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Anthropometric indicators are only o f operational value if they have functional significance by identifying risk o f impaired function or higher morbidity or mortality. In contrast to the emphasis on the relationship between high BM1 and morbidity and mortality, similar relationships for low BMI are relatively lacking especially for developing countries. Little research has been done on the functional impact o f low BMI except for working capacity.

physical activity levels and pregnancy and lactation. Being underweight has been found to be associated with lower activity levels and limited productivity. François reported that below a BM1 o f 17 kg/m2 Rwandan women were m ore likely to be ill and more frequently confined to bed. Their ability and willingness to engage in heavy work was also greater above a BMI o f 18.7 kg/m2 (Shetty & James, 1994). Similarly among Bengali men, work-disabling morbidity was significantly greater below the BMI ‘threshold’ o f 17 kg/m2 (Pryer, 1993).

Body functions become considerably compromised in severe undemutrition. Among other outcomes this results in increased susceptibility to disease, thus infectious diseases are likely to occur more in the undernourished (Fischer, 1990). Ageing and undemutrition exert cumulative effects on immuno-competence and the positive effect o f nutrition on immunity has been demonstrated (Roebothan & Chandra, 1994; Lesourd, 1997; Chandra, 1997). Among young adult samples o f four developing country populations Garcia & Kennedy (1994) only found evidence in two that illness predisposed for low BMI. Nevertheless morbidity and mortality risk appear to increase rapidly for extreme low and high BMI values, although not all studies controlled for pre-existing disease (Campbell et al, 1990; Fischer, 1990; Shetty & James, 1994; WHO, 1995). A protective effect o f a higher BMI in old age has also been suggested (Matilla et a l 1986; Potter, 1988).

A number o f studies indicated that a BM I around 11-12 kg/m2 appeared to be the lower limit o f survival (Henry, 1990). Data collected during World War II have shown that in starvation, a loss o f more than 40% o f one's normal lean body mass is fetal and the same seems to apply to normal ageing (Roubenoff, 1991). There are however data available indicating that, under certain circumstances, a BMI o f less than 10 kg/m2 is not yet fetal. BMI values as low as 8.7 and 10.1 kg/m2 were found for younger adults and older adults respectively in Somalia (Collins, unpublished b) and similarly low aduh BMIs have been reported from the Sudan (Collins, 1993).

In addition to the dem onstrated relationship between anthropom etric measurem ents and increased risk o f death, a similar relationship between m ortality and overall self-rated functional ability (comprising ADL, 1ADL and dimensions o f mobility) has also been suggested (Koyano et al, 1989; R ozzini et al, 1991; Bernard et al, 1997). The effect

remained significant even after controlling for age, sex, medical conditions, functional status and access to assistance from others (Bernard et al, 1997).

However, relating nutritional status to morbidity and mortality may de-emphasise the aspect o f ‘quality o f life’ compared with functional ability as outcome indicator. Moreover, mortality is relatively imminent for older people and both the long and short term causes o f morbidity (disease, diet, lifestyle) will be hard to disentangle (Manandhar, 1995). Physical fitness and work performance will also have decreased as a result o f both physiological and behavioural changes. Thus some other functional outcome o f significance must probably be used with older adults. The ability to function independently in basic activities o f daily life will be the main concern o f older adults as they struggle to maintain their quality o f life. Therefore the focus o f research appears to be shifting from mortality and morbidity to the measurement o f active and disability-free life expectancy. The presence o f a relationship between nutrition and functional status would suggest a potentially modifiable factor for the enhancement o f (functional) well-being in the elderly. The WHO (1995, 1998) also recognised the practical significance o f functional ability against which to measure older people’s nutritional status.

Several dietary intervention studies by Hyatt et al (1990) showed that the relationship between functional impairment and nutritional deficiency is plausible. Russell et al (1983a,b) and Lopes et al (1982) carried out studies among anorexia nervosa patients, malnourished patients with various gastro-intestinal disorders and obese subjects. Although the studies were very small, all confirmed abnormal muscle function during fasting that returned to normal after refeeding. Castaneda et al (1995) followed twelve older women who were fed a weight-maintenance diet either low or adequate in protein for nine weeks. Women on low protein diets lost lean tissue, and were compromised in muscle function and immune response. M oreover, changes in the latter tw o occurred earlier than body com position changes. Although the scale o f the study was very small, these findings may indicate that an inadequate diet compromises functional capacity.

