Insulin, in addition to its known metabolic effects, has sympatho-excitatory and vasodilatory actions on muscular blood vessels. The goal of this study was to evaluate insulin sensitivity in young women with vasovagal syncope and positive tilt test results (HUT+) and to compare it with that in patients with negative tilt test results (HUT–) and in control subjects without a history of syncope.

Different indices of insulin sensitivity were obtained by an oral glucose tolerance test (OGTT) in 13 young women with syncope and HUT+ (age 26.8 ± 9.1 years, body mass index 20.4 ± 2.1), 8 patients with HUT– (age 26 ± 5.6 years, body mass index 21.9 ± 2.4), and 13 control subjects without syncope and HUT– (age 28.9 ± 8.8 years, body mass index 23.1 ± 1.7). The following parameters were assessed: fasting glucose and insulin levels (G₀, I₀); G₀/I₀ ratio; G₀ × I₀; areas under the curve for glucose and insulin; homeostatic model assessment (HOMA); quantitative insulin sensitivity check index (QUICKI); and composite whole-body insulin sensitivity index (ISI).

G₀ and I₀ values were significantly lower in patients with HUT+ than in control subjects (G₀ 4.9 vs 81.9, P < .05, I₀ 4.7 vs 9.1, P < .005). All the fasting values-based indices (ie, HOMA 0.9 vs 1.9, P < .005) and the ISI (12.8 vs 7.1, P = .01) differed significantly in both groups. None of the parameters showed significant differences between patients with HUT– and control subjects. Sixty-one percent of patients with HUT+ had a vasovagal reaction during OGTT.

Young women with vasovagal syncope and HUT+ have a greater insulin sensitivity. They have a propensity to reproduce symptoms during the OGTT. This hypersensitivity could be one of the predisposing factors for vasovagal episodes.