Elevated sialic acid, but not CRP, predicts features of the metabolic syndrome independently of BMI in women
AIMS: C-reactive protein (CRP) is a predictor of many diseases including type II diabetes and cardiovascular disease. Fewer studies have similarly shown sialic acid (SA) to be a predictor of obesity-related diseases, but importantly SA shows less intraindividual variability than CRP and acts as an integrated marker of the activity of a number of acute-phase proteins. This study examines the association between both CRP and SA with individual and combined features of the metabolic syndrome. SUBJECTS: In all, 257 women with a body mass index (BMI) ranging from 25.1 to 54.5kg/m2 (geometric mean 33.1 ± 5.8 kg/m2) and aged 19-71 y (mean 45.6 ± 12.1y) were studied. Subjects had no symptoms of intercurrent infection, known diabetes, treated dyslipidaemia, a chronic inflammatory condition, liver disease or malignancy. RESULTS: Linear regression demonstrates that both CRP and SA were positively associated with weight, BMI, insulin resistance, dyslipidaemia and hypertension. There was a highly significant (P<0.0001) positive association of both SA and CRP with none, one, two, three or four features of the metabolic syndrome. For a 1 s.d. (4.0 mg/l) increase in CRP, there was a significant increased risk when comparing the odds of having metabolic syndrome (defined as three or more individual features) compared with the remainder of the population (odds ratio = 1.7, P<0.0001), but this was not significant after adjustment for BMI. However, for a 1 s.d. (0.34mmol/l) increase in SA, the odds of having metabolic syndrome compared with those without metabolic syndrome was 2.5 (P<0.0001), and persisted after additional adjustment for BMI (adjusted odds ratio = 1.9, P<0.0001). CONCLUSIONS: While SA and CRP are both univariately associated with individual features of the metabolic syndrome, SA, but not CRP, is significantly associated with the metabolic syndrome, independent of BMI. We conclude that SA identifies a subgroup of overweight individuals with an inflammatory phenotype, who are at the greatest risk of metabolic syndrome.