Gender differences in psychiatric diagnoses in older people with intellectual disability: a register study

In the general population, there are well-known gender differences with respect to psychiatric ill-health. Whereas women are at higher risk for e.g. affective disorders [1], anxiety disorders [2], and dementia [3], men are more likely to suffer from e.g. disorders due to alcohol and drug abuse and dependence [4]. Although part of the gender differences may be attributable to biological and genetical differences [5, 6], societal factors, such as gender roles and gender equality [7, 8], and work-related gender inequality [9‐11] may also be of importance. As people with intellectual disability (ID) are likely to differ from the general population with respect to societal factors, the results regarding the association between gender and psychiatric ill-health may not necessarily be applicable to this population.

Over the past decades, only few studies have focused specifically on assessing gender differences in psychiatric disorders among people with ID [12‐14], and a further few have included gender as one of several potentially explanatory predictors [15‐20]. The results from these studies suggest that there may be gender differences with respect to overall psychiatric disorders [13, 17] as well as some specific diagnoses and diagnostic categories [12‐15, 18, 20]. However, the results are far from consistent. Thus, further investigation into this topic is needed.

Recent years have seen a steady increase in the number of people with ID who reach older age [21‐23]. In the general population, the gender differences for psychiatric ill-health have been found to vary with age. For example, the increased risk of depression among women is primarily found during the early teenage years and up to menopause [24, 25]. Yet, we have found only one study, the Dutch “Healthy Ageing and Intellectual Disabilities” study [15, 20], that have investigated psychiatric diagnoses other than dementia among older people with ID specifically, and their analyses were restricted to diagnoses of depression and anxiety. Thus, more knowledge is needed to be able provide gender specific support and service for ageing people with ID.

The aim of the present study was to describe and investigate possible gender differences in psychiatric diagnoses among older people with ID in Sweden, using data from national registers.

During the study period, 649 (18%) women and 725 (17%) men had at least one psychiatric diagnosis (OR for women vs men 1.11, 95% CI 0.99–1.25). Among those with at least one diagnosis, 465 women (72%) and 529 men (73%) had only one diagnosis, the most common one among women being affective disorders and among men psychotic disorders (Table 1).

Women were 33% more likely than men to have been diagnosed with affective disorders and 40% more likely to have been diagnosed with dementia (Table 2). However, they only had 59% of the risk displayed by men to have been diagnosed with alcohol/substance use related disorders. No statistically significant gender differences were found for psychotic, anxiety, or personality disorders. With respect to single diagnoses, women were more likely than men to have been diagnosed with unspecified nonorganic psychosis, depressive episode, recurrent depressive disorder, other anxiety disorder, or dementia in Alzheimer disease. They were less likely to have been diagnosed with psychiatric and behavioral disorders due to use of alcohol. No statistically significant gender differences were found for any of the other investigated diagnoses.

There was a statistical significant interaction between gender and year of birth with respect to anxiety disorders (p < 0.001) and alcohol/substance use related disorders (p = 0.009), but not for any of the other diagnostic categories (data not shown). The ORs for women vs men regarding diagnoses of anxiety disorders increased with birth cohort, with a lower OR of diagnosis for women born in or before 1946 to a higher OR for women born in or after 1953 (Table 3). For diagnoses of alcohol/substance use related disorders, the increased risk found for men when analyzing all data seemed to be driven by a risk increase among those born in or before 1952.

Among older people with ID, women were more likely than men to have a diagnosis of affective disorders and dementia, whereas men were more likely to have a diagnosis of alcohol/substance use related disorders. The majority of those with psychiatric illness were diagnosed in only one diagnostic category during the 11-year study period.

Before attempting to explain the results found, some weaknesses with the present study need to be acknowledged. Firstly, we used receiving service for ID or ASD as a proxy for having ID. One drawback with this is that the ID cohort may contain people with ASD but without ID. However, older people are not as likely as younger to have been diagnosed with ASD, and a large part of people with ASD have a combination of ID and ASD diagnoses [28]. Thus, a possible dilution of the ID cohort with people with ASD without ID should be small enough not to distort the results in any major way. Another problem that may arise from using the LSS register to define the ID cohort is that people who have ID but are coping without support would not be included in the cohort. Nevertheless, older people with ID often have parents that have passed away, which make them more dependent on the support from the society for daily life. Thus, we believe that in using the LSS register to define the ID cohort, we have included the large majority of people with ID in the older age group.

