Drawing on disparate lines of evidence, some researchers have been building a case that dietary fat intake affects dementia risk (see related news item). For example, higher dietary cholesterol increased cerebral Aβ deposition in some animal experiments, and certain polyunsaturated fats may have antiinflammatory properties, which might counteract the alleged inflammatory contribution to dementia. Some, but not all, epidemiologic studies have linked higher serum levels of cholesterol (mostly during midlife) with higher dementia risk, and cholesterol-lowering drugs such as statins appear to reduce the risk of Alzheimer's dementia. Indeed, earlier results from the Rotterdam study have contributed to this theory (see Kalmijn et al., 1997), finding that high intake of total fat and low intake of fish (with its high levels of cis n-3 polyunsaturated fatty acids) were significantly associated with risk of dementia at the two-year follow-up in the Rotterdam study.

Now Monique Breteler and her colleagues in the Netherlands at the Erasmus Medical Center and at the University of Utrecht report the findings of six years of follow-up in the study of elderly residents (55 years or older at baseline) of a suburb of Rotterdam. Of the 5,395 subjects whose baseline and follow-up exams included complete dietary data, 197 (seven percent) had developed dementia (146 with AD; 29 with vascular dementia; and 22 with other dementias).

The researchers found no contribution to dementia risk from the intake of total fat, saturated fatty acids, or trans-unsaturated fatty acids, or from dietary cholesterol (adjusted for age, gender, total energy intake, and vitamin E intake). Conversely, dietary intake of the so-called "good" fatty acids, the cis mono- or polyunsaturated fatty acids, failed to reduce AD risk. These findings held true for all dementias, vascular dementia, and AD, and when additional lifestyle elements were factored in (e.g., smoking, alcohol, fruit and vegetables, dietary supplements, body mass index). Similarly, excluding patients using lipid-lowering drugs, or those with myocardial infarction or diabetes, did not change the results.

"Given the limited number of studies on fat intake and risk of dementia, we think it is premature to conclude from our observational study that cholesterol or cholesterol-affecting fats are not associated with risk of dementia or its subtypes. Larger, prospective studies with longer follow-up periods are needed to confirm our findings," the authors caution in their conclusion.Hakon Heimer.

References:
Englehart MJ, Geerlings MI, Ruitenberg A, van Swieten JC, Hofman A, Witteman JCM, Breteler MMB. Diet and risk of dementia: Does fat matter? Neurol. 2002;59:1915-21. Abstract

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