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Recent research: fish and n-3 fatty acids

Fish, fish oils, and n-3 fatty acids are often in the health news.  Here are seven recent papers illustrating the breadth of fish oil relevance.  The papers look at treatment of rheumatoid arthritis, the potential of flax as a dietary source of n-3 fatty acids, effects on indicators of cardiovascular disease, potential protection against dementia, reduction in mortality, and importance in pregnancy.  The papers also illustrate the patchwork, three steps forward/one step back, meandering, spreading, accretion of scientific knowledge.  As the proverb goes "One swallow doesn't make a summer".  Similarly, a single research study is usually simply one brick in the gradual building of our knowledge.  For more on fish and n-3 fatty acids, see other relevant blog posts I've written, articles in the linked Connotea database, and some recommended websites.     

Arbor (2008). "Can fish oil treat rheumatoid arthritis? (296)." Arbor Clinical Nutrition Updates (296): 1-3.  These updates are apparently "the world's most widely read electronic nutrition publication for health professionals, with 100,000 readers in 186 countries."  See the Arbor website accessed November 6, 2008.
In this review of recent research, the authors conclude "ω:3 LCPUFA supplements have a role in treating RA, and may help the patient to reduce their need for NSAID drugs.  Although the impact may be moderate in comparison with conventional medication, the safety profile offers a clear potential advantage."

Barcelo-Coblijn, G., E. J. Murphy, et al. (2008). "Flaxseed oil and fish-oil capsule consumption alters human red blood cell n-3 fatty acid composition: a multiple-dosing trial comparing 2 sources of n-3 fatty acid." Am J Clin Nutr 88(3): 801-809.  [Abstract/Full Text]
Background: An increase in plasma n-3 fatty acid content, particularly eicosapentaenoic acid (20:5n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA), is observed after consumption of fish oil-enriched supplements. Because {alpha}-linolenic acid (18:3n-3; ALA) is the direct precursor of EPA and DHA, ALA-enriched supplements such as flax may have a similar effect, although this hypothesis has been challenged because of reported low conversion of ALA into DHA. Objective: To address this question, we designed a clinical trial in which flax oil, fish-oil, and sunflower oil (placebo group) capsules were given to firefighters (n = 62), a group traditionally exposed to cardiovascular disease risk factors. Design: Firefighters were randomly divided into 6 experimental groups receiving 1.2, 2.4, or 3.6 g flax oil/d; 0.6 or 1.2 g fish oil/d; or 1 g sunflower oil/d for 12 wk. Blood was drawn every 2 wk, and the total phospholipid fatty acid composition of red blood cells was determined. Results: As expected, fish oil produced a rapid increase in erythrocyte DHA and total n-3 fatty acids. The consumption of either 2.4 or 3.6 g flax oil/d (in capsules) was sufficient to significantly increase erythrocyte total phospholipid ALA, EPA, and docosapentaenoic acid (22:5n-3) fatty acid content. There were no differences among groups in plasma inflammatory markers or lipid profile. Conclusions: The consumption of ALA-enriched supplements for 12 wk was sufficient to elevate erythrocyte EPA and docosapentaeoic acid content, which shows the effectiveness of ALA conversion and accretion into erythrocytes. The amounts of ALA required to obtain these effects are amounts that are easily achieved in the general population by dietary modification.

Harris, W. S. (2008). "n-3 Fatty acids and health: DaVinci's code." Am J Clin Nutr 88(3): 595-596.  [Free Full Text
Freely viewable full text editorial on fish oils and aging - suggesting benefits for reduced mortality and slowing of dementia with long term use, but less benefit with short term interventions for mood.

He, K., K. Liu, et al. (2008). "Intakes of long-chain n-3 polyunsaturated fatty acids and fish in relation to measurements of subclinical atherosclerosis." Am J Clin Nutr 88(4): 1111-1118.  [Abstract/Full Text]
Background: Data on the relations of different types of fish meals and long-chain n-3 polyunsaturated fatty acids (PUFAs) to measures of atherosclerosis are sparse. Objective: We examined intakes of long-chain n-3 PUFAs and fish in relation to clinical measures of subclinical atherosclerosis. Design: A cross-sectional study was conducted in a multiethnic group of 5488 adults aged 45-84 y and free of clinical cardiovascular disease. Diet was assessed by using self-administered food-frequency questionnaires. Subclinical atherosclerosis was determined by measurements of common carotid intima-media thickness (cCIMT, >80th percentile), internal CIMT (iCIMT, >80th percentile), coronary artery calcium score (CAC score, >0), or ankle-brachial index (ABI, <0.90). Results: After adjustment for potential confounders, intakes of long-chain n-3 PUFAs and nonfried (broiled, steamed, baked, or raw) fish were inversely related to subclinical atherosclerosis determined by cCIMT but not by iCIMT, CAC score, or ABI. The multivariate odds ratio comparing the highest to the lowest quartile of dietary exposures in relation to subclinical atherosclerosis determined by cCIMT was 0.69 (95% CI: 0.55, 0.86; P for trend < 0.01) for n-3 PUFA intake; 0.80 (95% CI: 0.64, 1.01; P = 0.054) for nonfried fish consumption; and 0.90 (95% CI: 0.73, 1.11; P = 0.38) for fried fish consumption. Conclusions: This study indicates that the dietary intake of long-chain n-3 PUFAs or nonfried fish is associated with a lower prevalence of subclinical atherosclerosis classified by cCIMT, although significant changes in iCIMT, CAC score, and ABI were not observed. Our findings also suggest that the association of fish and atherosclerosis may vary depending on the type of fish meal consumed and the measures of atherosclerosis.

