DFA: Linoleic Acid (LA) and Intermediate Health Outcomes (2011)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To test the hypothesis that, independent of potential confounders, total plasma PUFA levels or specific fatty acids are cross-sectionally correlated with peripheral nerve function, and low compared with normal total PUFA levels or specific fatty acids levels predict accelerated decline of peripheral nerve function over a three-year follow-up.

Inclusion Criteria:

Participants were a part of a population-based sample of men and women enrolled in the InCHIANTI study in the Tuscany region of Italy.


Exclusion Criteria:

Individuals not enrolled or excluded from the InCHIANTI study.

Description of Study Protocol:


Individuals participating in the InCHIANTI longitudinal study.


Prospective, observational, longitudinal study among an aging population.

Statistical Analysis

Log-transformed values were used in the analysis. Continuous values were reported as means with standard deviation information. Age- and sex-adjusted partial correlation coefficients and Spearman partial rank-order correlation coefficients were used to study the correlation between baseline characteristics and follow-up measurements. Mean values of the main classes and the specific types of fatty acids were compared across groups at enrollment. Multivariate regression analyses were performed on the independent and dependent variables.

Longitudinal analysis were restricted to the participants who had complete baseline and three-year follow-up data. They performed a repeated-measures analysis. The effect of baseline plasma PUFA levels on change over time in nerve function was tested in step-wise regression models, where follow-up nerve function was the dependent variable, baseline plasma PUFA levels were the main independent variable and baseline nerve function and other potential confounders were considered covariates.

Data Collection Summary:
  • Timing of measurements: Baseline and three-year follow-up
  • Dependent variables: Nerve conduction velocity (NCV)
  • Independent variables: Fatty acid concentrations
  • Control variables: Aging population drawn from the Tuscany Region of Italy.
Description of Actual Data Sample:
  • Initial N: 1,530 subjects; 94% or 1,453 subjects agreed to participate in this study
  • Attrition (final N): 1,076 subjects were re-evaluated at the three-year follow-up, 854 underwent a new nerve study and 827 had a new interview at the three-year point
  • Age: 68.2 years with a range of 24 to 97 years
  • Ethnicity: Italian adults
  • Other relevant demographics: 384 men and 443 women in the study
  • Anthropometrics: BMI of about 27 for the participants. BMI held steady for the duration of the study.
  • Location: Tuscany region of Italy.
Summary of Results:

Key Findings

At baseline, BMI and triglycerides were positively correlated with nerve conduction velocity (NCV). Total cholesterol was positively and diabetes negatively correlated with both NCV and compound mass action potential (CMAP). Peripheral artery disease (PADs) was negatively correlated with NCV. Similar results were observed at follow-up.

At enrollment, omega-6 fatty acids and linoleic acid were positively associated with nerve velocity. However, NCV was significantly different between age groups (higher in the youngest subjects) and, overall, declined significantly over the three-year followup period. For CMAP, they found that CMAP was significantly different between age groups (higher in the youngest) and, overall, declined over the three-year period. The decline in CMAP is steepest in the youngest subjects and becomes progressively less steep in the older subjects. 

Total PUFA, omega-3 and omeg-6 concentrations declined with age. Saturated fatty acids were associated with more decline of NCV and CMAP in participants between 65 and 84 years of age. Higher baseline total plasma PUFA and omega-6 fatty acids predicted significantly less decline between 65 and 84 years of age. Linoleic acid predicted significantly less decline of CMAP in all participants.

The ratio of n-6 to n-3 was associated with significantly less reduction of NCV after the three-year follow-up period.

Other Findings

When the analysis was restricted to the 753 subjects free of diabetes, the results were unchanged. 

Author Conclusion:

Low plasma omega-6 and omega-3 fatty acid levels were associated with accelerated decline of peripheral nerve function with aging. The findings of this study raise the possibility that omega-6 fatty acids and DHA supplementation may be effective in treatment of peripheral neuropathy. This possibility should be carefully considered and examined in future trials of essential fatty acid supplementation.

Funding Source:
Government: NIH, National Inst. of Agining, USA and Italian Ministry of Health
Reviewer Comments:
  • A better description of the InCHIANTI study recruitment procedures would have been helpful
  • Also, it was somewhat unclear if the participants made an attempt to change their diet or follow a particular diet during this time frame.
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? Yes
  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? Yes
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) N/A
  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.) No
  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? Yes
  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.) Yes
  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? Yes
  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? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  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.) N/A
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? Yes
  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? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  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? No
  6.6. Were extra or unplanned treatments described? No
  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? N/A
  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)? Yes
  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? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes