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stroke belt
Prostaglandins, Leukotrienes and Essential Fatty Acids 148 (2019) 30–34
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Prostaglandins, Leukotrienes and Essential Fatty Acids journal homepage: www.elsevier.com/locate/plefa
Short communication
Survey of the erythrocyte EPA+DHA levels in the heart attack/stroke belt W.S. Harris
a,b,⁎
a
c
d
e
f
, K.H. Jackson , J.T. Brenna , J.C. Rodriguez , N.L. Tintle , L. Cornish
T
a
OmegaQuant Analytics, LLC, Sioux Falls, SD, USA Sanford School of Medicine, University of South Dakota, Sioux Falls, SD, USA Dell Medical School, University of Texas at Austin, Austin, TX, USA d Brooks College of Health, University of North Florida, Jacksonville, FL, USA e Dordt College, Sioux Center, IA, USA f Seafood Nutrition Partnership, Washington, DC, USA b c
ARTICLE INFO
ABSTRACT
Keywords: Fish oil Eicosapentaenoic acid Docosahexaenoic acid Fish Omega-3 index Community survey
Background: The Omega-3 Index (O3I; erythrocyte EPA+DHA as a percent of total fatty acids) is inversely related to risk for cardiovascular disease (CVD). The cardioprotective target O3I is 8%–12%. O3I levels in American regions with high CVD risk are poorly characterized. Purpose: To determine the O3I in individuals participating in a Seafood Nutrition Partnership (SNP) survey in seven US cities in the CVD “belt.” Methods: Fingerstick blood samples were analyzed for the O3I. Results: The SNP cohort (n = 2177) had a mean (SD) O3I of 4.42% (1.12%). Only 1.2% were in the desirable range, whereas 42% had an undesirable (<4%) O3I. The mean (SD) O3I in a subset of 772 SNP subjects who were matched for age and sex with the Framingham study was 4.6% (1.2%) compared 5.3% (1.6%) in the Framingham cohort (p < 0.0001). Conclusions: Individuals in the CVD “belt” had relatively low O3I levels. Since in other settings, a low O3I is associated with increased risk for CVD, this may be one factor contributing to the higher risk for CVD in this region of the US.
Abbreviations: CVD, Cardiovascular disease CHD, Coronary heart disease O3I, Omega-3 index EPA, Eicosapentaenoic acid DHA, Docosahexaenoic acid SNP, Seafood nutrition partnership HDLab, Health diagnostic laboratory FHS, Framingham heart study
1. Introduction There is a clear geographical disparity in risk for cardiovascular disease (CVD) in the US, with a “heart attack/stroke belt” (hereafter the CVD belt) located primarily in the south east/central region (Fig. 1). Low omega-3 fatty acid levels in the blood are known to be a risk factor for CVD independent of traditional lipid and inflammatory biomarkers, blood pressure, diabetes and smoking status [1-6]. The extent to which a relatively low omega-3 level contributes to this increased risk in this region is unknown. The Omega-3 Index (O3I) is the erythrocyte level of eicosapentaenoic and docosahexaenoic acids (EPA and DHA, respectively) and is expressed as a percent of total erythrocyte fatty acids. It is a validated biomarker of omega-3 status [7], and low levels have been linked with higher risk for CVD, CHD and death from any cause [2,6,8,9]. While no formal survey of the Omega-3 Index in the US has been conducted, such a survey in Canada revealed that only about 3% of Canadians had an
⁎
Omega-3 Index in the cardioprotective zone (i.e., 8–12%) [10]. In this study, we conducted screenings in seven medium-sized cities in the “belt.” These surveys were conducted under the auspices of the Seafood Nutrition Partnership (SNP), a U.S. non-profit, as part of a national public health campaign. The mission of SNP is “to build awareness of the health benefits of seafood using educational programs to inspire Americans to incorporate more seafood and omega-3 s into their diet, with a view towards reducing the burden of nutritionallyrelated chronic diseases in the US.” This 7-city cohort will be referred to as the SNP cohort hereafter, and the Omega-3 Index in this cohort will be compared to that of two other cohorts for which data on this metric are available. 2. Methods The free public health screenings of the O3I were conducted in the following cities: Charleston, WV; Jacksonville, FL; Indianapolis, IN;
Corresponding author at: WSH, 5009 W. 12th St, Ste 7, Sioux Falls, SD 57106, USA. E-mail address: [email protected] (W.S. Harris).
https://doi.org/10.1016/j.plefa.2019.07.010 Received 28 February 2019; Received in revised form 9 July 2019; Accepted 12 July 2019 0952-3278/ © 2019 Elsevier Ltd. All rights reserved.
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Fig. 1. Locations of surveyed cities and heart disease death rates by county. The stars indicate the tested cities: Charleston, WV; Jacksonville, FL; Indianapolis, IN; Lexington, KY; Memphis, TN; Oklahoma City, OK and Toledo, OH.
