Over the past two decades, China has been undergoing rapid socio-economic and nutrition transitions. Along with these transitions, chronic non-communicable diseases, such as obesity and type 2 diabetes, are becoming serious public health problems. However, only few studies on determinants of type 2 diabetes, such as fetal exposure, dietary patterns, physical activity, and obesity, have been carried out in China.
The 2002 China National Nutrition and Health Survey (CNNHS), which is a nationally representative cross-sectional survey, was the source of data for this study. Body weight, height, and fasting blood glucose levels were measured by trained technicians and persons whose fasting glucose was >5.5 mmol/l were given an oral glucose tolerance test. Information on food intake was collected using the 24h recall method for three consecutive days. The amounts of cooking oil and condiments consumed during the three survey days were obtained using a food weighing method. A semi-quantitative food frequency questionnaire was used to investigate the usual diet of persons aged above 14 years in the year before the study. Information on physical activity was collected by trained investigators using a 1-year recall physical activity questionnaire.
Central obesity is a better predictor of the presence of glucose tolerance abnormalities than BMI. The optimal cut-off value for waist to height ratio (WHtR) was 0.5, and the prevalenceratio (PR) for this cut-off was 2.85 (95% CI 2.54, 3.21) for men and 3.10 (95% CI 2.74, 3.51) for women.
Dietary patterns and are associated with the presence of glucose tolerance abnormalities in China. Persons in the ‘Green Water’ dietary pattern had the lowest prevalence of glucose tolerance abnormality (3.9%). Persons in the ‘Yellow Earth’ dietary pattern (PR 1.22, CI: 1.04–1.43) and the ‘New Affluence’ dietary pattern(PR 2.05 CI: 1.76–2.37) had significantly higher prevalence rates than the ‘Green Water’ dietary pattern.
A high fat/protein–low carbohydrate diet score was associated with a higher prevalence of type 2 diabetes in the Chinese population. The odds ratio comparing the highest with the lowest quintile was 2.75 (95% CI: 2.09–3.61). The odds ratio was 1.87 (95% CI: 1.35–2.58) after further adjustment for socioeconomic status and physical activity.
The ‘Green Water’dietary pattern was related to the lowest prevalence of metabolic syndrome (MS) (15.9%). Compared to the ‘Green Water’ dietary pattern, the ‘Yellow Earth’and the ‘Western/New Affluence’dietary patterns resulted in an odds ratio of1.66(95% CI: 1.40–1.96)and 1.37 (95% CI: 1.13–1.67),respectively. Physical activity showed a significant interaction with the dietary patterns in relation to MS risk (P for interaction = 0.008). Participants with a combination of sedentary activity and a ‘Yellow Earth’ or a ‘Western/New Affluence’ dietary patternboth had more than three times (95% CI: 2.8–6.1) higher odds of MS than active persons with a ‘Green Water’dietary pattern.
In areas severely affected by famine in 1959–1961, fetal-exposed persons had an increased risk of hyperglycemia compared to non-exposed persons (OR=3.92; 95% CI: 1.64–9.39; P=0.002). Also, in severely affected famine areas, fetal-exposed persons who followed a ‘Western/New Affluence’dietary pattern (OR=7.63; 95% CI: 2.41–24.1; P=0.0005) or had a high economic status in later life experienced a substantially elevated risk of hyperglycemia (OR=6.20; 95% CI: 2.08-18.5; P=0.001).
The findings in this thesis indicate that early life environment, central obesity, dietary pattern, and physical activity are associated with the risk of diabetes and metabolic syndrome in the general Chinese population. Keeping body weight in the normal range, improving diet quality, and promoting physical activity would be benefit for Chinese population to prevent diabetes.