Foods and Nutrition October 2012 FN-12 Omega-3 Fatty Acid, Selenium, and Mercury Content of Aquaculture Products in Hawai‘i Corilee A. Watters1, Lee S. Rosner1, Adrian A. Franke2, Alfred E. Asato3 1 University of Hawai‘i at Manoa, Department of Human Nutrition, Food and Animal Science, 1955 East West Road, Agricultural Science Room 216, Honolulu, HI 96822 (email: [email protected]) 2 University of Hawai‘i Cancer Center, 1236 Lauhala Street, Honolulu, HI 96813 3 Hawaii Department of Health, State Laboratory Division, 2725 Waimano Home Road, Pearl City, HI 96782 Numerous health benefits have been associated with lipoxygenase enzymes in lipid metabolism pathways, increased dietary intakes of long-chain omega-3 fatty they may prevent excessive inflammation that is associ- acids. Dietitians recommend consumption of at least two ated with negative outcomes in chronic inflammatory 4-oz servings of fish per week. Fish is the major source diseases (Calder 2006). The American Heart Association of selenium and long-chain ω-3 fatty acids but can also (2012) currently recommends that individuals without contain methylmercury. Dietitians recommending fish coronary heart disease eat fish (preferably fatty) at least intake need to be familiar with omega-3, mercury, and twice per week. The Academy of Nutrition and Dietetics selenium levels in commonly available fish in order (AND) recommends at least two 4-oz (~100-g) servings to make recommendations that maximize benefits and of fish (preferably oily) per week, or approximately 500 minimize risks. The purpose of this study was to gather mg of EPA and DHA per day, to support overall health baseline data on the fatty acid profile and selenium (Kris-Etherton and Innis 2007). and mercury concentrations of aquaculture products LC ω-3 PUFA content varies naturally among dif- in Hawai‘i. ferent fish species. In aquaculture it is also affected by farming practices, particularly the nutrient composition Introduction of fish feed used. Fish require LC ω-3 PUFA for growth Fish is the major source of long-chain omega-3 polyun- and development like other vertebrates, and exclusive saturated fatty acids (LC ω-3 PUFA), eicosapentaenoic or high use of plant-based fish feeds with high omega-6 acid (EPA, 20:5 ω-3), and docosahexaenoic acid (DHA, fatty acid (ω-6 FA) content results in increased ω-6 FA 22:6 ω-3) in the human diet. Numerous health benefits and decreased LC ω-3 FA tissue concentrations in aqua- have been associated with increased dietary intakes of cultured fish (Weaver et al. 2008). The fatty acid profiles LC ω-3 PUFA, including decreases in blood pressure, of fish are further influenced by their ability to elongate serum triglycerides, and blood platelet aggregation (Kris- shorter-chain ω-3 FA to LC ω-3 PUFAs; for example, Etherton et al. 2003), and decreased incidence of coro- omnivorous fresh-water fish have a greater ability to nary heart disease (Hu et al. 2002), cardiac arrhythmias elongate shorter-chain ω-3 FA than carnivorous marine (Calder 2004), and ischemic stroke (He 2004). DHA plays fish (Watanabe 1982) and may therefore be raised on an important role in neurogenesis and neurotransmission diets lower in LC ω-3 PUFAs. and is thus critical for optimal neurological development Methylmercury is the organic form of mercury of (Innis 2007). Because EPA and DHA are competitive greatest concern in human toxicology. Methylmercury inhibitors of arachidonic acid for cyclooxygenase and is formed from inorganic mercury by anaerobic bacteria Published by the College of Tropical Agriculture and Human Resources (CTAHR) and issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in co- operation with the U.S. Department of Agriculture, under the Director/Dean, Cooperative Extension Service/CTAHR, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i 96822. Copyright 2011, University of Hawai‘i. For reproduction and use permission, contact the CTAHR Office of Communication Services, [email protected], 808-956-7036. The university is an equal opportunity/affirmative action institution providing programs and services to the people of Hawai‘i without regard to race, sex, gender identity and expression, age, religion, color, national origin, ancestry, disability, marital status, arrest and court record, sexual orientation, or status as a covered veteran. Find CTAHR publications at www.ctahr.hawaii.edu/freepubs. UH–CTAHR Omega-3 Fatty Acid, Selenium, and Mercury Content of Aquaculture Products in HI FN-12 — Oct. 2012 in aquatic sediments and bioaccumulates in long-lived Evidence from animal and in-vitro studies suggests predatory fish at the top of the food chain (Clarkson et that selenium and selenoprotein antioxidant systems may al. 2003). Human exposure to methylmercury occurs protect the cardiovascular system against methylmer- almost exclusively by consumption of seafood. Long- cury-induced free-radical damage through a variety of term health effects of chronic low-level methylmercury mechanisms (Ganther 1978, Iwata et al. 1982, Sasakura exposure in populations consuming large amounts of fish and Yang et