Table 3. Relationship between endogenous testosterone (T) levels and cognitive function in available population-based studies.

Reference (year)	Study	Country	Population	Type of T assay used	Cognitive outcome
Barrett-Connor et al (1999) [34]	Rancho Bernardo	USA	547 men aged 59–89 years at baseline	Radioimmunoassay	↓ In men with reduced TT
Yaffe et al (2002) [35]	Study of osteoporotic risk in men	USA	310 men aged 50 years or older	Radioimmunoassay	↓ In men with reduced BT
Moffat et al (2004) [36]	Baltimore longitudinal study of aging	USA	1,148 men aged 32 to 87 years at baseline	Radioimmunoassay	↓ In men with reduced FTI
Fonda et al (2005) [37]	Massachusetts male aging study	USA	981 men aged 40–70 years at baseline	Radioimmunoassay	↔
Muller et al (2005) [38]		Netherlands	400 men aged 40–80 years at baseline	Radioimmunoassay	↓ In men with reduced TT
Geerlings et al (2006) [39]	Honolulu-Asia aging study	Honolulu-Asia	2,974 men aged 71 to 93 years at baseline	Radioimmunoassay	↔
Thilers et al (2006) [40]	Betula study	Sweden	1,107 men aged 35 to 90 years at baseline	Radioimmunoassay	↓ In men with reduced cFT
Yeap et al (2008) [41]	Health in men study	Australia	2,932 men aged 70 to 89 years at baseline	Radioimmunoassay	↓ In men with reduced cFT
LeBlanc et al (2010) [42]	Osteoporotic fractures in men study	USA	5,995 men aged 65 years or older at baseline	Mass spectometry in a random sample of 1,602 men	↔
Wu et al (2010) [43]	European male aging study	Europe	3,369 aged 40 to 79 years at baseline	Mass spectometry	↔

↓: impairment, TT: total T, BT: bioavailable T, FTI: free T index, ↔: no difference, cFT: calculated free T.