Schizophrenia is a chronic mental disorder with a 12-month prevalence of 3.70 per 1,000 or 0.33% and a median life time prevalence of 6.35 per 1,000 or 0.48% according to Moreno-Küstner et al. (1) or Simeone et al. (2), respectively. Schizophrenia is complicated by significant social and physical disabilities resulting in a number of years of potential life lost, which was assessed to amount to an average of 14.5 (95% CI 11.2–17.8) and is accompanied by an average life expectancy that was calculated to be 64.7 years (95% CI 61.1–68.3) (3). A primary cause of this excess of mortality may be the high incidence of cardiovascular disease, which was estimated to amount to 1.53 (CI95% 1.27–1.86) for schizophrenia in comparison with the reference group according to a meta-analysis involving over 3.5 million participants combining 13 studies (4). A major contribution to the risk of developing cardiovascular disease may be the existence of metabolic syndrome (MetS). The relative risk for cardiovascular disease over 5–10 years amounted approximately twofold in the general population with a diagnosis of MetS, and the risk for type 2 diabetes was even fivefold increased (5). MetS has an overall rate of 32.5% (95% CI 30.1%–35.0%) in patients with schizophrenia (6). Older age, and particularly illness durations, had a strong influence on the prevalence of MetS (6). This is probably partly, but not exclusively, related to the usage of psychotropic drugs such as clozapine and second-generation antipsychotics (SGAs). Although the prevalence of MetS is not significantly different in first-episode, antipsychotic-naïve patients in comparison to healthy controls (7, 8), abnormalities of glucose homeostasis already exist (9). This may be related to a shared underlying pathophysiology between schizophrenia and diabetes mellitus involving inflammation (10, 11). The same is probably true for the relationship between schizophrenia and dyslipidemia [in MetS defined as a decreased high density lipoprotein (HDL)-cholesterol and elevated triglycerides] (12). Over 20% of the treatment-naïve (prodromal or first-episode) schizophrenia patients have a lowered HDL-cholesterol level and a glucose dysregulation/insulin resistance (7, 13).

Although dyslipidemia is already more prevalent in schizophrenia patients before or during the debut of their disorder, treatment with antipsychotic drugs (particularly SGAs) has profound metabolic effects (14, 15, 16). Vancampfort et al. (8) found that schizophrenia patients with multiple episodes had a significantly (p < 0.001) higher prevalence of abdominal obesity, low high-density lipoprotein cholesterol, hypertriglyceridemia, and MetS compared to first-episode and drug-naïve patients. A typical component of MetS in patients with schizophrenia is central obesity as reflected by increased waist circumference, which is due to expansion of the amount of abdominal fat (5, 11). This abdominal type obesity consists of two components: visceral and subcutaneous. Especially visceral type obesity correlates with an unfavorable course of MetS (17, 18). In patients with schizophrenia, visceral fat has increased relative to properly matched healthy controls (19). This is particularly true for pericardial and, to a lesser extent, to intra-abdominal obesity (20).

Comparison of the weight gain after the initiation of antipsychotic treatment showed that all first- and second-generation antipsychotics may cause this phenomenon; however, the amount varies largely between different substances: clozapine and olanzapine seem to be the two compounds with the highest risk, a mid-risk group is composed of amisulpride, asenapine, iloperidone, paliperidone, quetiapine, risperidone, and sertindole and compounds with the lowest risk are aripiprazole, lurasidone, and ziprasidone (16). Weight gain mostly occurs during the first weeks of treatment, but does not seem to plateau in longer treatment phases (16). Nevertheless, an important difference is expected when patients with or without MetS start with an SGA. Whether or not other components of MetS (specifically HDL) react in parallel to the weight change is hitherto unknown. Until now, insufficient attention has moreover been paid to changes in the fatty component of body composition and biochemical parameters during the treatment of patients with schizophrenia in routine psychiatric practice.

The aim of our study is to assess changes of weight, body fat composition, and biochemical parameters of patients with schizophrenia receiving atypical antipsychotics, between groups with and without MetS.

We recruited 114 newly admitted patients with schizophrenia from the Mental Health Research Institute Inpatient Department (Table 1); these patients were divided into two groups with (n = 43; 37.7%) and without (n = 71; 62.3%) MetS. No differences were observed between treatment upon admission, but significant differences existed in age (p = 0.0005) and in duration of illness (p = 0.0003).

