Serum Albumin Levels: A Simple Answer to a Complex Problem? Are We on the Right Track of Assessing Metabolic Syndrome?

Serum albumin makes up a major portion of circulating proteins in our body. Serum albumin level is closely linked to the body’s nutritional (malnutrition/overnutrition) and inflammatory status. Insulin resistance is the main pathogenetic mechanism underlying metabolic syndrome, a condition that is associated with obesity and chronic vascular inflammation [1]. Several studies have focused on the association between serum albumin level and factors/diseases related to metabolic syndrome (insulin resistance, diabetes, and cardiovascular disease). In this issue, Bae et al. [2] reported that a high serum albumin level is associated with insulin resistance, but they failed to show a significant correlation between serum albumin level and the development of diabetes in a longitudinal follow-up. The authors analyzed data for a large cohort from a health promotion center located in an urban area, Seoul, South Korea. Cho et al. [3] also reported a positive relationship between serum albumin level and metabolic syndrome, although they studied a healthy adult population located in a rural area. Bae et al. [2] explained that the positive association between serum albumin level and insulin resistance might be a consequence of increased albumin production in the liver under insulin-resistant conditions. Insulin resistance goes handin-hand with increased insulin levels and insulin is known to stimulate albumin production in hepatocytes [4]. On the other hand, some reports have shown that albumin has a cardioprotective effect [5,6] that may be due to albumin acting as an antioxidant and a protective protein against chronic inflammation [1,7]. Albumin is a main constituent of serum proteins and, owing to its presence in vast amounts, it accounts for approximately 80% of thiol’s antioxidant effect in the body [8]. The free cysteine (Cys) residue of albumin reacts with reactive oxygen species, generating two reversible intermediate derivatives, and finally sulfonic-albumin, which is susceptible to enzymatic digestion compared with the nonoxidized counter molecule [9]. Therefore, serum albumin seems to have complicated effects on metabolic syndrome and related factors/ diseases. Several reports have shown a negative correlation between serum albumin level and cardiovascular risk factors, as well as cardiovascular disease [10,11]. However, there have also been conflicting reports that serum albumin level is not associated with atherosclerosis as evaluated by carotid imtima media thickness [12]. To make matters even more difficult to interpret, there are also papers demonstrating positive relationships between serum albumin level and vascular dysfunction as measured by pulse wave velocity [6], as well as early carotid atherosclerosis [5]. These differences in findings between pa-