The Relationship Between Blood Glucose and Cortisol Levels After Exercise Ramona Granat 1053457 Biology 493

Introduction Cortisol is a sterol lipid secreted by the glucocorticoid region of the adrenal cortex. Stress (Emotional, physiological or social) activates the adrenal gland to secrete cortisol (Nieman 1999). Cortisol influcences T and B cell activity, Corticosteroid globulin and gluconeogenisis.

Cortisol binds to receptors in adipose tissue to stimulate gluconeogenesis (Bonifazi 2001). Gluconeogenesis is responsible for maintaining normal blood glucose levels during stress by breaking down glycogen and mobilizing fat from adipose tissue. Gluconeogenesis occurs when glucose levels drop and blood glycogen is depleted, as a result noncarbohydate sources are used to produce glucose.

Studies have shown that exercise increases serum cortisol concentrations (Gleeson 2000, Kraemer 2001, Fisher 2001). Other studies have found no significant increase in cortisol levels after exercise (Nieman 1995).

Intensity of exercise affects results. Endurance and age of participant may influence cortisol secretion (Davie 1999 and Izquierdo 2001). Time of day influences cortisol response (Kanaley 2001)

Purpose If blood glucose levels decrease following exercise then the cortisol levels should increase. Purpose of this study was to determine the relationship between blood glucose and cortisol levels after exercise

Methods Ten subjects were tested, four males and six females. Subjects ages ranged from 19 years to 24 years in age. Each subject was required to fast for 12 hours prior to exercise. All tests were conducted between the hours of eight and eleven o’clock in the morning.

Blood glucose samples were taken immediately before and after exercise using a Precision Q-I-D blood glucose monitor. Cortisol samples were taken immediately before and after exercise by collecting saliva using cortisol collection tubes. Cortisol concentrations were measured by Salametrics Laboratory (College Park, PA).

Exercise bouts consisted of bicycling on a bicycle ergometer. Subjects were required to peddle until they reached their target heart rate (70% of the age predicted heart rate). Female subjects peddled for 20 minutes at their target heart rate Male subjects peddled for 30 minutes at their target heart rate.

The bike was set on a incline program that started with a resistance of 70 watts, subjects were instructed to keep a constant intensity measured in rotations per minute. Resistance increased 15 watts (one resistance level) every 30 seconds until a resistance level was reached where the subject was unable to maintain their target heart rate. At that point the watts were reduced one resistance level (15 watts) were the subject continued to peddle for the remainder of the test period. Data Analysis consisted of a paired t-test and a regression analysis. Significance was established at 0.05.

Results Individual variation for pre and post glucose concentrations were high.

Table 1. The pre and post exercise blood glucose and cortisol concentrations for each subject tested. Subject Number Pre blood glucose (mg/dL) Post blood glucose (mg/dL) Pre cortisol (ug/dL) Post Cortisol (ug/dL) 1 75 0.0542 0.540 2 66 51 0.472 0.482 3 73 38 0.236 0.302 4 58 56 0.657 0.691 5 49 46 0.209 0.311 6 50 52 0.407 0.491 7 40 65 0.591 0.585 8 59 0.419 9 85 54 0.451 0.509 10 63 80 0.603 0.711 Average 61.8 58.2 0.45 0.50 Standard deviation 13.57 12.99 0.16 0.14

Results Individual variation for pre and post glucose concentrations were high. There was no significant difference in the blood glucose levels in response to the exercise test. There was a significant (p<0.05) increase in cortisol as a result of the exercise.

Table 1. The pre and post exercise blood glucose and cortisol concentrations for each subject tested. Subject Number Pre blood glucose (mg/dL) Post blood glucose (mg/dL) Pre cortisol (ug/dL) Post Cortisol (ug/dL) 1 75 0.0542 0.540 2 66 51 0.472 0.482 3 73 38 0.236 0.302 4 58 56 0.657 0.691 5 49 46 0.209 0.311 6 50 52 0.407 0.491 7 40 65 0.591 0.585 8 59 0.419 9 85 54 0.451 0.509 10 63 80 0.603 0.711 Average 61.8 58.2 0.45 0.50 Standard deviation 13.57 12.99 0.16 0.14

Table 2. The paired t-test results for pre and post exercise blood glucose and cortisol. Paired t-value 0.6 -3.95 P-value 0.564 0.003

Results Individual variation for pre and post glucose concentrations were high. There was no significant difference in the blood glucose levels in response to the exercise test. There was a significant (p<0.05) increase in cortisol as a result of the exercise. The regression between blood glucose and cortisol at the end of exercise demonstrated a significant direct relationship (p<0.05), however, there was still a lot of variation (R2= 0.49)

Figure 3. The regression between blood glucose and cortisol after exercise for each of the subjects tested.

Table 3. Analysis of the regression between blood glucose and cortisol after exercise. F-value 7.76 P-value 0.024

Discussion There was no change statistically in blood glucose concentrations due to the exercise in this study Failure for a decrease in blood glucose may be due to two factors 1. Intensity 2. Gluconeogenesis

Figure 1: The comparison of pre and post exercise blood glucose levels of each subject tested.

Discussion There was no change statistically in blood glucose concentrations due to the exercise in this study Failure for a decrease in blood glucose may be due to two factors 1. Intensity 2. Gluconeogenesis

Intensity: Exercise protocol appeared to be sufficient to lower blood glucose in some individuals, it may not have been intense enough for all individuals

Gluconeogenesis: Onset appears quicker than it was anticipated. Exercise protocol was sufficient to cause a cortisol response. Individuals with higher cortisol concentrations also exhibited higher glucose concentrations as shown in the regression between glucose and cortisol after exercise. This is a positive direct relationship. The effect of cortisol on gluconeogenesis may occurs rapidly, resulting in an elevation in blood glucose.

Figure 2. The comparison of pre and post exercise cortisol levels of each subject tested.

Gluconeogenesis Onset appears quicker than it was anticipated. Exercise protocol was sufficient to cause a cortisol response. Individuals with higher cortisol concentrations also exhibited higher glucose concentrations as shown in the regression between glucose and cortisol after exercise. This is a positive direct relationship. The effect of cortisol on gluconeogenesis may occurs rapidly, resulting in an elevation in blood glucose.

Acknowledgements Dr. Day Biology Faculty My Subjects My husband Brinn

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