As we've been talking about in the last few lectures, over the past 50 years, most nutrition research and policy in low and middle income countries has focused on poverty and its effects on under-nutrition. In this regard, the take home message is arguably very simple. Better nutrition is associated with better growth. However, as we have been discussing, increasingly, not just in high income countries, but in many of those same low and middle income countries. That are challenged by under-nutrition, there is growing evidence of a major shift towards overweight and obesity. Understanding trends in child and adolescent obesity is important, as we've just shown. And in this lecture, it's also important to appreciate how overweight and obesity track across childhood, adolescence and adulthood. This is because obesity in adolescents has many adverse affects on health in both adolescents and adulthood as well as the next generation. But there are important windows to think about in terms of the timing of preventive interventions. Most of you will be aware of the range of complications of obesity as I've outlined in a figure like this. Indeed, such graphics may feel so familiar that if you're like me, you'll probably feel somewhat like tuning out, feeling quite overwhelmed from this amount of information. When we take a life course perspective, we can start to think about the complications of obesity in a different way. Unpacking the extent of risks of obesity in adolescence itself, risks due to continuities of obesity from childhood and adolescence into adulthood, and risks as a result of increased problems to the mother during pregnancy and the subsequent risks for the next generation. And as discussed, we can also think about the different opportunities for prevention of overweight in different stages of the life course and indeed, in different stages of obesity. My sense is that many people believe that obesity is only problematic for physical health in adults, rather than in adolescents. But this is certainly not the case, while the cumulative effects of obesity in adults such as increased rates of cardiovascular deaths, and cancer in obese adults are clear. There are also some highly significant health effects that can be first manifest in adolescence. Type two diabetes, fatty liver, hypertension, obstructive sleep apnea and certain orthopaedic conditions just are some examples of the health impact of obesity. That can be experienced during the adolescent years themselves. Not surprisingly, the greatest health impacts in adolescence are experienced in those who are most over their healthiest weight. The key point here is that while physical health consequences of overweight increase across the life course, adolescents are by no means immune from these. Cardiovascular disease is a major contributor to the burden of non-communicable diseases in adults. Let's look at the example of high blood-pressure or hypertension. We know there is evidence of increasing weight in adolescence, but is there also evidence of increasing blood-pressure in children and adolescents? And how does this track with weight? Zhang and colleagues examined the trend in high blood pressure in children and adolescents across a ten-year period in China. They studied three waves of 7 to 17 year old students, measuring their height, weight, and blood pressure at each time point. They’ve defined relatively high blood pressure as systolic blood pressure and diastolic blood pressure greater than or equal to the 95th percentile for age and gender. Over this ten-year period, the prevalence of overweight and obesity increased, as we've seen in previous slides or previous lectures, to affect about a third of boys and about a fifth of girls. However, of great interest is across this same period, there were dramatic increases in the prevalence of high blood pressure. Focusing on boys here in blue, the overall prevalence of relatively high blood pressure increased from 19% in the year 2000 to 26% in 2010, while in girls it increased from 15% to 20%. The particular public health concern is that adult hypertension has its origins in childhood. Children and adolescents with elevated blood pressure are more likely to become hypertensive adults. At least in China, these figures suggest that adolescent hypertension is a new public health problem. Such increases in blood pressure would be even more concerning if there were continuities of overweight and obesity across adolescence into adulthood. Interestingly, there are relatively few studies investigating how overweight and obesity track from adolescence into adulthood. Our group explored this question using a ten-year prospective cohort study in Melbourne, Australia that measured weights at ten different time points. The study showed that the proportion of overweight individuals increased from 20% in mid adolescence to 33% at 24 years of age. And the proportion who were obese effectively doubled from 3.6% during adolescence, to 6.7% when these same adolescents were young adults. For those with persistent obesity in adolescence, no one had a BMI less than 25 at the age of 24 years, that is the most overweight, stayed overweight. This is exactly what we would expect to see in terms of continuities of weight. However, what this studied showed was that there were also substantial shifts in overweight and obesity between adolescence and young adulthood. With some very interesting discontinuities as well. One shift was around young adulthood. Around 40% of overweight young adults had persistently normal weight during adolescence. These young adults had new onset overweight. And of all young adults who were overweight, about 80% had been, at some point during adolescence, a normal weight. Also of interest is that around half of the obese young adults had never been classified as obese as adolescents. 