Lexington, KY; Memphis, TN; Oklahoma City, OK and Toledo, OH (Fig. 1). The screenings took place at church health fairs, malls, Departments of Public Health, medical clinics, and other public settings from October 2014 to November 2015. This project was organized by SNP in cooperation with local health partners, such as health insurance providers, schools of public health, local health clinics and centers. In order to facilitate participation and to minimize the amount of personal health information collected, we attempted to gather only data on name, email address (to send O3I results), age, and sex. All advertising and screening locations were targeted towards the general public. Many of the screening locations served lower socio-economic status populations, but no specific data on this were gathered. Fingerstick blood samples were collected by nurses and sent to OmegaQuant Analytics (Sioux Falls, SD) for fatty acid analysis (below). Two other populations were used as comparators for the SNP cohort. The first was a very large (∼160,000) dataset from a national clinical laboratory (Health Diagnostic Laboratory, HDLab; Richmond, VA) which included data from individuals across the same age spectrum as the SNP survey [11]. The second comparison population was the Framingham Heart study Offspring cohort (FHS, from a suburb of Boston, MA) [12]. These individuals (n = 3196) averaged 66 years of age. To compare the FHS O3I values with those of the SNP cohort, an age- and sex-matched subset of the former was identified such that each individual in the SNP cohort was matched with an individual of the same age and sex as in the FHS sample. A comparison of death rates from coronary heart disease (both unadjusted and adjusted for race and sex) in the SNP cities (counties) versus Framingham was undertaken using the Heart Disease and Stroke Map Widget from the Centers for Disease Control and Prevention [13]. Approval to use de-identified, existing data for studies such as this was obtained from the University of South Dakota Institutional Review
Board. 2.1. Laboratory methods Because of the unscheduled screening setting, subjects were not required to have fasted before the O3I test. In order to assess the effects of a recent meal on the O3I, a preliminary study was undertaken at OmegaQuant with 16 healthy subjects whose O3I was tested before and four hours after the consumption of a high-fat (43 g, containing no EPA or DHA), fast-food breakfast. The O3I decreased slightly (but statistically significantly, p = 0.01 by paired t-test) from 6.0 ± 2.6% to 5.8 ± 2.4%. (A previous study showed that an acute high omega-3 load did not acutely affect the O3I [14]). The fact that the O3I was affected by <4% after an extreme dietary perturbation suggests that this screening test performs adequately in field settings. At the screenings, a single drop of blood was collected by fingerstick directly onto a filter paper (Ahlstrom 226, PerkinElmer, Greenville, SC) that had been pretreated with an antioxidant cocktail to protect unsaturated FAs from oxidation. After collection, cards were stored in a plastic bag in a freezer (at least −20 °C) and batch shipped to OmegaQuant Analytics at ambient temperature for analysis by capillary gas chromatography as described previously [15]. The coefficient of variation for the O3I from dried blood spots is <5% [16]. 2.2. Statistical methods The distributions of the O3I across risk categories (<4%, 4–8%, 8% +) when comparing the HDLab sample to the SNP sample, was calculated using a chi-squared test of independence. The comparison between the SNP and the age-matched FHS subcohort was done using a paired t-test. Associations of the O3I by age and sex were evaluated by 31
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Fig. 2. Omega-3 Index Distribution: Seafood Nutrition Partnership surveyed cities (SNP; n = 2177) vs Health Diagnostic Laboratory (HDLab; n = 159,771). *P<0.0001 for the proportion of subjects in each category using a 1df chi-square test.
different multiple regression models including first testing for evidence that the O3I changed by age differently for males and females (age by sex interaction). If the interaction was determined to be non-significant it was dropped from the model and age and sex were entered into the model simultaneously. A p-value of <0.05 was considered statistically significant in all cases. All statistical analyses were conducted in R version 3.5.1 [17].
shown in Supplementary Materials Table 1). 4. Discussion O3I is a marker of EPA and DHA status as well as a risk factor for fatal CHD [18]. An O3I of 8% or more is associated with a 35% lower risk compared with an O3I of 4% [8]. Although clearly not the only risk factor for CHD, a low O3I contributes independently to increased risk for CVD and death from any cause [6], and was a better predictor than serum cholesterol of this endpoint in the Framingham Offspring cohort [2]. The purpose of this study was to gather preliminary information on the O3I in people living in the “CVD” belt. Because screenings were generally conducted in lower income parts of town, the SNP cohort is likely to have been of a lower socio-economic status (SES). However, because we were unable to collect SES data on this cohort, no conclusions regarding SES and the O3I can be drawn from this study. Our analysis suggests that the SNP cohort in these cities have a depressed O3I levels compared to Americans in general (HDLab) and to Framingham in specific. The fraction of individuals in the SNP cohort with an O3I in the desirable zone (8%−12%) was 83% lower than that in a very large sample of Americans from a clinical laboratory dataset (i.e., 1.2% vs 7%), and the fraction in the undesirable zone (<4%) was 20% higher (i.e., 42% vs 35%). The mean O3I in this cohort was also 13% lower than that of the well-characterized FHS cohort. This is perhaps not surprising since the latter, being from a suburb of Boston, would have more ready access to fresh seafood. Importantly, even in a formal nationwide survey of the O3I in Canadians, 3% were in the desirable zone compared with about 1% of the SNP cohort (although the proportion in Canada who were in the <4% zone was similar (43%) to what we observed here). Furthermore, in another independent sample (the Women's Health Initiative Memory Study), we found higher mean levels of the O3I in the Northeast (5.8%, n = 4450) and West (5.5%, n = 1738) than in the South/Midwest (4.9%, n = 2861) (unpublished data [19]). Overall, our study provides support for the conclusion that the SNP cohort has a relative EPA+DHA deficiency. The logical extension of our findings that O3I levels are low in this region is that raising the O3I by increasing EPA and DHA intake could potentially reduce their elevated risk for CVD. There is accumulating evidence that higher intakes of fish and omega-3 capsules (both of which increase the O3I) are good for the heart. Support for increasing fish intake comes most recently from the NIH-AARP Diet and Health study [20]. This study looked at risk for death from a variety of causes in over 420,000 older individuals as a function of reported fish intake. They found reductions in mortality from Alzheimer's disease of 38%
