Introduction
In Chapter 5, we identified depression as a major driver of health-care costs in obese patients. This analysis uses EHRs to investigate the possible impact of bariatric surgery on clinical depression. Obese people are at higher risk of depression but depression is also a predictor of weight gain and future obesity.147 People who are obese experience the onset of morbidity at younger ages than those with lower body weight3 and the multiple morbidities associated with obesity may contribute to a higher prevalence of depression.51 Patients selected for bariatric surgery often have a high prevalence of clinical depression.18,148 However, evidence for an effect of bariatric surgery on depression is limited. Several longitudinal studies have explored the relationship between bariatric surgery and depression, identifying significant reductions in depression149 and depressive symptoms150,151 following surgery. One study found a decrease in depression from 32.7% at baseline, to 16.5% at 6–12 months, and 14.3% at 2–3 years following surgery.152 However, other studies suggest that improvements following surgery may not be maintained after the first postoperative year151 and depressive symptoms may deteriorate in some patients.153 Previous reports have often drawn on data from hospital-based series that did not include control groups, often with short durations of follow-up.
This analysis aimed to evaluate whether or not bariatric surgery is associated with a reduction in clinical depression up to a maximum of 7 years following the procedure. A population-based cohort provided the data source for an interrupted time-series design with matched controls, facilitating a pragmatic evaluation of the impact of bariatric surgery on clinical depression recorded in primary care EHRs. The results in this chapter were published open access in the Journal of Affective Disorders in 201590 under the terms of the Creative Commons Licence CC BY-NC-ND 4.0.
Results
There were 4793 participants with bariatric surgery recorded; 1324 participants with bariatric surgery first recorded < 1 year after the start of the patient record were excluded, as were 14 participants aged < 20 years at the index date, and 401 participants with either no BMI record before surgery or BMI values < 30 kg/m2 prior to surgery. Nine participants with a record of gastric band removal before the index date were also excluded. There were then 3045 participants identified as having bariatric surgery for obesity and 3045 matched controls. Bariatric surgery procedures included LAGB in 1297 (43%), GBP in 1265 (42%), SG in 477 (16%) and six of undefined type. Utilisation of bariatric surgery increased over the period and LAGB accounted for 97% of 104 procedures before 2006, but only 20% of 924 procedures from 2012 onwards, with increasing use of GBP and SG. The median year of procedure was 2010 and, consequently, only a minority of participants contributed more than 3 years of follow-up data.
Characteristics of the surgery and control participants at the index date are presented in . The majority of surgical procedures were conducted in women (79%) and in participants with morbid obesity (65%). The mean age at surgery was 45.9 years. Participants undergoing bariatric surgery more frequently had T2DM (29% vs. 14%; p < 0.001), hypercholesterolemia (35% vs. 25%; p = 0.022) and were more likely than controls to be prescribed antihypertensive drugs and statins.
Comparison of baseline characteristics of BS participants and controls. Figures are frequencies (column %) unless otherwise indicated
shows the number of participants analysed by year before and after surgery. There were 63% contributing to follow-up after the end of 2 years and 31% in the fifth year of follow-up. In the year prior to surgery, 36% of surgery participants met the criteria for prevalent clinical depression in comparison with 21% of control participants ( and see ). In the 2 years following surgery, this reduced to 32% in the participants who underwent surgery before rising to pre-surgery levels (37%) in the seventh year of follow-up. Rates of depression in control participants remained stable. In the surgery group, 41% of participants were prescribed antidepressants in the year leading up to surgery, falling to 36% in the subsequent year. The proportion of participants prescribed antidepressants began to rise again after the first year and surpassed pre-surgery levels in the fifth year following bariatric surgery.
Changes before and after surgery in diagnosis and treatment of depression. Figures are frequencies for person-years and row per cent for depression and antidepressant prescribing
Prevalence of clinical depression for bariatric surgery cases (black) and controls (green) for 3 years before and 7 years after index date.
presents the results of the multiple logistic regression model for the outcomes of clinical depression and antidepressant prescribing. Compared with control participants, the between-group effect shows that bariatric surgery participants were more likely to be diagnosed with clinical depression (OR 2.02, 95% CI 1.75 to 2.33; p < 0.001) or to be prescribed antidepressant drugs (OR 1.97, 95% CI 1.72 to 2.25; p < 0.001). There was evidence of increasing trends in diagnosis of depression and prescription of antidepressant drugs over the study period. Estimation of the effect of time since surgery, in comparison with all person-time without surgery from both groups, revealed a reduction in clinical depression and antidepressant prescribing in the first 3 years following the procedure. The adjusted relative odds of clinical depression were 0.82 (95% CI 0.78 to 0.87; p < 0.001) and 0.83 (95% CI 0.76 to 0.90; p < 0.001) in the first 2 years following the procedure. Similar changes were observed for the related outcome of antidepressant prescribing. However, from the fourth postoperative year onwards there was no longer any evidence for a reduction in clinical depression or antidepressant prescribing.
Logistic regression analysis of the association of bariatric surgery with clinical depression and antidepressant prescribing
There was no evidence that the effect of bariatric surgery varied by type of procedure (test for interaction, p = 0.2885). presents the prevalence of depression for each of the three procedures included in the study, after omitting six with undefined procedure type. There were more participants with LAGB at long durations of follow-up while fewer than 25% of participants receiving SG, and 35% receiving GBP, contributed data after the end of 3 years’ follow-up because these procedures were utilised more recently. The effect in each subgroup was generally similar to the one observed overall, and in the absence of an interaction effect, possible subgroup differences were not explored further.
