Something is wrong with the model

Back in grad school when a theory came up with a wrong prediction, we all clapped hands because it showed us exactly where a new theory was needed, and just how it failed. No casting about for something to work on. A program that crashes intermittently is very hard to fix. Once you’ve found input that consistently makes it crash the job becomes much easier.

The Center for Disease Control released new data for 2007 (based on 90% of all USA death certificiates) showing that mortality rates dropped again (by over 2%) to 760/100,000 population. It’s been dropping for the past 8 years, and viewed longer term is half of what it was 60 years ago. Interestingly death rates from heart disease dropped a staggering 5% and even cancer dropped 2%.

But the populace is fat and getting fatter. This has been going on for 30 years. You can Google NHANES for the gory details, but the following should be enough. [ Science vol. 299 pp. 853 – 855, 856 – 858 ’03 ] The data from a recent NHANES (’99 – ’00) shows that the percentage of obese (as opposed just overweight) increased from 23% in the surveys from ’88 to ’94 to 31%. This is based on the body mass index (BMI). Someone 6′ 1″ would have to weigh 225 pounds to be obese.

We are told to be prepared for an epidemic of diabetes, high blood pressure, elevated blood lipids because of this. Every doc has seen blood sugar drop, blood pressure lowered, lipids come down in people with any/all of the above when they are able to lose a significant amount of weight. These diseases are significant only if they kill people, which they certainly seem to do in my experience. The next time you’re visiting a friend in the hospital, look at what’s lying in the beds. Very likely, many more than 31% of them are obese.

So why are death rates dropping and people living longer? Something must be wrong with the model — it’s pretty hard to quarrel with the data as being inadequate. Certainly the increased incidence of obesity should have produced something by this time (it started 30 years ago).

Well, the self serving answer for the drug developers is that their drugs are better. MDs would like to think it’s due to better care. Possibly. Here’s some detail.

#1: More people are exercising than they used to. How many joggers and walkers did you see on the streets 20, 30 years ago?

#2: Fewer people are smoking. Forget lung cancer (if you can). The big risk for smokers is premature vascular disease. Normally we all have carbon monoxide in our blood (it comes from the breakdown of hemoglobin). [ Brit. Med. J. vol. 296 pp. 78 – 79 ’88 ] Natural carbon monoxide production would lead to a carboxyhemoglobin level of .4 – .7%, but normal levels in nonsmokers in urban areas are 1 – 2%. Cigarette smoke contains 4% carbon monoxide, so smokers have levels of 5 – 6%. This can’t be good for their blood vessels.

#3: Doctors know more than they did. My brother is a very competent internist. He took over the practice of a similarly competent internist after his very untimely many death years ago. Naturally he got all the medical records on the patients. He found letters (now over 25 years old) from the late MD to his patients informing them of their lab results, and assuring them that their cholesterol was just fine at 250 mg%.

#4: The drugs are better. In addition they may be working in ways that we have yet to fathom. Consider the statins — their effect on vascular disease is far greater than their effect on blood lipids (cholesterol, triglyerides) — particularly when compared to other agents that lower blood lipids to the same extent.

Any further thoughts?

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  • Curious Wavefunction  On August 21, 2009 at 10:33 am

    Good post. It’s also interesting to note the different metrics used for assessing health. For instance as you probably know, in case of people of Asian and especially East Asian descent, one variable more than any other seems to correlate with proclivity toward heart disease and diabetes- waist circumference. BMI does not seem to be very helpful here.

    As for smoking, it raises an interesting question in my mind. When I was in Germany I noted a lot of women smoking, and I am told this is even more widespread in Italy and France (apparently Italy constitutes the largest market for Philip Morris). How has this affected life expectancy in Europe? Or have the adverse effects of smoking simply been outweighed by some of the other factors which you stated?