3. Results The SNP cohort included a total of 2177 individuals over the age of 12. The mean (SD) O3I was 4.42% (1.12%) and the median was 4.20%. Of the entire cohort, only 27 (1.2%) had an O3I of 8%−12% (desirable), whereas 914 (42%) had an O3I ≤4% (undesirable) (Fig. 2). Compared with the HDLab data, there was an overall difference in the distribution of the O3I when comparing the proportion of individuals ≤4%, 4–8% and 8–12% ( 22 = 133.4 , p<0.0001). In particular, there were significantly more SNP subjects in the undesirable range (42% vs 35%, 12 = 45.7, p<0.0001) and fewer SNP subjects in the desirable range (1.2% vs 7%, 12 = 109.7 , p<0.0001). The 95% confidence interval around the mean difference between these latter two proportions [i.e., 7% (HDL) −1.2% (SNP) = 5.8%] was 5.3% to 6.3%. Another comparison was made with the FHS Offspring cohort using age- and, when available, sex-matched individuals (age and sex matched n = 772; able to match only by age n = 315; no match available n = 1090). Among the age- and sex-matched participants (n = 772; 23% male), the average (SD) O3I was significantly lower (p<0.0001) in the SNP cohort [4.6% (1.2%)] vs. FHS [5.3% (1.6%)]. Similar results were obtained when also including the individuals matched only on age. In the SNP cohort, the O3I was directly and significantly (p<0.0001) associated with age, with an average increase in the O3I of approximately 0.16% per decade. As shown in Fig. 3, teenagers had an average O3I of approximately 4% and people over 79 averaging about 5% (Fig. 3). Data on sex were available from 64% of the cohort. Among these, 78% of the sample were women. There was no significant difference in the O3I by sex (p = 0.99), and estimated differences in the O3I by Age were similar after adjusting for sex (0.16% per decade; p<0.0001), with no evidence of differential association of age with O3I levels by sex (p = 0.99). The coronary heart disease death rate in Framingham (Middlesex county, MA) was compared to the average of those in the seven SNP cities. On average, the rate (per 100,000 person) was higher in the latter (342) than in Framingham, both before (260, p = 0.002) and after (211, p = 0.0002) matching by sex and ethnicity. (Calculations 32
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Fig. 3. The mean Omega-3 Index by decade of life in the Seafood Nutrition Partnership cohort (n = 2177).
and 24% in women and men, respectively, between highest and lowest quintiles of non-fried fish intake. Reductions in all-cause mortality, CVD, cancer, and respiratory disease were all significant though smaller in magnitude. No reduction in risks were found for consumption of fried fish. Because omega-3 is highly correlated with intake of non-fried seafood [21, 22], this study points to the EPA and DHA component of non-fried fish as playing a role in this longevity benefit. There are also new data from randomized controlled trials (RCTs) with omega-3 in CVD. In 2018 three such RCTs were reported. One was the largest (n = 25,871, primary prevention subjects) study of omega-3 and CVD ever conducted [23]. It found that, although their composite endpoint (which summed a variety of CVD events) was not significantly reduced, there was a 28% statistically significant reduction in heart attacks in the omega-3 group (which was given 840 mg of EPA+DHA per day for about 5.3 years). In another study, vascular death was reduced by 19% in patients with type 2 diabetes given the same dose of EPA+DHA for 7.4 years [24]. Finally, a high-dose (4 g/d) study with EPA tested in statin-treated, hypertriglyceridemic patients for 4.9 years reported a 25% reduction in CVD events [25]. A meta-analyses of omega-3 RCTs from before 2018 found a consistent reduction in risk for cardiac death [26]. Hence there is considerable evidence for a CVD benefit from increasing the intake of EPA+DHA, and consuming more fish remains a strong recommendation of the American Heart Association [27]. Since both consuming non-fried fish [28] and fish oil capsules [29] raises the O3I, the low O3I in the SNP cohort could clearly be improved by consuming more EPA+DHA. Based on the discussion above, this would likely lower risk in the CVD belt. There are many ways to increase omega-3 fatty acid intake. Besides taking fish oil supplements or eating more oily fish (salmon, mackerel, herring, sardines, albacore tuna, etc.), there are now several kinds of EPA/DHA-fortified foods (eggs, fruit juices, milk, bread, spreads, peanut butters) available to consumers. With proper education regarding the selection, preparation and consumption of seafood, the overall health of these communities could be significantly improved.
sampling techniques to gather our participants in these cities; they were self-selected and thus potentially biased. The use of a clinical laboratory-derived dataset as a comparator population is potentially problematic as well. This is because these data are from individuals whose blood tests were ordered by their doctors, presumably out of potential concern that they might be at increased risk for CVD. Since people who are truly at risk for CVD (because of the presence of other risk factors/ behaviors) appear to have lower O3I values [1,31,32], one would expect that this population would tend to have lower O3I values than the general population. Our observation that the SNP cohort had even lower O3I levels than this large cohort argues for a true relative deficiency. In further support for the representativeness of the HDLab data, we have reported that classic CHD lipid and glycemic risk factors from this specific population are similar to the values of average Americans derived from national surveys [33]. Thus, it is not unreasonable to assume that the O3I values from the dataset would also be similar to national values.
4.1. Strengths and limitations
In this survey of 2177 individuals living in medium-sized cities in the CVD belt we found evidence for relatively low EPA+DHA status. Increased intake of seafoods rich in omega-3 fatty acids should be recommended to raise the O3I and thereby reduce risk for CVD in this high-risk region.
