Background To investigate the associations between the body mass index (BMI), Mini Nutritional Assessment-Short Form (MNA-SF) scores, and 2-year mortality. Methods A nationwide cohort study using data from a national quality register of older (age >= 65 years) nursing home residents (N = 47,686). Individuals were categorized according to BMI as underweight (< 18.5 kg/m(2)), normal-weight (18.5-24.9 kg/m(2)), overweight (25.0-29.9 kg/m(2)), and obese (class I, 30.0-34.9 kg/m(2); class II, 35.0-39.9 kg/m(2); class III, >= 40.0 kg/m(2)). Participants' nutritional status were categorized as good (MNA-SF score 12-14), at risk of malnutrition (MNA-SF score 8-11), or malnutrition (MNA-SF score 0-7). Associations with mortality were analysed using Cox proportional-hazards models. Results At baseline, 16.0% had obesity, and 14.6% were malnourished. During 2 years of follow-up, 23,335 (48.9%) individuals died. Compared with normal-weight individuals, mortality was greater among underweight individuals [hazard ratio (HR) 1.62, 95% confidence interval (CI) 1.55-1.69] and lesser among individuals with class I (HR 0.63, 95% CI 0.60-0.66), class II (HR 0.62, 95% CI 0.56-0.68), and class III (HR 0.80, 95% CI 0.69-0.94) obesity. Compared with individuals with good nutritional status, mortality was increased for those with malnutrition (HR 2.98,95% CI 2.87-3.10). Lower mortality among obese individuals was also seen in subgroups defined according to MNA-SF scores. Conclusions Among older nursing home residents, obesity, including severe obesity, was associated with lower 2-year mortality. Higher BMIs were associated with better survival, regardless of nutritional status according to MNA-SF.
