Weight, Physical Activity, and Smoking as Determinants of Insulinemia in Adolescents

Abstract

Background

It is known that insulinemia is the result of the interaction among several factors, such as weight, body fat pattern distribution, and physical activity as well as ethnicity. There is little information regarding this question among Mexican adolescents. The association among fasting insulin levels, weight, fat distribution, physical activity, and cigarette smoking was studied in Mexican adolescents.

Methods

Cross-sectional data were collected from 352 Mexican adolescents aged 14–19 years (response rate 41.5%). Fasting insulin levels were measured by microparticle enzyme immunoassay; body mass index (BMI), waist-to-hip ratio (WHR), and waist circumference (WC) were determined using standardized techniques, while physical activity was determined by 7-day Stanford physical activity inventory. Cigarette smoking was defined as number of cigarettes/year.

Results

Increased BMI and waist circumference, low physical activity, younger age, and non-smoking were associated with high insulin levels. Non-smokers had higher fasting insulin levels compared to smokers (57.8 pmol ± 1.84 vs. 49.7 pmol/L ± 2.8; p = 0.034). However, adjusted odds ratio (OR) between insulin and smoking status was not significant. Multivariate analysis showed the following: insulin increased 1.06 pmol/L for each unit of change in BMI; increased 1.02 pmol/L for each unit of change in waist circumference; increased 1.16 pmol/L for non-smoking, and decreased 1.07 pmol/L for each 250 kcal/day of energy expenditure.

Conclusions

Our results support the concept that Mexican adolescents who are overweight have abdominal fat distribution and physical inactivity, and significant hyperinsulinemia. The relationship between smoking and lower insulinemia found in this research warrants further study.

Introduction

In Mexico, type 2 diabetes has recently become the second single cause of death in the general population (1). Hyperinsulinemia is the strongest predictor of type 2 diabetes occurrence (2). Recent data show that abnormalities of the prediabetic state are already present early in life. In adolescents, hyperinsulinemia is associated with an altered lipid profile, hypertension, and obesity 3, 4. Hyperinsulinemia may persist in the adult from childhood (5) and is the result of the interaction between genetic (6) and environmental factors such as physical activity 7, 8, 9, cigarette smoking (10), diet 11, 12, and weight 13, 14.

In adolescents, higher body mass index (BMI) is associated with hyperinsulinemia 13, 14 but in contrast to data found in adults, hyperinsulinemia is not associated with higher waist-to-hip ratio (WHR) 4, 15, and waist circumference (WC) is only related to hyperinsulinemia in male adolescents (16). Higher physical activity levels have been associated with lower insulin levels 7, 9. In adults, a positive association between cigarette smoking and insulin has been reported 10, 17, although a negative association has also been described (18). In adolescents, it is not clear which anthropometric parameters of abdominal fat distribution best predict hyperinsulinemia and whether smoking status is related to fasting insulin levels. Moreover, no studies in Mexico have contemplated the relationship between environmental factors and hyperinsulinemia in adolescents. Adolescents represent 24.7% of the total Mexican population (19); 25% smoke cigarettes (20), and 8.6% of female adolescents are overweight (21). As hyperinsulinemia is related to environmental as well as to hereditary factors, it is important to evaluate the predictors in populations at high risk of type 2 diabetes. We designed a study to examine the association between fasting insulin levels, overweight, abdominal fat distribution, physical activity, and cigarette smoking in Mexican adolescents.