A second weakness may be the use of the NPR to identify diagnoses of psychiatric disorders, as this register does not include primary care. Thus, less severe cases of psychiatric ill-health may be lacking from our data. As a consequence, the prevalence estimates in each gender group cannot be viewed as disease prevalence, but only be used for gender comparisons. However, if men and women with the same disorder are not equally likely to receive specialist or inpatient care for this disorder, failure to include primary care diagnoses would affect the estimated gender differences in the present study. In a Canadian study among people with major depression, women were found to be less likely than men to visit specialist care and general practitioner, but more likely than men to visit a general practitioner only as opposed to no service use [29]. The authors concluded that primary care physicians might have a greater tendency to treat women and to refer men to specialist services. In addition, among people with anxiety or depression in Norway, the higher use of health care in the male part of the population was mainly evident in older groups [30]. If a similar pattern is found for older people with ID in Sweden, we would most likely underestimate the risk when it is higher for women and overestimate it when it is higher for men.

To the best of our knowledge, only one study has previously investigated gender differences in psychiatric disorders other than dementia among older people with ID. Data from the Dutch “Healthy Ageing and Intellectual Disability” were used to investigate depression and anxiety in older people with ID [15, 20]. The study is based on an administrative cohort of people aged 50+ years and receiving services and support for people with ID. As screening for depression and anxiety was made using self-reports, only people with borderline, mild, or moderate ID were included. People who had at least one score above the threshold value for one of the screening instruments were further examined with a standardized psychiatric interview. The analyses of these data revealed increased, but not statistically significantly so, risks for increased anxiety symptoms and anxiety disorders for women [20]. However, no gender differences were found for increased depressive symptoms or major depressive disorder. Those with depression or anxiety according to the standardized psychiatric interview were further assessed using the PAS-ADD [15]. The analyses based on these data did not reveal any increased risk for depression or anxiety for either gender.

Although onset of dementia occur earlier among people with ID than in the general population, it is still a disorder which becomes more common with increasing age [31, 32]. Thus, studies regarding dementia have an inherent focus on older people. While the prevalence estimate of dementia varies with the age group studied, studies performed so far suggest an increased risk of dementia among women compared with men [13, 31, 32].

Other studies regarding possible gender differences in psychiatric ill-health among people with ID have not focused specifically on older people. Some published results indicate that women are more likely to have at least one psychiatric diagnosis [13, 17], whereas others found no gender effects with respect to this outcome [12, 19]. Regarding specific diagnostic groups, previous studies indicate that women are more likely to be diagnosed with depression [12, 18, 33]. There are also some suggestions that women more often are diagnosed with schizophrenia [12] and overall psychotic disorders [34], although not all studies point in this direction [12, 13]. Similarly, men have been found more likely to have diagnoses of personality disorders [13], but these results are not consistent [12]. No studies so far have found gender differences with respect to anxiety disorders [12, 13, 16], affective disorders excluding depression [12], or alcohol/substance use related disorders [12].

In the present study, there was a pattern of increased risks of diagnoses for women in the diagnostic categories affective disorders, anxiety disorders, and dementia, as well as for the diagnoses included in these categories. The opposite was found for alcohol/substance use related disorders, whereas no pattern was found for psychotic disorders. Combining these results with previous research, the results may, at a first glance, seem inconclusive. However, it is noteworthy that there is no outcome for which different studies present opposite results. Thus, overall psychiatric diagnoses are either more common among women or do not differ between the genders. The same holds true for anxiety disorders, affective disorders/depression, dementia, and schizophrenia/psychotic disorders. The opposite, i.e. an increased risk for men or equal risk for both genders, is seen for personality disorders and alcohol/substance use related disorders. As only a few studies so far have focused on older people with ID, more information is needed to determine if the gender differences are similar for older and younger groups.

The occurrence of a diagnosis in a population is affected by the occurrence of the disorder, the inclination of the individuals to seek professional help, and the ability of professionals to correctly identify the disorder. Thus, gender differences in diagnoses would occur if there were gender differences with respect to any of these factors. Each of them is in turn a result of interaction of several underlying processes. For example, in the general population, gender differences with respect to the occurrence of affective disorders – and specifically depression – have been suggested to be associated with e.g. biological processes [6], societal factors [8], family situation [35], and work culture and circumstances [9‐11]. There are indications that women are less inclined to seek care than men [29, 30]. Moreover, a number of factors that are associated with gender are also related to a person’s inclination to seek health care. For instance, in most western societies, the female part of the population tend to have lower socioeconomic status than the male, and a lower socioeconomic status has been associated with lower frequency of health care, regardless of actual psychiatric health [36]. Another example is coping strategies, the use of which may cause a person to reduce his or her need for care, and for which gender differences have been found when it comes to psychiatric health [37, 38]. Finally, if the disorder is displayed differently in women and men, such as is the case for e.g. depression [39], gender differences may arise regarding the correct identification of the disorder. As discussed above, in the present study, gender differences may also be present due to different health care utilization patterns among men and women regarding primary care vs specialist care.

The present study, taken together with previous research, indicates that there may be gender differences in several types of psychiatric diagnoses. If this is due to differences in occurrence of disorder, inclination to seek care, differences in health care utilization patterns, or the ability to correctly identify disorders is yet unknown. This is important to consider when trying to achieve gender equality in health care for people in general as well as for people with ID.