Here are a couple of studies on the prevalence of depression and anxiety, and four on risk factors for depression, bipolar disorder and suicide.  Strine et al report on a major survey of depression and anxiety in the United States.  They found "The overall prevalence of current depressive symptoms was 8.7% (range by state and territory, 5.3%-13.7%); of a lifetime diagnosis of depression, 15.7% (range, 6.8%-21.3%); and of a lifetime diagnosis of anxiety, 11.3% (range, 5.4%-17.2%)."  Smoking, lack of exercise, and excessive drinking were all associated with increased likelihood of mental disorders, as too was physical ill health.  Young et al, in a separate study, looked at the likelihood of depression and anxiety becoming persistent.  They estimated - at nearly 3 year follow-up - that the US prevalence of persistent depressive or anxiety disorder was 4.7%.  Only about a quarter of these sufferers were using appropriate medication and only about a fifth appropriate counselling.

I also include four studies on risk.  Fergusson and colleagues explored the mental health effects of undergoing an abortion.  They conclude "The evidence is consistent with the view that abortion may be associated with a small increase in risk of mental disorders."  This data both suggests that a history of abortion is usually only a minor contributor to risk of subsequent mental disorder, but that it is worth checking for and considering whether it has been adequately come to terms with.  Etain et al reviewed the literature on childhood abuse and bipolar disorder.  They concluded "Childhood trauma is associated with bipolar disorder and its clinical expression and may interact with genetic susceptibility factors."  A study by Keenan and colleagues looks at risk factors for depression in 8 to 11 year girls.  They found "Early-emerging symptoms of depression in girls are stable and predictive of depressive disorders and impairment. The results suggest that secondary prevention of depression in girls may be accomplished by targeting subthreshold symptoms manifest during childhood."  Finally Tidemalm et al considered the risk of subsequent suicide after an initial suicide attempt.  They concluded "Type of psychiatric disorder coexistent with a suicide attempt substantially influences overall risk and temporality for completed suicide. To reduce this risk, high risk patients need aftercare, especially during the first two years after attempted suicide among patients with schizophrenia or bipolar and unipolar disorder."

Strine, T. W., A. H. Mokdad, et al. (2008). "Depression and Anxiety in the United States: Findings From the 2006 Behavioral Risk Factor Surveillance System." Psychiatr Serv 59(12): 1383-1390.  [Abstract/Full Text] 
OBJECTIVE: This study examined the unadjusted and adjusted prevalence estimates of depression and anxiety at the state level and examined the odds ratios of depression and anxiety for selected risk behaviors, obesity, and chronic diseases. METHODS: The 2006 Behavioral Risk Factor Surveillance Survey, a random-digit-dialed telephone survey, collected depression and anxiety data from 217,379 participants in 38 states, the District of Columbia, Puerto Rico, and the U.S. Virgin Islands. Current depressive symptoms were assessed with the standardized and validated eight-item Patient Health Questionnaire, and lifetime diagnosis of depression and anxiety was assessed by two additional questions (one question for each diagnosis). RESULTS: The overall prevalence of current depressive symptoms was 8.7% (range by state and territory, 5.3%-13.7%); of a lifetime diagnosis of depression, 15.7% (range, 6.8%-21.3%); and of a lifetime diagnosis of anxiety, 11.3% (range, 5.4%-17.2%). After sociodemographic characteristics, adverse health behaviors, and chronic illnesses were adjusted for, cardiovascular disease, diabetes, asthma, smoking, and obesity were all significantly associated with current depressive symptoms, a lifetime diagnosis of anxiety, and a lifetime diagnosis of depression. Physically inactive adults were significantly more likely than those who were physically active to have current depressive symptoms or a lifetime diagnosis of depression, whereas those who drank heavily were significantly more likely than those who did not to have current depressive symptoms or a lifetime diagnosis of anxiety. CONCLUSIONS: Depression and anxiety were strongly associated with common chronic medical disorders and adverse health behaviors. Examination of mental health should therefore be an integral component of overall health care.

