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[A1CR]

In this post (February 7, 2004 ), MR provides evidence that when factors like weight loss due to smoking and illness are properly accounted for, there is a clear inverse relationship between body mass index (BMI) and longevity. In other words, the thinner you are, the longer you're likely to live. This contrasts with the J-shaped or U-shaped mortality curve as a function of weight reported by some poorly controlled (according to MR) studies.

Someone wrote:
>
> On 5 Feb 2004, Another Someone wrote:
> >
> >Just how much does just cutting back on obesity help? CR starts from the
> level of benefit realized by only being normal weight versus obese.

> The article [1] describes a U shaped longevity curve with
> optimum BMI at 23-25 for whites. Of course, we know that some people with
> low BMI have low BMI because they're sick, so this could possibly account
> for part of the reason why the minimum is at a reasonably high BMI (in CR
> terms).

Indeed, many previous studies have pointed out just this problem; (2)
found that "The [j-shaped] shape of the morality risk vs baseline BMI
curve varied due to a bias (late-life bias) caused by a steep decrease
in BMI among the elderly toward the end of the lifespan [suggesting
late-life cachexia or disease-associated weight loss] ... Using
average-adulthood BMI as mortality predictor and baseline BMI as
covariate was very effective in removing the late-life bias. .. and
yielded robustly positive mortality risk vs average-adulthood BMI curves
in all analyses in which it was tested. ... Among non-elderly persons,
being leaner meant a lower mortality risk, down to the lowest category
of leanness in the study: <20 kg/m(2)."

(3) reports that "In analyses adjusted only for age, we observed a
J-shaped relation between body-mass index and overall mortality", but
"When women who had never smoked were examined separately, no increase
in risk was observed among the leaner women, and a more direct relation
between weight and mortality emerged ... In multivariate analyses ...
in which *the first four years of follow-up were excluded* [again
screening out early mortality relateed to cachexia or wasting from
disease], the relative risks of death from all causes ... were as
follows: body-mass index < 19.0 (the reference category), relative risk
= 1.0; 19.0 to 21.9, relative risk = 1.2; 22.0 to 24.9, relative risk =
1.2; 25.0 to 26.9, relative risk = 1.3; 27.0 to 28.9, relative risk =
1.6; 29.0 to 31.9, relative risk = 2.1; and > or = 32.0, relative risk
= 2.2 (P for trend < 0.001)."

Most recently, (4), which included women from the Nurses' Health Study &
men in the Health Professionals Follow-up Study (ie, the most powerful
epidemiology in the world today, based on cohort size, uniformity of
socioeconomic status, funding, duration, quantity & quality of data
collectioin, etc) found that "the dose-response relationship between BMI
and the risk of developing chronic diseases was evident even among
adults in the upper half of the healthy weight range (ie, BMI of
22.0-24.9), suggesting that adults should try to maintain a BMI between
18.5 and 21.9 to minimize their risk of disease." -- and lest anyone
think that this means that BMI between 18.5 and 21.9 was thus BETTER
than a lower BMI, this article actually fudges the issue, by NOT
including anyone with a BMI < 18.5: subjects "were excluded from the
analysis if they ... were underweight (BMI in 1986 <18.5; 1131 women
and 151 men)"; ie, the implication that a BMI <18.5 is somehow not as
healthy as one in the 18.5 - 21.9 range is based on first THROWING OUT
anyone who was in the former range!

Many epidemiological reports fail to make these kinds of adjustment. (5)
reports that when the Harvard epidemiological team "examined the 25
major prospective studies on the subject[,] Each study had at least one
of three major biases: failure to control for cigarette smoking,
inappropriate control of biologic effects of obesity, such as
hypertension and hyperglycemia, and failure to control for weight loss
due to subclinical disease. The presence of these biases leads to a
systematic underestimate of the impact of obesity on premature mortality."

" Although these biases preclude a valid assessment of optimal weight
from existing data, available evidence suggests that minimum mortality
occurs at relative weights *at least* 10% below the US average" -- this,
NB, before the explosion of obesity from overconsumption of carbohydrates in the
late 80s and onward.

> Nonetheless, the statement you made above certainly doesn't follow
> from the article that you posted.

You're right; but of course, the study isn't equipped to do so. The
effects of CR are distinct from those of obesity-avoidance, AND CR is
about Calorie consumption rather than body weight in any case. I rather
wish folks would stop posting abstracts of studies that show little else
than the hazards of obesity
or the benefits of normal weight as only vs. 'healthy weight' -- they're
off-topic yawners.

A valid epidemiological test of CR's human applicability is to assess
Calories, not weight, and to look at EXTREME longevity (ages > 80),
where simple environmental toxicity is no longer cutting peoples' lives
SHORT and aging per se becomes the overwhelming factor in mortality (6).

> The CR experiments compare lifespan enhancements to those of overweight
> control mice,

As most people who read the List or the primary literature know by now,
this is NOT the case for nearly any modern CR studies: the 'AL' cohorts
are restricted by 10-20%, precisely to avoid the confounding effects of
obesity.

> so it's not fair to say that CR lifespan enhancement starts
> (at least as far as the experiments go) at normal weight.

It's not fair to say that CR lifespan enhancement starts at ANY weight.
CR is about *Calorie intake* -- not body weight (or BMI, %fat, etc etc).

-MR

>
1. McGoldrick, Kathryn E.
Years of Life Lost Due to Obesity.
Survey of Anesthesiology. 48(1):56-57, February 2004.
[No PMID]

2. Greenberg JA.
Biases in the mortality risk versus body mass index relationship in the
NHANES-1 Epidemiologic Follow-Up Study.
Int J Obes Relat Metab Disord. 2001 Jul;25(7):1071-8.
PMID: 11443509 [PubMed - indexed for MEDLINE]

3. Manson JE, Willett WC, Stampfer MJ, Colditz GA, Hunter DJ, Hankinson SE,
Hennekens CH, Speizer FE.
Body weight and mortality among women.
N Engl J Med. 1995 Sep 14;333(11):677-85.
PMID: 7637744 [PubMed - indexed for MEDLINE]

4. Field AE, Coakley EH, Must A, Spadano JL, Laird N, Dietz WH, Rimm E,
Colditz GA.
Impact of overweight on the risk of developing common chronic diseases
during a 10-year period.
Arch Intern Med. 2001 Jul 9;161(13):1581-6.
PMID: 11434789 [PubMed - indexed for MEDLINE]

5. Manson JE, Stampfer MJ, Hennekens CH, Willett WC.
Body weight and longevity. A reassessment.
JAMA. 1987 Jan 16;257(3):353-8.
PMID: 3795418 [PubMed - indexed for MEDLINE]

6. Perls T.
Genetic and environmental influences on exceptional longevity and the AGE
nomogram.
Ann N Y Acad Sci. 2002 Apr;959:1-13. Review.
PMID: 11976180 [PubMed - indexed for MEDLINE]