FNOA: Antioxidants (2011-2012)

Citation:
 
Study Design:
Class:
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Quality Rating:
Research Purpose:

To evaluate the effects of supplemental docosahexaenoic acid (DHA) and lutein on several cognitive domains in older adults.

Inclusion Criteria:

Healthy, non-smoking women, aged 60-80 years.

Exclusion Criteria:

Exclusion criteria included:

  • any history or biochemical evidence of lactose intolerance, liver, kidney or pancreatic disease, anemia, active bowel disease or resection, insulin-dependent diabetes, easy bruising or bleeding, bleeding disorders, hyperglycemia, hyperlipoproteinemia or alcoholism
  • individuals taking mineral oil or medications suspected of interfering with fat-soluble vitamin absorption
  • current use of steroids or non-steroidal anti-inflammatory drugs, antihistamine drugs, vaccinations within the previous 2 weeks, taking any nutrient supplement for the previous 2 months or carotenoid supplements for the previous 6 months.
Description of Study Protocol:

Recruitment

Fifty-seven healthy, non-smoking women (aged 60-80 years) were recruited from the general population for a 4 month study. 

Design  Randomized controlled trial 

Blinding used (if applicable):  double-blind.  Subjects and the experimenter were masked to the experimental groups. 

Intervention (if applicable)

Intervention trial with subjects receiving on of the following:

  • DHA (800 mg/day)
  • lutein (12 mg/day)
  • a combination of DHA and lutein
  • placebo 

Statistical Analysis

  • All cognitive outcomes were adjusted for age and education.
  • Differences between cognitive and mood scores at baseline and after supplementation were tested with Student's paired t-test within each treatment group.
  • For those variables where a significant change was found from baseline to end of study, correlations were calculated between age, education, serum levels of DHA and lutein and test scores when the distribution of test scores were normal to near-normal.
  • Regression analysis were used to examine significant associations further (p<.05) or those marginally significant (p<.1) found in initial analyses.  In those cases in which age or education were significantly related to performance on a particular test, they were entered as co-variates.
  • Because this study of cognitive performance is exploratory, unadjusted p values are reported despite the use of multiple statistical tests.
Data Collection Summary:

Timing of Measurements

  • Serum levels of DHA and lutein were obtained from blood samples taken at baseline, 2 months and 4 months
  • Food frequency questionnaires were completed at baseline, 2 months and 4 months
  • Cognitive tests were administered at baseline and 4 months 

Dependent Variables

Cognitive tests including:

  • Verbal Fluency
  • Digit Span Forward and Backward
  • Word List Memory Test
  • Memory in Reality (MIR) Apartment Test
  • Stroop Test
  • NES2 Mood Scales

Independent Variables

  • DHA supplement
  • Lutein supplement
  • DHA and lutein combination supplement
  • Placebo 

Control Variables

  • Age
  • Education
  • Dietary intakes of lutein and DHA at baseline and throughout the study
  • Changes in serum concentrations of lutein and DHA 
Description of Actual Data Sample:

Initial N: 57 women

Attrition (final N):  49 women

Age:  60 - 80 years

Ethnicity:  Not specified 

Other relevant demographics

Years of Education:

  Placebo DHA Lutein DHA+lutein
Education (years) 13.6(1.1) 16(1) 13.8(.5) 14.8(.5)

Anthropometrics:  

  • There were no significant differences among groups in terms of age or education.  Nor were there differences in dietary intakes of lutein and DHA at baseline or throughout the study.
  • At baseline, neither age nor years of education in the total samples was significantly associated with cognitive test scores of self-reported moods.
  • There were no differences in cognitive scores at baseline among the groups.

Dietary intake lutein/zeaxanthin and DHA:

  Placebo DHA Lutein DHA+lutein
Lutein/zeaxanthin (mg/day) 2.2(.5) 3.5(.7) 3(.7) 2.7(.6)
DHA (mg/day) 92(32) 143(29) 126(35) 181(71)

Location:  Boston, Massachusetts, USA  

Summary of Results:

Key Findings

Characteristics of the Study Groups

  • There were no significant differences among groups in terms of age or education.  Nor were there differences in dietary intakes of lutein and DHA at baseline or throughout the study.
  • Compliance for intake of supplements and nutrition drink was > 97%.  Furthermore, changes in serum concentrations of lutein and DHA indicated adherence to the study protocol.

Verbal Fluency

  • After supplementation, subjects in the DHA (p=.03), lutein (p=0) and DHA+lutein (p=0) supplement groups named significantly more items from a category within a minute than at baseline.  Subjects in the placebo group did not name significantly more items.

Memory and Rate of Learning

  • There were no significant increases in memory capacity, the number of items (either span or total number of items) subjects recalled on the short-term memory Forward Digit Span or Backward Digit Span tasks.
  • On the Shopping List and Word List memory tests, none of the subject groups significantly increased the number of items they recalled on the first trial during the study.
  • However, on the Shopping List memory test, subjects in the DHA+lutein supplement group learned all 10 items significantly faster, within five trials or less, after supplementation (p=.03).
  • In this group, there was also a trend toward more efficient learning on the Word List memory test, which had a maximum of three trials in which to learn the list (p=.07).
  • On the delayed recall, subjects in the DHA+lutein (p=.02) supplement group recalled significantly more items on the MIR Apartment memory test after supplementation.  However, none of the treatment groups increased the number of items they recalled after a delay on the Shopping List and Word List memory tests.

