nos-trum. pronunciation: \nos'-trum\. noun. Etymology: Latin, neuter of noster our, ours.
1. a medicine of secret composition recommended by its preparer but usually without scientific proof of its effectiveness.
2. a usually questionable remedy or scheme.
See here for more discussion.

Sunday, December 5, 2010

"I'm Just A Little Overweight. Isn't That OK?" Apparently Not.

 
I'm feeling guilty that I haven't published an in-depth look at a piece of research in a while.  Here's one.  This post addresses the conflicting evidence over whether being a little overweight is good, bad, or neutral.

For some time now, population studies have been published that tried to pin down whether there's a higher mortality rate in those people who are overweight, but not obese.  It's clear that obesity predisposes to other health problems that can shorten life, but what about if you're just 20 pounds over your ideal?  Some studies have shown that having a little heft is actually beneficial, some have not.

A group of public health researchers decided to take a huge population base, factor out people with significant health problems, and see whether a BMI in the range of 25-30 is a mortality risk by itself.  New England Journal of Medicine, 2 Dec 2010, "Body-Mass Index and Mortality among 1.46 Million White Adults."

Recall that below 25 is not overweight, 25-30 is overweight, and over 30 is obese.

They pooled data from 19 studies.  This gave them about 1.5 million subjects (ranging in age from 19-84, 58% women).  All were White (Non-Hispanic), which is the largest subset they could have chosen.  It's a limitation, but they weren't trying to be inclusive; leaving out other ethinicities eliminates some cultural and genetic differences that could have been confounding variables.

Over a 10-year median followup there were 160,000 deaths.  Hazard ratios were calculated against BMI, and the graphs showed:


 
There's an increased hazard ratio both below and above optimal weight (called a J-curve).

Caveats:  (1) "Healthy" subjects meant that they didn't have heart disease or cancer--other potential causes of mortality weren't included.  (2) Healthy also was ascertained only at the beginning:  subjects could have gotten sick later.  (3)  This is a meta-analysis of pooled previous study data (we've talked about this in previous posts...not bad, just a caution.  (4) Data on height, weight, and health were from self-reporting, which is fallible.

And lastly, BMI as a measure of "fatness" is not perfect;  a short weight-lifter could have little fat, but a high BMI.

For Onion Peelers,
Here's the data for women.  With a BMI of 22.5 to 24.9 as the reference category, hazard ratios were 1.13 (95% CI, 1.09 to 1.17) for a BMI of 25.0 to 29.9; 1.44 (95% CI, 1.38 to 1.50) for a BMI of 30.0 to 34.9; 1.88 (95% CI, 1.77 to 2.00) for a BMI of 35.0 to 39.9; and 2.51 (95% CI, 2.30 to 2.73) for a BMI of 40.0 to 49.9.  Men were similar. [CI = confidence intervals]

You might be asking yourself why "healthy" people with very low BMI's are at increased risk.  The authors speculate that it's due to persons who subsequently developed a health problem, or are malnourished.

As research, this is not completely definitive (none ever is), but it's a strong indicator that even being overweight--and not obese--is a risk factor.

However, given the other thousands of risk factors we participate in, it's not anywhere near the top.

Doc D

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