No statistically significant differences existed with respect to changes of indicators for the total body fat percentage (p = 0.3090), visceral fat level (p = 0.5408), body weight (p = 0.1148), and body mass index (p = 0.2579) during a 6-week re-installed treatment of patients with MetS. Only total fat fold and waist circumference underwent statistically significant change (p = 0.0067 and p = 0.0342, respectively). Statistically significant changes, however, across all indicators in the group without MetS were noted: total body fat percentage (p < 0.0001), visceral fat level (p = 0.0010), total fat fold (p < 0.0001), waist circumference (p = 0.0002), body weight (p < 0.0001), and body mass index (p < 0.0001) (Table 2).

We observed no significant differences with respect to parameters of glucose metabolism in patients with schizophrenia with MetS after a 6-week re-installed treatment. Both TC level and atherogenic index had significantly increased in this patient group (p = 0.021 and p = 0.029, respectively). In contrast, we found a significant increase of both glucose metabolism [glucose (p < 0.001), HOMA-IR (p = 0.023)] and lipid metabolism parameters [triglycerides (p < 0.001), VLDL (p < 0.001), and atherogenic index (p = 0.042)] in patients without MetS at entry after a 6-week re-installed treatment (Table 3).

In addition, changes in body fat composition and biochemical parameters, depending on the drug taken, were analyzed, with the exception of seven patients taking clozapine due to sample size.

Patients with MetS treated with olanzapine, quetiapine, and risperidone did not have statistically significant changes in the indicators of fat composition after a 6-week treatment (Tables 4, 6, and 8); on the contrary, in patients without MetS who took olanzapine and quetiapine, all indicators of fat composition increased significantly (Tables 4 and 6). In patients without MetS who used risperidone, the following fat parameters were significantly increased (Table 8): total body fat percentage (p = 0.020), waist circumference (p = 0.020), body weight (p = 0.002), and body mass index (p = 0.001)

Also, patients with MetS treated with olanzapine, quetiapine, and risperidone did not have statistically significant changes in the biochemical parameters after a 6-week treatment (Tables 5, 7, and 9). In patients without MetS who used olanzapine, the following biochemical indicators were significantly increased (Table 5): triglycerides (p = 0.030), high-density lipoproteins (p = 0.027), very low-density lipoproteins (p = 0.030), and atherogenic index (p = 0.040). In patients without MetS who used quetiapine, the following biochemical parameters were significantly increased (Table 7): glucose (p < 0.001), HOMA-IR (p = 0.050), triglycerides (p = 0.009), and very low-density lipoproteins (p = 0.009). In patients without MetS who used risperidone only, triglycerides (p = 0.001) and very low-density lipoproteins (p = 0.001) were significantly increased (Table 9).

In the present study, we observed that patients with MetS were significantly older than patients without MetS (Table 1). This result is consistent with the meta-analysis data of Mitchel et al. (6), which indicates an increase in the frequency of MetS in patients with schizophrenia over 38 years old. But according to this meta-analysis, the strongest influence on the rate of MetS is the duration of schizophrenia. This conclusion fully corresponds to our findings regarding the significantly longer disease duration and similar age of onset in the group of patients with in comparison to those without MetS.

The observation period with an assessment of body fat composition and biochemical parameters was 6 weeks. A short period of time for assessing changes in body fat composition and biochemical parameters was chosen due to the need to find ways to earlier assess the risk of developing MetS. Also, according to the “Meta-guidelines” for the management of patients with schizophrenia by Stahl et al. (26), the adequacy of the treatment trial must be assessed as a minimum of 3 weeks and a maximum of 6 weeks before making a major change to the treatment regimen.

The variables indicating the body fat composition show significant increase during a 6-week reinstated SGA treatment concerning all indicators in the group without MetS. This contrasts the results in patients with MetS, which only showed significant increase in total fat fold and waist circumference. The other indicators in this group were relatively stable (Table 2). Thus, in patients with MetS, the changed body fat composition only reflected an increase in the amount of subcutaneous fat, while in the group of participants without MetS, both subcutaneous and visceral fat were raised. It has been suggested that visceral obesity is the primary determinant of insulin resistance representing the basic pathophysiological changes leading to MetS and, as a consequence, diabetes (27). A limitation of our study may be the presence of statistically significant age difference between groups with and without MetS (Table 1). However, the average age of patients in each group is in the same age cohort (20–39 years) for measuring the percentage of body fat according to data obtained in a study of different ethnic groups (28).