Speed and Accuracy

  • On the Pattern Recognition task, only the subjects in the placebo group (p=.04) who originally had the longest response times on average of all the groups, significantly increased their mean response speed for correct decisions.
  • None of the groups increased their accuracy rate significantly.  On average, subjects in all groups were close to ceiling in accuracy and, therefore, had little room for improvement
  • On the computerized version of the Stroop Test, none of the treatments changed mean response times for reading words or naming colors on any of the four lists. 

Mood

  • None of the groups reported significantly different moods after supplementation

Relationship Between Serum Nutrient Levels and Cognitive Performance

  • Age was the only co-variate that was significantly associated with final Verbal Fluency score.  Although subjects' scores on the Verbal Fluency test at baseline did not differ significantly by age, younger subjects recalled more instances of a category than older subjects at the end of the study (p<.05).
  • There was a trend toward a significant relationship between DHA serum levels and Verbal Fluency scores after supplementation.  With further adjustment of the model for age, DHA serum level remained significantly related to Verbal Fluency score (p=.04).  There was also a trend toward a relationship between serum DHA levels and Trials to Learn Shopping List scores with higher DHA serum levels associated with learning the list in fewer trials.
  • In contrast, the relationships between final lutein serum levels and cognitive scores in the total subject sample were not consistent with the cognitive improvement found in the lutein group after supplementation.  Because the distribution of lutein serum level at the end of the study was highly positively skewed, the variable was log-transformed to produce a more normal distribution.  No significant relationship was found between final lutein serum levels with or without log-transformation and Verbal Fluency scores.  Also, in juxtaposition to the findings for DHA, higher lutein serum levels were significantly associated with needing more trials to learn shopping lists.  However, subjects in the lutein group had the highest baseline scores for the variable Trials to Learn Shopping List and, therefore, the poorest verbal learning capacity.
Author Conclusion:

This is the first study to evaluate the effects of supplemental lutein, both alone and in combination with DHA, on cognitive performance in older adults.  The positive effects observed in this small and relatively short-term randomized trial should encourage investigation of the potential benefits of these compounds in more extensive studies. 

In this investigation, supplementation with both DHA and lutein was most reliably associated with a significant result on several cognitive tests measuring different aspects of memory.  Each of these tests required subjects to retrieve or learn and retrieve information from memory most often in a time limited or efficient fashion.  Although subject groups did not show improvement in capacity or span, indicated by the number of items they recalled on the first trial of any test, the DHA+lutein supplementation group improved in efficiency, learning shopping lists or lists of words with fewer trials on average after supplementation.  The MIR Apartment test required subjects to remember objects after only one learning opportunity with control of speed and of how they organized and remembered items as they placed them in the apartment box.   For this test, subjects in the DHA+lutein supplementation group recalled significantly more objects after a delay.   In comparison, subjects did not increase number of items recalled after a delay on other memory tests in which items were presented to them in multiple trials at a constant rate of speed by interviewer or on a computer monitor. 

It should be noted that a similar relationship between final serum levels of lutein and Verbal Fluency scores was not found.  Perhaps it is not the amount of lutein in the circulation that is important but how lutein is transported in circulating lipoproteins or integrated into tissue.  Although, macular pigment densities did not correlate with measures of cognition in this study, the enhancement of lutein accumulation across the blood-brain barrier suggests that lutein content of other cognitively important DHA-rich structures might also have been enhanced.

Supplementation of these elderly women with lutein, DHA and the combination of both significantly improved verbal fluency.  Also, the combination of supplements significantly improved subjects' memory rate of learning and learning efficiency.  Both DHA and lutein accumulate in the brain, so these effects may have occurred through increased concentrations in the brain or influences on metabolic processes that modulate brain function.  The data reported from this study suggests that combined intake of DHA and lutein has significant benefit in improving cognitive function for the elderly.  Further studies are warranted to confirm and evaluate these potential benefits.

Funding Source:
Government: US Department of Agriculture
Industry:
Mead Johnson Nutritionals and Martek Biosciences Corporation
Pharmaceutical/Dietary Supplement Company:
In-Kind support reported by Industry: Yes
Reviewer Comments:

The authors note the following limitations:

  • On the Verbal Fluency test, subject groups who had been supplemented with either DHA or lutein showed significant improvement.
  • Because this test evoked one of the least restricted ranges of scores in this subject sample, there is reason to believe that further studies might elicit improvements in cognitive status with either nutrient alone, given subject samples with more variability and possibly test with similar characteristics.
  • In particular, DHA supplementation might be better assessed in a subject group with scores less close to ceiling.  The DHA supplementation group had less room to improve than the other treatment groups.
  • On average, subjects in the placebo group appear to have been among the strongest performers at baseline on capacity or span measures of memory .
  • As with the DHA supplementation group, initially high scores might have limited the ability to detect improvement on some cognitive measures. 
  • However, placebo subject scores were not among the highest at baseline on the Verbal Fluency test, so these subjects would be at least as likely to improve as subjects in other groups.
  • Therefore, the lack of significant change on the Verbal Fluency test by the placebo group suggests that other groups' improvement should be attributed to supplementation.

Although it was stated that none of the authors had any advisory board affiliations or financial interest in any organization sponsoring the research, it was noted that two of the authors have a patent pending form the results of this research.

The sample may not have been an adequate representation of the target population as the final N was 49 and the sample contained only women.

 

Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? No
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? No
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? ???
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? Yes
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? Yes
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? No
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? No