In contrast, the study found that in adult men, a lower education level was inversely associated with obesity. A lower household income was also not clearly associated with being overweight or obese in for men.
The study examined relationships among these elements of Socioeconomic Status (SES) and the likelihood of being underweight, overweight or obese according to sex and age groups.
“We found several gender differences in the relationships among elements of SES and BMI categories,” said the researchers.
“In men, living alone was associated with being underweight, and a lower education level was inversely associated with obesity.
“In women, lower education level, lower household income, and living alone were associated with being overweight/obese."
They added that differences in basic living abilities for food preparation between men and women may have resulted in the differences observed in this relationship.
According to the researchers from various Japanese universities and part of the Nippon Data2010 Research Group, the findings on overweightness and obesity in adult Japanese women were consistent with previous findings.
Employment and BMI
The report said that a cross-sectional study in Japan showed that men who exclusively ate alone, which may result in the skipping of meals, were more likely to be underweight than those who ate with others.
The study found no relationships between employment status and BMI groups. The researchers said that the relationships among job categories and BMI groups need to be examined in more detail.
The mean age of participants was 60 years (range 20–91) for men, and 58.4 years (range 20–90) for women. In adult women, it was found that the mean age was significantly younger in the underweight group, but significantly older in the overweight group as compared to the normal BMI group.
In elderly men (above 65), the mean age was significantly older in the underweight group as compared to the normal BMI group.
Among high-income countries, the average BMI in Japan was the lowest for men and women. The percentage of those who were overweight or obese was 29.5% for men and 19.2% for women in 2015.
Although there have been no significant changes in the percentage of men who are overweight or obese in the past 10 years, the percentage of overweight or obese women in that period has significantly decreased.
Meanwhile, the percentage of underweight women aged 20–29 years was 22.3%, while that of the elderly (older than 65 years) with malnutrition was 16.7% in 2015.
Therefore, the researchers found that being underweight also has the potential to become a public health issue in Japan.
Strengths and weaknesses
The authors said that the strengths of this study were that they investigated a randomly selected sample of a general population of Japan, as well as that they examined relationships among elements of SES and each BMI category after adjustments for confounding factors.
Nonetheless, they admitted that the study has some limitations.
Among them, as it was a cross-sectional study, the researchers were unable to clarify whether there was a causal relationship between SES and the prevalence of being underweight, overweight or obese.
The World Health Organization reported that more than 1.9 billion adults in the world were overweight or obese, with more than 600 million being obese in 2014.
Source: Journal of Epidemiology
“Relationship Between Socioeconomic Status and the Prevalence of Underweight, Overweight or Obesity in a General Japanese Population: NIPPON DATA2010”
Authors: Tomiyo Nakamura et al.