Age-Dependent Decline of Association Between Obesity and Hyperglycemia in Men and Women

The subjects were Japanese workers (37,686 men and 19,890 women), aged 35–70 years, who had received periodic health examinations at workplaces in Yamagata Prefecture in Japan and were divided into four groups by age (35–39, 40–49, 50–59, and 60–70 years). Histories of alcohol consumption, cigarette smoking, habitual exercise, and treatment for any illnesses were surveyed by questionnaires. This study was approved by the Yamagata University School of Medicine Ethics Committee.

BMI was calculated as weight in kilograms divided by the square of height in meters. The criterion for obesity evaluated by using each adiposity index was defined as BMI ≥25 kg/m², waist circumference ≥85 cm for men and ≥80 cm for women, and waist-to-height ratio (WHtR) ≥0.5. Fasted blood was sampled from each subject, and hemoglobin A_1c, triglycerides, and LDL cholesterol were determined. The hemoglobin A_1c values were calibrated by using a formula proposed by the Japan Diabetes Society (11) as hemoglobin A_1c (National Glycohemoglobin Standardization Program) (%) = hemoglobin A_1c (Japan Diabetes Society) (%) + 0.4%. Hyperglycemia including diabetes and prediabetes was defined as hemoglobin A_1c ≥5.7% (12) and/or current history of drug therapy for diabetes.

Statistical analyses were performed using SPSS 16.0 J software (SPSS Inc., Chicago, IL). Crude odds ratios (ORs) and ORs after adjustment for age, smoking, alcohol intake, and habitual exercise were calculated by using logistic regression. Trends for crude ORs across the age groups were tested by using the Breslow-Day test. P values < 0.05 were defined as significant.

Prevalences of hyperglycemia, high triglycerides, and high LDL cholesterol were, respectively, 24.2, 36.0, and 21.3% in men and 19.3, 14.1, and 19.4% in women. Prevalences of high BMI, large waist circumference, and high WHtR were, respectively, 30.8, 44.2, and 46.5% in men and 20.6, 41.3, and 47.8% in women.

In all of the age groups of men and women, crude and adjusted ORs for hyperglycemia of subjects with a high or large adiposity index versus subjects without a high or large adiposity index were significantly higher compared with a reference level of 1.00 (Table 1). There were significant trends for the crude ORs for hyperglycemia to be lower in higher age groups, and the adjusted ORs also tended to be lower as age increased. Crude and adjusted ORs for high triglycerides and high LDL cholesterol of subjects with a high or large adiposity index versus subjects without a high or large adiposity index also tended to decrease with age in men and women (Table 1).

The association between obesity and hyperglycemia declined with age in men and women, although the association remained significant even in the highest age group. This age-dependent trend was consistent in any analyses using different adiposity-related indices. This study is, to the best of our knowledge, the first study showing an age-dependent significant attenuation of the association between obesity and glycemic status both in men and women. In addition, significant age-dependent declines were also found in the associations of obesity with dyslipidemias such as high triglycerides and high LDL cholesterol. Therefore, the associations between obesity and metabolic disorders, such as diabetes and dyslipidemia, are thought to decline with age.

There is limited information on whether and how age influences the relationship between obesity and diabetes. Two recent studies have reported results related to this topic. Effects of obesity evaluated by BMI on incidence of type 2 diabetes have been reported to decline with age in women but not in men, and the authors speculated that the sex difference observed was due to the smaller population size of male subjects than that of female subjects (13). Another study showed that the correlation coefficient between waist circumference and fasting blood glucose tended to be higher in younger (≤51 years) than in older (>51 years) men and women, although the differences in the correlation between the younger and older subjects were not significant (14). The current study clearly demonstrated significant age-dependent declines of the associations of obesity with hyperglycemia and dyslipidemia in men and women.

Taken together with these findings, our results suggest that the effect of obesity on development of diabetes is stronger in younger people than in older people. This also suggests that correction of obesity is more effective for prevention of diabetes in younger people than in older people and agrees with a consensus that young people should be encouraged to attain and maintain a weight-for-height ratio in the normal range to prevent type 2 diabetes (15). The age-dependent declines in the associations of obesity with hyperglycemia and dyslipidemia may partly explain the weaker association between obesity and the risk for coronary heart disease in older men than in younger men (8,9).

In conclusion, the association between obesity and hyperglycemia is stronger in younger men and women than in older men and women, respectively, and this finding supports a general concept of the necessity of body weight control in young people from the viewpoint of prevention of type 2 diabetes.

This work was supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (21390211).

No potential conflicts of interest relevant to this article were reported.

I.W. researched data, performed the statistical analyses, wrote the manuscript, and is guarantor for the article. T.D. performed the statistical analyses.