  • luysii  On August 21, 2009 at 5:51 pm

    There are a lot of problems with the BMI, but in its favor, measuring height and weight isn’t rocket science, and is quite easy to do. Skin fold thickness, waist hip ratio are probably better, but less available. The BMI skeptics might be interested in the following notes I took on an excellent article in Nature this year.

    [ Nature vol. 459 pp. 340 – 342 ’09 ] There really isn’t an epidemic of obesity. Variation in body weight has a Gaussian distribution (e.g. a continuous distribution) and if you define a BMI > 25 as overweight then a small shift in the mean value of weight in the population leads to a disproportionate number of people exceeding the threshold. A 33% increase in the incidence of obesity in the USA from the 80’s to the 90’s means an average weight gain of 6.6 – 12 pounds in the population as a whole (that’s still a lot — 2 to 4 trillion pounds for the US population). So the secular trend toward obesity is less profound than is generally appreciated.

    The variation in weight over a year is minimal, despite the intake of on average 1,000,000 calories — so weight maintenance is largely unconscious. This is much more than monitoring food intake could insure, so weight maintenance is largely unconscious.

    Based on twin studies (identical vs. non-identical) the genetic factor in obesity is variously reported as 70 – 80% — much more than diabetes, heart disease and cancer. The only trait with consistently higher heritability than obesity is height.

    Only 5 – 10% of morbid obesity (BMI > 40) is due to defects in known genes (leptin, leptin receptor, POMC, BDNF, MC4).

    When fat people lose weight, they use less energy than lean individuals of that weight who haven’t ever been fat. To maintain their reduced weight they must consume fewer calories than their initially lean counterparts. This is one reason that diets don’t stick.

    Most people who have had bariatric surgery remain fat (BMI > 30) despite a marked reduction in food intake. True of my neice sad to say.

  • luysii  On August 22, 2009 at 8:58 am

    Many thanks to Megan McArdle for mentioning the article ( — it kicked up a lot of looks here, and 60 comments there. There were a variety of suggestions I hadn’t thought of about why mortality might be falling. These include — fewer traffic accident and better worker safety.

    The most interesting (to me) was the decline in pollutants. The problem with this sort of thinking, is that you have to accept the bad along with good. Just plot the drop in ambient lead levels over the past 30 – 40 years against time. Now plot the drop in College Board scores the same way (before the Board normed them up so they wouldn’t look so bad — this really happened). The two curves look the same.

    Correlation is not causation

  • Jim  On August 22, 2009 at 3:21 pm

    Agree that BMI has major shortcomings, but the advantage of easy data availability. I’d still like to nuke it. I have started measuring what I call WARM (Waist-to-Arm Ratio Measurement) in men and WHARM (Waist-to-Hips-to-Arm Ratio Measurement) in women to account for frame size (see my blog post I believe these measurements will correlate better with mortality than the BMI data, at least at the high end (the low end data is confounded by malnourished states, cancer, etc.)

  • HalifaxCB  On August 22, 2009 at 3:58 pm

    I don’t know, but couldn’t this be simply a case of trying to determine trends just from the noise in the measurements? (I’m a math guy, not a stats guy, but because I am forced to work with such low-lifes I’ve become very familiar with their congenital problems). Years ago – I think in the 70’s – someone pointed out to me that if you got to 50 you had about the same life expentecy as someone who hit 50 maybe 200 years ago. In other words, once you got to late middle age you had a good chance of the full 3 score and ten to 4 score. Violence, disease, and childbearing were the great killers.

    On top of that, there were all the advances in medicine – the eradication of polio, to a large extent TB, malaria (in the west), the control of STD’s, and even simple hygenic improvements that meant that people no longer contracted diseases that while not killing them outright left them with significantly shorter lives.

    And how do you control for the fact that many of the premature deaths among the cohort now counted as elderly (had they lived) were ones whose youth was scarred by the wants of the depression and the stresses of WWII? It’s only an impression, but it seems to me that those among my parent’s generation who had the hardest war were the first to be lost many years later. Similarly for survivors of the Depression.

