Adiposity and weight change in mid-life in relation to healthy survival after age 70 in women: prospective cohort study
BMJ 2009; 339 doi: https://doi.org/10.1136/bmj.b3796 (Published 30 September 2009) Cite this as: BMJ 2009;339:b3796
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Some questions remain: Firstly, what happened with the remaining 78% of the NHS inception cohort (n=95 283)? The reader can conclude that these women were not healthy in mid-life. However, no data are reported concerning morbidity, mortality, and BMI distribution. Such information is also needed to discuss the clinical relevance of “healthy surviving” in association to BMI. Who died and who died first, lean unhealthy or overweight unhealthy women? These important questions remain unanswered. In contrast, our own recent systematic review2 and the recent Prospective Collaboration Study3 found that a BMI between approx. 22 and 28 is associated with the lowest all-cause mortality.
We also may ask, whether the analysis by Sun and colleagues was really prospective, as stated in the title of the current publication. Was the analysis of healthy survival related BMI prospectively planned in 1976? Or is it rather a retrospective analysis of self reported BMI? Sun and colleagues state that weight maintenance throughout adulthood might be associated with optimal overall health in older age. In the light of lacking transparency and probable methodological weaknesses, it is difficult to follow these conclusions.
1. Sun Q, Townsend MK, Okereke OI, Franco OH, Hu FB, Grodstein F. Adiposity and weight change in mid-life in relation to healthy survival after age 70 in women: prospective cohort study. BMJ 2009;339:b3796.
2. Lenz M, Richter T, Mühlhauser I. The morbidity and mortality associated with overweight and obesity in adulthood: A systematic review. Dtsch Arztebl Int 2009;106(40):641-648.
3. Whitlock G, Lewington S, Sherliker P, Clarke R, Emberson J, Halsey J, et al. Body-mass index and cause-specific mortality in 900.000 adults: collaborative analyses of 57 prospective studies. Lancet 2009;373(9669):1083-96.
Competing interests:
None declared
Competing interests: No competing interests
This was an unilluminating study whose results are unsurprising. The
key is in the definition of "healthy survival."
The press release describes this as being "free of major chrnoic
diseases, and [having] good cognitive, physical and mental health." The
article, however, makes clear that people were not considered to be
"healthy survivors" if they were limited "a little" in climbing a flight
of stairs, moving a table, or walking more than a mile, or if they were
limited "a lot" in running, lifting heavy objects, or climbing several
flights of stairs.
Plenty of women over 70 probably consider themselves both happy and
healthy without being able to do all these things. In fact the
definitions excluded all but 9.9% of the study group. I suspect a much
larger proportion feel like they are quite healthy and doing fine for
their age.
But if they had said fat women are much less likely to be able to
climb lots of stairs at ages over 70, or less likely to be in the top
quartile of fitness, this study would seem far less impressive! Duh!
Competing interests:
None declared
Competing interests: No competing interests
In Reply:
Lenz et al. raise three basic issues regarding our study. First, they
question the number of participants included in the analyses presented. As
indicated in the Methods, the primary and secondary analyses were
generally based on the oldest women in the cohort, since women who were
healthy, but had not yet reached age 70 years, would not qualify for
inclusion in this study of survival to age 70 years or greater as of 2000.
Thus, the participants not presented in the analyses simply did not yet
qualify for inclusion, and were not of interest for our particular
research question: the relation of mid-life adiposity to healthy survival
among those who survive age 70. Lenz et al. also pose questions regarding
who died and who died first in our study. Again, our interest here was not
in death, but in healthy survival; a quite different question. For
information regarding body mass index (BMI) and mortality, Lenz et al. can
read previous research by our group on mortality.1
Third, regarding the study design, our data were prospective since
baseline BMI was assessed well before any study outcome components were
ascertained. The definition of a prospective study is based on the data
collection procedures, since it is those procedures which can cause or
diminish bias; the timing of investigators’ conception of a particular
research question does not have any impact on the prospective nature of
our analysis and, thus, will not impair the validity of our analysis.
1. van Dam RM, Li T, Spiegelman D, Franco OH, Hu FB. Combined impact
of lifestyle factors on mortality: prospective cohort study in US women.
Bmj 2008;337:a1440.
Competing interests:
None declared
Competing interests: No competing interests