Adolescent Obesity Kills Middle-Aged Adults

Yes, there's a childhood and adolescent obesity epidemic out there. The word on the street now is that "this is the first generation of kids, who will not outlive their parents".

But is this really true? Where is the data showing that childhood obesity is really a risk factor for early death?

This question is now answered by perhaps the largest study on this issue to date published by Tone Bjørge and colleagues from the University of Bergen, Norway, in the American Journal of Epidemiology.

Bjørge and colleagues studied the relationship between BMI (measured height and weight) and mortality in 227,000 adolescents (aged 14-19 years) recruited in Norwegian health surveys in 1963-1975. During follow-up (8 million person-years), 9,650 deaths were observed. Cause-specific mortality was compared among individuals whose baseline BMI was below the 25th percentile, between the 75th and 84th percentiles, and above the 85th percentile in a US reference population with that of individuals whose BMI was between the 25th and 75th percentiles.

Risk of death from endocrine, nutritional, and metabolic diseases and from circulatory system diseases was increased in the two highest BMI categories for both sexes. Relative risks of ischemic heart disease death were 2.9 for males and 3.7 for females in the highest BMI category compared with the reference. There was also increased risk of death from colon cancer (males: 2.1; females: 2.0), respiratory system diseases (males: 2.7; females: 2.5), and sudden death (males: 2.2; females: 2.7).

The authors conclude that adolescent obesity is related to increased mortality in middle age from several important causes.

Clearly not a good sign for what awaits our sons and daughters unless we get a hold on the obesity crisis.

AMS
Edmonton, Alberta

Accuracy of BMI for Diagnosing Obesity

Body mass index (BMI) is currently widely recommended and used as the best measure of obesity both in population and clinical studies. It dates back to the Belgian statistician Adolphe Quételet, who between 1830 and 1850 described this index as a way to characterize the level of adiposity in sedentary adults.

But how accurate is this index really to identify individuals with excess body fat?

This question was recently addressed by Abel Romero-Corral and colleagues from the Mayo Clinic, MN, USA, who analysed the relationship between BMI and body fat percent (BF%) as measured by bioelectrical impedence in 13,601 subjects (age 20-79.9 years; 49% men) from the Third National Health and Nutrition Examination Survey (Int J Obesity).

In this study, the authors defined obesity based on the World Health Organization (WHO) reference standard for obesity of BF%>25% in men and >35% in women.

BMI-defined obesity (>=30) was present in 19% of men and 25% of women, while BF%-defined obesity was present in 44% of men and 52% of women.

A BMI>=30 had a high specificity (men=95%, women=99%), but a poor sensitivity (men=36%, women=49%) to detect BF%-defined obesity. This means that while the BMI definition does identify the vast majority of men and women who have increased body fat, it also misses a significant number of individuals who have high percent body fat and would be considered obese by the BF% definition.

The diagnostic performance of BMI diminished as age increased and in the intermediate range of BMI (25-29.9), BMI failed to discriminate between BF% and lean mass in both sexes.

The authors conclude that accuracy of BMI in diagnosing obesity is limited, particularly for individuals in the intermediate BMI ranges, in men and in the elderly. Thus, the currently recommended BMI cutoff of >=30 kg for obesity has good specificity but misses more than half the people with excess fat.

The scary part of these results of course is in the fact that based on actual BF% the prevalence of obesity in this population doubled! On the other hand, we know that %body fat or body composition alone is not a particularly reliable measure of health.

I prefer to continue using my operational clinical definition of obesity: the presence of excess body fat that threatens or affects your health.

Given the wide variation in the inter-individual susceptibility to develop adiposity-related health problems, the diagnosis of obesity and the question of whether or not reducing the proportion of body fat will indeed benefit your health will always remain a matter of clinical judgement.

AMS
Duschesnay, Quebec

Obesity and Prostate Cancer

Looks like this week is about obesity and men's health. So after blogging about male self-esteem and erectile dysfunction, what about obesity and risk for prostate cancer?

Well, after a quick search of the literature, I can happily state that the data on this is pretty inconsistent.

Probably the best study, a prospective cohort study in 34,754 men residing in Washington State (aged 50-76 years at baseline) studied by Alyson Littman and colleagues from the Fred Hutchinson Cancer Research Center, Seattle, WA, published in the American Journal of Epidemiology, succeeded in confusing me more than providing any definitive answers.

