Health benefits of dietary omega-3 fatty acids


Introduction


“Make food your medicine” has always been recommended by professional health practitioners. Some food does more than just providing us with the basic nutrients that we need for normal body functions. Foods that contain bioactive compounds with health promoting effects are considered as functional foods. There are many claims from the mass media, scientific papers, food and medical institutions that omega-3 fatty acids showed positive effects on cardiovascular disease, prevention of arthritis and cancers, depression, neurological diseases; as well as improvement in maternal well-being (Harris, 2004). Some of the positive effects were documented with scientific evidence; while others either lack of strong scientific support or are simply just hoaxes. Therefore there is a lot public interest in unveiling the truth from scientific papers and understanding how omega-3 fatty acids work in our body.
Omega-3 fatty acids are long chain fatty acids with double bonds along the chain. Omega-3 fatty acids belong to the family of essential fatty acids (EFAs). EFAs are ="color: windowtext; text-decoration: none;">fatty acids that can’t be synthesized within our body from other sources by any known chemical pathways, and therefore must be obtained from the diet (Kris-Etherton et al., 2000). EFAs with more than one double bond are known as polyunsaturated ="color: windowtext; text-decoration: none;">fatty acids (PUFA). Food sources that have been identified containing PUFA include vegetables, nuts and seeds, legumes and seafood (Kris-Etherton et al., 2000). Omega-3 fatty acids can also be written as (ω-3) and the number three represents the third double carbon counting from the methyl group (Figure 1).

Figure 1. Eicosapentaenoic acid (EPA) 20: 5n-3EPA.gif

DHA.gif
Figure 2. Docosahexaenoic acid (DHA) 20:6n-3
(Bieganski, 2001)

EFAs are the precursors to many hormone-like compounds known as eicosanoids. Eicosanoids are then oxygenated by enzymes like cyclooxygenase, lipoxygenase and epoxygenase to form different types of eicosanoids. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have received much attention in health promoting activities in recent years (Harris, 2004). EPA and DHA are both long chain fatty acids with 20 carbon groups and the first double bond is positioned on the 3rd left from the methyl group (Figure 1 and 2). It is noteworthy to mention that long chain fatty acid also means PUFA and these terms can be used interchangeably (Kris-Etherton et al., 2000). EPA consists of five double bond carbons; in comparison, DHA consists of six double bond carbons (Dyerberg et al., 1978). Both EPA and DHA are beneficial to cardiovascular health, and therefore a daily recommended intake of approximate 1g for high risk people and 500mg for normal risk people has been suggested by Kris-Etherton (2002).

In general, EPA and DHA are more abundant in seafood compared with food sources from legumes, vegetable, seeds and nuts. Commonly eaten seafood such as herring, mackerel, salmon, sardines, tuna and Alaskan king crab legs contain high amounts of EPA and DHA (="color: #000064;">www.nalusda.gov/fnic/foodcomp). EPA and DHA are made available in fortified infant formulae, because these are important components for the rapid growth and development of the infant’s brain and neural system (Harris, 2004 and Insel et al., 2003). Interestingly, the sources of EPA and DHA for infant formulae were from algae and fungi instead of seafood (Harris, 2004). One possible reason could be that seafood may impart a fishy odour, and therefore will ruin the sensory properties of infant formulae. Since there has been much emphasise on the positive effects on dietary ω-3, it is of great importance to summarise the findings from scientific researches.

