Osteoporosis, a disease characterized by low bone mineral density (BMD) and increased risk of fractures, is a major public health problem that is prevalent among the populations of developed and developing countries (Looker et al, 2010; Holt et al, 2002; Aggarwal et al, 2011; Lippurer, 2012; Kim et al, 2012). Among a sample of the U.S. population, there was a decline in the prevalence of low BMD in the femoral neck in 2005–2006 compared to 1988–1994, however, the absolute number of older adults with low BMD increased in 2005–2006 (Looker et al, 2010). Major risk factors for low BMD include older age, white race, female gender, cigarette smoking, use of medications such as corticosteroids, nutritional deficiencies (particularly vitamin D, calcium and magnesium), and low estrogen (Prentice, 2004; Bab & Yirmiya, 2010; Haney & Warden, 2008; Wynn et al, 2010; Falahati-Nini et al, 2000). Low BMD results in increased risk of fractures and increased medical costs, and has been associated with other factors including increased disability and premature death (Leboime et al, 2010; Broussard & Magnus, 2008).

Studies investigating the association between clinical depression and BMD have shown inverse relationships but these results have been inconsistent (Cizza et al, 2010; Wu et al, 2009). Police officers are a group that may be of particular interest to study as research has found that exposure to traumatic events and shift work is related to higher rates of depressive symptoms (Violanti and Aron, 1993; Wang et al, 2010). While an abundance of published studies on clinical depression and BMD exist, there are very few that studied depressive symptoms (Williams et al, 2011; Robbins et al, 2001; Tolea et al, 2007) and to our knowledge, none in police officers. Our objective was to examine the cross-sectional association between depressive symptoms and BMD among female and male police officers. We hypothesized that higher depressive symptoms will be associated with lower BMD among both women and men.

Characteristics of the study sample are presented in Table 1. Their ages ranged from 29 to 64 years with the majority of study participants being white (76.3%), under 50 years of age (75.3%), male (57.7%), and completing at least 4 years of college (55.7%). The prevalence of current smoking was 25% in women and 10.4% in men. A higher percentage of women were classified as having a normal BMI (51.2%) compared to 12.5% among men. As expected, the mean BMD values on every site measured were significantly higher among men than among women.

The following results are not presented in the tables. Among men only, CES-D score was negatively associated with education (p = 0.021) and positively associated with BMI (p = 0.009). BMD was inversely and significantly associated with age for most of the anatomical sites measured among both men and women, with those <40 years having the highest mean BMD and those ≥50 years having the lowest value. BMI was positively and significantly associated with BMD in the total hip (among men, p = 0.010) and in the femoral neck (among women, 0.018) with obese participants having the highest density compared to normal or overweight persons. Smoking status was significantly associated with BMD of the femoral neck among men (current smokers = 0.85 ± 0.06 g/cm²; former smokers = 0.99 ± 0.14 g/cm²; and never smokers = 0.93 ± 0.10 g/cm²; p = 0.048), and with the AP spine among women (current smokers = 1.03 ± 0.13 g/cm²; former smokers = 1.06 ± 0.13 g/cm²; and never smokers = 1.16 ± 0.13 g/cm²; p = 0.043). Compared to white women, black women had higher mean BMD of the wrist (0.62 vs. 0.58 g/cm²; p = 0.009) and of the whole body (1.23 vs. 1.16 g/cm²; p = 0.040). Mean BMD of the other sites were not significantly different between black and white women, nor were mean BMD of any location between black and white men significantly different.

Among men, no significant correlations were observed between CES-D score and BMD at any of the sites (Table 2). However, among women CES-D score was negatively and significantly correlated with BMD at the total hip (r = −0.344, p = 0.030), AP spine (r = −0.317, p = 0.046), and whole body (r = −0.397, p = 0.011) after adjustment for age.

The mean values of BMD at the five anatomical sites are presented across tertiles of CES-D scores for women (Table 3). Mean values of BMD at the total hip decreased with increasing tertiles of CES-D scores before (p = 0.026) and after adjustment for age (p = 0.030), however this significant association was somewhat attenuated after further adjustment for education, smoking status, BMI, alcohol intake, physical activity, and medication/supplement use (low CES-D = 1.07 ± 0.03; medium CES-D = 0.98 ± 0.04; high CES-D = 0.95 ± 0.03 g/cm²; p = 0.111). CES-D score was inversely and significantly associated with BMD of the AP spine (low CES-D = 1.22 ± 0.04; medium CES-D = 1.05 ± 0.05; high CES-D = 1.03 ± 0.04 g/cm²; p = 0.035) and the whole body after full risk factor adjustment (low CES-D = 1.26 ± 0.03; medium CES-D = 1.20 ± 0.03; high CES-D = 1.11 ± 0.03 g/cm²; p = 0.018). In contrast, CES-D score was not significantly associated with BMD at any of the sites among men (Table 4). Inclusion of race/ethnicity in the models did not change any of the associations so this variable was excluded from the final models.

Sensitivity analyses were conducted between depressive symptoms and BMD as follows: (a) by excluding all officers (7 women and 10 men) who reported taking any medications that affected BMD; (b) by including in the multivariate model adjustment for medications and supplements that increase BMD; and (c) by including in the multivariate model adjustment for medications and supplements that decrease BMD. When we excluded all officers who took medication or supplements known to affect BMD, the association among men was unchanged, however among women, CES-D score was inversely and significantly associated with BMD at all locations except for wrist. When medications and supplements that either increased or decreased BMD were included in the model, the results among women were similar to that obtained in Table 3. Regardless of the sensitivity analyses attempted, CES-D score was not associated with BMD at any location among men.