al. 2008). Because selenium has a high affin- and seafood are an area of investigation. Main areas of ity for mercury, it is thought to scavenge methylmercury concern are neurological impairment during development in the body (Ralston 2010). However, once selenium (Grandjean et al. 1997, Grandjean et al. 1998, Grump et binds to methylmercury, it can no longer function en- al. 1998, Davidson et al. 2011, Jedrychowski et al. 2006) zymatically or as a selenoprotein; thus, selenium must and risk of cardiovascular disease in adults (Ahlqwist be replaced through the diet (Ralston 2010). The molar 1999, Hallgren 2001, Guallar et al. 2002, Virtanen et ratio of mercury to selenium in seafood is thought by al. 2005, Yoshizawa et al. 2002, Wennberg et al. 2007). some to be a key mediator of potential toxicity (Kaneko Due to concerns about gestational mercury exposure, the and Ralston 2007, Ralston 2010). However, any putative FDA (2004) currently maintains an advisory for women protection against mercury exposure by selenium intake who may become pregnant, pregnant women, nursing has yet to be shown in human studies, but many studies mothers, and young children, with guidelines intended to may be limited by a high baseline selenium status in the reduce mercury consumption by avoiding consumption of population (Mozaffarian et al. 2011). fish with the highest levels of methylmercury. However, a Because of the potential variability in fatty acid recent consultation by international experts determined content among aquacultured and wild-harvested seafood that benefits of fish consumption outweigh risks, even products, actual intakes of LC ω-3 PUFAs currently can- when it is consumed in the vulnerable pregnancy period, not be reliably estimated. Moreover, depending on the among all geographic populations that have been studied actual ω-6 FA and LC ω-3 PUFA content, consumption (FAO/WHO 2011). This conclusion is consistent with the of certain aquacultured seafood products, such as catfish findings of other authors, who have concluded benefits and tilapia, may no longer confer the health benefits as- outweigh risks when intake is moderate and relevant sociated with fish intake (Weaver et al. 2008). Although advisories are followed (Clarkson et al. 2003, Sidhu certain macroalgaes commonly sold in dry form, such 2003, Mozaffarian and Rimm 2006, Sioen et al. 2008). as wakame and hijiki, have been shown to contain sig- Currently there are no FDA guidelines for restricted fish nificant amounts of EPA and DHA (Dawczynski et al. consumption by non-pregnant, non-nursing adults. 2007), there is little published data describing the fatty Fish is one of the best sources of selenium, an es- acid profiles of fresh seaweeds. Dietitians recommend- sential mineral micronutrient involved in numerous ing seafood intake need to be familiar with omega-3, metabolic pathways. In the body selenium is incorpo- mercury, and selenium levels in commonly available fish rated into selenoproteins after it is bound to the amino and seaweeds in order to make recommendations that acid cysteine to form selenocysteine (Lu and Holmgren maximize the benefits and minimize the risks. Fatty acid, 2009). Some important selenoprotein families in the body mercury, and selenium analysis of aquacultured seafood include thioredoxin reductases, which play an important products is clearly warranted. The purpose of this study role in DNA synthesis; iodothyronine deiodinases, which was to gather baseline data on the fatty acid profile and regulate thyroid hormone activation; and glutathione selenium and total mercury content of 24 aquaculture peroxidases, which are major components of the body’s products in Hawai‘i. antioxidant defenses and may reduce cardiovascular dis- ease risk through a variety of mechanisms (Mozaffarian Methods 2009). However, there is a lack of conclusive evidence Aquaculture products were obtained from May through linking increased selenium consumption to reduced car- August 2011 from sources on O‘ahu and Hawai‘i islands diovascular disease risk, nor is it known what threshold (Table 1). ‘Opihi (Cellana sp.) is a wild-collected mollusk level of selenium intake would be needed to confer pos- but was included because there is a lack of published sible protection (Mozaffarian 2009). data on its fatty acid profile and selenium and mercury 2 UH–CTAHR Omega-3 Fatty Acid, Selenium, and Mercury Content of Aquaculture Products in HI FN-12 — Oct. 2012 Table 1. Common name, species, and source of sampled products Common name, species Source company, location in Hawai‘i Prep method Sablefish (butterfish),Anoplopoma fimbria Troutlodge Marine Farms, NELHA – Kailua-Kona Raw Pacific threadfin (moi), Polydactylus sexfilis Troutlodge Marine Farms, NELHA – Kailua-Kona Raw Ezo (Japanese Northern abalone), Haliotis Big Island Abalone Corp., NELHA – Kailua-Kona Raw discus hannai Russian sturgeon, Acipenser gueldenstaedti UH-Hilo Agricultural Farm, Pana‘ewa, Hilo Raw Siberian sturgeon, Acipenser baerii UH-Hilo Agricultural Farm, Pana‘ewa, Hilo Raw Hawaii Fish Co., Waialua; Tilapia, Oreochromis sp.