['Health and lifestyle factors are associated with variations in serum testosterone levels in ageing men. However, it remains unclear how age-related changes in testosterone may be attenuated by lifestyle modifications. The objective was to investigate the longitudinal relationships between changes in health and lifestyle factors with changes in hormones of the reproductive endocrine axis in ageing men.', 'A longitudinal survey of 2736 community-dwelling men aged 40-79 years at baseline recruited from eight centres across Europe. Follow-up assessment occurred mean (±S.D.) 4.4±0.3 years later.', 'Paired testosterone results were available for 2395 men. Mean (±S.D.) annualised hormone changes were as follows: testosterone -0.1±0.95\u200a nmol/l; free testosterone (FT) -3.83±16.8 \u200apmol/l; sex hormone-binding globulin (SHBG) 0.56±2.5\u200a nmol/l and LH 0.08±0.57\u200a U/l. Weight loss was associated with a proportional increase, and weight gain a proportional decrease, in testosterone and SHBG. FT showed a curvilinear relationship to weight change; only those who gained or lost ≥15% of weight showed a significant change (in the same direction as testosterone). Smoking cessation was associated with a greater decline in testosterone than being a non-smoker, which was unrelated to weight change. Changes in number of comorbid conditions or physical activity were not associated with significant alterations in hypothalamic-pituitary-testicular (HPT) axis function.'] Are age-associated changes in hypothalamic-pituitary-testicular function in middle-aged and older men modified by weight change and lifestyle factors : longitudinal results from the European Male Ageing Study?