Bone mineral density and body composition in underweight and normal elderly subjects

The importance of malnutrition as a risk factor in osteoporosis is emphasiz ed by the evidence that patients with fractures of the proximal femur are o ften undernourished. In this study, nutritional status, bone mineral mass a nd its association with body composition were investigated in underweight a nd normal weight elderly subjects. Moreover the hypothesis that malnutritio n in elderly is associated with a higher risk of osteoporosis was tested. T he participants were 111 elderly subjects divided into two groups according to body mass index (BMI): 51 patients were underweight (BMI < 22 kg/m(2)) while in 60 subjects BMI ranged from 22 to 30 kg/m(2). In all patients anth ropometric parameters and blood indices of malnutrition and of bone turnove r were measured. Fat-free soft mass (FFSM), fat mass (FM), bone mineral con tent (BMC) and bone mineral density (BMD) 'total body' and at the hip were obtained by dual-energy X-ray densitometry. Dietary intake was evaluated wi th the diet history method, while resting energy expenditure (REE) was meas ured by indirect calorimetry, Underweight subjects had other signs of malnu trition, such as low visceral proteins, sarcopenia, and an inadequate energ y intake. Moreover they showed a significant reduction of BMC and BMD compa red with normal subjects. In men with BMI (22 kg/m(2), T-score was below -2 .5 (-3 at femoral neck and -2.7 at total hip) while men in the control grou p had normal bone mineral parameters. T-score at different sites was lower in underweight women than in underweight men, always showing values under - 3.5, with clear osteoporosis and a high fracture risk. In healthy women the T-score values indicated the presence of mild osteoporosis. In underweight subjects, low levels of albumin (< 35 g/l) were associated with higher fem oral bone loss. Using a partial correlation model, BMC, adjusted for age, b one area, knee height and albumin showed a significant association with FM in women (r = 0.48; p < 0.01) and with FFSM in men (r = 0.48; p < 0.05). Al bumin, when adjusted for other variables, was significantly correlated (r = 0.52; p < 0.05) with femoral neck BMC only in women. In conclusion, the un derweight state in the elderly is associated with malnutrition and osteopor osis; other factors occurring in malnutrition, besides body composition cha nges, such as protein deficiency, could be involved in the association betw een underweight and osteoporosis. Moreover bone mineral status seems to be related to fat-free soft mass tissue in men while in women it is much more closely associated with total body fat.