Association of reported fish intake and supplementation status with the omega-3 index

https://doi.org/10.1016/j.plefa.2019.01.002 Get rights and content

Highlights

  • An Omega-3 Index of >8% is associated with lower cardiovascular risk.

  • Consuming oily fish and/or taking omega-3 supplements will raise the Omega-3 Index.

  • Based on self-reported data, it appears that on average >2 oily fish meals per week plus an omega-3 supplement are required to achieve an Index of >8%.

Abstract

Background

An Omega-3 Index (O3I; EPA+DHA as a % of erythrocyte total fatty acids) in the desirable range (8%-12%) has been associated with improved heart and brain health.

Objective

To determine the combination of fish intake and supplement use that is associated with an O3I of >8%.

Design

Two cross-sectional studies comparing the O3I to EPA+DHA/fish intake.

Participants/setting

The first study included 28 individuals and assessed their fish and EPA+DHA intake using both a validated triple-pass 24-hr recall dietary survey and a single fish-intake question. The second study used de-identified data from 3,458 adults (84% from US) who self-tested their O3I and answered questions about their fish intake and supplement use.

Statistical analyses performed

Study 1, chi-squared, one-way ANOVA, and Pearson correlations were computed. In Study 2, multi-variable regression models were used to predict O3I levels from reported fish/supplement intakes.

Results

The mean ± SD O3I was 4.87 ± 1.32%, and 5.99 ± 2.29% in the first and second studies, respectively. Both studies showed that for every increase in fish intake category the O3I increased by 0.50–0.65% (p < 0.0001). In the second study, about half of the population was taking omega-3 supplements, 32% reported no fish intake and 17% reported eating fish >2 times per week. Taking an EPA+DHA supplement increased the O3I by 2.2% (p < 0.0001). The odds of having an O3I of ≥8% were 44% in the highest intake group (≥3 servings/week and supplementation) and 2% in the lowest intake group (no fish intake or supplementation); and in those consuming 2 fish meals per week but not taking supplements (as per recommendations), 10%.

Conclusions

Current AHA recommendations are unlikely to produce a desirable O3I. Consuming at least 3 fish servings per week plus taking an EPA+DHA supplement markedly increases the likelihood of achieving this target level.

Introduction

In 2018, the American Heart Association (AHA) updated its 2002 recommendations regarding fish and seafood consumption from “…a variety of (preferably oily) fish at least twice a week” [1] to “…1 to 2 seafood meals per week” [2]. This apparent downgrade in the recommendation (i.e., removal of “preferably oily” and “at least”) was made despite evidence that consuming fish more frequently (such as daily or multiple times per day) may impart even greater cardioprotection [3], [4], [5]. An online commentary by Kuller that accompanied the publication of the new AHA guidelines questioned whether the new fish intake recommendations would produce cardioprotective blood omega-3 levels [6]. He argued that intake recommendations should be based on those that achieve a target blood level.

Asking individuals about their fish intake is often a proxy measure for intake of omega-3 fatty acids (FAs) eicosapentaenoic (EPA) and docosahexaenoic acids (DHA), because, in nature, EPA and DHA are found almost exclusively in oily fish, such as salmon, herring and mackerel. Blood levels of EPA and DHA have been shown to be related to reported fish intake [7] and supplementation [8], and to cardiovascular health [9], a single biomarker representing both dietary intake and risk for disease.

The Omega-3 Index (O3I) is a measure of the proportion of EPA and DHA in erythrocytes (EPA+DHA/total FAs) and was originally proposed as a risk factor for cardiac death in 2004 by Harris and Von Schacky [10]. Recently, a pooling study of 10 cohort studies confirmed that an O3I of 8% was related to a risk reduction of 35% for cardiovascular death, as compared to 4% (typical O3I in low-fish intake individuals) [9]. While the O3I is a significant predictor of fatal cardiovascular events, research has shown that higher blood omega-3 levels are beneficially related to other aging-related health conditions also, such as congitive function [11] and brain volume [12] and increased longevity [13], [14].

There is some controversy regarding the effects of fish intake on the O3I. For example, Block et al reported that individuals reporting an intake of at least 2 fish meals per week had an O3I of 5.1% [7], and Harris et al. found that after 4 months of consuming 2 oily fish meals per week, the mean O3I was 6.1% [15]. On the other hand, Sands et al. reported a mean O3I of 8% in non-supplementing subjects reporting this weekly intake [16]. So, whether a diet including only 2 servings of fish per week would result in a cardioprotective O3I (8%) or not is unclear. To address this question, we conducted two studies. The first was a small but intensive study using standard dietary intake tools to quantify both fish and EPA+DHA intake and then to correlate these with the O3I. The second was conducted in a “real-world” setting to determine the associations between self-reported intake of fish and/or omega-3 (i.e., EPA and DHA) supplements and the O3I.

Section snippets

Study 1

The study utilized a cross-sectional design with one clinic visit and three, 24-h dietary recalls collected within two weeks of the visit. A sample of generally healthy adults was recruited by email and fliers in two sites, State College, PA and Sioux Falls, SD, US, and screened via telephone or in person during the summer of 2009. Eligibility criteria included generally healthy men and women, aged 19–65 years, BMI 19–40 kg/m2, not taking any fish oil or other EPA or DHA-containing supplements

Study 1 (n = 28)

Demographic characteristics were not significantly different among the five fish intake groups (Table 1). Overall, the mean age was 32 years and BMI, 24.3 kg/m2. All participants were from the US, 82% were Caucasian, and 75% were female (Table 1). Based on the 24-hour dietary recall data, the most commonly eaten fish was tuna (32% of fish eaten) followed by salmon (16%), both of which are species known for their high EPA+DHA content. Eight other varieties of fish and shellfish (cod, imitation

Discussion

The overall purpose of these studies was to answer the question, “How much EPA+DHA from fish and/or supplements is needed to achieve a desirable O3I?” Using the answers to two simple dietary questions – “How often to you eat tuna or other non-fried fish?” and, “Do you take an omega-3 supplement?” – allowed us (along with age) to begin to answer that question.

Two studies were reported here. The aim of the first study was to determine whether the answer to a simple fish intake question was as

Conclusion

The current study again validates the O3I as a useful biomarker of EPA+DHA intake. Reports of higher fish intake corresponded with higher O3I values in a dose-dependent manner. Reported supplementation with EPA+DHA (fish, krill, or algal oils) was associated with an approximately 2 percentage point higher O3I. The current fish intake recommendations (1–2 servings of seafood per week) are unlikely to produce a cardioprotective O3I level, but consuming primarily oily fish 3 times or more per week

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Disclosures

KHJ and JMP are employees, and WSH is the President of OmegaQuant, LLC, a commercial laboratory that offers the Omega-3 Index test. NLT and PMKE have nothing to disclose.

Author contributions

All authors participated in (1) the conception and design of the study, or acquisition of data, or analysis and interpretation of data, (2) drafting the article or revising it critically for important intellectual content, and (3) final approval of the version to be submitted.

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