Does Cardiorespiratory Fitness Modify the Association between Birth Weight and Insulin Resistance in Adult Life?

OBJECTIVE Lower birth weight is associated with higher insulin resistance in later life. The aim of this study was to determine whether cardiorespiratory fitness modifies the association of birth weight with insulin resistance in adults. METHODS The subjects were 379 Japanese individuals (137 males, 242 females) aged 20-64 years born after 1943. Insulin resistance was assessed using a homeostasis model assessment of insulin resistance (HOMA-IR), which is calculated from fasting blood glucose and insulin levels. Cardiorespiratory fitness (maximal oxygen uptake, VO2max) was assessed by a maximal graded exercise test on a cycle ergometer. Birth weight was reported according to the Maternal and Child Health Handbook records or the subject's or his/her mother's memory. RESULTS The multiple linear regression analysis revealed that birth weight was inversely associated with HOMA-IR (β = -0.141, p = 0.003), even after adjustment for gender, age, current body mass index, mean blood pressure, triglycerides, HDL cholesterol, and smoking status. Further adjustments for VO2max made little difference in the relationship between birth weight and HOMA-IR (β = -0.148, p = 0.001), although VO2max (β = -0.376, p<0.001) was a stronger predictor of HOMA-IR than birth weight. CONCLUSIONS The results showed that the association of lower birth weight with higher insulin resistance was little modified by cardiorespiratory fitness in adult life. However, cardiorespiratory fitness was found to be a stronger predictor of insulin resistance than was birth weight, suggesting that increasing cardiorespiratory fitness may have a much more important role in preventing insulin resistance than an individual's low birth weight.