Let's continue to discuss puberty and its effects on health. In the previous lecture I discussed the effect of puberty on many of the body's systems that are affected by hormonal change, those changes that most mark the pubertal process. But the most important organ system affected by puberty is the brain, and it is therefore not surprising that some of the biggest changes that we see in health related to puberty are around mental health and behaviour. This slide lists some of those syndromes that become common as children make the transition through puberty. If we look at rates of deliberate self harm, for example, that's self-cutting and self-poisoning, of children in late puberty compared to those in early or mid puberty, we see tremendous differences in girls. Right so around three times higher in girls of the same age who are in late puberty. This has almost certainly something to do with the greater difficulties that girls report with emotions and emotional control as they pass through puberty. Whether it be feelings of anxiety, guilt, social embarrassment, unhappiness, anger, or simply not knowing how to relax when you feel tense. These experiences all increase for girls as they pass through puberty. These are the same emotional difficulties that girls with self-harm often report. If we look at patterns of substance abuse, and here I'm talking about things like daily smoking, smoking, frequent binge drinking, or cannabis use at least weekly. Again, the rates of substance abuse increase as children pass through puberty. In large part this is due to the different orientation to peers. As children reach later puberty, fitting in with a peer group becomes important. More so, than at any other age peers are the context in which identity is set to the extent that high status peers are party-going and substance-using, so too, the emerging adolescent is likely to adopt those values, those behaviours, and that lifestyle. Major depression and depressive symptoms are one of the largest contributors to burden of disease, particularly in adolescent girls, during the adolescent years, and if we look at the change in levels of high depressive symptoms reported by girls of the same age, but different in pubertal stage we see a clear trend across different surveys for symptoms to more than double by late puberty. This is very much a phenomenon that we see in girls but not in boys. And, we can look at these changes over time. That is with the passage through puberty. So, if we look at which girls are likely to develop depressive symptoms in the next twelve months, girls in late puberty have twice the risk of those of the same age who are in early puberty. And if we talk further about what it is In late puberty that explains their higher risk. It is the higher level of difficulties with emotions. The same emotions of anxiety, anger, knowing how to relax when tense, social embarrassment. It explains why girls in late puberty go on to have more new episodes of depressive symptoms. And it's not just rates of new episodes that change as girls go through puberty. For a girl who has an episode of depressive symptoms, she is two and a half times more likely for those symptoms to persist if she's in late puberty. If we look at some of the other factors that also predict the systems of depressive symptoms, it’s things like conflict at home, or being bullied by peers, that make depressive symptoms more likely to continue. But even taking these factors into account, does not explain why these symptoms are so much more likely to continue for girls once they've reached late puberty. If we look at some of these risky social interactions, like bullying, we also find that these change as children pass through puberty. So, social rather than physical aggression, is the typical form of bullying in girls. That's about spreading rumours, teasing, deliberate social exclusion. These all increase for girls, and for boys, as they pass through puberty. Until now I've emphasised pubertal stage or the passage through puberty of effecting health. I previously mentioned that there is considerable variation in the timing of puberty between individuals growing up in the same physical and social context. This slide shows that five of over five year variation in the age of onset of menarche, that is onset of first menstruation in girls in the United States, you'll see that there are differences between girls of different racial backgrounds. There is a tendency for girls with Black American and Hispanic backgrounds to have puberty at a earlier point. So if we look at girls who have had a first period by the age of eleven years, the proportion of Black American and Hispanic girls is considerably higher than for White American girls. This matters for health, girls who have reached puberty at an earlier point tend as a group to have higher rates of emotional and behavioural problems then their peers - a risk that continues through the adolescent years. We also now recognise that those reaching puberty earlier have greater risks in later life health. For boys and girls, early puberty is linked to greater risk for metabolic problems, such as type 2 diabetes, as well as cardiovascular disease later in life. And early puberty is also linked to greater risks for cancers of the breast and reproductive tract. I hope that I've managed to illustrate the many ways in which the transition through puberty is linked to health. This is important because this phase of life may offer some of the best opportunities that we have for intervening to promote health and prevent some of the leading causes of disease in later adult life.