4.2. Future research Future studies of this question should naturally use more formalized population sampling techniques and gather more extensive demographic and dietary information from the participants. Simultaneous inclusion of other comparator populations would be essential to properly compare omega-3 status by region of the country. Whether increasing EPA+DHA intake in the CVD belt would reduce risk for CVD events will of course have to be tested by RCT, not observational studies. Future studies should also be undertaken to establish harmonized methods for assessing EPA+DHA levels. Although there have been no formal interlaboratory comparisons of the erythrocyte EPA+DHA metric with other measures of omega-3 fatty acid status, Hu et al. have published equations that can be used to interconvert plasma or plasma phospholipid EPA+DHA levels into erythrocyte equivalents [34]. 4.3. Conclusions
Strengths of this study include the analysis of samples from a relatively large number (>2000) individuals in several US cities in the CVD belt. The use of a standardized and widely-researched marker of omega3 biostatus (the O3I) (instead of a dietary intake survey) is another strength that allows the results of this study to be compared to those of many others besides the FHS and HDLab cohorts (e.g., a global O3I survey [30]). Weaknesses include the lack of complete demographic and health information among the participants, especially metrics of SES and omega-3 intake. Also, we did not use formal population
Funding The costs for organizing and conducting the surveys in each city and for blood testing were covered by SNP. Data analysis and manuscript preparation were covered by OmegaQuant Analytics, LLC. Otherwise, 33
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this research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
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Acknowledgements The authors wish to express our gratitude to the following groups and individuals for their help in the making the SNP surveys reported here possible: American Heart Association – Indianapolis; Asher Agency; Baptist Health; BlueCross BlueShield TN; Carter Malone; Charleston Area Medical Center; Church Health; Clark County Community Services; Coles Marketing; Doctor's Express Urgent Care; Health Right; Integris Hospital; Lutheran Social Services; Methodist Healthcare; Norman Regional Hospital; OKC County Health Department; OKC Regional Food Bank; Quirk Communications; Trifecta Communications; Tucker Hall; University of North Florida; University of Oklahoma Health Science Center; WV Nurse's Association; and YWCA Toledo. Supplementary materials Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.plefa.2019.07.010. References [1] J.D. Fontes, F. Rahman, S. Lacey, M.G. Larson, R.S. Vasan, E.J. Benjamin, W.S. Harris, S.J. Robins, Red blood cell fatty acids and biomarkers of inflammation: a cross-sectional study in a community-based cohort, Atherosclerosis 240 (2015) 431–436. [2] W.S. Harris, N.L. Tintle, M.R. Etherton, R.S. Vasan, Erythrocyte long-chain omega-3 fatty acid levels are inversely associated with mortality and with incident cardiovascular disease: the framingham heart study, J. Clin. Lipidol. 12 (2018) 718–724. [3] H. Saber, M.Y. Yakoob, P. Shi, W.T. Longstreth Jr., R.N. Lemaitre, D. Siscovick, K.M. Rexrode, W.C. Willett, D. Mozaffarian, Omega-3 fatty acids and incident ischemic stroke and its atherothrombotic and cardioembolic subtypes in 3 US cohorts, Stroke 48 (2017) 2678–2685. [4] H.T. Lai, M.C. de Oliveira Otto, R.N. Lemaitre, B. McKnight, X. Song, I.B. King, P.H. Chaves, M.C. Odden, A.B. Newman, D.S. Siscovick, D. Mozaffarian, Serial circulating omega 3 polyunsaturated fatty acids and healthy ageing among older adults in the cardiovascular health study: prospective cohort study, BMJ 363 (2018) 363 k4067. [5] L.C. Del Gobbo, F. Imamura, S. Aslibekyan, M. Marklund, J.K. Virtanen, M. Wennberg, M.Y. Yakoob, S.E. Chiuve, L. Dela Cruz, A.C. Frazier-Wood, A.M. Fretts, E. Guallar, C. Matsumoto, K. Prem, T. Tanaka, J.H. Wu, X. Zhou, C. Helmer, E. Ingelsson, J.M. Yuan, P. Barberger-Gateau, H. Campos, P.H. Chaves, L. Djousse, G.G. Giles, J. Gomez-Aracena, A.M. Hodge, F.B. Hu, J.H. Jansson, I. Johansson, K.T. Khaw, W.P. Koh, R.N. Lemaitre, L. Lind, R.N. Luben, E.B. Rimm, U. Riserus, C. Samieri, P.W. Franks, D.S. Siscovick, M. Stampfer, L.M. Steffen, B.T. Steffen, M.Y. Tsai, R.M. van Dam, S. Voutilainen, W.C. Willett, M. Woodward, D. Mozaffarian, Omega-3 polyunsaturated fatty acid biomarkers and coronary heart disease: pooling project of 19 cohort studies, JAMA Int. Med. 176 (2016) 1155–1166. [6] W.S. Harris, J. Luo, J.V. Pottala, M.A. Espeland, K.L. Margolis, J.E. Manson, L. Wang, T.M. Brasky, J.G. Robinson, Red blood cell polyunsaturated fatty acids and mortality in the women's health initiative memory study, J. Clin. Lipidol. 11 (2017) 250–259. [7] W.S. Harris, C. von Schacky, The Omega-3 index: a new risk factor for death from coronary heart disease? Prev. Med. 39 (2004) 212–220. [8] W.S. Harris, L. Del Gobbo, N.L. Tintle, The Omega-3 index and relative risk for coronary heart disease mortality: estimation from 10 cohort studies, Atherosclerosis 262 (2017) 51–54. [9] M.E. Kleber, G.E. Delgado, S. Lorkowski, W. Marz, C. von Schacky, Omega-3 fatty acids and mortality in patients referred for coronary angiography. The ludwigshafen risk and cardiovascular health study, Atherosclerosis. 252 (2016) 175–181. [10] K. Langlois, W.M. Ratnayake, Omega-3 index of Canadian adults, Health Rep. 26 (2015) 3–11.