In this cohort of female and male police officers, we examined the association between depressive symptoms and BMD at five anatomical sites. To our knowledge, this is the first investigation of its kind among an occupational group that is exposed to a wide variety of conventional and unconventional work place stressors.

Among women, higher levels of depressive symptoms were significantly associated with lower mean levels of BMD for the AP spine and the whole body, after full adjustment. Inverse associations were also observed between depressive symptoms and BMD of the hip although this association was not statistically significant. We did not observe any significant associations with BMD at any of the sites among men. Police work has been shown to be more stressful to female officers because they may experience sexual harassment and racial discrimination which most white male officers do not usually experience (Hassell & Brandl, 2009). Females may have more non-occupational responsibilities such as childcare and household chores. Female officers may therefore be more vulnerable to higher levels of depression and consequently experience a higher prevalence of decreased BMD (Altindag et al, 2007).

Our results of inverse associations between depressive symptoms and BMD are supported by other work. Clinical depression and depressive symptoms have been shown in previous studies to be associated with lower BMD, and the association sometimes differed by gender and among the various anatomical sites (Cizza et al, 2010; Wu et al, 2009; Williams et al, 2011; Altindag et al, 2007; Mussolino et al, 2004; Eskandari et al, 2007). Other studies did not find an association between depression or depressive symptoms and lower BMD (Yazici et al, 2005; Whooley et al, 2004; Reginster et al, 1999). The differences among the studies may be due to several factors. Several of the studies assessed depressive symptoms using questionnaires other than the CES-D (e.g., Hamilton Depression Scale, Montgomery Asberg Depression Rating Scale, General Health Questionnaire, Geriatric Depression Scale, General Well-Being Schedule, etc.). Study designs, use of patients versus community populations, control of different confounding variables, and sample sizes (ranging from <100 to >6000) also varied in the studies and may have contributed to differences in the findings. Police officers in this study, because of their profession, may be particularly exposed to events leading to depression.

When medications and supplements that either increase or decrease BMD were adjusted for as potential confounders in the models, the results among women were similar to that reported above. However, when we analyzed the association between CES-D score and BMD after excluding the 17 officers who took medications or supplements known to affect BMD in any direction, the associations with BMD were stronger among women at all sites measured except for the wrist. Additional investigation into this difference showed that the results from the model that excluded these 17 officers were overly influenced by a single officer, therefore, results presented included these 17 officers. Regardless of the type of analyses employed, CES-D score was not associated with BMD at any location among men. The absence of an association among men may be due to the fact that osteoporosis develops in a more gradual manner in men than in women (Seeman, 2003). Bone loss occurs due to a decrease in the volume of bone formed rather than an increase in the volume of bone removed during remodeling. In menopausal women, bone loss increases rapidly because decreased estrogen production increases the rate of bone remodeling. However, this rapid bone loss is not present in men because the trabecular surface that is available for remodeling is better preserved (Seeman, 2003).

The cross-sectional design of the study was a limitation in that causal inferences could not be drawn. Some police officers may have underestimated their alcohol consumption due to the stigma attached to this habit. If this were the case, information bias may have occurred but the influence of this covariate in the multivariate model is likely to be minimal. There was no information on hormonal levels so we were unable to adjust for this potentially confounding variable. In addition, we were unable to assess effect modification for variables other than gender due to a relatively small sample size. Although characteristics of officers may vary across police departments, the findings of this study may be generalized to other urban departments of a similar size. However, there are several strengths to this study. Although use of a cross-sectional design prevents us from making causal inferences, the cross-sectional study design allows epidemiological investigations to be conducted quickly and relatively inexpensively. To our knowledge, this is the first study to investigate the association between depressive symptoms and BMD in female and male police officers. We had standardized assessment of CES-D score (Radloff, 1977) and objective assessment of BMD. In addition, BMD data were available for five anatomical sites. We were able to adjust for medications and supplements that affect BMD. Studies have provided evidence that production of excess glucocorticoid or ingestion of corticosteroids and several other drugs decrease BMD and increase bone resorption (Chiodini et al, 1998; Pearce et al, 1998; Lovas et al, 2009; Man and Sin, 2009; Schubert, 2009), and that a healthy diet with increased supplementation of several vitamins and minerals are necessary for bone health (Prentice, 2004). Finally, given that policing has historically been a male-dominated profession, assessment of women, due to over-sampling, allowed for a unique examination of women officers in our study. The topic is highly relevant for all women given the higher burden and related consequences of osteoporosis among this group.

In conclusion, our findings show that depressive symptoms, as measured by CES-D, are associated with lower levels of BMD among women but not among men. Researchers estimate that the annual number of fractures in the world will reach 2.6 million by 2025 and 4.5 million by 2050 in comparison with 1.7 million cases in 1990 (Gulberg et al, 1997). According to the National Institutes of Health (NIH, 2000), osteoporosis is largely preventable. One must take regular steps to optimize bone health throughout life to prevent osteoporosis and its devastating consequences. Protective measures include dietary modifications (e.g., increased intake of calcium, vitamin D, etc.), implementation of stress management programs, low to moderate alcohol consumption, frequent involvement in bone strengthening exercises, and judicious use of corticosteroid therapy and other medications that adversely affect bone density. Future studies should investigate the association between depressive symptoms and BMD, especially in groups with high proportions of depressive symptoms, using a longitudinal study design and larger samples. Evaluation and implementation of effective interventions are also warranted.