Association of reported fish intake and supplementation status with the omega-3 index
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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2022, Clinical NutritionCitation Excerpt :Circulating fatty acids, polyunsaturated fatty acids (PUFA) in particular, are established biomarkers and commonly used to reflect dietary fat composition and multiple validation studies have been performed using food frequency questionnaires and dietary food records as references [1–3]. Especially, circulating linoleic acid (LA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are PUFAs that are recognized to reflect past diet exposure, i.e. accepted as valid biomarkers of dietary intake [4,5]. Importantly, several controlled feeding studies have been conducted to validate these fatty acids in various populations reflecting dietary fat changes over the past few weeks [1,6–13], but also during long term follow-up of several years [14,15].