Vitamin D and cardiovascular disease: a potential novel agent for reducing cardiovascular risk
Vitamin D deficiency is often found in patients with cardiovascular disease.
Myth or Fact? All omega-3 fatty acids are equal
The normal human diet contains a wide range of fatty acids. These are present from fats and oils that are consumed either separately as butter or cooking oil, or that are naturally present in many foods but particularly in nuts, oily fish and dairy products. Most foods contain a mixture of many different fatty acids. Chemically speaking, fatty acids have an acid on one end, connected to a chain of variable length and “degree of saturation”. Both these qualities affect the health effects of the fatty acids. Fatty acid chain size is referred to as short, medium or long chain. The degree of saturation denotes the number of double bonds that are found when looking at the chain of the fatty acid. Saturated fats do not contain any double bonds, and are thus “saturated”, monounsaturated fats contain a single double bond, and polyunsaturated fats contain more than one double bond. The omega classification (e.g. 3, 6, 7, or 9) refers to the position of the first double bond.
“Omega-3” therefore refers to long chain fatty acids that are polyunsaturated, and have the first double bond in the third position. The three most important omega-3 fatty acids are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Each of these three omega-3 fatty acids has different roles in the body, and this is reflected in separate dietary recommendations. International intake guidelines recommend that ALA makes up at least 0.5 percent of energy intakes (50 kcal, or 5.5 g ALA for a 2000 kcal diet) to avoid deficiency symptoms . In addition, adults should consume at least 250 mg EPA+DHA for heart health and possible links to protection against other degenerative diseases of aging. Pregnant or lactating women should consume at least 300 mg EPA+DHA to meet the needs of the fetus or infant. Infants, toddlers and children have their own separate guidelines on intakes of ALA, EPA and DHA.
These three important omega-3 fatty acids are also biochemically connected because the body can interconvert between the three: ALA is converted to EPA and then DHA, and back again. This has given rise to the assumption that consuming one type of fatty acid (particularly ALA from plant-based oils) is enough to meet requirements for all three. Unfortunately, the efficiency of conversion from ALA to EPA is rather low, and the final conversion to DHA is lower still . While consuming more ALA seems to increase EPA concentrations a little, it has no noticeable effect on DHA concentrations . The most reliable way to consume enough EPA and DHA is to consume them directly and not rely on interconversion to meet needs.
Bottom line: Myth. Omega-3 fatty acids have distinct roles in the body and it is important to consume adequate amounts of ALA, EPA and DHA.
Myth or Fact? Omega-3 supplements help lower cholesterol
The omega-3 fatty acids EPA and DHA are recommended for heart health . In addition, replacing saturated fat in the diet with either mono- or polyunsaturated fat will lower cholesterol . So it is not surprising that people link omega-3 supplements with lowering cholesterol. This is not correct, however.
A meta-analysis that investigated the effects of EPA and DHA, both against each other and compared to placebo, on the lipid profile summarizes the main effects . EPA does not affect LDL-cholesterol levels, and most studies show small, insignificant deviations from baseline levels after supplementation. DHA tends to increase LDL-cholesterol (“bad” cholesterol) a little, but this is matched by an increase in HDL-cholesterol (“good”-cholesterol), with a net effect considered to decrease overall CVD risk.
On the other hand, omega-3 fatty acids have been clinically proven to reduce another component of the lipid profile: elevated triglycerides. High fasting triglyceride levels are considered to be an independent risk factor for cardiovascular disease . Omega-3 fatty acids significantly reduce circulating triglyceride levels , and this is why they have been approved as prescription medication for triglyceride reduction , and recently as health claim on food products by Health Canada .
Bottom line: Myth. Omega-3 LC PUFAs given as medication have been proven to lower elevated triglycerides. Replacing “bad” saturated fats in the diet with “good” polyunsaturated fats, including omega-3 polyunsaturated fatty acids, will lower cholesterol.