The results of a number of studies have suggested that antipsychotics contribute to altered glucose metabolism in psychiatric patients compared to the general population (29, 30, 31), which is consistent with our findings (Table 3). Nevertheless, certain reports describe that no significant relationship exists between glucose metabolism and SGA treatment (29, 32). It can be hypothesized that these contradictions are related to insufficient division of the applied antipsychotics into first- and second-generation drugs and the lack of diagnosing MetS in patients with schizophrenia.

The observed changes of the serum lipid parameters (Table 3) largely correspond to literature data, which are reported as primarily marked elevations of serum triglyceride levels (12, 33, 34). The change was significant in patients without MetS. It is suggested that hypertriglyceridemia may be caused by SGAs through stimulation of hepatic triglyceride production and secretion or through inhibition of lipoprotein lipase-mediated triglyceride hydrolysis. In addition, an indirect mechanism may contribute, associated with obesity and insulin resistance, via exerting unfavorable effects both on the central nervous system and on the biology of adipose tissue (35). The increase in the total cholesterol level was small but significant in patients with MetS, but non-existent in patients without MetS.

All SGAs used in this study had a comparable effect on changes in body fat composition and biochemical parameters (Tables 4–9), with the exception of risperidone, which did not significantly affect glucose metabolism (Table 9). This confirms the evidence that these SGAs have the highest risk or mid-risk of metabolic disturbances in patients receiving these drugs (16). Treatment with olanzapine, quetiapine, risperidone, and clozapine was not randomly selected, which limits the relevance of the study. But all recruited patients were already using these drugs before admission, reflecting existing clinical reality.

Based on our findings and on literature data, we want to suggest that altered glucose and lipid metabolism may play a more important role during the onset of MetS. Six-week treatment with SGAs leads to significant changes in biochemical parameters in patients without MetS. However, schizophrenia patients with already established MetS do not suffer from these side effects in a similar severity. The absence of a change in glucose and most of lipid parameters may be related to wearing off of the tendency to increase fasting lipids and glucose once after MetS has developed. Our data are consistent with the findings in a study of Smith et al. (36, 37), which observed no significant differences in fasting measures of lipids and glucose after 5 months of treatment with olanzapine or risperidone in chronic patients with schizophrenia. It should be noted that triglyceride levels at entry were much higher in patients with MetS than in those without this diagnosis. Apparently a further increase in these levels is less likely to occur. The atherogenic index is the only parameter that differs after 6 weeks of treatment both in patients with and without MetS, which indicates the need for calculating this parameter routinely when monitoring for disturbed lipid metabolism.

In most studies, the MetS problem in patients with schizophrenia is evaluated through calculating its prevalence or the prevalence of the individual MetS components. In our study, we demonstrated for the first time through monitoring specific parameters that even within a relatively short period of 6 weeks treatment with SGAs, several indices of body fat composition may increase. This may indicate the necessity of carefully monitoring SGA-treated patients at the beginning of their usage. Moreover, a number of MetS indicators are reversible with proper case management. Measurement of waist circumference, carried out in most studies for the diagnosis of abdominal obesity, provides only conditional ideas about its severity, and computer-assisted tomography is a rather expensive and not suitable for continuous monitoring. Hence, there exists room for improvement.

The method of non-invasive bioimpedance analysis used by the current study is low cost, is easily reproducible, and can be widely applied in routine psychiatric practice. This method yields objective data on the composition of the body fat compartment of patients with schizophrenia. Concomitant monitoring of biochemical lipid and glucose parameters provides a complete picture of the formation of MetS in SGA-taking patients.

The datasets generated for this study are available on request to the corresponding author.

The studies involving human participants were reviewed and approved by Local Bioethics Committee of the Mental Health Research Institute, Tomsk, Russia, protocol N187, 24.04.2018. The patients/participants provided their written informed consent to participate in this study.

EK and SI designed and supervised the study. IM and VD collected the blood samples, anthropometrics, and clinical information. AB measured the biochemical data. AK and IM carried out the statistical analysis. EK, AK, and IM wrote the first draft of the manuscript. SI, AL, and NB commented on this draft and contributed to the final manuscript.

This work was supported by the Russian Science Foundation, grant # 18-15-00011.

The authors declare that this research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.