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Results

In CNS-82, 13 340 individuals (men 7191, women 7113) of 20 years or older were measured. The average body weight was 57.2 ± 7.4 kg for men, and 50.7 ± 8.0 kg for women. The body weight of urban men and women was 3.1 kg and 2.7 kg respectively more than those living in rural areas (Table 1). The mean weight of various age groups is illustrated in Fig. 1. It increased with age in urban populations until ~50 years of age, and then was less in the older groups. In rural populations, however, body weight decreased with age, especially in women.

Part of these age-related changes was dependent on the differences in height of older adults. The average height was 165.3 ± 7.3 cm for men and 153.5 ± 6.3 cm for women with an urban-rural difference of 4.4 cm for men and 2.2 cm for women (Table 2). The distribution of the mean height of various population groups by age is shown in Fig. 2. All the four groups showed the same trend, i.e. declining with age. The differences between the youngest and the oldest groups were between 5.1 cm and 8.9 cm.

Table 2. Height of Chinese adults (CNS-82)

Table 3. Percentage of individuals with a low or high body mass index (BMI)

These differences are too great to be explained by the physiological changes of ageing alone, and suggest that the younger generation are taller because they grew up in a better environment.

The distribution of the BMI data of a subsample of the CNS-82 of adults aged 20-45 is presented in Table 3 to allow comparison with the CHNS-89 adults. The percentage of individuals with a BMI <18.5 was 11.5% in the urban and 9.0% in the rural areas, with 7.2% and 5.5% of adults in urban and rural areas having a BMI >=25.0. Figure 3 illustrates the different mean BMIs of men and women of different ages. The BMI values of women are above those of men in all age groups except those of 70 years or older when in both urban and rural populations the women have a lower BMI. The urban young adults tend to be thinner than the rurals, but urban men and women over 30 years were relatively heavier than the rural inhabitants. The overall age differences in BMI are, however, modest with the urban adults showing a consistent increase in middle age whereas the rural adults have few differences in weight until the age of 50 or older.

CHNS-89

In the 1989 China Health and Nutrition Survey, heights and weights were measured in adults of 20-45 years. The sample size was 5134 (urban 1609, rural 3550) individuals. As shown in Table 3, the proportions of adults with a BMI of <18.5 or 225 were larger in urban populations than in the rural areas. By comparison with the CNS-82 results, the percentage of subjects with a low BMI value was slightly reduced by 1.4% in the urban and by 1.3% in the rural samples. However, the proportion of adults with high BMI values was greater in both samples. In the urban areas 4.8% more adults were overweight in 1989 than in 1982 and the comparable figure for the rural sample was 2%.

The distribution of adults' BMI by fertile of per capita income is shown in Table 4. Interestingly, the percentages of adults with a BMI either <18.5 or >25 were higher in the urban adults. More underweight individuals (BMI <18.5) were from the low-income group in the urban communities whereas the overweight individuals (BMI >25) were fewer in the low-income rural group.

Table 4. Distribution of body mass index (BMI) in relation to per capita income (CHNS-89)

Percentage with BMI in these categories

a/b, c/d e/f: P < 0.01.

Table 5. Distribution of body mass index (BMI), per capita energy and income by Province (CHNS-89)

Table 6. Distribution of body mass index (BMI) by occupation (CHNS-89)

Table 7. Distribution of body mass index (BMI) in association with dietary energy sources (CHNS-89)

The eight provinces are arranged in Table 5 in order of increasing proportions of individuals with low BMIs. The average per capita income, energy intake, and energy from fat were not associated with the prevalence of either underweight or overweight.

BMI, as shown in Table 6, is associated with occupation. The highest proportion of overweight is found among government officials while the lowest proportion occurs among farmers. Housewives are relatively more at risk both of undernutrition and overweight.

Table 7 shows the distribution of BMI in connection with the amount of energy derived from animal sources. The percentage of overweight (BMI 225) subjects increases with the increase in dietary energy of animal origin being especially evident in those with the highest intake of animal foods. The differences in the proportions of those with a low BMI (<18.5) are small across these dietary groups.

An analysis of the influence of education on BMI revealed no clear trends, except in so far as underweight was less common in both the illiterate and highly educated groups. Overweight was also more common in the illiterate group but no differences were observed among other groups.

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