Eum et al. is critical because the prevalence of mood disorders and anxiety is twice as common in women as in men (Beekman et al. 1999; Kessler et al. 1994), and measures of cumu- lative exposure to lead may be of particular importance. Therefore, we explored the asso- ciation between cumulative lead exposure—as measured by lead in bone—and mental health among middle-age and elderly women partici- pating in the Nurses’ Health Study (NHS). Because of the influence of menopause and subsequent hormone replacement therapy (HRT) on bone dynamics (Nelson et al. 2002; Seeman 2003), including the accumu- lation of lead in bone, we also examined the influence of these factors. Materials and Methods Study population. The NHS is a cohort of 121,700 registered nurses recruited between the ages of 30 and 55 years in 1976 and fol- lowed up via biennial mailed questionnaires (Colditz et al. 1997). Our study population was drawn from two subsamples of the NHS cohort that was evaluated for lead exposure. The first is a sample of women who partici- pated in a case–control study of lead expo- sure and hypertension (Korrick et al. 1999). Women were invited to participate if they lived in the Greater Boston metropolitan area, Massachusetts, were not obese (body mass index < 29 kg/m2), and did not have a history of major, chronic disease—mental health prob- lems were not an exclusion criterion. Women who first reported a diagnosis of hypertension between 1990 and 1994 were invited to par- ticipate as cases; women free of major chronic disease participted as controls and were fre- quency matched to cases by 5-year age groups. In total, between 1993 and 1995, 302 NHS participants agreed to participate. The women in the second sample were recruited for a study of lead exposure and osteoporosis. Similar eligibility criteria used for controls in the hypertension study were applied, with participants being free of chronic diseases (not including mental health problems) up to the time of recruitment (2001 through 2004), at which time they underwent their lead exposure measurements. This sample comprised 320 NHS partici- pants. Altogether, lead content was measured in cortical (tibia) and trabecular (patella) bone in 621 and 620 women, respectively, from these two studies. After providing a complete description of the study to the participants, written informed consent was obtained before participation in each substudy. The present study was approved by the institutional review boards of the Brigham and Women’s Hospital and the Harvard School of Public Health. Measures of psychological symptoms were obtained as part of several of the regular biennial NHS mailed questionnaires. Depressive symptoms were measured using the Mental Health Index 5-item (MHI-5) subscale, which was included on the 1992, 1996, and 2000 questionnaires. Anxiety symptoms were measured using the phobic anxiety scale of the Crown-Crisp Index (CCI) which was included on the 1988 and 2004 questionnaires. Of the 621 women who participated in the lead exposure studies, 617 completed at least one psychological symptom assessment. Of these 617 women, 613 (99.4%) completed at least one MHI-5 questionnaire, and 609 (98.7%) completed at least one CCI questionnaire. Individual women completed the MHI-5 in up to three separate study cycles for a total of 1,696 MHI-5 assessments, and the CCI in up to two separate study cycles for a total of 1,117 CCI assessments. We excluded 26 MHI-5 assessments (1.5%) and 17 CCI assessments (1.5%) for which data were missing on pack-years of smoking (n = 10 women). Thus, the final analytic sample included 603 women with 1,670 MHI-5 assessments (24 women with one, 91 with two, and 488 with three), and 599 women with 1,100 CCI assessments (98 women with one and 501 with two; Figure 1). All responses to the 2004 CCI (n = 554) occurred after bone lead measurement, whereas all responses to the 1988 CCI (n = 546) occurred before the bone lead measurements (mean ± SD, 10.0 ± 4.2 years; range, 4.4–15.9 years). Of the MHI-5 Calendar year Calendar year Bone lead (1993–1995; n = 302) Bone lead (2001–2004; n = 319) 88 90 92 94 96 98 00 02 04 88 90 92 94 96 98 00 02 04 (n = 269) (n = 287) (n = 281) (n = 253) (n = 287) (n = 293) (n = 279) (n = 263) (n = 267) (n = 291) MHI-5 (total 296 women, 837 MHI-5) CCI (total 294 women, 542 CCI) MHI-5 (total 307 women, 833 MHI-5) CCI (total 305 women, 558 CCI) Figure 1. Timeline of MHI-5 and CCI assessments among women with bone lead measurements from study subsample 1 (A) and subsample 2 (B), as described in “Materials and Methods.” assessments, 1,102 (66.0%) occurred before the bone lead measurements (5.1 ± 3.5 years earlier; range, 0.4–12 years). Because bone lead reflects many years of past exposure, we included all psychological assessments in our primary analyses regardless of their timing with respect to bone lead measurement. Nonetheless, we also did sensitivity analyses restricted to those psychological assessments that occurred after bone lead measurement. Lead exposure assessment. Participants vis- ited the outpatient General Clinical Research Center of the Brigham and Women’s Hospital for measurement of lead content in their bone by K-shell X-ray fluorescence (KXRF) (Aro et al. 1994), expressed as micrograms of lead per gram of bone mineral (micrograms per gram). Bone lead measurements were taken at each woman’s midtibial shaft and patella. These sites are targets for bone lead research, because the half-life of lead in tibia and patella differs. In a cohort of older men, the half-life of lead in patella has been esti- mated to be on the order of years, whereas in tibia it is estimated to be on the order of decades (Wilker et al. 2011). Among women, however, faster bone turnover (Seeman 2003) likely makes these half-lives shorter. When we began measuring the women’s bone lead, we used an instrument developed by ABIOMED Inc. (Danvers, MA) (Burger et al. 1990). In 1999, we replaced our pro- totype ABIOMED instrument with an upgraded instrument designed to improve measurement precision (Aro et al. 1994). Intercalibration data from persons who were measured on both instruments demonstrated a linear relationship between the two mea- surements with a slope of 0.87. Using this correction factor, we are able to combine data from our prototype and upgraded KXRF machines (Nie et al. 2008). To reduce the impact of any additional scaling differences in these readings on our epidemiologic analyses, we included in all of our bone lead regression models a term for lead substudy, which effec- tively adjusts for instrument, because women from the hypertension substudy were assessed on the ABIOMED instrument, and women from the osteoporosis substudy were assessed on the upgraded instrument. P s y c h o l o g i c a l s y m p t o m a s s e s s m e n t . Symptoms of depression and anxiety were assessed with the MHI-5 and the CCI, respec- tively, each of which has been validated and has an extensive history in research and been used in populations of a similar age as ours (Albert et al. 2005; Beusterien et al. 1996; Burgess et al. 1987; Friedman et al. 2005). The MHI-5 is a five-item subscale derived from the Short Form-36 health status survey designed to capture, among other aspects of psychologi- cal functioning, psychological distress versus well-being (Ware and Sherbourne 1992). The 818 ovlume 120 | number 6 | June 2012 • Environmental Health Perspectives