Asthma cases demonstrated significantly higher leptin level than that in non-asthma controls among overall populations (SMD: 1.061, 95% CI: 0.784–1.338, p < 10–4), Caucasians (SMD: 0.287, 95% CI: 0.125–0.448, p = 0.001), Asians (SMD: 1.500, 95% CI: 1.064–1.936, p < 10−4) and Africans (SMD: 8.386, 95% CI: 6.519–10.253, p < 10−4) (Table 2, Fig. 2). This evidence concerns the gene LEP and asthma.