Fiatarone et al (1994) studied the effect o f low er extremity exercise training and multi­ nutrient supplementation on people over 70 years. Training improved muscle strength and size (the first to a higher extent) and was accompanied by improved mobility and increased spontaneous activity. In contrast, nutrient supplementation show ed no

independent or additive effect. However baseline nutritional status may not have been sufficiently compromised to benefit from a 10-week intervention (mean BMIs ranged between 24.5 and 25.8 kg/m 2 in the four study groups). Low muscle mass and muscle weakness were strongly related to impaired mobility, independent o f the effects o f chronic disease, dementia, depression and other characteristics o f old age. Correction o f muscle disuse was accom panied by enhanced activity levels and functional mobility. It was suggested that older people should participate in strength training in addition to aerobic exercise to maintain muscular strength and endurance.

Several US studies among healthy community-living elderly reported a relationship between BM1 and functional impairment. Ensrud (1994) demonstrated among women that a combination o f factors including obesity, medical conditions, physical inactivity and direct measures o f neuromuscular performance were independent risk factors for reported difficulty in three or more ADLs. High BMI as well as other health conditions, poverty and base-line performance were also found to predict three year decline in physical performance (Seeman, 1994). Galanos et al (1994) provided strong evidence that both low and high BM I were still related to functional status after controlling for relevant variables concerning demography, cognition, depression, medical conditions and self-rated health.

Contrasting results w ere described by Lehman and Bassey (1996) who found no correlation between (change in) body weight and physical, psychological and social well being four years later in community living UK elderly. How ever average weight changes were very small and nearly as many gained as lost weight.

A relationship between nutrition and function has also been found in elderly people living in developing countries. In Malawi and India low BMI w as independently related to poor handgrip strength and significant associations with (a history o f) anaemia w ere found (Anklesaria, 1995; Chilima, 1998; Manandhar, 1999). G uatem alan elderly w ho rated themselves in good health tended to have BM Is in the normal range and could perform ADLs independently. Am ong those who rated themselves in poor health, a larger proportion reported having difficulties in ADLs and the majority o f the females had high BMIs (Herman et al, 1998). Excess adipose tissue may reduce mobility and the ability to

perform self-care activities, or poorer function may be caused by metabolic changes due to obesity.

Nutrition indicators other than BM1 and weight have also been related to function. A Yugoslavian study among institutionalised elderly demonstrated that low micronutrient blood param eters in the absence o f clinical signs can still impair function. About 36% o f the variability in cellular immunity was explained by sub-clinical micronutrient deficiencies. Vitamin supplementation improved immune function significantly. Handgrip strength also improved slightly in the whole group and significantly in those subjects with initial low grip strength (Suboticanec et al, 1989). Independently living Canadian elderly were supplemented w ith physiological am ounts o f m icronutrients for one year. Compared to subjects w ho had received a placebo, a significant improvement in several indices o f immunocompétence was observed in the supplem ented group (Chandra, 1992).

Nutritional factors such as poor appetite, low albumin concentration, eating problems and eating alone showed independent associations with functional limitation among rural American elders (Jensen et al, 1997). O f Swedish elderly who were dependent in activities o f daily life, a threefold higher proportion had low thiamine and protein intakes as compared to independent elderly (Steen et al, 1991). Generally home-living but recently hospitalised Norwegian elderly m ore ofien had reduced appetite and taste, dental problems and difficulties in shopping and cooking compared to home-living elderly. It was suggested that this m ay contribute to their w orse nutritional and functional status and to the need for hospitalisation (M ow e & Bohm er, 1996).

A recent extensive literature review o f longitudinal studies regarding risk factors for functional ability decline in community living older people, rep o rted strong evidence for the following risk factors: low and high BMI, disease burden, low er extremity functional limitation, low level o f physical activity, poor self-perceived health, depression, cognitive impairment, low frequency o f social contacts, smoking, vision impairment and no alcohol use. It w as noted that risk factors such as nutrition and environm ental factors have been neglected in past research (Stuck et al, 1999).