Young, A. S., R. Klap, et al. (2008). "Persistent Depression and Anxiety in the United States: Prevalence and Quality of Care." Psychiatr Serv 59(12): 1391-1398.  [Abstract/Full Text] 
OBJECTIVE: Although effective treatments exist, individuals with depressive and anxiety disorders can remain ill for years. Little is known regarding mental health status and treatment use in this population. This study provided national estimates of the prevalence of persistent depression and anxiety, as well as estimates of illness severity, treatment use, and quality of care in this population. METHODS: Data were from a prospective, community-based cohort study of 1,642 adults with probable major depression, dysthymia, panic disorder, or generalized anxiety disorder who were part of a U.S. probability sample. Telephone surveys were conducted during 1997-1998 and again an average of 32 months later. Surveys assessed diagnosis, quality of life, treatment satisfaction, medical conditions, suicidal ideation, insurance, medications, and treatment use. RESULTS: At follow-up, 59% no longer met criteria for a disorder. The estimated national prevalence of a persistent depressive or anxiety disorder was 4.7%. In this subgroup, 87% had a chronic comorbid medical disorder. During the past year, 88% had seen a primary care practitioner, and 22% had seen a mental health specialist. Between baseline and follow-up, the percentage using appropriate medication increased (21% to 29%), but there was no significant change in use of appropriate counseling (23% to 19%). Only 12% were receiving both appropriate medication and counseling at follow-up. Treatment was less likely for men and people with less education. Suicidal ideation was present in 51% at follow-up. CONCLUSIONS: Strategies are needed to increase treatment use and intensity for people with persistent depressive and anxiety disorders. This may require improved access to mental health specialists.

Fergusson, D. M., L. J. Horwood, et al. (2008). "Abortion and mental health disorders: evidence from a 30-year longitudinal study." The British Journal of Psychiatry 193(6): 444-451.  [Abstract/Full Text]
Background Research on the links between abortion and mental health has been limited by design problems and relatively weak evidence. Aims To examine the links between pregnancy outcomes and mental health outcomes. Method Data were gathered on the pregnancy and mental health history of a birth cohort of over 500 women studied to the age of 30. Results After adjustment for confounding, abortion was associated with a small increase in the risk of mental disorders; women who had had abortions had rates of mental disorder that were about 30% higher. There were no consistent associations between other pregnancy outcomes and mental health. Estimates of attributable risk indicated that exposure to abortion accounted for 1.5% to 5.5% of the overall rate of mental disorders. Conclusions The evidence is consistent with the view that abortion may be associated with a small increase in risk of mental disorders. Other pregnancy outcomes were not related to increased risk of mental health problems.

Etain, B., C. Henry, et al. (2008). "Beyond genetics: childhood affective trauma in bipolar disorder." Bipolar Disorders 10(8): 867-876.  [Abstract/Full Text]
Objectives:  Despite the demonstrated high heritability of bipolar disorder, few susceptibility genes have been identified and linkage and/or association studies have produced conflicting results. This search for susceptibility genes is hampered by several methodological limitations, and environmental risk factors for the disease (requiring incorporation into analyses) remain misunderstood. Among them, childhood trauma is probably the most promising environmental factor for further investigation. The objectives are to review the arguments in favor of an association between childhood trauma and bipolar disorder and to discuss the interpretations of such an observation.  Methods: We computed a literature search using PubMed to identify relevant publications concerning childhood trauma and bipolar disorder. We also present some personal data in this field.  Results: Growing evidence suggests that incidences of childhood trauma are frequent and severe in bipolar disorder, probably affect the clinical expression of the disease in terms of suicidal behavior and age at onset, and also have an insidious influence on the affective functioning of patients between episodes. The relationships between childhood trauma and bipolar disorder suggest several interpretations, mainly a causal link, a neurodevelopmental consequence, or the intergenerational transmission of traumatic experiences. The neurobiological consequences of childhood trauma on a maturing brain remain unclear, although such stressors may alter the organization of brain development, leading to inadequate affective regulation.  Conclusions:  Although not completely understood, the relationships between childhood trauma and bipolar disorder require further attention. Several suggestions for further exploration of this environmental factor and of its interaction with susceptibility genes are proposed.

