The objective of this study was to investigate whether there is a bidirectional association between
testosterone concentrations and
insulin resistance, in a prospective population study. A random population sample of 1400 men, aged 30-74, was examined in 2002-2005 in southwestern Sweden and followed up in 2012-2014 (N = 657). After excluding subjects without information on
sex hormones and
insulin resistance, 1282 men were included in the baseline study. Fasting measurements of plasma
glucose,
insulin and
hormones were performed.
Insulin resistance was defined using HOMA-Ir. Mean age at baseline was 47.3 ± 11.4 years. From the follow-up survey 546 men were included, mean age 57.7 ± 11.6 years. Low concentrations of total
testosterone at baseline were significantly associated with high logHOMA-Ir at follow-up in a multivariable model including age, waist-hip ratio, physical activity, alcohol intake, smoking,
LDL, CRP,
hypertension, diabetes and logHOMA-Ir at baseline as covariates (β = -0.096, P = 0.006). Similar results were observed for bioavailable
testosterone. Men within the lowest quartile of total
testosterone at baseline had significantly higher logHOMA-Ir at follow-up than other quartiles (Q1 vs Q2 P = 0.008, Q1 vs Q3 P = 0.001, Q1 vs Q4 P = 0.052). Multivariable analysis of the impact of
insulin resistance at baseline on
testosterone levels at follow-up revealed no significant associations regarding
testosterone concentrations (β = -0.003, P = 0.928) or bioavailable
testosterone (β = -0.006, P = 0.873), when adjusting for baseline concentrations of total
testosterone, age, waist-hip-ratio,
LDL, CRP, physical activity, alcohol intake, smoking,
hypertension and diabetes. Low
testosterone concentrations at baseline predicted higher
insulin resistance at follow-up, but high
insulin resistance at baseline could not predict low
testosterone at follow-up.