We read with interest the recent article by Reis et al. (1), who concluded that neither parathyroid hormone (PTH) nor 25-hydroxyvitamin-D [25(OH)D] level predicts any of the three biochemical components (hyperglycemia, hypertriglyceridemia, and low HDL cholesterol) of metabolic syndrome. Since 25(OH)D and PTH may play a role in the etiology of metabolic syndrome, we retrospectively analyzed associations between results of PTH, 25(OH)D, fasting plasma glucose (FPG), triglycerides, and HDL cholesterol tests, which were performed on an entire cohort of outpatients aged >35 years who were consecutively referred to our clinical laboratory by general practitioners for routine blood testing over the past 2 years.
Venous blood from outpatients was routinely collected in the morning on fasting subjects. FPG, HDL cholesterol, and triglycerides were measured by enzymatic procedures on a Roche/Hitachi Modular System P (Roche Diagnostics, Mannheim, Germany), whereas PTH and 25(OH)D were measured by chemiluminescence assays on Liaison (DiaSorin, Vercelli, Italy). Participants were classified as having abnormal values of the biochemical components of the metabolic syndrome if they had triglycerides >1.69 mmol/l (150 mg/dl), HDL cholesterol <1.3 mmol/l (50 mg/dl), and FPG >6.1 mmol/l (110 mg/dl). Significance of differences and frequency distribution of values were assessed by the Kruskal-Wallis and the χ2 tests (for categorical variables), respectively. Multiple linear regression analysis was used to test the association between FPG, HDL cholesterol, triglycerides (singularly entered as the dependent variable), PTH, and 25(OH)D. Because of the low number of results retrieved (n = 112), male patients were excluded from statistical analysis. Cumulative results for the above-mentioned parameters were retrieved for 738 female outpatients aged >35 years (mean ± SD age 65 ± 11 years).
The study population was clustered in tertiles of PTH (<50, 50–71, and >71 ng/l) and 25(OH)D (<56, 56–127, and >127 nmol/l). No significant differences were observed in the value distribution among the lower, medium, and top tertiles of PTH (FPG: 5.6 ± 1.3, 5.4 ± 1.1, and 5.5 ± 1.1 mmol/l, respectively, P = 0.994; triglycerides: 1.2 ± 1.6, 1.2 ± 1.5, and 1.2 ± 1.6 mmol/l, P = 0.996; and HDL cholesterol: 1.7 ± 1.3, 1.7 ± 1.3, and 1.7 ± 1.3 mmol/l, P = 0.580) and 25(OH)D (FPG: 5.5 ± 1.2, 5.4 ± 1.2, and 5.5 ± 1.3 mmol/l, P = 0.497; triglycerides: 1.2 ± 1.6, 1.2 ± 1.5, and 1.2 ± 1.5 mmol/l, P = 0.361; and HDL cholesterol: 1.6 ± 1.3, 1.8 ± 1.3, and 1.7 ± 1.3 mmol/l, P = 0.052). Accordingly, no significant differences were observed in the frequency of abnormal values among the lower, medium, and top tertiles of PTH (FPG: 20, 15, and 18%, respectively, P = 0.647; triglycerides: 15, 15, and 20%, P = 0.549; and HDL cholesterol: 18, 15, and 15%, P = 0.800) and 25(OH)D (FPG: 20, 15, and 19%, P = 0.622; triglycerides: 17, 15, and 19%, P = 0.753; and HDL cholesterol: 20, 12, and 15%, P = 0.291). Finally, neither PTH nor 25(OH)D was significantly associated with FPG, triglyceride, or HDL cholesterol in multiple linear regression analysis. The results of this retrospective analysis confirm no effect of PTH and 25(OH)D concentrations on individual biochemical components of the metabolic syndrome in women.