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Contents lists available at ScienceDirect
Prostaglandins, Leukotrienes and Essential Fatty Acids journal homepage: www.elsevier.com/locate/plefa
Short communication
Survey of the erythrocyte EPA+DHA levels in the heart attack/stroke belt W.S. Harris
a,b,⁎
a
c
d
e
f
, K.H. Jackson , J.T. Brenna , J.C. Rodriguez , N.L. Tintle , L. Cornish
T
a
OmegaQuant Analytics, LLC, Sioux Falls, SD, USA Sanford School of Medicine, University of South Dakota, Sioux Falls, SD, USA Dell Medical School, University of Texas at Austin, Austin, TX, USA d Brooks College of Health, University of North Florida, Jacksonville, FL, USA e Dordt College, Sioux Center, IA, USA f Seafood Nutrition Partnership, Washington, DC, USA b c
ARTICLE INFO
ABSTRACT
Keywords: Fish oil Eicosapentaenoic acid Docosahexaenoic acid Fish Omega-3 index Community survey
Background: The Omega-3 Index (O3I; erythrocyte EPA+DHA as a percent of total fatty acids) is inversely related to risk for cardiovascular disease (CVD). The cardioprotective target O3I is 8%–12%. O3I levels in American regions with high CVD risk are poorly characterized. Purpose: To determine the O3I in individuals participating in a Seafood Nutrition Partnership (SNP) survey in seven US cities in the CVD “belt.” Methods: Fingerstick blood samples were analyzed for the O3I. Results: The SNP cohort (n = 2177) had a mean (SD) O3I of 4.42% (1.12%). Only 1.2% were in the desirable range, whereas 42% had an undesirable (<4%) O3I. The mean (SD) O3I in a subset of 772 SNP subjects who were matched for age and sex with the Framingham study was 4.6% (1.2%) compared 5.3% (1.6%) in the Framingham cohort (p < 0.0001). Conclusions: Individuals in the CVD “belt” had relatively low O3I levels. Since in other settings, a low O3I is associated with increased risk for CVD, this may be one factor contributing to the higher risk for CVD in this region of the US.
Abbreviations: CVD, Cardiovascular disease CHD, Coronary heart disease O3I, Omega-3 index EPA, Eicosapentaenoic acid DHA, Docosahexaenoic acid SNP, Seafood nutrition partnership HDLab, Health diagnostic laboratory FHS, Framingham heart study
1. Introduction There is a clear geographical disparity in risk for cardiovascular disease (CVD) in the US, with a “heart attack/stroke belt” (hereafter the CVD belt) located primarily in the south east/central region (Fig. 1). Low omega-3 fatty acid levels in the blood are known to be a risk factor for CVD independent of traditional lipid and inflammatory biomarkers, blood pressure, diabetes and smoking status [1-6]. The extent to which a relatively low omega-3 level contributes to this increased risk in this region is unknown. The Omega-3 Index (O3I) is the erythrocyte level of eicosapentaenoic and docosahexaenoic acids (EPA and DHA, respectively) and is expressed as a percent of total erythrocyte fatty acids. It is a validated biomarker of omega-3 status [7], and low levels have been linked with higher risk for CVD, CHD and death from any cause [2,6,8,9]. While no formal survey of the Omega-3 Index in the US has been conducted, such a survey in Canada revealed that only about 3% of Canadians had an
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Omega-3 Index in the cardioprotective zone (i.e., 8–12%) [10]. In this study, we conducted screenings in seven medium-sized cities in the “belt.” These surveys were conducted under the auspices of the Seafood Nutrition Partnership (SNP), a U.S. non-profit, as part of a national public health campaign. The mission of SNP is “to build awareness of the health benefits of seafood using educational programs to inspire Americans to incorporate more seafood and omega-3 s into their diet, with a view towards reducing the burden of nutritionallyrelated chronic diseases in the US.” This 7-city cohort will be referred to as the SNP cohort hereafter, and the Omega-3 Index in this cohort will be compared to that of two other cohorts for which data on this metric are available. 2. Methods The free public health screenings of the O3I were conducted in the following cities: Charleston, WV; Jacksonville, FL; Indianapolis, IN;
Corresponding author at: WSH, 5009 W. 12th St, Ste 7, Sioux Falls, SD 57106, USA. E-mail address: [email protected] (W.S. Harris).
https://doi.org/10.1016/j.plefa.2019.07.010 Received 28 February 2019; Received in revised form 9 July 2019; Accepted 12 July 2019 0952-3278/ © 2019 Elsevier Ltd. All rights reserved.
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Fig. 1. Locations of surveyed cities and heart disease death rates by county. The stars indicate the tested cities: Charleston, WV; Jacksonville, FL; Indianapolis, IN; Lexington, KY; Memphis, TN; Oklahoma City, OK and Toledo, OH.
