Shih et al. studies are associations between bone lead levels and cognitive function. The associa- t i o n s i n t h e B M S w e r e c r o s s - s e c t i o n a l , whereas the predominant associations in the NAS were with change in cognitive function over time, although a significant cross-sec- tional association with MMSE score was also observed in this sample. Taken together, these data suggest that at environmental exposure levels, the effects of cumulative exposure are more pronounced than recent effects of cur- rent exposure. The absence of associations in t h e S t o k e s e t a l . ( 1 9 9 8 ) s t u d y c o u l d b e because of the younger age of studied sub- jects, the very low current blood and tibia lead levels, or the inadequacy of tibia lead in Table 2. Continued. Percent male [mean age in Design years (SD)] Sample size (no.) 80 Author Bleecker et al. 1997 Chia et al. 50 (E) 1997 97 (NE) Osterberg et al. 1997 38 (E) 19 (NE) Hanninen et al. 1998 486 XS XS XS 100 44.1 (8.4) 100 (E) 35.7 (10.6) (NE) 33.9 (3.7) 100 (E) median: 41.5 79.6 Low blood lead 41.7 (9.3) High blood lead 46.6 (6.2) Race/ ethnicity (%) White 100 Source of Pb exposure Canadian lead smelter (Canada Lead Study) 100% Lead battery Asian manufacturing (48 factory (E) Chinese) Vehicle (E) maintenance 100 workshop (NE) Asian (43 Chinese) (NE) NR Secondary lead smelter— inorganic lead (E) Nearby mechanical manufacturing plant (NE) 54 XS NR Helsinki lead acid battery factories the third decade of life to estimate early life dose (Hoppin et al. 2000). Studies of occupationally exposed workers. Fifteen articles were identified of workers with current or past occupational exposure to lead. Eight of these studies used a surrogate measure of cumulative lead dose (i.e., IBL) rather than a direct measure of lead in bone. Among these studies, which compared blood and IBL lead dose, when the lead exposure was primarily current (e.g., relatively high blood lead levels), most studies found an asso- ciation between increasing blood lead values and worse cognitive function (Barth et al. 2002; Bleecker et al. 1997; Lucchini et al. 2000). However, studies in which the exposure was primarily in the past demonstrated that surrogate measures of cumulative dose were a stronger predictor of worse cognitive function compared with blood lead levels (Bleecker et al. 2005; Chia et al. 1997; Lindgren et al. 1996). Studies that used bone lead levels as a direct indicator of retained cumulative lead dose are summarized below. One study of currently exposed lead workers in South Korea (n = 803) found strong and consistent associations of blood lead levels with worse cognitive function after adjustment for covariates, but tibia lead levels were not as consistently associated (Schwartz et al. 2001). The same ﬁndings for bone lead levels were observed in two smaller Primarily current/ past exposure Current 4–26 years of exposure Current Current 2–35 years of exposure Past 12.3, 20.5 years of exposure (means across groups) Lead dose measure [mean (SD)] Blood: 26.4 (7.1) IBLa: 903.1 (305.9) TWAb: 42.3 (8.4) Tibia: 41.0 (24.4) Covariates adjusted for outcome measures Age, education Battery of tests— 5 domains Blood: (E) 37.1 (range, 13.2–64.6) (NE) 6.14 (range, 2.4–12.4) CumPbc: (E) 175.9 (range, 10.0–1146.2) Age, education, smoking history, ethnic groups, drinking habits Battery of tests— 5 domains Current blood leadd: (E) median, 1.8 (range, 0.9–2.4) (NE) median, 0.18 (range, 0.07–0.34) Peak blood leadd: (E) median, 3.0 (range, 2.2–4.3) CBLIe: (E) median, 233 (range, 74–948) Finger bone: (E) median, 32 (range, 17–101) (NE) median, 4 (range, –19 to 18) Low blood leadd: TWAf: 1.4 (0.3) Peak blood leadd: 1.9 (0.4) IBLg: 15.7 (9.5) Calcaneus: 78.6 (62.4) mg/kg Tibia: 19.8 (13.7) mg/kg High blood leadd TWAf : 1.9 (0.4) Peak blood leadd: 3.3 (0.7) IBLg: 39.2 (18.5) Calcaneus: 100.4 (43.1) mg/kg Tibia: 35.3 (16.6) mg/kg Matched on age, education, job level Battery of tests— 5 domains Age, sex, education Battery of tests— 6 domains Summary of ﬁndings Signiﬁcant amount of variance in verbal memory performance accounted for only by measures of blood lead and TWA Visuomotor ability had signiﬁcant variance accounted for by measures of TWA, IBL and tibia lead E and NE groups signiﬁcantly different in tests involving motor dexterity, and visuomotor and psychomotor speed Cumulative blood associated with Digit Symbol and Trail Making Part A scores Cumulative blood lead a stronger predictor of neurobehavioral effects than concurrent blood lead levels Neither blood (current or peak) lead nor ﬁnger bone lead levels were associated with any neurobehavioral measures None of the bone lead measures were signiﬁcantly associated with any test scores The low blood lead group showed associations between historical blood lead measures and visuospatial, visuomotor, attention and verbal comprehension performance The high blood lead group had worse performance than the low blood lead group on tests of attention (Digit Symbol), visual memory (memory for design), and visuoperception (embedded ﬁgures) Continued, next page VOLUME 115 | NUMBER 3 | March 2007 • Environmental Health Perspectives