Clinical depression following different bariatric surgical procedures
There was no evidence that the effect of bariatric surgery on clinical depression varied by type of procedure (test for interaction, p = 0.2885).
shows the results divided by depression status in the preoperative year. Among participants who were not depressed in the preoperative year, the prevalence of depression increased to 18% in the sixth postoperative year, while up to 9% were depressed 2 years before the procedure. Among participants who were depressed in the preoperative year, the prevalence of depression was generally close to 75% postoperatively. However, in the second preoperative year, 77% were depressed. These results are consistent with depression being episodic and frequent in this population.
Prevalence of depression by year following bariatric surgery divided by presence or absence of depression in preoperative year
Discussion
Summary of findings
Patients undergoing bariatric surgery have higher levels of depression than other obese patients with similar BMI and of the same age and sex. Frequent comorbidities, including diabetes mellitus, might be associated with this increased frequency of depression. The results of this analysis indicate that bariatric surgery in obese patients may be associated with a modest reduction in the prevalence of depression, and the use of antidepressant medications in primary care, but these effects do not appear to persist more than 3 years following the procedure. The reasons why patients with depressive illness are disproportionately represented among patients undergoing bariatric surgery in this population are unclear. In the UK, only a very small minority of patients with severe obesity undergo bariatric surgery and it is possible that psychological symptoms may be one of the considerations that influence whether or not an obese patient receives surgery. Obese patients seeking treatment may generally have higher levels of psychological distress. In a study in Germany, Herpertz et al.154 found that patients undergoing bariatric surgery had similar levels of depression to those receiving non-surgical weight-loss therapy, with both being higher than obese controls. Comparison of patients who were either depressed or not depressed in the preoperative year showed a decline in depression in the former and an increase in the latter after surgery. This is compatible with regression to the mean and is consistent with the episodic nature of depression symptoms. Our results do not provide strong evidence that patients should be prioritised in the hope that bariatric surgery will provide long-term relief of clinical features of depression, even though short-term effects might be judged clinically relevant.
Comparison with other results
Previous studies have generally shown larger effects than the present study but these generally used samples drawn from specialist centres that might be susceptible to bias. One of the largest studies was conducted by the Longitudinal Assessment of Bariatric Surgery-2 (LABS-2) group. The included 2148 participants from 10 US hospitals with Beck Depression Inventory recorded at baseline and at least 1 follow-up within 3 years of the procedure. There were 40% who reported treatment for depression before surgery, while 28% had mild depressive symptoms and 5% moderate or severe depressive symptoms. The proportion with any depressive symptoms was < 10% in the first year after surgery but increased to 16% at 3 years. A similar pattern of change in depressive symptoms over time was reported by Burgmer et al.,155 in a 4-year study of 148 participants. However, changes in use of antidepressant medication in the LABS-2 study were modest, with 35% using antidepressant medication before operation and 28% in the second and third years following the procedure. These results emphasise the importance of long follow-up in future studies as well as the evaluation of different measures of depression. In the SOS study, a battery of health-related quality of life measures, including the Hospital Anxiety and Depression Scale, showed improvement followed by deterioration.92 An initial improvement is associated with the period of greatest weight loss in the first 2 years following surgery, sometimes viewed as a ‘honeymoon period’,156 followed by a subsequent deterioration associated with weight regain.92 However, in the SOS study there was evidence of some improvement in depression symptoms up to 10 years of follow-up. Premorbid depression was less frequent in the SOS study than in the present sample.
Strengths and limitations
This analysis had the strengths of a large, population-based sample of patients undergoing bariatric surgery with prospectively recorded data for depression diagnoses and antidepressant prescribing. The interrupted time-series design is generally considered to be more resistant to bias than other non-randomised designs.157 However, there were clear differences between the intervention and matched comparison group with respect to the outcome of interest, indicating that individuals undergoing surgery represent a highly selected group that is not typical of all patients with the same BMI, age and sex. Patients undergoing surgery may receive a package of supportive care and improved clinical management to prepare them for surgery, which may confound the effect of the surgical procedure. Patients in the control group received the usual care offered at their general practice, which was unlikely to include standardised management of obesity or depression.
The types of surgical procedure and patient case mix changed over time and, though access remained restricted, the numbers of procedures increased. There were small numbers of patients with long follow-up with reduced statistical power for evaluation of later time points. Furthermore, there is a risk of bias because patients operated on longer ago may have different characteristics from those operated on more recently, with shorter periods of follow-up. Use of clinical data may also introduce bias because patients must consult with their physician, and have their symptoms recognised, before a depression diagnosis may be recorded. Some evidence shows rates of diagnosed clinical depression are lower than those found in epidemiological studies.158 An important limitation is that there was very limited recording of body weight during the period of follow-up and we cannot determine whether changes in depression were associated with weight loss or regain.
Our assessment of depression was based on clinical diagnoses and antidepressant prescribing; the limited changes observed over time might result from difficulty in stopping antidepressant therapy once initiated. A previous CPRD study found that depression is often treated with short-term courses of antidepressant medications, with only a small proportion of patients being prescribed drugs over a long period for chronic depression.157 The high rates of antidepressant use observed in this study may represent met need and not merely the result of repeat prescribing to patients who might no longer require clinical treatment for depression. Several previous studies used self-report measures to evaluate depressive symptoms and these measures might be associated with greater sensitivity for depression and responsiveness to change.159,160 For all of the reasons, it would be desirable to test hypotheses using well-designed randomised trials with prospective documentation of depression.
Conclusions
The results of this analysis suggest that bariatric surgery may have only a limited and short-lived effect on clinical depression. However, we caution that patients are presently highly selected for bariatric surgery. If bariatric surgery were to be more widely accessible, it is possible that different effects might be observed. Randomised studies of the effect of bariatric surgery on depression are required.