Lexington, KY; Memphis, TN; Oklahoma City, OK and Toledo, OH (Fig. 1). The screenings took place at church health fairs, malls, Departments of Public Health, medical clinics, and other public settings from October 2014 to November 2015. This project was organized by SNP in cooperation with local health partners, such as health insurance providers, schools of public health, local health clinics and centers. In order to facilitate participation and to minimize the amount of personal health information collected, we attempted to gather only data on name, email address (to send O3I results), age, and sex. All advertising and screening locations were targeted towards the general public. Many of the screening locations served lower socio-economic status populations, but no specific data on this were gathered. Fingerstick blood samples were collected by nurses and sent to OmegaQuant Analytics (Sioux Falls, SD) for fatty acid analysis (below). Two other populations were used as comparators for the SNP cohort. The first was a very large (∼160,000) dataset from a national clinical laboratory (Health Diagnostic Laboratory, HDLab; Richmond, VA) which included data from individuals across the same age spectrum as the SNP survey [11]. The second comparison population was the Framingham Heart study Offspring cohort (FHS, from a suburb of Boston, MA) [12]. These individuals (n = 3196) averaged 66 years of age. To compare the FHS O3I values with those of the SNP cohort, an age- and sex-matched subset of the former was identified such that each individual in the SNP cohort was matched with an individual of the same age and sex as in the FHS sample. A comparison of death rates from coronary heart disease (both unadjusted and adjusted for race and sex) in the SNP cities (counties) versus Framingham was undertaken using the Heart Disease and Stroke Map Widget from the Centers for Disease Control and Prevention [13]. Approval to use de-identified, existing data for studies such as this was obtained from the University of South Dakota Institutional Review
Board. 2.1. Laboratory methods Because of the unscheduled screening setting, subjects were not required to have fasted before the O3I test. In order to assess the effects of a recent meal on the O3I, a preliminary study was undertaken at OmegaQuant with 16 healthy subjects whose O3I was tested before and four hours after the consumption of a high-fat (43 g, containing no EPA or DHA), fast-food breakfast. The O3I decreased slightly (but statistically significantly, p = 0.01 by paired t-test) from 6.0 ± 2.6% to 5.8 ± 2.4%. (A previous study showed that an acute high omega-3 load did not acutely affect the O3I [14]). The fact that the O3I was affected by <4% after an extreme dietary perturbation suggests that this screening test performs adequately in field settings. At the screenings, a single drop of blood was collected by fingerstick directly onto a filter paper (Ahlstrom 226, PerkinElmer, Greenville, SC) that had been pretreated with an antioxidant cocktail to protect unsaturated FAs from oxidation. After collection, cards were stored in a plastic bag in a freezer (at least −20 °C) and batch shipped to OmegaQuant Analytics at ambient temperature for analysis by capillary gas chromatography as described previously [15]. The coefficient of variation for the O3I from dried blood spots is <5% [16]. 2.2. Statistical methods The distributions of the O3I across risk categories (<4%, 4–8%, 8% +) when comparing the HDLab sample to the SNP sample, was calculated using a chi-squared test of independence. The comparison between the SNP and the age-matched FHS subcohort was done using a paired t-test. Associations of the O3I by age and sex were evaluated by 31
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Fig. 2. Omega-3 Index Distribution: Seafood Nutrition Partnership surveyed cities (SNP; n = 2177) vs Health Diagnostic Laboratory (HDLab; n = 159,771). *P<0.0001 for the proportion of subjects in each category using a 1df chi-square test.
different multiple regression models including first testing for evidence that the O3I changed by age differently for males and females (age by sex interaction). If the interaction was determined to be non-significant it was dropped from the model and age and sex were entered into the model simultaneously. A p-value of <0.05 was considered statistically significant in all cases. All statistical analyses were conducted in R version 3.5.1 [17].
shown in Supplementary Materials Table 1). 4. Discussion O3I is a marker of EPA and DHA status as well as a risk factor for fatal CHD [18]. An O3I of 8% or more is associated with a 35% lower risk compared with an O3I of 4% [8]. Although clearly not the only risk factor for CHD, a low O3I contributes independently to increased risk for CVD and death from any cause [6], and was a better predictor than serum cholesterol of this endpoint in the Framingham Offspring cohort [2]. The purpose of this study was to gather preliminary information on the O3I in people living in the “CVD” belt. Because screenings were generally conducted in lower income parts of town, the SNP cohort is likely to have been of a lower socio-economic status (SES). However, because we were unable to collect SES data on this cohort, no conclusions regarding SES and the O3I can be drawn from this study. Our analysis suggests that the SNP cohort in these cities have a depressed O3I levels compared to Americans in general (HDLab) and to Framingham in specific. The fraction of individuals in the SNP cohort with an O3I in the desirable zone (8%−12%) was 83% lower than that in a very large sample of Americans from a clinical laboratory dataset (i.e., 1.2% vs 7%), and the fraction in the undesirable zone (<4%) was 20% higher (i.e., 42% vs 35%). The mean O3I in this cohort was also 13% lower than that of the well-characterized FHS cohort. This is perhaps not surprising since the latter, being from a suburb of Boston, would have more ready access to fresh seafood. Importantly, even in a formal nationwide survey of the O3I in Canadians, 3% were in the desirable zone compared with about 1% of the SNP cohort (although the proportion in Canada who were in the <4% zone was similar (43%) to what we observed here). Furthermore, in another independent sample (the Women's Health Initiative Memory Study), we found higher mean levels of the O3I in the Northeast (5.8%, n = 4450) and West (5.5%, n = 1738) than in the South/Midwest (4.9%, n = 2861) (unpublished data [19]). Overall, our study provides support for the conclusion that the SNP cohort has a relative EPA+DHA deficiency. The logical extension of our findings that O3I levels are low in this region is that raising the O3I by increasing EPA and DHA intake could potentially reduce their elevated risk for CVD. There is accumulating evidence that higher intakes of fish and omega-3 capsules (both of which increase the O3I) are good for the heart. Support for increasing fish intake comes most recently from the NIH-AARP Diet and Health study [20]. This study looked at risk for death from a variety of causes in over 420,000 older individuals as a function of reported fish intake. They found reductions in mortality from Alzheimer's disease of 38%
