1.6.1 Morbidity in the developed world
The associations between anthropometric indices and morbidity have not been studied as frequently as those with mortality. However, many studies of mortality have considered the underlying cause of death and hence inferences may be made about the relationship between various anthropometric indices and morbidity.
It appears that high weight-for-height and low weight-for-height measurements bring with them risks for different types of diseases. Low weight-for-height is typically characterised by tuberculosis (Waaler, 1984), lung cancer (Waaler, 1984; Kabat & Wynder, 1992; Kushner, 1993) and obstructive lung diseases. Whereas high weight-for-height is characterised by cerebrovascular diseases (Waaler, 1984, Kushner, 1993; Rexrode et al, 1997) cardiovascular diseases (Waaler, 1984, Fitzgerald & Jarrett, 1992; Kushner,1993; Tuomilehto et al, 1987;
Rabkin et al, 1997; Tavani et al, 1997), non-insulin dependent diabetes mellitus (Rabkin, 1997), cancer of the colon (Waaler, 1984, Kushner, 1993), prostate cancer (Cerhan et al, 1997) and gastric cancer (Hansson et al, 1994).
1.6.2 Morbidity in the developing world
There has not yet been a systematic prospective longitudinal study of the relationship between adult anthropometric indices and morbidity in the developing world. Hence the long term effects of low values of adult anthropometric indices on morbidity experience in the developing world are not yet known.
The studies which have been conducted to date have been either cross-sectional (Pryer, 1990 &
1994; Strickland & Ulijaszek, 1993a; Francois, 1990; de Vasconcellos, 1994; Ulijaszek, 1997 - in press) or retrospective (Campbell & Ulijaszek, 1994) or a mixture o f methods (Garcia &
Kennedy, 1994). In general, cross-sectional studies which have results consistent with plausible biological mechanisms provide some, although not sufficient, support for causality (Susser, 1991;
Rothman & Greenland, 1998). However, the relationship between low BMI or MUAC and morbidity is circular. If a person is ill they may lose weight, on the other hand, if a person is thin they may be more likely to become ill. If low BMI or MUAC is found to be associated with
biologically credible hypotheses which may account for the associations seen in a cross-sectional study of this nature. An analysis into the relationships of the BMI or MUAC with morbidity must be based on subjects who are fundamentally healthy i.e.: have no chronic illness. None of the studies above control for pre-existing illness and hence no causal inferences about the association between anthropometrical status and morbidity can be drawn.
Given the problems described above, it is still worth looking at the studies listed above in some detail as they are the only ones which have considered the relationship between the BMI and morbidity in the developing world.
Pryer (1990 & 1994) examined the relationship between BMI and “number o f complete working days missed in the month prior to interview due to incapacitating illness” in men living in an urban slum in Bangladesh. She found a significant inverse association between BMI and work- disabling morbidity. Below a BMI o f 16.0 kg/m2 (Grade III CED) 55% of the men lost one or more working day. This proportion dropped to 35% among those with a BMI o f 16.0-17.0 kg/m2 (Grade II). Above a threshold BMI of 17.0 kg/m2 the percentage o f men incapacitated from work was similar in each BMI category. The association held true when loss o f working days due to work-related accidents was excluded. Table 1.5 shows the relative risks o f morbidity at various BMI grades.
Table 1.5: The relative risks o f morbidity* at various BMI grades in Pakistani men.
BMI (kg/m2) RR of morbidity*
< 16.0 5.9
16.1-17.0 3.8
17.1-18.5 1.8
>18.5 1
* Relative risk of being incapacitated from wage work for one or more days in month prior to interview
De Vasconcellos (1994) performed a similar study to that o f Pryer’s in Brazil. Adults were asked how many days they had spent in bed during the two weeks before they were surveyed. A U- shaped association was seen between this proxy measure for morbidity and the BMI. The largest increase in “morbidity” rate occurred in the BMI range o f 16.0 - 17.0 kg/m2, the rate was much lower in BMIs above this range. Francois (1990) has also shown that at BMI<17.0 kg/m2 Rwandan women have a greater likelihood o f illness and are more frequently confined to bed (James, 1994a).
Strickland and Ulijaszek (1993) studied the relationship between anthropometric indices and reported morbidity on the day of interview in the same population as the current study. They found that the BMI and AMBA (arm muscle and bone area) were sensitive to reported single symptoms of any kind in men over 40 years, significantly so for respiratory conditions. In women the BMI alone was sensitive to reports of two concurrent symptoms in women under 40 years and to respiratory complaints. Morbidity was significantly related to the BMI and AMBA independently of age in men. In older women, reported morbidity showed no effects on BMI or AMBA, while age effects were more pronounced than in men. The authors suggested that this is consistent with the evidence that female lean tissue is more resilient to the insults o f malnutrition and disease than that of males (Stini, 1968; Henry, 1990).
Ulijaszek (1997, in press) examined the association between anthropometric indices and blood pressure in a small sample of adults in Papua New Guinea. Blood pressure was not associated with height or weight. Rather it was associated with fat patterning, with increasing trunkal fatness being associated with greater systolic blood pressure for both males and females.
Campbell and Ulijaszek (1994) studied the relationship between current anthropometry and retrospective morbidity in very poor men who attended the Middleton Row Street clinic in Calcutta. Using discriminant analysis techniques (after Mascie-Taylor, 1994) it was found that the BMI was a better discriminator of overall retrospective morbidity in men <65 years than weight, height, age, arm circumference, arm fat area and body fat percent. However, in certain disease categories (e.g.: tuberculosis) calf circumference , height, weight and age were more significant discriminators. Moreover, in men above 65 years the BMI was much less useful as a discriminatory tool.
The study of Garcia and Kennedy (1994) is difficult to discuss. They have attempted to assess the linkage between BMI and morbidity in adults in four developing countries. They conclude that, although their results are mixed, the probability of being sick does not vary substantially between those with low BMI and those with normal BMI. Furthermore, they state that the 18.5 kg/m2 proposed CED cut-off point is not generally consistent with the threshold at which morbidity begins to rise. This study is difficult to interpret as the methods employed both in the collection and analysis of the data are unclear.
It is important to state, again, that these studies only show an association between low BMI and morbidity. Causality cannot be inferred from cross-sectional data o f this nature. Campbell and
circularity between the BMI and morbidity. The paucity o f studies examining the relationships between the BMI or MUAC and mortality or morbidity measured in the developing world provided the main impetus for this study.