Most discussed health benefits


People with heart problems, high cholesterol level, obesity and diabetes are often having high triglycerides in the blood (Bays, 2006). Excess triglycerides in the blood can consequently increase the incidence of blocked arteries. A dosage of 4 g of ω-3 fatty acids per day had been proven as an effective treatment to improve the lipid profile in the blood (Bays, 2006; Bays, 2008 and Bays et al., 2008). Well established data have had proven that ω-3 fatty acids are effective for the reduction of triglycerides in the blood (Harris, 1997; Kris-Etherton et al., 2002 and von Schacky and Harris, 2007). Triglycerides profile in the blood does not solely contribute as a source of energy but also important substrates for genes expression in the peroxisome proliferation activator receptor (PPAR). PPARs regulate genes expression for the encoding of key proteins which control fatty acids uptake and metabolism (Berger and Mollar, 2002). Moreover, PPARs regulation also determines the level of very-low-density-lipoproteins (VLDL) formation and carries triglycerides in the liver (Berger and Mollar, 2002 and Huang et al., 2002). Information on the actual biochemical interactions between ω-3 fatty acids and triglycerides in the blood is currently limited but there are well documented evidences on the effectiveness of dietary ω-3 being used as a treatment on hyperlipidemia patients (Davidson et al., 2007; Harris, 1997; Huang et al., 2002). In general, 3-4 g of ω-3 per day could reduce triglycerides levels by 30%-40% in hyperlipidemia patients with triglycerides level of >500 mg/dl (Harris, 1997). Huang et al. (2002) had identified that dietary ω-3 was an effective sole treatment for hyperlipidemia patients. The outcomes of the treatment showed: amounts of triglycerides were reduced by 45%, an increase of good cholesterol (high-density-lipoprotein/ HDL) by 9% and a reduction of 14% on bad cholesterol (low-density-lipoprotein/LDL). Single treatment on simvastatin drug and combination treatment of simvastatin along with ω-3 supplement (4g ω-3) did not show significant reduction in LDL but the amount of blood triglycerides were reduced by 30% (Davidson et al., 2007). When different types of ω-3 fatty acids (EPA and DHA) were prescribed to hyperlipidemia patients, EPA was notably effective to lower the LDL by 10% (Yokoyama et al., 2007). ="display: block; font-family: 'Times New Roman',Times,serif; font-size: 14pt; text-align: left;">To date, the evidences on dietary ω-3 fatty acids are effective for the improvement triglycerides profile are conclusive but the effect to reduce LDL level remains elusive.



There is ample evidence that mental and psychiatric illnesses are associated with impaired cerebral blood flow (CBF) or the impairment in blood-brain barrier (BBB) (Sinn and Howe, 2008). A few possible reasons that could interrupt blood flow either in the cerebral or cardiovascular compartments are suggested to be associated with inflammation, aggregation of the platelets and poor vasodilation of the blood vessels (Freeman et al., 2008). Poor vasolidation of the blood can affect the efficiency of CBF and delivery of oxygen and glucose to brain tissues (Bourre, 2006). Current research is not limited to just investigate dietary ω-3 on cardiovascular health but more open to other diseases such as cerebral related illness, neurological and psychiatric diseases (Freeman et al., 2008; Mazza et al., 2007 and Sinn and Howe, 2008).

Research on the importance of long-chain fatty acids to the development of brain structure and function like ω-3 fatty acids was first completed in the 1970s (Crawford and Sinclair, 1971 and Sinclair, 1972). Our brains consisted of 60% lipids while the largest amount of DHA is concentrated in the nervous system, brain and retina (Salem, 2001). The lipids in the brains have important functions to facilitate CBF (Salem, 2001). When CBF is being interrupted one will experienced poor memory or memory loss (Waldstein et al., 2007). In extend, Waldstein et al. (2007) identified that poor CBF is associated with arterial stiffness. Hypotensive patients may experience memory lost and their memory are usually poorer than people of the same age with normal blood flow (Duschek et al., 2007). In other words, arterial stiffness and arterial blood flow can affect cognitive mental process. DHA has the potential to mediate cognitive related problems as mentioned above because DHA is an important substrate to regulate blood flow (Duschek et al., 2007). Extreme deficient of the long chain fatty acids may result in neural related diseases such as ="color: black;">schizophrenia, depression, dementia and Alzheimer’s disease (AD) and developmental disorders including attention deficit hyperactivity disorder (ADHD), dyslexia, dyspraxia, and the autistic spectrum disorders (Freemantle, 2006). As mention earlier, interrupted blood flow may have various reasons but one of the reasons may be due to tissues inflammation (Freeman et al., 2008). Omega-3 fatty acids are capable to reduce the incidence of inflammation by signaling the body’s immune, central nervous and the inflammatory system to come about (Sinn and Howe, 2008). Increase dietary intake of EPA and DHA rich sources have shown to increase production of anti-inflammatory substrates thus reduce the synthesis of inflammatory tissues in the body (Gibson, 1998 and Simopoulos, 1991).