3. Results The SNP cohort included a total of 2177 individuals over the age of 12. The mean (SD) O3I was 4.42% (1.12%) and the median was 4.20%. Of the entire cohort, only 27 (1.2%) had an O3I of 8%−12% (desirable), whereas 914 (42%) had an O3I ≤4% (undesirable) (Fig. 2). Compared with the HDLab data, there was an overall difference in the distribution of the O3I when comparing the proportion of individuals ≤4%, 4–8% and 8–12% ( 22 = 133.4 , p<0.0001). In particular, there were significantly more SNP subjects in the undesirable range (42% vs 35%, 12 = 45.7, p<0.0001) and fewer SNP subjects in the desirable range (1.2% vs 7%, 12 = 109.7 , p<0.0001). The 95% confidence interval around the mean difference between these latter two proportions [i.e., 7% (HDL) −1.2% (SNP) = 5.8%] was 5.3% to 6.3%. Another comparison was made with the FHS Offspring cohort using age- and, when available, sex-matched individuals (age and sex matched n = 772; able to match only by age n = 315; no match available n = 1090). Among the age- and sex-matched participants (n = 772; 23% male), the average (SD) O3I was significantly lower (p<0.0001) in the SNP cohort [4.6% (1.2%)] vs. FHS [5.3% (1.6%)]. Similar results were obtained when also including the individuals matched only on age. In the SNP cohort, the O3I was directly and significantly (p<0.0001) associated with age, with an average increase in the O3I of approximately 0.16% per decade. As shown in Fig. 3, teenagers had an average O3I of approximately 4% and people over 79 averaging about 5% (Fig. 3). Data on sex were available from 64% of the cohort. Among these, 78% of the sample were women. There was no significant difference in the O3I by sex (p = 0.99), and estimated differences in the O3I by Age were similar after adjusting for sex (0.16% per decade; p<0.0001), with no evidence of differential association of age with O3I levels by sex (p = 0.99). The coronary heart disease death rate in Framingham (Middlesex county, MA) was compared to the average of those in the seven SNP cities. On average, the rate (per 100,000 person) was higher in the latter (342) than in Framingham, both before (260, p = 0.002) and after (211, p = 0.0002) matching by sex and ethnicity. (Calculations 32
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Fig. 3. The mean Omega-3 Index by decade of life in the Seafood Nutrition Partnership cohort (n = 2177).
and 24% in women and men, respectively, between highest and lowest quintiles of non-fried fish intake. Reductions in all-cause mortality, CVD, cancer, and respiratory disease were all significant though smaller in magnitude. No reduction in risks were found for consumption of fried fish. Because omega-3 is highly correlated with intake of non-fried seafood [21, 22], this study points to the EPA and DHA component of non-fried fish as playing a role in this longevity benefit. There are also new data from randomized controlled trials (RCTs) with omega-3 in CVD. In 2018 three such RCTs were reported. One was the largest (n = 25,871, primary prevention subjects) study of omega-3 and CVD ever conducted [23]. It found that, although their composite endpoint (which summed a variety of CVD events) was not significantly reduced, there was a 28% statistically significant reduction in heart attacks in the omega-3 group (which was given 840 mg of EPA+DHA per day for about 5.3 years). In another study, vascular death was reduced by 19% in patients with type 2 diabetes given the same dose of EPA+DHA for 7.4 years [24]. Finally, a high-dose (4 g/d) study with EPA tested in statin-treated, hypertriglyceridemic patients for 4.9 years reported a 25% reduction in CVD events [25]. A meta-analyses of omega-3 RCTs from before 2018 found a consistent reduction in risk for cardiac death [26]. Hence there is considerable evidence for a CVD benefit from increasing the intake of EPA+DHA, and consuming more fish remains a strong recommendation of the American Heart Association [27]. Since both consuming non-fried fish [28] and fish oil capsules [29] raises the O3I, the low O3I in the SNP cohort could clearly be improved by consuming more EPA+DHA. Based on the discussion above, this would likely lower risk in the CVD belt. There are many ways to increase omega-3 fatty acid intake. Besides taking fish oil supplements or eating more oily fish (salmon, mackerel, herring, sardines, albacore tuna, etc.), there are now several kinds of EPA/DHA-fortified foods (eggs, fruit juices, milk, bread, spreads, peanut butters) available to consumers. With proper education regarding the selection, preparation and consumption of seafood, the overall health of these communities could be significantly improved.
sampling techniques to gather our participants in these cities; they were self-selected and thus potentially biased. The use of a clinical laboratory-derived dataset as a comparator population is potentially problematic as well. This is because these data are from individuals whose blood tests were ordered by their doctors, presumably out of potential concern that they might be at increased risk for CVD. Since people who are truly at risk for CVD (because of the presence of other risk factors/ behaviors) appear to have lower O3I values [1,31,32], one would expect that this population would tend to have lower O3I values than the general population. Our observation that the SNP cohort had even lower O3I levels than this large cohort argues for a true relative deficiency. In further support for the representativeness of the HDLab data, we have reported that classic CHD lipid and glycemic risk factors from this specific population are similar to the values of average Americans derived from national surveys [33]. Thus, it is not unreasonable to assume that the O3I values from the dataset would also be similar to national values.
4.1. Strengths and limitations
In this survey of 2177 individuals living in medium-sized cities in the CVD belt we found evidence for relatively low EPA+DHA status. Increased intake of seafoods rich in omega-3 fatty acids should be recommended to raise the O3I and thereby reduce risk for CVD in this high-risk region.
