Using data from a population of elderly home-care clients with clearly defined differences in cognitive function and dementia status, we found moderately strong correlations between dietary intake of EPA + DHA, estimated from an interviewer-administered FFQ, and the total very-long-chain omega-3 fatty acid content of plasma phospholipids. Our results were consistent in subjects with lower cognitive function (MMSE score ≤ 24) and those clinically diagnosed with mild cognitive impairment or dementia. These results suggest that the FFQ, in the context of interviewer administration, may be a valid method of assessing very-long-chain omega-3 fatty acid intake in mildly-to-moderately impaired elderly adults.
In mild-to-moderate cognitive impairment and dementia and, to a lesser extent, in normal aging, episodic memory
or recall of specific details becomes reduced, while recognition
or generic memory is generally maintained (6
). Because FFQs rely on the ability to recognize and report usual dietary routines rather than more specific details of individual meals (3
), we hypothesized that the FFQ would be a valid method of collecting dietary intake data in mildly-to-moderately cognitively impaired elderly persons. Our results support this hypothesis.
Our results are also consistent with biomarker-based validations of this FFQ conducted in populations of non-cognitively impaired adults. Coefficients for the correlation between FFQ estimates of omega-3 fatty acid intake (percentage of total fat) and adipose tissue concentrations have been reported for postmenopausal women (EPA + DHA, r
), male health professionals (EPA only, r
), and older African-American prostate cancer patients (EPA + DHA, r
). In a study of older Costa Rican adults, Baylin et al. (35
) reported lower correlations between adipose tissue concentrations and dietary EPA (r
0.15) and DHA (r
0.18), possibly because of infrequent fatty fish consumption in the population. Correlations between diet and erythrocyte membrane concentrations of EPA and DHA have been reported in 2 analyses of middle-aged participants in the Nurses’ Health Study (for EPA, r
0.38 and for DHA, r
); for EPA, r
0.32 and for DHA, r
)). Correlations between estimated DHA and EPA intakes (g/day) and plasma phospholipid concentrations (for EPA, r
0.19; for DHA, r
0.38) have also been reported among middle-aged men and women in the Atherosclerosis Risk in Communities Study (38
). Data in our unique population are comparable to those in these reports and suggest that this FFQ, with interviewer administration, performs equally well despite the measurable cognitive impairments in our study population.
Reporting of type of fish consumed appeared less accurate in the lower cognitive function and dementia diagnosis groups. This may indicate a reduced ability of these persons to recall specific details on food items consumed. Correlations with “total fish” were not weaker; thus, the ability to self-report overall frequency
of consumption, the general pattern of intake, appeared to be preserved. Despite these differences, our results are consistent with a previous report of associations between self-reported fish consumption using this FFQ and biomarkers of very-long-chain omega-3 fatty acids. In middle-aged women in the Nurses’ Health Study, r
values for correlation between total fish intake (servings/week) and whole plasma or erythrocyte membrane concentrations of very-long-chain omega-3 fatty acids were 0.35 and 0.42, respectively (37
The NAME Study had several strengths with regard to the investigation of cognitive function and the validity of dietary self-reports in older adults. Thirty-two percent of the NAME validation sample met the definition of impaired cognitive function, based on MMSE scores less than or equal to 24. This large proportion allowed us to assess the data on the basis of a commonly used and clinically relevant cutoff score. Additionally, we had large proportions of subjects with clinical diagnoses of dementia (23%) and mild cognitive impairment (30%). While MMSE scores, and thus cognitive functioning, are known to be significantly lower in subjects with dementia, the two do not necessarily coexist in individuals. In our sample, 52% of the low-MMSE group was also clinically diagnosed with dementia, whereas 21% was clinically normal. Thus, we were able to assess the impact of cognitive functioning as well as clinical disease on the validity of the FFQ to estimate EPA and DHA intakes.
One important difference from previous validation studies of this FFQ was our use of interviewer administration. The NAME population was entirely composed of elderly home-care clients who had some degree of functional disability or chronic disease and a wide range of educational backgrounds. Proxy respondents were not utilized during data collection, since the majority of subjects (72%) lived alone. Interviewer administration was used to maximize the completeness of the FFQ data in all possible subgroups and to ensure that physical disability would not affect completion or mailing of the form. While our results cannot be generalized to populations in which the FFQ is self-administered, we expect that interviewer administration was one factor responsible for our consistently strong results across cognitive groups.
Limitations of our results include the inability to generalize our findings to more severely impaired persons. The low MMSE scores in our sample were indicative of only mild-to-moderate impairment (the range was 16–24 in the low group), while severe impairment is represented by MMSE scores closer to and below 10. However, we would not expect the FFQ to perform similarly well among severely impaired persons. Our use of a widely used cognitive screening tool, the MMSE, does allow our findings to be interpreted in many populations and research settings.
We were also limited by our use of a single fasting blood sample as a biomarker for long-term dietary intake. Plasma phospholipid fatty acid composition reflects dietary intake over the previous 1–2 months (39
), and measurements at multiple time points would have better reflected long-term intake of dietary EPA + DHA and matched the time frame captured by the FFQ. However, because our analysis was an ancillary addition to an existing observational study, we were unable to obtain fatty acid profile data beyond the single blood drawing. Correlation coefficients observed in the current analysis may be underestimates of the true associations.
We confined our analyses to dietary very-long-chain omega-3 fatty acids. This decision was based upon the potential importance and utility of the results (direct measurement of fatty acid status in most research settings is not feasible), as well as the unique opportunity provided by the narrow distribution of these fatty acids in the food supply. The known relative differences in concentrations of very-long-chain omega-3 fatty acids between types of fish (i.e., fatty vs. lean) allowed us to explore possible differences in the self-reporting of information stored as generic memory (reporting a regular pattern of intake) as compared with episodic memory (recall of specific details of intake). Caution may be required when the analytic focus of research is an individual food item (i.e., a specific type of fish) rather than total estimated intake of a nutrient.
Our data suggest that interviewer administration of the FFQ may be a valid method of estimating EPA + DHA intake among community-dwelling elders regardless of the presence of mild-to-moderate cognitive impairment or a diagnosis of dementia. Whether this conclusion can be extended to other nutrient intakes is yet to be determined.