Estrogen is the female sex hormone responsible for female sexual and reproductive development, although men also have estrogen in small quantities. The female body makes three types of estrogen called estrone, estradiol and estriol. The level of each varies according to factors such as age, time of month, and whether the woman is pregnant. Estrogen also plays a role in the control of cholesterol, protects bone health, and affects our mood, appetite and sleep, as it is linked to serotonin.Hormone Health Network. (2018). Estrogen. [online] Available at: https://www.hormone.org/hormones-and-health/hormones/estrogen [Accessed 15 Nov. 2018]. Amin, Z., Canli, T. and Epperson, C.N., 2005. Effect of estrogen-serotonin interactions on mood and cognition. Behavioral and cognitive neuroscience reviews, 4(1), pp.43-58.