）]。较高的体脂百分比与更高的虚弱程度相关。体脂百分比显著中介了 BMI 水平与虚弱之间的关系，但没有中介 BMI 水平与死亡率风险之间的关系。
超重或肥胖与更高的虚弱水平相关。在这项研究中，我们发现超重是中度/重度虚弱人群死亡的保护因素，肥胖 1 级可能是至少轻度虚弱人群死亡的保护因素。相比之下，肥胖 2 级和 3 级可能与非虚弱人群的更高死亡率风险相关。BMI 与虚弱之间的关系部分由体脂解释。
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