Body mass index and its effect on serum cortisol level

Cortisol measurement is indicated in suspected over or under production of cortisol by the adrenal cortex. The finding of low cortisol can create concern and initiate further investigations for the exclusion of adrenal insufficiency. Cushing's syndrome is frequently included in the differential diagnosis of obesity. Some literature describes reduced serum cortisol levels in obesity, however, this is not a well-recognized phenomenon.

The aim of this study was to determine the relationship between body mass index (BMI) and serum cortisol levels.

Seventy healthy participants agreed to take part in the study. The anthropometric measurements (weight, height, and waist and hip circumferences) were done. Exclusion criteria include those with a history of adrenal/pituitary disease or medications altering cortisol level. The basal cortisol (BC) sample was taken at 8 a.m. immediately before administration of an intravenous bolus injection of 250 μg adrenocorticotropic hormone (ACTH). BMI categories were defined as normal and high if BMI was 18.5-24.99 kg/m² and ≥ 25 kg/m², respectively.

Forty (57.1%) participants had normal BMI while 30 (42.9%) participants had BMI ≥ 25 kg/m² (P0 = 0.053). The mean BC level was lower in participants with BMI ≥ 25 kg/m² but not significant. There was a negative correlation between BMI and BC level ( r = -0.205, P = 0.88) while a positive correlation existed between stimulated cortisol level and BMI (r = 0.009, P = 0.944).

Persons with BMI above 25 kg/m² had lower BC level though not statistically significant, the trend was noticed. Subjecting people whose BMI is above 25 kg/m² to further stimulation with ACTH because of low BC is not advised because their response to ACTH stimulation was similar to those who have normal BMI.