Endocrine Abstracts

Objective: Aromatase deficiency in mice or men prevents conversion of androgens to oestrogens and results in central obesity and insulin resistance. In idiopathic obesity, higher aromatase mRNA levels in adipose tissue predict peripheral rather than central fat distribution, but any contribution of aromatase to metabolic complications is unknown. Here, we measured plasma steroids in a large cohort of men and post-menopausal women, in whom aromatase is the major source of oestrogens, and correlated these with indices of metabolic syndrome.

Method: A cross-sectional study of 197 men and 101 women aged 66–77 years. Sex steroid hormones were measured in serum by ELISA. Data are Pearson correlation coefficients: *P≤0.05, **P<0.005.

Results: There were strong positive correlations between testosterone and oestradiol (r=0.48**) and between androstenedione and oestrone (r=0.34**), even after adjustment for gender and waist circumference. In men, higher oestradiol and oestrone levels were associated with lower fasting plasma glucose, triglycerides and improved insulin sensitivity (Table), but not with body fat or its distribution; these associations were absent in women. Further, only in men were testosterone concentrations negatively correlated with indices of obesity; indeed, associations of testosterone with metabolic variables were entirely confounded by obesity (Table).

Conclusions: The principal determinant of serum oestrogen levels may be the concentrations of androgens available as substrates for aromatase, rather than the mass of adipose tissue. In male obesity, lower androgen substrate supply may offset any increase in whole body aromatase activity in adipose tissue, thereby reducing oestrogen generation and potentially contributing to adverse metabolic parameters.