In this cohort of older women, we found that MUFA intake was associated with less cognitive decline over a three year period. Previous studies generally but not invariably support this association. One previous prospective study found increased dietary MUFA intake to be associated with less cognitive decline,10
a second found a trend in the same direction,9
a third found a trend in the same direction in restricted analyses,6
and three others were null.7, 8, 11
Among the null studies, none of them had multiple measures of diet, although one assessed diet through a measure of fatty acid composition of erythrocyte membranes.7
However, that study assessed cognitive decline exclusively with the Mini-Mental State Examination, which is likely not as sensitive as the neuropsychological test battery used in this study.
MUFAs are thought to be one of the major protective components of the traditional Mediterranean diet, where they are consumed primarily from olive oil (46 g/d or 4 tbs/d).10
Two recent prospective studies of Mediterranean diet have found greater adherence to be associated with less cognitive decline or Alzheimer Disease (AD) incidence.31, 32
One of these studies found an effect of Mediterranean diet on an individual cognitive domain, namely memory.31
This finding is consistent with the observed protective effect of MUFAs on memory in the WHI CCW. In addition, we found an association of MUFAs with less decline in visual-spatial abilities (copying and matching), a finding not previously made to our knowledge. Decline in visuospatial function has been associated with driving errors in older adults 33
and has also been suggested as a potential predictor (along with amnestic impairment) of transition from mild cognitive impairment to Alzheimer's disease.34
Several pathways may explain the apparent relationship of MUFA intake with cognitive function. MUFAs and MUFA derivatives have anti-inflammatory effects in vivo
This may be important since chronic inflammation appears as a precursor of symptomatic AD.37-39
Oxidative stress has also been demonstrated in patients with mild cognitive impairment and AD,40
and derivatives from MUFAs, including low molecular weight phenols, have been found to have anti-oxidant effects.41
MUFAs may also exert their potentially beneficial effects on cognition indirectly by decreasing cardiovascular risk through reducing macrophage uptake of plasma oxidized low-density lipoprotein, reduction of apolipoprotein B and reduction of triglycerides.42-44
Intakes of SFA, TFA and DC were not associated with cognitive decline in this cohort of relatively healthy elderly women. SFA had a protective effect on cognitive decline in the partial model, which is likely due to confounding by MUFA, which was moderately correlated with SFA. However, there was no association between SFA and cognitive decline in the fully adjusted model. Previous prospective studies found dietary SFA intake to be either deleterious(5-8) or null10, 11
in associations with cognitive decline. Similarly, previous prospective studies found TFA intake to be either deleterious9
or trending towards deleterious effects6
. Of note, these studies had substantially higher absolute and relative SFA and TFA intakes than did the women in this study, and hence the deleterious effects of these fatty acids may be limited to individuals with higher levels of intake.
Strengths of this study include the use of a battery of sensitive cognitive tests, rather than a global cognitive instrument in order to better detect the fairly small changes that were anticipated over 3 years in this group of generally healthy, well-educated women who were cognitively intact at baseline. Assessment of multiple domains of cognition allowed for a more detailed characterization of cognitive effects. Another strength of this study is the administration of a validated FFQ at two time-points rather than a single measurement, as was done in most prospective studies of MUFAs and cognitive decline.6-11
Finally, the WHI and CCW measured a wide variety of characteristics of subjects, allowing for the ability to control for various potential confounders and interactions in a systematic fashion.
Limitations of this study include the modest sample size and follow-up time of 3 years, which may preclude detection of modest long-term effects on cognition. This limits the ability to adjust for potential confounding among dietary fatty acids and to detect non-linear associations. This may contribute to why associations between SFA and TFA intake and cognitive decline were null. Limitations of using FFQs for dietary assessment include restrictions imposed by a fixed list of foods, reliance on memory, perception of portion sizes, and interpretation of questions. Also, blood fatty acid measurements, which are objective but can also have limitations of measurement error, were not available for our analyses. However, the FFQ used in this study was validated against a 4-day food record, which does not share these limitations. As with any observational study, we can not rule out the possibility of residual confounding by unknown risk factors, such as a generally healthier lifestyle of individuals with a higher MUFA intake. Finally, our study population consisted of primarily healthy, highly educated, older, Caucasian women, which limits the generalizability of these findings to other populations.
In conclusion, we found dietary MUFA intake to be associated with less cognitive decline in older women. Dietary intakes of SFA, TFA and DC were not associated with cognitive decline. Further larger, prospective studies with longer follow-up time are needed to confirm the possible protective effects of MUFAs for cognitive decline