Introduction: Fat-free mass has a functional significance in aging. The objective of this study was to evaluate the prevalence of underweight in a Portuguese population of centenarians and their relationship with dehydration or sarcopenia.
Methods/design: Anthropometric data were obtained using standard procedures from 252 centenarians (100.26±1.99 years), 77.8% women (W). Body composition was assessed by tetrapolar bioimpedance. It was considered dehydration: total body water (TBW) (%) <45 (W) and <50 male (M), and excess of fat mass (FM) (%): >35 (W) and >25 (M). The fat mass index (FMIndex): FM (kg)/height (m2) and muscle mass index (MMIndex): MM (kg)/height (m2) were calculated. Statistical methods: T-student, ANOVA, χ2, linear correlation.
Results: In the sample, 61.4% had normal weight (BMI=21.42±1.86), but 25.3% were underweight (BMI=16.84±1.51), and of these, 28.8% were women. Instead, overweight (BMI=27.52±2.40) checked in 13.3% subjects, was predominant in men (10.6 vs 22.6%). Dehydration was observed in 12.9% of subjects and was tendentiously higher in women (15.4 vs 5.0%, P=0.087). Excess of FM was found in 6.0% of subjects with no gender differences (P=0.225). In the overweight subgroup there were differences in TBW (P=0.003) and FM (P=0.022) between genders, which was not observed in the underweight subgroup. The FMIndex in underweight or overweight subgroups did not vary significantly with gender. Muscle mass and MMIndex were different between genders, with the lowest values observed in underweight W compared to M (31.7±3.96 vs 36.3±2.84; P=0.01) or to the other subgroups. There was a direct linear correlation between BMI and MM (β(M)=0.749; β(W)=0.683) and inverse with TBW (β(M)=−0.428; β(W) =−0.397), men and women, P<0.001.
Conclusion: The underweight was more represented in the Portuguese centenarians. More than body water and FM, sarcopenia may be responsible for this low weight particularly in the women.