Thus, while on one hand obese men had a reduced risk of nonaggressive disease, overweight (but not obese) men, had an increased risk of aggressive disease. Body mass index of >25 at age 18 years was associated with increased risk of aggressive prostate cancer; obesity at ages 30 and 45, but not 18, years was associated with reduced risk of nonaggressive prostate cancer.

I can only concur with the authors, who conclude that this study demonstrates the complexity of prostate cancer epidemiology and the importance of examining risk factors by tumor characteristics.

So is obesity a significant risk factor for prostate cancer? I guess the answer is "depends".

AMS
Edmonton, Alberta

Obesity Paradox also Holds in Denmark

Regular readers of this blog will have noted previous entries on the "paradoxical" reverse epidemiology of obesity and cardiovascular mortality, where risk is apparently higher in underweight compared to normal weight, overweight or even mildly obese individuals (for e.g. of previous blog entries on this click here, here or here).

Now a new Danish study by Jawdat Abdull and colleagues published in the European Heart Journal that looks at pooled data from 5 large registries with over 21,500 consecutive high-risk patients with myocardial infarction or heart failure finds essentially the same story:

After a follow-up of 10.4 years, compared with normal weight individuals (BMI 18.5-24.9) all-cause mortality was higher in underweight (BMI < 18.5) but not in overweight (BMI 25.0-29.9) or class I obese (BMI 30-34.9) individuals. Only with class II obesity (BMI 35-39.9) and higher was there a significantly increased risk for myocardial infarction and increased death risk.

This finding is very much in line with the mounting evidence that moderate overweight and mild obesity does not automatically translate into higher cardiovascular mortality in high-risk individuals with established heart disease.

As argued before, given that increased weight is a well-established risk factor for high blood pressure, diabetes, and other risk factors for cardiovascular disease, the reasons for this rather consistent "paradoxical" relationship are not clear.

Possible explanations include the idea that being underweight is a sign of general ill health and that thin people may be less able to cope with life-threatening illnesses like a heart attack at least compared to people with some extra "nutritional reserve". Of course there are a couple of more sophisticated theories out there that to me appear highly speculative (which is why I will not mention them today).

Nevertheless, in light of this "paradox", we may have to look beyond reducing cardiovascular morbidity and mortality to justify aggressive treatments of overweight and class I obesity with established cardiovascular disease - perhaps the aim of obesity treatment in high-risk individuals should simply be to prevent further weight gain rather than to reduce it?

I guess it would take intervention trials to find out - thankfully, these are already well underway.

AMS

Obesities and What to do About Them

Over the last couple of days I have been reading a new 160 page report on "Tackling Obesities: Future Choices" produced by the UK Government's Foresight Program which is run under the Government Office for Science.

The report was prepared by some 200 experts (mostly from the UK) and ends with several "what if" scenarios that model the outcomes of possible policy decisions.

The first point of note is that the title of the work refers to "Obesities" rather than "Obesity", thereby formally recognizing that this is a heterogeneous entity and that there are many forms of obesity.

Over all the work is impressive and discusses obesities in all their complexities - the biological and environmental system map is enough to let anyone serious about trying to understand the causes of the epidemic throw up their hands in despair and flee the room.

Nevertheless, the work is useful in that it contains a lot of interesting bits that are "quotable" and deserve discussion.

Sentences like:

"The forces that drive obesity are, for many people, overwhelming."

are notable because they depart from the usual idea that obesity is essentially a consequences of individuals' choices and decisions and all anyone has to do is to be "smarter" about their health.

This obviously we know is not true - in fact, if, as stated elsewhere in the report,

"People [in the UK] today don't have less willpower and are not more gluttonous than previous generations."

and

"...for an increasing number of people, weight gain is the inevitable - and largely involuntary - consequence of exposure to a modern lifestyle."

we need to be careful not to blame the victims.

It will rather be changes in social values and the way society as a whole chooses to respond to this epidemic that will make a difference. Amongst the experts, there was clearly no expectation of any spontaneous reversal of obesity trends.

The report is a challenging but fun read. I will probably be posting more on stuff I find in it over the next few weeks.

For those wanting to read the full report, you can download it by clicking here.

AMS