    Put together the passing of the Greatest generation, and the aging of the most self-involved (the Boomers) introduces a heavy bias into the stats. It’ll probably be another twenty or thirty years before anyone could gather sufficiently robust statistics to determine whether eating arugula wile you jog actally increases your lifespan….

    Speaking of jogging, I would also like to add that virtually evey person my age (pushing 60) I know that was once rabidly into exercise is now hobbling around on blown knees and stiffened backs. Pardon my schadenfreude while light up the last of my Nat Shermans (sadly not available in Canada) and enjoy my coffee with a touch of cream, and ponder that trade off between how many years one lives and how much living one does…..

  • BGSUfan  On August 22, 2009 at 6:21 pm

    One thing to keep in mind when it comes to changes in life expectency from birth (“LEFB”) is that decreases(improvements) in infant mortality have huge impacts on LEFB. In fact, most of the increases in LEFB in the recent past have come from more children living through their infancies. I haven’t researched enough to know how on-point this is for this discussion, but this fact can easily explain how LEFB can increase while the adult population is seemingly becoming unhealthier.

  • fredtopeka  On August 22, 2009 at 7:32 pm

    Since a post of mine has been automatically linked to (mine is the ‘is being overweight not’ link), I thought I would comment here. I have a few points:

    people who are ‘overweight’ have a lower death rate than those who have a ‘normal’ weight (see my post). This means, if the mean weight in the US used to be normal, that an increase in the mean weight should decrease mortality.

    people might be exercising more now, but there is less exertion at jobs. There are a lot more sedentary jobs now, so overall we might have less total exertion even though we exercise more (I think people are also more likely to drive to work now since more people live in suburbs as opposed to cities).

    life expectancy has gone up in the US, but has slipped compared to the rest of the world. The US used to be near the top, but is now near the middle/bottom of developed countries.

    it would be interesting to see if weight dropped as the number of smokers increased. I seem to remember that the number of people who smoked jumped during/after the world wars (soldiers were given free cigarettes), so we shouldn’t have to look that far back to check.

  • luysii  On August 22, 2009 at 8:08 pm

    Fredtopeka — I’m not sure how that happened. Are you offended? At any rate, I note that you’re a mathematician. Hopefully you’ll keep an eye on the blog and set me straight on any mathematical questions (see the end of the first post)

  • Shaky Barnes  On August 22, 2009 at 9:17 pm

    We could brainstorm reasons all day but seems to me the simple fact is that there are thousands of things affecting mortality, and obesity is just one of those thousands. This isn’t a ceterus peribus situation — this would be one nasty model equation with a lot of variables that are all changing all the time. Therefore one shouldn’t even expect mortality rates and obesity to move in lockstep, inversely or otherwise.

  • The Captain  On August 22, 2009 at 10:11 pm

    “The next time you’re visiting a friend in the hospital, look at what’s lying in the beds. Very likely, many more than 31% of them are obese.”

    Uh… since over 40% of the US population is obese, doesn’t that mean that obese people are LESS sick than others?

  • The Captain  On August 22, 2009 at 10:13 pm

    Sorry… I guess your numbers are saying 31% are obese.

  • AliasUndercover  On August 22, 2009 at 10:38 pm

    According to BMI, Arnold Schwarzenegger is obese…

  • Guest  On August 22, 2009 at 11:30 pm

    Most people categorized as “obese” by BMI aren’t built like Arnold. They’re built like John Candy. And it would be better for them if they accepted that.

  • luysii  On August 23, 2009 at 11:30 am

    First a response to some of the commenters and then a few final points.

    Curious WaveFunction — everywhere smoking has been studied, without exception, it results in increased mortality. It is my understanding that smoking rates are higher in East Asia and Europe than they are here.

