Results of this study provides evidence of the double burden of underweight and overweight/obesity experienced in Danang City, Vietnam. Our 12.3% overall prevalence of underweight status was similar to the 12.6% reported by Walls and colleagues  for their study conducted in 2004 among provinces surrounding Hanoi, where the population characteristics (i.e. urban, mixed urban–rural, and rural) and economic development were similar to our population. On the other hand, our underweight prevalence was much lower than the 20.4% for the 2004 urban Ho Chi Minh City (HCMC) cohort  and 20.9% reported by Ha and colleagues for the 2005 Vietnam National Adult Obesity Survey (VNAOS) . The comparision needs to take into consideration that data for all three studies above were collected between 2004–2005 while ours were collected in 2010. The prevalence of underweight status for Vietnam as a whole and for HCMC and Hanoi areas have likely decreased over that time period.
We observed higher prevalences of overweight, 14.9% and 29.8%, as defined by WHO standard and Asian-specific definitions, respectively, compared to 6.6% and 16.3% for the 2005 VNAOS . However, the prevalences are similar to those reported for the 2004 urban HCMC residents cohort (WHO standard, 15.4%; Asian-specific, 26.2%) and for Hanoi and adjacent provinces (WHO standard, 12.2%, Asian-specific, 27.5%). The prevalence of being overweight as defined by the WHO standard cut-off in our population and in Vietnam overall remain lower than the 20% to 30% reported for many Southeast Asian countries such as Japan, Malaysia, Philippines, Singapore, Thailand, and South Korea with data collected between 1998 and 2004 . Given the trend towards increasing prevalence of overweight/obesity in low- to middle-income countries, particularly those in Asia , prevalence estimates of overweight/obesity for the countries noted above have likely risen.
Obesity by WHO standard remained low at 1.1% for our cohort but increased to 4.0% when the Asian-specific cut-off was applied. These prevalences are higher than the 0.4% and 1.7%, respectively, reported for the 2005 VNAOS, which was collected 5 years earlier. Possibly, our prevalence estimates reflect the continuing trend towards decreasing prevalence of underweight status and increasing prevalence of overweight and obesity in Vietnam overall . Furthermore, our population resides in a city that is undergoing higher than national average economic growth; expansion of urban development; growth of urban areas; and shrinkage of rural areas. Urbanization is coupled with greater influences of globalization and increased availability of fatty and high caloric foods and higher food expenditure per capita . Indeed, our obesity prevalences were more closely aligned with those reported for Hanoi City and adjacent provinces (0.5%, WHO standard; 2.2%, Asian-specific) and HCMC (1.8%, WHO standard; and 6.4%, Asian-specific); both regions have economic growth and development similar to if not greater than that in Danang City . Interestingly, HCMC also showed much higher prevalence of underweight status, 20.4%, compared to 12.4% in Danang and 12.6% in Hanoi. Perhaps, the situation in HCMC – the economic hub of Vietnam – could be attributed to the increasing disparity in wealth and the existence of urban slums.
Similar to the national study and study conducted in Hanoi, patterns in prevalence of body weight status were evident across communes by urbanization. That is, lower underweight and higher overweight/obesity prevalence were associated with greater urbanization. The highest prevalence of underweight status occurred in rural communes at 23.5%. In the urban communes, 43.3% had BMI ≥ 23 kg/m2 while 21.3% had a BMI ≥ 25 kg/m2. These trends likely reflect continuing national and regional expansion of urbanization, growth of mixed urban–rural areas and reduction of rural populations.
The prevalence of underweight increased with age for both standard WHO and Asian-specific definitions of overweight/obesity prevalence decrease after age 65 years. These are in agreement with results reported in the 2005 national survey. The trend of having lower BMI at older ages is not unusual, even in western nations, as age is affiliated with physical parameters such as frailty , and mental conditions such as dementia , that are manifested by weight-loss.
The prevalence of overweight was highest for those 35–64 and peaks between 55–64 years of age. For Asian-specific BMI definition, factors associated with overweight/obesity included age, living in urban communes, increased systolic blood pressure, and diabetes. Age was not an associated factor when using the WHO standard definition; however, a reported history of myocarial infarction became highly significant. While income did not remain in the model, urbanization was highly associated with overweight status suggesting that urban living, which provides greater opportunities to access inexpensive processed foods and foods with high refined carbohydrate content, may be the driving force in the rise of overweight/obesity occuring in Danang City and perhaps throughout urban Vietnam. Similar to results found for underweight status, the association of overweight/obesity with health conditions such as diabetes, systolic hypertension, and heart attacks are likely consequences of increased BMI. Knowledge of these associations may provide stimulus for interventions in Danang City and in Vietnam to address the increasing prevalences of overweight/obesity and their impact on the chronic disease burden evident in many other low- and middle-resource countries .
Overall, our study suggests that important chronic conditions such as diabetes, higher systolic blood pressure, and cardiovascular risk factors are significantly and independently associated with being overweight/obese when defined by WHO standard. With the exception of heart attack, these same factors remain importantly related to being overweight/obese as defined by the Asian-specific definition. Although it remains unclear which cut-off points are appropriate for which Asian ethnic groups, what is clear is the need to consider alternative BMI definitions of overweight and obesity as a number of important chronic diseases risk factors appear to remain important at BMI cut-offs lower than the WHO standard definition. Non-communicable diseases such as heart disease, diabetes and cancer are now the leading causes of death in low- to middle-income countries. The WHO reports that non-communicable diseases make up the highest proportion of deaths among both men and women in low- and middle-income countries. Twenty-nine percent of these deaths occur in people under the age of 60 in these countries compared to 13% in high-income countries .
Several limitations exist in our study. The cross-sectional design precludes the ability to discern temporality, although it is reasonable to suggest that lifestyles may precede diseases and diseases may result from weight status, an indicator of nutritional status. Second, besides blood pressure, which was objectively measured as part of the study, medical conditions such as arthritis, myocardial infarction, hypercholesterolemia were self-reported. Precise knowledge of personal medical history depends on health care utilization behaviors and interest in one’s own health that are likely to vary according to history with the health care system, education, income, and geographical location of residence. Third, our sample was restricted to participants 35 years and older; therefore, our results are not generalizable to those younger than 35 years of age.