Some scientific statements suggested that ω-3 fatty acids have beneficial effects on impaired endothelial tissues (Abeywardena and Head, 2001; De Caterina and Massaro, 2005 and White et al., 2000). Endothelial tissues play a key role in neural functions by providing optimum blood, oxygen and nutrients supply to the brain regions (Abeywardena and Head, 2001). The BBB is made up by interconnected cerebral endothelial cells and are highly sensitive on substances transported across the BBB. Phospholipids bi-layers are the key components on the endothelial cells’ lining thus dietary intake of EPA may protect the endothelial lining against inflammation and loosen the BBB’s tight junctions (Abbott et al., 2006).

Populations that consume more dietary ω-3 fatty acids are less likely to suffer from depression (Edwards et al., 1998; Frasure-Smith et al., 2004 and Makrides et al., 1994). These scientific data were collected from patients with different types of depression: women with postpartum depression, clinical depression and mood depression. In general, depressed patients have low level of long chain fatty acids especially DHA and low level of cerebrospinal fluid in the blood (Hibbeln et al., 1998). The profound reason is deficiency in dietary ω-3 fatty acids had altered the brain composition and functions (Hibbeln et al., 1998) and resulted in low cerebrospinal fluid production (Frasure-Smith et al., 2004). Low cerebrospinal fluid is an indication of low serotonin production, which exhibits anti-depression effect (Frasure-Smith et al., 2004). Results presented by other authors also indicated similar observations that depressed patients have significantly low ω-3 fatty acid when compared with normal people (Edwards et al., 1998; Maes et al., 1996; Peet et al., 1998 and Tiemeier et al., 2003). These also recommend, depressed patient to increase dietary ω-3 fatty acids. Contradicted results were observed by Fehily et al, (1981) and Ellis and Sanders, (1977) when the concentration of EPA and DHA were actually significantly higher in severely depressed patients compared with non-depressed patients. Although majority concluded that dietary ω-3 fatty acids are beneficial to minimise depression but there are authors that disagree with the conclusion. Therefore further scientific research is required to explain this.

Children and adolescents with higher amount of ω-6 fatty acids than ω-3 fatty acids in the brain exhibited attention-deficit hyperactivity disorder (ADHD) (Antalis et al., 2006) and depression (Freeman et al., 2006). Persons with ADHD have poor judgement on emotional status of others especially anger and fear (Singh et al., 1998). This is also associated with children and adolescents being seen with misconduct behaviour and has offending behaviour in schools (Singh et al., 1998). ADHD is also a type of neural disorders therefore growing children are encourage to include more ω-3 fatty acids through their dietary intake. Product labels with display like “DHA added” or “enriched with DHA and EPA” are often seen on formulated infant products. EPA and DHA are the key ingredients for maintaining membrane fluidity and involve in neural activities such as neurotransmission, activate ion channel, enzyme regulation, gene expression and myelination (Gordon et al, 2005 and Sinn and Howe, 2008).

Canadian nutritional board (1989) highly recommend parents to introduce two to three serving of fish per week in their children’s diet. The total amount of the serving provides an approximate of 900-1200 mg of ω-3 fatty acids per week. As discussed before, ω-3 fatty acids are beneficial for the majority of neural and cardiac health and therefore introducing diet rich in ω-3 can reduce the risk of developing atherosclerosis, cardiac diseases, hypertension and cancer later in life (McGill et al., 1997). Inflammatory disease such as asthma may be prevented with regular fish intake in children (McGill et al., 1997).