Keenan, K., A. Hipwell, et al. (2008). "Subthreshold symptoms of depression in preadolescent girls are stable and predictive of depressive disorders." J Am Acad Child Adolesc Psychiatry 47(12): 1433-42.  [PubMed]
OBJECTIVE: Given the risk for adolescent depression in girls to lead to a chronic course of mental illness, prevention of initial onset could have a large impact on reducing chronicity. If symptoms of depression that emerge during childhood were stable and predictive of later depressive disorders and impairment, then secondary prevention of initial onset of depressive disorders would be possible. METHOD: Drawing from the Pittsburgh Girls Study, an existing longitudinal study, 232 nine-year-old girls were recruited for the present study, half of whom screened high on a measure of depression at age 8 years. Girls were interviewed about depressive symptoms using a diagnostic interview at ages 9, 10, and 11 years. Caregivers and interviewers rated impairment in each year. RESULTS: The stability coefficients for DSM-IV symptom counts for a 1- to 2-year interval were in the moderate range (i.e., intraclass coefficients of 0.40-0.59 for continuous symptom counts and Kendall tau-b coefficients of 0.34-0.39 for symptom level stability). Depressive disorders were also relatively stable at this age. Poverty moderated the stability, but race and pubertal stage did not. Among the girls who did not meet criteria for a depressive disorder at age 9 years, the odds of meeting criteria for depressive disorders and for demonstrating impairment at age 10 or 11 years increased by 1.9 and 1.7, respectively, for every increase in the number of depression symptoms. CONCLUSIONS: Early-emerging symptoms of depression in girls are stable and predictive of depressive disorders and impairment. The results suggest that secondary prevention of depression in girls may be accomplished by targeting subthreshold symptoms manifest during childhood.

Tidemalm, D., N. Langstrom, et al. (2008). "Risk of suicide after suicide attempt according to coexisting psychiatric disorder: Swedish cohort study with long term follow-up." BMJ 337(nov18_3): a2205-.  [Free Full Text] 
Objective To investigate the impact of coexistent psychiatric morbidity on risk of suicide after a suicide attempt. Design Cohort study with follow-up for 21-31 years. Setting Swedish national register based study. Participants 39 685 people (53% women) admitted to hospital for attempted suicide during 1973-82. Main outcome measure Completed suicide during 1973-2003. Results A high proportion of suicides in all diagnostic categories took place within the first year of follow-up (14-64% in men, 14-54% in women); the highest short term risk was associated with bipolar and unipolar disorder (64% in men, 42% in women) and schizophrenia (56% in men, 54% in women). The strongest psychiatric predictors of completed suicide throughout the entire follow-up were schizophrenia (adjusted hazard ratio 4.1, 95% confidence interval 3.5 to 4.8 in men, 3.5, 2.8 to 4.4 in women) and bipolar and unipolar disorder (3.5, 3.0 to 4.2 in men, 2.5, 2.1 to 3.0 in women). Increased risks were also found for other depressive disorder, anxiety disorder, alcohol misuse (women), drug misuse, and personality disorder. The highest population attributable fractions for suicide among people who had previously attempted suicide were found for other depression in women (population attributable fraction 9.3), followed by schizophrenia in men (4.6), and bipolar and unipolar disorder in women and men (4.1 and 4.0, respectively). Conclusion Type of psychiatric disorder coexistent with a suicide attempt substantially influences overall risk and temporality for completed suicide. To reduce this risk, high risk patients need aftercare, especially during the first two years after attempted suicide among patients with schizophrenia or bipolar and unipolar disorder.