In addition to the hypothesis of sex hormones mediating the effect of early menarche on asthma, another proposed mechanism is through obesity: Early menarche would increase the risk of adult obesity, which would in turn affect asthma, possibly through an effect of higher leptin levels on the immune system and airway inflammation, although it could be the other way round, with higher childhood BMI and leptin increasing the risk of early menarche, which would increase the risk of asthma [7,8]. This evidence concerns the gene LEP and obesity due to melanocortin 4 receptor deficiency.