Background Metabolic syndrome (MetS) has been shown to be associated with depression in older adults but the results are mixed. We summarized and evaluated the association between depression and MetS in people aged 60 years or over. Methods Relevant published studies from January 1997 to July 2017 were identified by searching two electronic databases: PubMed/Medline and EMBASE. Observational studies were considered. Results Twelve studies were included in the systematic review. Depression seemed to be related with MetS in the majority of the studies (10/12 = 83.3%). As far as the longitudinal studies are concerned, the onset of depression was related to MetS in 2 out of 3 studies (66.6%), while a relation between chronicity of depression and MetS was reported (1 study). Regarding cross-sectional studies, 7 out of 9 (77.7%) concluded that there was a positive association between depression and MetS. Mixed evidence was found among studies concerning the association between depression and the individual components of MetS. Four out of ten studies (40%) reported that depression was significantly associated with the waist circumference, a component of MetS. Limitations There was a high degree of heterogeneity between studies regarding their design. Only studies written in English, from peer-reviewed journals were included. Conclusions Depression seemed to be significantly associated with MetS in people aged 60 years or over. Among the components of MetS, abdominal obesity seemed to be associated more strongly and consistently with depression. The direction of the causality and mechanisms underlying the relationship are still largely unknown.

Introduction

The number of older persons -60+ years old- has increased substantially in recent years in most countries and regions, and that growth is projected to accelerate in the coming decades (United Nations, 2015). Population ageing has many implications for nearly all sectors of society. Increasing life expectancy has been associated with increasing risk of aging-associated diseases and with an increased chronic disease burden (Prince et al., 2015). The leading contributors to disease burden in older people are cardiovascular diseases (CVDs). Also, depression is one of the main disorders that afflict older people (worldwide 7.5 million older adults suffer from major depressive disorder) (Prince et al., 2015). The clustering of several metabolic and cardiovascular risk factors is a common phenomenon among older adults. Within this framework, metabolic syndrome (MetS), which is a combination of factors thought to predispose an individual to CVDs is considered to be a major public health issue in this age group. In particular, MetS is characterized by elevated abdominal obesity, high level of triglycerides, low level of high-density lipoprotein cholesterol (HDL-C), high blood pressure (BP) and elevated fasting plasma glucose (FPG) or diabetes. The prevalence of MetS peaks around the age of 60–۷۵ years (Knut Borch-Johnsen, 2013). MetS is a heterogeneous disorder, with substantial variability in the prevalence of component traits within and across populations (Denys et al., 2009). The prevalence of MetS in older adults varies from 11% to 43% according to the World Health Organization (WHO), and 23% to 55% according to National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP-III) (Denys et al., 2009).