Re: The Joint Effects of Physical Activity and Body Mass Index on Coronary Heart Dis

[Guest guest]

Hi Bill:

Thank you, what a very interesting study. It seems to confirm what many of us have long suspected - that plenty of exercise is clearly beneficial for people who are obese or overweight, but almost certainly counter-productive for people at an essentially-healthy BMI of, say, 20.

Take a look at what the numbers from this study seem to say (my comments about them follow):

Relative Risk

-----------------------

BMI active inactive

------ ------------ -----------

~32 1.87 2.53

diff 0.33 0.65

~27.5 1.54 1.88

diff 0.54 0.80

~23.5 1.00 1.08

------ ------------ ----------

diff 0.54? 0.80?

~20 0.46? 0.28?

What I have done in the above table is this:

First, I have assumed that the average BMI of those in the study with a BMI above 30 was ~32·5. That for those defined as 'overweight' the average BMI was 27·5. And for those of 'normal weight' the BMI averaged 23·5 (since there will be few at the lower end of the 18·5 to 25·0 range).

Second, I have entered the risk data provided by the abstract associated with those three groups in the table.

Third, I have calculated the change in risk ('diff') as BMI declines, and entered those data in the table also.

Note the following: As BMI declines, risk declines much more quickly for those who are inactive than for those who are active. So, while the risk is much higher for the inactive obese than for the active obese, there is hardly any difference in risk between the active and inactive at the lowest BMI category in the study (1.00 vs. 1.08 not statistically significant).

So the question which immediately rears its head is: what would the risks be for people with, say, a BMI of 20 (i.e. for people ~like us)?

It seems very likely that as BMI declines to around 20 the risk will continue to fall faster for the inactive than for the active, as it did at higher BMI levels. The inevitable result must be that, since the benefit of exercise at BMI=~23·5 is only marginal, and with risk falling faster with BMI for inactive individuals, then at a BMI of ~20 the risk for inactive people will be lower than for active people.

This confirms the data we saw in a mouse experiment posted recently which showed higher mortality among restricted exercising mice, than in restricted sedentary mice.

This strongly suggests that if one is intrinsically healthy and at the kind of body weight we here take as being appropriate (BMI ~20 perhaps) then the best health and longevity is going to be associated with that modest threshold amount of activity that, as we all acknowledge, is vital for decent health. (Little old ladies who are bed-ridden do not survive for long. And, for that metter, not even totally inactive middle aged males either - Reeve for example).

As Dr. Henry said in 'The Exercise Myth', and contines to believe today: "Fitness has absolutely nothing to do with health." These data seem to confirm that exercise in an amount beyond the rather modest threshold amount required is counter-productive for people established on a significant degree of CRON.

But of course, as with everything else concerned with health, we each must place our own bets where we judge them likely to provide the most benefit.

: ^ )))

Rodney.>> The Joint Effects of Physical Activity and Body Mass Index on Coronary> Heart Disease Risk in Women> > Amy R. Weinstein, MD, MPH; D. Sesso, ScD, MPH; I-Min Lee, MBBS,> ScD; M. Rexrode, MD, MPH; R. Cook, ScD; JoAnn E. Manson,> MD, DrPH; E. Buring, ScD; J. Gaziano, MD, MPH> > Arch Intern Med. 2008;168(8):884-890.> > ABSTRACT > > Background Physical activity and body mass index (calculated as> weight in kilograms divided by height in meters squared) independently> alter the risk of coronary heart disease (CHD); however, their> combined effect on CHD is not established. Our objective was to study> the combined association of physical activity and body mass index on CHD.> > Methods Prospective cohort study of 38 987 women free of> cardiovascular disease, cancer, and diabetes at baseline in the> Women's Health Study, with 10.9 mean years of follow-up. Weight,> height, and recreational activities were reported on entry. Body mass> index was categorized as normal weight (<25), overweight (25 to <30),> and obese ( & #8805;30). Active was defined as 1000 kilocalories or more> expended on recreational activities weekly. Six joint body> weight–physical activity categories were defined. The main outcome> measure was the occurrence of incident CHD during follow-up, defined> as a cardiovascular event including nonfatal myocardial infarction,> coronary artery bypass graft, percutaneous transluminal coronary> angioplasty, or CHD death.> > Results A total of 948 cases of incident CHD occurred during> follow-up. Higher body mass index and physical inactivity were> individual predictors of CHD. In joint analyses, compared with active> normal-weight individuals, the multivariate-adjusted hazard ratios> (95% confidence intervals) were 1.54 (1.14-2.08) for> overweight-active; 1.87 (1.29-2.71) for obese-active; 1.08 (0.84-1.39)> for normal weight–inactive; 1.88 (1.46-2.42) for overweight-inactive;> and 2.53 (1.94-3.30) for obese-inactive. Increasing levels of walking> also resulted in significant reductions in CHD risk for overweight and> obese individuals.> > Conclusions The risk of CHD associated with elevated body mass index> is considerably reduced by increased physical activity levels.> However, the risk is not completely eliminated, reinforcing the> importance of being lean and physically active.> > Full text:> > http://archinte.ama-assn.org/cgi/content/full/168/8/884>