Stress and suicide in the Nurses' Health Study - NCBI

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RESEARCH REPORT

Stress and suicide in the Nurses’ Health Study D Feskanich, J L Hastrup, J R Marshall, G A Colditz, M J Stampfer, W C Willett, I Kawachi .............................................................................................................................

J Epidemiol Community Health 2002;56:95–98

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....................... Correspondence to: Dr D Feskanich, Channing Laboratory, 181 Longwood Avenue, Boston, MA 02115, USA; diane.feskanich@channing. harvard.edu Accepted for publication 3 July 2001

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Study objectives: Although stress is thought to be a risk factor for suicide, most research has been retrospective or has focused on attempted suicides or suicide ideation. This study examined prospectively the associations between self perceived stress, diazepam use, and death from suicide among adult women. Design: A cohort study was conducted with 14 years of follow up. Stress at home and at work were assessed by questionnaire and scored on a four point scale: minimal, light, moderate, or severe. Setting: Eleven states within the United States. Participants: Female nurses (n=94 110) who were 36 to 61 years of age when they answered questions on stress and diazepam use in 1982. Results: During 1 272 000 person years of observation 73 suicides were identified. After adjustment for age, smoking, coffee consumption, alcohol intake, and marital status, the relation between self reported stress and suicide remained U shaped. Compared with the light home and work stress categories, which had the lowest incidences of suicide, risks were increased among women reporting either severe (relative risk (RR) = 3.7, 95% confidence intervals (CI) 1.7 to 8.3) or minimal (RR=2.1, 95% CI 1.0 to 4.5) home stress and either severe (RR=1.9, 95% CI 0.8 to 4.7) or minimal (RR=2.4, 95% CI 0.9 to 6.1) work stress. When responses to home and work stress were combined, there was an almost fivefold increase in risk of suicide among women in the high stress category. Risk of suicide was over eightfold among women reporting high stress or diazepam use compared with those reporting low stress and no diazepam use. Conclusions: The relation between self reported stress and suicide seems to be U shaped among adult women. The excess risk for those reporting minimal stress may reflect denial or undiagnosed depression or an association with some other unmeasured risk factor for suicide.

O

ver 30 000 suicide deaths are recorded per year in the US,1 contributing significantly to years of potential life lost.2 However, few prospective studies of suicide have been reported. Studies of people who attempted suicide or who have suicidal thoughts are more common, though the factors associated with these situations may differ from those that characterise completed suicides.3 In the case of a completed suicide, information provided by family or friends may be subject to recall bias. Consequently, there is a need to study suicide in prospectively evaluated cohorts of persons systematically followed up for many years. Stress is thought to be a major contributor to suicide. A stressful life event, such as the death of a spouse or loss of employment, may trigger the suicide.4 However, such events are more likely to act as triggers in already vulnerable people.5 High levels of perceived stress have been observed in people with early signs of suicidal thoughts.6 Physiological changes characteristic of chronic stress have been associated with suicide. One study reported significant enlargement of the adrenal cortex in suicide victims.7 Also, peripheral-type benzodiazepine receptors are decreased during exposure to chronic stressful conditions and were found to be decreased among patients with a history of at least three suicide attempts.8 In this study, we examined the association between self reports of stress at home and at work and regular use of diazepam, a minor tranquiliser for stress and anxiety, and subsequent risk of suicide over a 14 year period among women in the Nurses’ Health Study.

METHODS The Nurses’ Health Study began in 1976 when 121 700 US married female registered nurses between the ages of 30 and 55 responded to a mailed questionnaire concerning their

medical history and health related behaviours, such as smoking and oral contraceptive use. Approximately 98% of the cohort is white. Every two years, a follow up questionnaire has been sent to ascertain incident diseases and to update lifestyle characteristics. If a participant does not respond after repeated mailings, a short form of the questionnaire is sent that includes only the disease reports and the most important behavioural information. A response rate of over 90% has been maintained throughout follow up. In 1980, a food frequency questionnaire was added to the mailing, and diet has been reassessed about every four years. Questions on stress and diazepam use were included on the full questionnaires in 1980 and 1982. In 1980, participants were asked whether they were currently taking valium (diazepam) and if so, their duration of use. In 1982, current diazepam use was again included on the questionnaire. Participants were also asked to rate their experience of stress at home and at work as either minimal, light, moderate, or severe. Seventy six per cent of the participants were employed outside the home in 1982; among the employed women, 90% held jobs in the nursing profession. Most deaths in this cohort are reported by relatives or by postal authorities. The National Death Index is also searched for records of death among the non-respondents. More than 98% of all deaths in the cohort are successfully identified.9 Death certificates are sought for all deaths and reviewed by a physician who is unaware of exposure information. As of June, 1996, 7% of the cohort (n=8505) had died and 166 deaths were attributable to suicide. One hundred and ten of the suicide deaths occurred after 1982 when the stress ratings were obtained. Of these, 73 (66%) responded to the full 1982 questionnaire with the stress and diazepam questions. This response rate was lower than the 78% rate for the full cohort and the 73% rate among those who died of other causes.

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The study population for this analysis consisted of the 94 110 women who responded to the full 1982 questionnaire. Participants contributed person-time from the return date of this questionnaire (mailed June, 1982) until death from any cause or end of study follow up on 1 June 1996. Incidence rates were computed for each category of home stress, work stress, and diazepam use. Relative risks were calculated as the age adjusted incidence rate (within five year age groups) in a specific category divided by the age adjusted rate in the lowest category. Proportional hazards models10 were used to adjust simultaneously for possible confounding variables, including smoking status (never, past, current), quantity among current smokers (1–14, 15–24, 25+ cigarettes/day), coffee consumption (none,