BMJ  2005;331:454 (20 August), doi:10.1136/bmj.331.7514.454-a

Letter

Obesity in middle age and future risk of dementia

Problem is probably greater for women

EDITOR—The paper by Whitmer et al supports the findings of an earlier study in showing that obesity in middle age predicts dementia in older age.^{1 2} The major apparent weakness of the study is the loss of 13 014 patients to follow-up. Their adiposity and sociodemographic characteristics at study entry (1964-73: n = 25 290) were reported to be the same as those who were followed up to 1994-2003. That is important. Their medical and physical characteristics are also important. We are left to accept that they were similar also. The similarity or otherwise needs to be presented with the paper.

Table 1 shows some marked differences among the people who were later diagnosed with dementia: education to grade school level only (11.1%) compared with additional education (6.9%), black race (8.9%) compared with white race (7.1%) and Asian or other races (5.5%). Adjustment for these confounders did apparently not modify the risk of the diagnosis of dementia related to obesity significantly.

The effect of obesity and overweight was more apparent in women. The lesser effect of obesity in men is dealt with by the statement that there were fewer obese and overweight men and that the power to detect an effect was therefore reduced. It is, however, clear from the text and table 2 that there were in fact more obese and overweight men (n = 2546) than women (n = 1804).

Further confusion arises from consideration of the sister paper derived from the same database.³ In that paper the effects of midlife risk factors (smoking, hypertension, cholesterol, and diabetes) on the subsequent diagnosis of dementia are reported. The exclusion of people with missing data reduces to 8845 the numbers followed up to 1994-2003. Fewer subjects have not been diagnosed with dementia (8124 v 9563), yet more are so diagnosed (721 v 713). How that came about is difficult to explain unless the follow-up was longer. Reading the two papers together indicates no difference in time bases for acquisition of the data.

Despite problems the paper by Whitmer et al shows that dementia in women (probably) and in men (possibly) is influenced by obesity in the middle of life and late life and overweight, determined by body mass index, and supported by measures of skinfold thickness. A study from Sweden generated similar conclusions, applicable to women but not to men.⁴

Heart Research Centre, Melbourne, VIC 3050, Australia heart{at}medicine.unimelb.edu.au

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Competing interests: None declared.

References

1. Whitmer RA, Gunderson EP, Barrett-Connor E, Quesenberry CP, Yaffe K. Obesity in middle age and future risk of dementia: a 27 year longitudinal population based study. BMJ 2005;330: 1360-2. (11 June.)[Abstract/Free Full Text]
2. Gustafson D, Rothenberg E, Blennow K, Steen B, Skoog I. An 18-year follow-up of overweight and risk of Alzheimer disease. Arch Intern Med 2003;163: 1524-8.[Abstract/Free Full Text]
3. Whitmer R.A, Sidney S, Selby J, Claiborne Johnston S, Yaffe K. Midlife cardiovascular risk factors and risk of dementia in late life Neurology 2005;64: 277-281.[Abstract/Free Full Text]
4. Rosengren A, Skoog I, Gustafson D, Wilhelmsen L. Body mass index, other cardiovascular risk factors and hospitalization for dementia. Arch Intern Med 2005;165: 321-6.[Abstract/Free Full Text]

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Relevant Article

Obesity in middle age and future risk of dementia: a 27 year longitudinal population based study

Rachel A Whitmer, Erica P Gunderson, Elizabeth Barrett-Connor, Charles P Quesenberry, Jr, and Kristine Yaffe
BMJ 2005 330: 1360. [Abstract] [Full Text] [PDF]