31% of females and 59% of males who had been overweight for only one or two waves of adolescent data collection were obese at 24 years. These data, as complex as they are, show that both the severity, and importantly the persistence of overweight matters in adolescence. Few adolescents who peak into obesity or who are persistently overweight, achieve a normal weight in young adulthood. Resolution is more common in those who are less persistently overweight as teenagers. This suggests a very different scope for targeting lifestyle interventions in those with new onset overweight. Rather than your typical interventions which currently tend to target those who are persistently overweight. Something to think about. Many studies suggest important associations between obesity and mental health with concerns about higher rates of bullying in obese children and adolescents. Parents of obese children rate bullying as their top health concern. And parents are right to be concerned, given that for all adolescents, bullying is associated with a nearly three fold increase in symptoms of depression and anxiety, particularly in girls. So what comes first? Is it bullying behaviours, or might it be obesity? What do you think? Longitudinal studies suggest that rather than bullying leading to young people feeling badly about themselves and overeating, perhaps, in response to that stress. That young people are bullied because they are obese. But there is growing interest in a far wider set of associations of nutrition and mental health beyond those simply relating to the bullying, as we've shown in the last slide. And this list of titles of various papers, I think, show cases some of these areas of interest. New interest is about how the quality of one's diet, rather than overweight itself, may also affect behaviour and emotional well-being. There are now multiple studies that suggest that diet may of itself affect behaviour and mental health. Now most of these studies are cross sectional in nature and therefore, while they describe associations they are not able to imply causative relations. Now, one such study is the West Australian Pregnancy Cohort. A prospective study of nearly 3,000 pregnancies that examined the cross-sectional association between dietary patterns and mental health in early adolescence. At 14 years of age, the child behaviour checklist was used to characterise behaviours reflecting mental health status. Higher scores represent poorer behaviour. Two dietary patterns that they called the Western and Healthy patterns were identified using a food frequency questionnaire. Relationships between dietary patterns, food group intakes, and behaviour were examined following adjustment for a wide range of potential confounding factors at the age of 14. Their results revealed that total, what's called internalising scores, characterised by being withdrawn or depressed, and higher externalising scores, characterised by more delinquent or aggressive behaviour, was significantly associated with the Western dietary pattern. With increased intake of take away foods, confectionery and red meat. But improved behavioural scores were significantly associated with higher intakes of leafy green vegetables and fresh fruit. Components of the Healthy dietary pattern. These part findings are really important to think about in terms of population level interventions. Such as the availability of food at and around schools, and about how to price food to make healthy food choices less expensive. Something we'll come back to in the policy and programming lectures later on. In addition to obesity reducing fertility through inhibiting normal ovulation, there are multiple complications that are more common when the pregnant woman is obese. Obesity increases the risk of pregnancy-related diabetes, the risk of hypertension, and the risk of pre-eclampsia, a life threatening form of hypertension and protein in the urine during pregnancy. Obesity increases the need for interventions during labor, and is associated with worse outcomes for the newborn. Specifically, obesity increases the risk of hypertension and pre-eclampsia. Infection risks are higher, including both urinary tract infections and postpartum infections. There are also increased rates of thrombosis, a particularly serious form of clotting that is already increased in pregnancy. Obesity increases the risk that pregnancy will continue beyond the expected due date. Induction of labor is more common in women who are obese and obesity can also interfere with the use of certain types of pain medication, such as an epidural. These factors all signal a greater likelihood of the need for elective and emergency Caesarian section. And finally, obesity also increases the risk of miscarriage and still birth. So, the health implications of over nutrition affect adolescents as adolescents, contribute to non-communicable disease risks in adulthood, a nd as we have seen here, increase pregnancy-related health risks, not just through the wider effects of hypertension and gestational diabetes. But through a wide range of effects which have the potential to increase the health risks to the next generation in ways that are only now just starting to be explored.