4.2. Future research Future studies of this question should naturally use more formalized population sampling techniques and gather more extensive demographic and dietary information from the participants. Simultaneous inclusion of other comparator populations would be essential to properly compare omega-3 status by region of the country. Whether increasing EPA+DHA intake in the CVD belt would reduce risk for CVD events will of course have to be tested by RCT, not observational studies. Future studies should also be undertaken to establish harmonized methods for assessing EPA+DHA levels. Although there have been no formal interlaboratory comparisons of the erythrocyte EPA+DHA metric with other measures of omega-3 fatty acid status, Hu et al. have published equations that can be used to interconvert plasma or plasma phospholipid EPA+DHA levels into erythrocyte equivalents [34]. 4.3. Conclusions
Strengths of this study include the analysis of samples from a relatively large number (>2000) individuals in several US cities in the CVD belt. The use of a standardized and widely-researched marker of omega3 biostatus (the O3I) (instead of a dietary intake survey) is another strength that allows the results of this study to be compared to those of many others besides the FHS and HDLab cohorts (e.g., a global O3I survey [30]). Weaknesses include the lack of complete demographic and health information among the participants, especially metrics of SES and omega-3 intake. Also, we did not use formal population
Funding The costs for organizing and conducting the surveys in each city and for blood testing were covered by SNP. Data analysis and manuscript preparation were covered by OmegaQuant Analytics, LLC. Otherwise, 33
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this research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
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Acknowledgements The authors wish to express our gratitude to the following groups and individuals for their help in the making the SNP surveys reported here possible: American Heart Association – Indianapolis; Asher Agency; Baptist Health; BlueCross BlueShield TN; Carter Malone; Charleston Area Medical Center; Church Health; Clark County Community Services; Coles Marketing; Doctor's Express Urgent Care; Health Right; Integris Hospital; Lutheran Social Services; Methodist Healthcare; Norman Regional Hospital; OKC County Health Department; OKC Regional Food Bank; Quirk Communications; Trifecta Communications; Tucker Hall; University of North Florida; University of Oklahoma Health Science Center; WV Nurse's Association; and YWCA Toledo. Supplementary materials Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.plefa.2019.07.010. References [1] J.D. Fontes, F. Rahman, S. Lacey, M.G. Larson, R.S. Vasan, E.J. Benjamin, W.S. Harris, S.J. Robins, Red blood cell fatty acids and biomarkers of inflammation: a cross-sectional study in a community-based cohort, Atherosclerosis 240 (2015) 431–436. [2] W.S. Harris, N.L. Tintle, M.R. Etherton, R.S. Vasan, Erythrocyte long-chain omega-3 fatty acid levels are inversely associated with mortality and with incident cardiovascular disease: the framingham heart study, J. Clin. Lipidol. 12 (2018) 718–724. [3] H. Saber, M.Y. Yakoob, P. Shi, W.T. Longstreth Jr., R.N. Lemaitre, D. Siscovick, K.M. Rexrode, W.C. Willett, D. Mozaffarian, Omega-3 fatty acids and incident ischemic stroke and its atherothrombotic and cardioembolic subtypes in 3 US cohorts, Stroke 48 (2017) 2678–2685. [4] H.T. Lai, M.C. de Oliveira Otto, R.N. Lemaitre, B. McKnight, X. Song, I.B. King, P.H. Chaves, M.C. Odden, A.B. Newman, D.S. Siscovick, D. Mozaffarian, Serial circulating omega 3 polyunsaturated fatty acids and healthy ageing among older adults in the cardiovascular health study: prospective cohort study, BMJ 363 (2018) 363 k4067. [5] L.C. Del Gobbo, F. Imamura, S. Aslibekyan, M. Marklund, J.K. Virtanen, M. Wennberg, M.Y. Yakoob, S.E. Chiuve, L. Dela Cruz, A.C. Frazier-Wood, A.M. Fretts, E. Guallar, C. Matsumoto, K. Prem, T. Tanaka, J.H. Wu, X. Zhou, C. Helmer, E. Ingelsson, J.M. Yuan, P. Barberger-Gateau, H. Campos, P.H. Chaves, L. Djousse, G.G. Giles, J. Gomez-Aracena, A.M. Hodge, F.B. Hu, J.H. Jansson, I. Johansson, K.T. Khaw, W.P. Koh, R.N. Lemaitre, L. Lind, R.N. Luben, E.B. Rimm, U. Riserus, C. Samieri, P.W. Franks, D.S. Siscovick, M. Stampfer, L.M. Steffen, B.T. Steffen, M.Y. Tsai, R.M. van Dam, S. Voutilainen, W.C. Willett, M. Woodward, D. Mozaffarian, Omega-3 polyunsaturated fatty acid biomarkers and coronary heart disease: pooling project of 19 cohort studies, JAMA Int. Med. 176 (2016) 1155–1166. [6] W.S. Harris, J. Luo, J.V. Pottala, M.A. Espeland, K.L. Margolis, J.E. Manson, L. Wang, T.M. Brasky, J.G. Robinson, Red blood cell polyunsaturated fatty acids and mortality in the women's health initiative memory study, J. Clin. Lipidol. 11 (2017) 250–259. [7] W.S. Harris, C. von Schacky, The Omega-3 index: a new risk factor for death from coronary heart disease? Prev. Med. 39 (2004) 212–220. [8] W.S. Harris, L. Del Gobbo, N.L. Tintle, The Omega-3 index and relative risk for coronary heart disease mortality: estimation from 10 cohort studies, Atherosclerosis 262 (2017) 51–54. [9] M.E. Kleber, G.E. Delgado, S. Lorkowski, W. Marz, C. von Schacky, Omega-3 fatty acids and mortality in patients referred for coronary angiography. The ludwigshafen risk and cardiovascular health study, Atherosclerosis. 252 (2016) 175–181. [10] K. Langlois, W.M. Ratnayake, Omega-3 index of Canadian adults, Health Rep. 26 (2015) 3–11.
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