Lindberg, M., I. Saltvedt, et al. (2008). "Long-chain n-3 fatty acids and mortality in elderly patients." Am J Clin Nutr 88(3): 722-729.  [Abstract/Full Text]
Background: Long-chain n-3 fatty acids may favorably modulate many diseases. The evidence is firm for coronary heart disease, less certain for stroke, and only speculative for other diseases. The impact of these fatty acids on mortality among acutely sick elderly patients is unknown. Objective: The objective was to investigate the relation between long-chain n-3 fatty acids and overall mortality in acutely sick elderly patients. Design: Frail, elderly patients (n = 254) acutely admitted to St Olavs Hospital in central Norway were examined. The plasma phospholipid concentration of eicosapentaenoic acid (EPA) was used as a surrogate marker for dietary intake of marine fatty acids. Mortality rates were evaluated after 3 y of follow-up. Cox proportional hazard analysis was used to calculate hazard ratios adjusted for important biochemical and clinical covariates. Results: The hazard ratio of overall mortality was significantly higher in patients with EPA concentrations in the lowest quartile than in patients in the upper 3 quartiles (adjusted hazard ratio: 0.52; 95% CI: 0.35, 0.77). The upper 3 quartiles were not significantly different from one another (P = 0.94). Conclusions: Overall mortality in frail, elderly, acutely sick patients was inversely and nonlinearly associated with EPA concentrations. Approximately 25% of the population had EPA concentrations below the indicated threshold for maximal protection, suggesting that only this part of the population might have benefited from additional EPA intake.

Oken, E., M. L. Osterdal, et al. (2008). "Associations of maternal fish intake during pregnancy and breastfeeding duration with attainment of developmental milestones in early childhood: a study from the Danish National Birth Cohort." Am J Clin Nutr 88(3): 789-796.  [Abstract/Full Text
Background: Few studies have examined the overall effect of maternal fish intake during pregnancy on child development or examined whether the developmental benefits of maternal fish intake are greater in infants breastfed for a shorter duration. Objective: We aimed to study associations of maternal prenatal fish intake and breastfeeding duration with child developmental milestones. Design: We studied 25 446 children born to mothers participating in the Danish National Birth Cohort, a prospective population-based cohort study including pregnant women enrolled between 1997 and 2002. Mothers reported child development by a standardized interview, which we used to generate developmental scores at ages 6 and 18 mo. We used multivariate cumulative ordinal logistic regression to evaluate the odds of higher developmental scores associated with maternal fish intake and breastfeeding, after adjustment for child age, sex, and growth; maternal size and pregnancy characteristics; and parental education and social status. Results: Higher maternal fish intake and greater duration of breastfeeding were associated with higher child developmental scores at 18 mo [odds ratio: 1.29 (95% CI: 1.20, 1.38) for the highest versus the lowest quintile of fish intake, and 1.28 (1.18, 1.38) for breastfeeding for greater than or equal to 10 mo compared with breastfeeding for less than or equal to 1 mo]. Associations were similar for development at 6 mo. Associations of fish intake with child development did not differ by breastfeeding duration. Conclusions: Maternal fish intake during pregnancy and the duration of breastfeeding are independently associated with better early child development. Future research and consumption guidelines, incorporating nutritional benefits as well as contaminant risks, should consider the overall effect of prenatal fish consumption on child development.

Samieri, C., C. Feart, et al. (2008). "Low plasma eicosapentaenoic acid and depressive symptomatology are independent predictors of dementia risk." Am J Clin Nutr 88(3): 714-721.  [Abstract/Full Text
Background: The potential preventive role of polyunsaturated fatty acids (PUFAs) in Alzheimer disease has aroused increasing interest. Plasma n-3 PUFAs have been shown to be inversely related to the risk of dementia and to depression, which is frequently associated with dementia. Objective: The objective was to ascertain whether plasma PUFAs predict the risk of incident dementia in a cohort of older persons, independently of their depressive status. Design: Of 1214 nondemented participants in the Three-City Study from Bordeaux (France) who were followed up for 4 y, 65 developed dementia. The association between the proportion of plasma fatty acids at baseline and the risk of incident dementia was assessed by multivariate proportional hazard models, taking into account depressive status assessed on the basis of the Center for Epidemiologic Studies Depression scale. Results: A higher plasma eicosapentaenoic acid (EPA) concentration was associated with a lower incidence of dementia [hazard ratio (HR) for 1 SD = 0.69; 95% CI: 0.48, 0.98], independently of depressive status and after adjustment for age, education, apolipoprotein E {varepsilon}4 allele, diabetes, and baseline plasma vitamin E and triacylglycerol. The relations between docosahexaenoic acid (DHA), total n-3 PUFAs, and incident dementia did not remain significant in multivariate models. Higher ratios of arachidonic acid (AA) to DHA and of n-6 to n-3 fatty acids were related to an increased risk of dementia, particularly in depressive subjects (n = 90): ratio of AA to DHA (HR: 2.65; 95% CI: 1.07, 6.56) and ratio of n-6 to n-3 (HR: 1.61; 95% CI: 1.04, 2.47). Conclusions: A high plasma EPA concentration may decrease the risk of dementia, whereas high ratios of n-6 to n-3 fatty acids and of AA to DHA may increase the risk of dementia, especially in depressed older persons. The role of EPA in dementia warrants further research.


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