Myth or Fact? Diet is enough to meet omega-3 recommendations
While the basis of dietary recommendations is nutrients, these are translated into food-based guidelines. The best source of long chain omega-3 fatty acids is fatty fish. While there are some variations, guidelines generally recommend consuming one or two servings of fish, particularly fatty fish, per week, for general health. For example, the Dietary Guidelines for Americans recommends 8 ounces (227 grams) per week of a variety of seafood to meet the 250 mg per day of EPA and DHA , and the Food and Agriculture Organisation recommends one or two meals of omega-3 rich seafood per week .
This is doable: 250 mg per day is equal to 1750 mg per week. 100 g of high omega-3 fish such as salmon, herring or anchovy contains more omega-3 than this, and 200 g of medium omega-3 fish such as sardines, mackerel, trout or halibut will also meet the recommendations. So by eating one portion of a high omega-3 fish, or two portions of a medium omega-3 fish, it is possible to meet the recommendations. However, fish and seafood such as cod, catfish, haddock, tinned light tuna and shrimp contain 300 mg or less per 100 g. If the diet does not include high omega-3 fish, these fish will not contribute enough omega-3 to reach 1750 mg per week unless they are consumed almost every day.
But in practice, it seems that many people are not able to meet the recommendations. Indeed, a wide range of studies show that fish, seafood and omega-3 intakes are far below recommendations. Studies conducted in individual countries such as the US , the Netherlands , Spain , China  and Denmark  show that the majority of individuals do not consume enough omega-3 fatty acids. Not only is fish consumption sub-optimal, with some people consuming no seafood or far too little, but the type of fish or seafood consumed tends to be low omega-3 fish such as shrimp, canned tuna, tilapia and pollock  rather than high or medium omega-3 fish. Global surveys find that fish supplies per capita do not meet requirements for omega-3 fatty acid consumption .
Bottom line: While it is possible to meet omega-3 fatty acid intake recommendations with the diet, few people do.
Myth or Fact? Only people with heart disease should be taking omega-3 supplements
Omega-3 fatty acid recommendations are made for different groups in the population based on needs. Children generally have lower requirements than adults due to their smaller size. Pregnant and lactating women on the other hand have higher requirements to support the growth and development of their infants. People with heart disease are advised to consume even higher amounts, for example, the American Heart Association recommends intakes of 500 to 1800 mg for heart health . The levels recommended for people with heart disease could potentially be met by the diet, however the levels are so high that it may be more practical to take a supplement rather than eat so much fatty fish. Dietary supplements are therefore recommended to help cardiovascular patients to meet recommendations.
While it is more realistic to expect that people without heart disease can meet recommendations with the diet, research shows that most people are not meeting recommendations with the diet . There are various reasons for this . Some consumers cannot eat fish due to allergies or vegetarianism, while others do not like the taste of fish, particularly fatty fish that has a stronger “fishy” aroma. Others dislike the smell of fish during preparation, are unsure how to prepare it, are confused by all the different types of fish or prefer not to eat it due to the risk of bones. Others have concerns about the sustainability of the fishing industry and levels of mercury in fish. The perceived perishability of fish and issues with obtaining it may be a further barrier to fish consumption. Still more see fish as a luxury product that does not fit into their budget compared to other protein foods. For these people, omega-3 supplements may offer a better way to obtain essential nutrients.
Bottom line: Myth. Omega-3 fatty acids are considered essential. Anyone not meeting recommendations for fatty fish consumption should take supplements EPA+DHA to fill their dietary gap.
Myth or Fact? The omega-6 to omega-3 ratio is important
The omega-6 fatty acids are another group of essential fatty acids that have a slightly different structure, and similar yet distinct functions, to those of omega-3 fatty acids . Both omega-3 and omega-6 fatty acids must be obtained from the diet to prevent deficiency symptoms. The essentiality of both groups of fatty acids is reflected in the composition of human breast milk, which naturally contains relatively high amounts of both omega-3 and omega-6 fatty acids to support infants’ neurological and visual development. In adults, both fatty acids are important for the normal functioning of the immune system as they are used for the production of various messenger molecules used to respond to potentially harmful stimuli. Omega-6 fatty acids are used to produce messenger molecules that strongly stimulate the immune system, which allows the body to react more aggressively to infections, but is linked to increased risk of chronic disease and childhood allergies . The messenger molecules produced from omega-3 fatty acids have a more moderate effect on the immune system .