    Halifax — my experience with WWII and depression survivors is quite the opposite of yours, two uncles passed away in the past year at 94 (Kasserine Pass, Battle of the Bulge) and 89 (Philippines) and the third (India, China) is going strong at 94. Even more interesting, 10 years ago one son was living downstairs from a wonderful 95 year old very hardnosed woman in Brooklyn. She thought people were HAPPIER during the depression than they were currently. Surprising, but she was a very cleareyed individual with no particular axe to grind.

    BGSUFan — What you say is quite true — saving an infant is equivalent to saving many 80 year olds, but (fortunately) infant mortality is low and fairly stable (although it could always be lower) in the USA

    Fredtopeka — they were giving free cigarettes to soldiers at the military hospital I served at from ’68 – ’70.

    Shaky Barnes “one shouldn’t even expect mortality rates and obesity to move in lockstep, inversely or otherwise”. Perhaps — but that’s what the model predicts, and why I wrote the post.

    AliasUndercover && Guest — for every Arnold (with a high BMI), there are a zillion John Candy’s — and John died at 43 of a heart attack. God he was funny. Jim and the latest commenter are right — the BMI has many shortcomings, but the virtue of simplicity (and relative accuracy). It would be difficult to train 50 – 100 or so people to do Jim’s measurements accurately and apply them to the 5,000 people each year NHANES studies.

    Now a few final points:

    First– an elaboration of possible explanation #1 for the data. At least in my neighborhood 75% of the walkers and 25% of the joggers would be considered obese by BMI standards. However, even if they don’t lose an ounce they are still getting some benefit. Exercise has the following beneficial effects (1) lowers blood pressure (2) makes the heart pump more efficiently (3) if you’re diabetic, it will lower your sugar (4) if you have glaucoma it lowers intraocular pressure (5) improves lung function. I’m not sure what it does to blood lipids (I should know this).

    Second — fat is no longer regarded as a turgid lump of goo just sitting around your middle or hips. Medicine defines an endocrine organ as something that secretes compounds (hormones) into the bloodstream which then circulate and act on an another organ — think of the pituitary gland secreting hormones to control bodily growth, the thyroid, the adrenal gland and the reproductive organs. We now know of at least 10 hormones secreted by fatty tissue (they’re called adipokines, but they’re hormones nonetheless). Their actions are in the early stages of being mapped out. One of them is Leptin (which you may have heard of). Very likely there are more adipokines to be found.

    Lastly — an exercise for the reader — a phrase that drives me nuts in math books — what about other countries? Do they have anything like NHANES? If they have it, how far back does it go? My gestalt impression (e.g. no data to back it up) is that Asians (in Asia) smoke a lot more but are a lot thinner than we are. The fact that we led the world in health and no longer do, may reflect the terrible shape most of the rest of the world was in after WWII. It is another exercise for the reader to plot life expectancy from ’46 to now in various countries (assuming the data is available and if available just how accurate it is).

    Thanks for all the comments. See you in a week or so.

  • Mike  On August 24, 2009 at 10:27 am

    How do we know that the obese people are living longer than they used to?

    If fat people died a year earlier than they would have a decade ago, but nonfat people died a few years later, life expectancy would increase for the population as a whole even if obesity was a drag on life expectancy.

  • Lemmy Caution  On August 26, 2009 at 7:59 pm

    This interesting NYT article suggests that it could be epigenetics:

  • wriggles  On October 17, 2009 at 6:54 am

    Very likely, many more than 31% of them are obese.

    Go to hospital and find out for yourself, I have recently and (and previously ) found your statment to be incorrect-in the UK anyway.

    Agree that BMI has major shortcomings, but the advantage of easy data availability.

    Yeah, IOW, facilitates laziness.

    fat is no longer regarded as a turgid lump of goo just sitting around your middle or hips.

    For ‘regarded’ read, somebody bothered to check that the metaphorical overspill from fat as all things sluggish and lazy, wasn’t correct.

    I just love it when people are so forgiving about their own indolence, it makes a nice change.


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