Midlife stress may raise women's dementia risk

"People who suffer excess stress in middle age are more likely to suffer dementia in later life," The Daily Telegraph reports.

The claim is prompted by a Swedish study that found a link between reported stressful events and dementia in later life.

The study assessed 800 middle-aged Swedish women for a number of factors and then followed them over a 38-year period. 

The assessments included questioning if the women had experienced what the researchers termed "psychosocial stressors" – that is traumatic, though often common, events, such as a divorce or a partner being affected by mental illness.

They were also questioned over the course of the study (once each decade) about self-reported feelings of distress – symptoms such as feelings of irritability or tension.

The women were then monitored to see if they developed dementia in later life.

The researchers found that a higher number of stressors at the beginning of the study was associated with increased risk of dementia.

Overall, this study suggests some associations between common stressors and dementia later in life.

However, the risk factors of dementia in general and Alzheimer’s disease in particular are not firmly established, and it is possible that other unmeasured factors may be involved. 

The researchers do make the interesting suggestions that finding ways to better cope with stress in middle age may have a protective effect against dementia in later life, however, this hypothesis is currently unproven.

Where did the story come from?

The study was carried out by researchers from the Sahlgrenska Academy at Gothenburg University, the Karolinska Institutet in Stockholm (both in Sweden), and Utah State University in the US. It was funded by The Swedish Medical Research Council, the Swedish Council for Working Life and Social Research, the Alzheimer’s Association, the National Institute of Health and National Institute on Aging, the University of Gothenburg and other Swedish grants and foundations.

The study was published in the peer-reviewed medical journal BMJ Open. The journal is open access so the study is free to read online or download.

The study was widely reported in the UK media, with some attention grabbing headlines of a ‘raised risk of dementia’. Once past the headlines, the study is reported appropriately.

What kind of research was this?

This was a prospective cohort study looking at the associations between common psychosocial stressors in mid-life, self-reported distress and development of dementia later in life. This type of study is useful for looking at whether particular exposures are associated with disease outcomes over time.

However, it cannot prove direct causation as various other factors may be involved in the relationship. This is particularly relevant when studying such non-specific exposures as stress and distress, which may mean different things to different people and have variable causes.

What did the research involve?

This study included a representative subsample of 800 Swedish women, born in 1914, 1918, 1922 or 1930 and residing in Gothenburg, obtained from a wider study called the Prospective Population Study of Women in Gothenburg, Sweden. The women were systematically selected to take part in the current study in 1968, when they were aged between 38 and 54 years.

At the start of the current study (1968), 18 predefined psychosocial stressors were asked about and rated by a psychiatrist during a psychiatric examination. They were rated as occurring any time prior to 1968 for some stressors and as only occurring in the previous year for other stressors. The psychosocial stressors included:

• divorce
• widowhood
• serious problems in children (such as physical illness, death or abuse)
• extramarital childbirth
• mental illness in spouse or first-degree relative
• receiving help from Social Security
• problem related to husband’s or own work (such as loss of job)
• limited social network

Symptoms of distress were also assessed at the start of the current study (1968) and were repeated in 1974, 1980, 2000 and 2005.

At each of these assessments, participants were asked whether they had experienced any period of stress lasting one month or longer in relation to circumstances of everyday life.

They were told distress referred to negative feelings of:

• irritability
• tension
• nervousness
• fear
• anxiety
• sleep disturbances

Responses ranged from a score of zero (have never experienced any period of distress), a score of three (have experienced several periods of distress during the last five years) to a maximum score of five (have experienced constant distress during the last five years). The researchers defined distress as a score rating of three to five.

The participants also underwent a series of psychiatric examinations carried out at the start of the study (1968) and each decade up until 2005. Diagnosis of dementia was made using standardised diagnostic criteria, and based on psychiatric examinations, informant interviews (such as from spouses), medical records, and a national hospital discharge registry. Specific types of dementia, such as Alzheimer’s disease or vascular dementia, were diagnosed according to pre-defined criteria.

The researchers then used statistical methods to determine the associations between psychological stressors and whether or not the women developed dementia. They adjusted the results in three different ways based on potential confounders:

• adjustments were made for age only
• adjustments were made for more factors including age, education, socioeconomic status, marital and work status and smoking status
• adjustments were made for age and psychiatric family history

What were the basic results?

At the start of the study, 25% of the women reported one psychosocial stressor, 23% reported two stressors, 20% reported three stressors and 16% reported four or more stressors. The most frequently reported stress was mental illness in a first-degree relative.

Over the course of the study, 153 women (19.1%) developed dementia. This included 104 women with Alzheimer’s disease and 35 with vascular dementia. The average age of dementia onset in this population was at age 78.

The main findings from this study were:

• Following multiple adjustments (including age, education and smoking status), the number of psychosocial stressors reported at the beginning of the study (1968) was associated with distress at each of the assessments (1968, 1974, 1980, 2000 and 2005). These results remained similar after making adjustments for psychiatric family history.
• Following multiple adjustments, an increased number of psychosocial stressors in 1968 was associated with increased risk of dementia overall, and Alzheimer’s disease specifically, but not vascular dementia, over 38 years (vascular dementia is caused by reduced blood flow to the brain so it may not have the same risk factors as Alzheimer’s).

How did the researchers interpret the results?

According to the researchers, the study shows that common psychosocial stressors may have severe and long-standing physiological and psychological consequences. They say that more studies are needed to confirm these results. Perhaps more importantly, research is needed to determine whether interventions such as stress management and cognitive behavioural therapy should be offered to people who have experienced psychosocial stressors, in order to reduce their dementia risk.

Conclusion

Overall, this study suggests an association between reported stressors, distress and dementia later in life among a group of women living in Sweden. It does not provide proof that stress occurring in mid-life leads to dementia.

The study has some strengths, including that the sample was reportedly representative of the population, and that women were followed for a long period of time (38 years). Also valid diagnostic criteria were used to diagnose dementia subtypes.

Despite these strengths, there remain several limitations of the study, some of which are reported by the authors. These include:

• Stress and distress are very non-specific exposures to examine. They may mean different things to different people and be caused by different things. The study only considered a select number of "stressors". Other stressors such as physical abuse or severe physical illness were not included. As such, women who had experienced other stressors may not have been captured in this study. 
• Related to this, participants were asked about the occurrence of some stressors anytime before the start of the study but only asked about other stressors in the previous year which may not be a reliable method of assessing stress.
• "Distress" was measured by self-report and the researchers did not include an objective measurement to assess this.
• Aside from increasing age and possibly genetics, the risk factors for Alzheimer’s disease are not firmly established. It is possible that other factors that the researchers did not account for contributed to the development of dementia.
• This study only included women residing in one city. The findings may not be generalisable to men or to groups from other geographical locations.

Overall the study does not prove that stress leads to dementia, and more research is needed to confirm these findings.

However, it is known that persistent stress in your life could be damaging to both your physical and mental health – read more about stress and ways you can control and cope with it.