Dietary ω-3 fatty acids may have potential benefits to reduce the proliferation of cancerous cells. Increased intake of dietary ω-3 showed inhibitory effects on tumour necrosis formation and the production of proinflammatory cytokines such as tumour necrosis factor-alpha and interleukin-1 (IL-1) (Dagnelie et al., 1994 and Saski et al., 1999). Intensive weight loss is observed among the patients suffering from cancer. In has been suggested that their satiation receptors were hypersensitive and therefore patients reduce their food intake unnoticeably. This is one of the mechanisms exhibited by cancerous cells to weaken the body’s immune system (McGahon et al., 1999). Cancer animal and human experimental models have had evident that increased dietary ω-3 fatty acids had reduced sudden weight loss (Barber et al., 1999 and Dagnelie et al., 1994). These authors observed an overall improved eating pattern, prevented weight loss and delayed the onset of tumour growth. In addition, Dagnelie et al., (1994) recommended that dietary intake of ω-3 fatty acids should be introduced in an early stage of tumour development. This is suggested to be more effective than at terminal stage.

Colon cancer is common among the people that consume more meat than vegetables and fish, diets that contain high saturated fat and have low physical activity. A study identified that dietary DHA can promote cell apoptosis and inhibit the expression of proinflammatory genes (Kato et al., 2002 and Narayanan et al., 2003). Cell apoptosis is crucial to “kill” unwanted or harmful cells like cancerous cells (Kato et al., 2002). Current evidence on beneficial effect of ω-3 on breast cancer is very limited (Hursting et al., 1990). Generally speaking, per capital fish consumption in a country has lower incidence of breast cancer (Chajes et al., 1999). Data was compared among these countries: Japan, Norway and United States of America and women in Japan are less likely to develop breast cancer followed by women in Norway then the United States of America. On the other hand, endothelial cancer showed variable experimental results (Goodman et al., 1997; McCann et al., 2000; Shu et al., 1993; Terry et al., 2002 and Zheng et al., 1995). Some results indicated that increase fish intake may increase the risk of endothelial cancer due to parallel increase on mercury intake (Shu et al., 1993 and Zheng et al., 1995). Whereas another group of studies pinpointed that fatty fish intake reduce the risk of endothelial cancers due to the abundant ω-3 fatty acids (McCann et al., 2000; Shu et al., 1993 and Terry et al., 2002).

Skin cancer is not normally treated with chemotherapy therefore it is of great interest to look at the potential effects on dietary intake of ω-3 (Demierre et al., 2003). Some scientific evident indicated that dietary intake of ω-3 especially from fish showed beneficial effects on melanoma cell lines but it is currently unknown whether the beneficial effect was due to vit D or ω-3 fatty acids (Albino et al., 2000 and Liu et al., 2003). Further studies are essential to clarify the compound responsible to the beneficial effects on melanoma cell lines. Dietary intake of ω-3 fatty acids has potential effects on ovarian, prostate and renal cell cancers but ω-3 fatty acids have not been officially included as part of cancer treatment. Current experimental results on the effectiveness of ω-3 fatty acids to treat cancer remain inconclusive, more define conclusion is required to be used along with cancer treatment.

Conclusion



In conclusion, dietary ω-3 fatty acids can be obtained from marine products such as shell fish and fish. Fatty fish species such salmon, tuna, mackerel and herring are recommended to be eaten regularly because of their health promoting benefits. The recommended intake is hard to establish due to various variation such as age, body condition, health status and sex. In general, 200-400 g of fatty fish as mentioned above, if eaten at least twice a week could reduce the incidence of sudden cardiac death among patients with cardiac complications. However, dietary ω-3 fatty acids did not show significant improvement on total cholesterol level in the blood or ischemic heart disease. Person with high triglycerides in the blood is recommended to consume more fish for the sources of ω-3 fatty acids as this will improve the overall blood triglycerides profile. In particular, more good cholesterol (high density lipoprotein) will be produced. The brain consisted of a large proportion of lipids and is essential for neurological functions, gene expressions, ions, blood and oxygen supply and nutrient regulations. Children in their growing and development stages are highly recommended to consume 900-1200 mg of ω-3 fatty acids per week. This may prevent them from life threatening diseases as describe in the content page. Omega-3 fatty acids may potentially use in conjunction with various cancer treatment especially to lessen the effect of sudden weight loss. While analysing the beneficial effects of ω-3 fatty acids, it is also important to evaluate its adverse effect, if any. All in all, further research studies have evident that ω-3 fatty acids can reduce sudden cardiac death but other potential benefits still require extensive studies to elucidate its functions and benefits.

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