Due to their structural similarities, omega-3 or omega-6 fatty acids compete with each other for the enzymes used to produce these messenger molecules. This means that diets containing a high proportion of omega-6 fatty acids can result in an immune system that over-reacts to infection. Individuals may be more prone to chronic diseases related to inflammation such as type 2 diabetes mellitus and Alzheimer’s Disease . Intakes of omega-3 and omega-6 fatty acids should be in balance with each other. It seems that Western diets contain relatively high amounts of omega-6 fatty acids from vegetable oils such as sunflower, corn (maize) and soybean, leading to a ratio of 10:1 or higher . Some experts recommend lowering the omega-6 to omega-3 ratio to 4:1 or less for chronic disease prevention .
Looking at the ratios of omega-3 to omega-6 fatty acids is a different approach to that taken by dietary guidelines. The current guidelines recommend a defined intake of both omega-6 and omega-3 fatty acids. While the concept of the omega-6 to omega-3 ratio is discussed, there is not enough research to support introducing a ratio to the recommendations . At any rate, most people will benefit from increasing intakes of omega-3 fatty acids , and this will also improve the omega-6 to omega-3 ratio.
Bottom line: The jury is still out on this one. Whether it is more important to obtain the right dose or ratio of omega-3 fatty acids, most people do not consume enough omega-3.
Myth or Fact? Omega-3 dose is not important
In nutrition, a healthy intake range has been estimated for the majority of nutrients. It is important to get enough to meet needs, however excessive intakes may also be harmful. This is true for omega-3 fatty acids. International recommendations set the range for healthy intakes of omega-3 fatty acids at 250 to 2000 mg per day, and higher consumption up to 3000 mg per day has been tested in short- and intermediate term intervention studies with no adverse effects . Dose is important whether omega-3 fatty acids are taken for general health, or a specific health concern. For triglyceride lowering, the effect is seen at a dose of 2000 – 4000 mg per day, and for blood pressure, a dose of 3000 mg per day helps to maintain normal blood pressure . The European Food Safety Authority has set a tolerable upper intake level for long term supplemental intakes of 5000 mg per day for combined EPA+DHA . The omega-3 dose is important: it should exceed the minimum requirement whilst not exceeding the maximum requirement.
Bottom line: Myth. Dose is always important in nutrition.
3. Brenna, J.T., et al., alpha-Linolenic acid supplementation and conversion to n-3 long-chain polyunsaturated fatty acids in humans. Prostaglandins, Leukotrienes and Essential Fatty Acids. 80(2): p. 85-91.
10. Bureau of Nutritional Sciences; Food Directorate; Health Products and Food Branch, Summary of Health Canada's assessment of a health claim about eicosapentaenoic acid, docosahexaenoic acid and triglyceride lowering. 2016.
12. Papanikolaou, Y., et al., U.S. adults are not meeting recommended levels for fish and omega-3 fatty acid intake: results of an analysis using observational data from NHANES 2003–2008. Nutrition Journal, 2014. 13: p. 31-31.
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24. Micha, R., et al., Global, regional, and national consumption levels of dietary fats and oils in 1990 and 2010: a systematic analysis including 266 country-specific nutrition surveys. BMJ, 2014. 348: p. g2272.
25. European Food Safety Authority, Scientific Opinion on the substantiation of health claims related to EPA, DHA, DPA and maintenance of normal blood pressure (ID 502), maintenance of normal HDL-cholesterol concentrations (ID 515), maintenance of normal (fasting) blood concentrations of triglycerides (ID 517), maintenance of normal LDL-cholesterol concentrations (ID 528, 698) and maintenance of joints (ID 503, 505, 507, 511, 518, 524, 526, 535, 537) pursuant to Article 13(1) of Regulation (EC) No 1924/2006. EFSA Journal, 2009. 7(9): p. 1263.
26. European Food Safety Authority, Scientific Opinion on the Tolerable Upper Intake Level of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA). EFSA Journal, 2012. 10(7): p. 2815.
Vitamin D deficiency is often found in patients with cardiovascular disease.