Friday, 24 December 2010

1-2 servings per week oily fish reduces the risk of coronary death by 36% and total mortality by 17%. Intake of 250 mg/day of Omega-3 Fatty Acids (EPA & DHA) is sufficient for primary prevention of Coronary Heart Disease.

Oily fish (salmon, mackerel, sardines, trout, tuna, mussels, oysters, anchovy, herring, crab) is very good for your heart. Eating fish means you could live 17% longer!

The Harvard School of Public Health reviewed existing studies (15 page Review - Full Text pdf) that looked at the health effects of eating fish.

The benefits of eating a modest amount of fish per week - 2 portions —about 3 ounces (90g) of farmed salmon or 6 ounces (180g) of mackerel - reduce the risk of death from coronary heart disease (CHD) by 36%. 180g of mackerel is about half a pound and costs £3. The benefit was related to the level of intake of omega-3 fatty acids, and thus benefits are greater for oily fish (e.g. salmon, bluefish), which are higher in beneficial omega-3 fatty acids, than lean fish (haddock, cod).

Some types of shellfish contain more omega 3 than others. For example, crab and mussels are quite good sources of omega 3, but prawns contain hardly any. Oily fish are the best sources of omega 3 according to UK Food Standards Agency.

You can check which fish are oily and which aren't in the table below:

Oily / fatty fish White / non-oily fish
Salmon Trout Mackerel Herring Sardines Pilchards Kipper Eel Whitebait Tuna* (fresh only - not tinned) Anchovies Swordfish Bloater Cacha Carp Hilsa Jack fish Katla Orange roughy Pangas Sprats Cod Haddock Plaice Coley Whiting Lemon sole Skate Halibut Rock salmon/Dogfish Ayr Catfish Dover sole Flounder Flying fish Hake Hoki John Dory Kalabasu Ling Monkfish Parrot fish Pollack Pomfret Red and grey mullet Red fish Red snapper Rohu Sea bass Sea bream Shark Tilapia Turbot Tinned tuna Marlin

*Fresh tuna is an oily fish and is high in omega 3 fatty acids. But when it's canned, these fatty acids are reduced to levels similar to white fish so doesn't count as oily fish.

How much oily fish?

Most people should be eating more oily fish because omega 3 fatty acids are very good for our health. However, oily fish can contain low levels of pollutants that can build up in the body. For this reason there are recommendations for the maximum number of portions of oily fish we should be eating each week (a portion is about 140g):


per 100g fish
g fish per week for

1750mg EPA+DHA*
salmon (farmed) 2648 66
anchovy 2055 85
herring (atlantic) 2014 86
mackerel (atlantic) 1203 145
salmon (wild) 1043 167
sardines 982 178
trout 935 187
tuna (white, albacore) 862 203
mussels 782 223
oysters 688 254
halibut 465 376
crab 413 423
mackerel (king) 401 436
tuna (light, skipjack) 270 648
cod (atlantic) 158 1107

*: 250mg per day = 1750mg per week = recommended EPA+DHA

The Harvard review also demonstrated that intake of fish or fish oil reduces total mortality—deaths from any causes--by 17%.

More than two decades ago, pioneering studies showed that Greenland Eskimos, who consumed high amounts of omega-3 fatty acids from seafood, had very low rates of CHD death. Some studies have shown that PCBs and dioxins may be carcinogenic. The authors found that the benefits of eating fish far outweighed the potential cancer risks from these chemicals.

The benefits of eating one to two servings of fish a week greatly outweigh the risks among adults and, except for a few species of fish, women of child-bearing age. Seafood is likely the single most important food one can consume for good health said Mozaffarian.

The UK Food Standards Agency advise eating two servings of fish a week - one of these servings should be oily fish.

What levels of omega-3 fatty acids are in seafood?
In Wikipedia article - the 3 refers to the first carbon atom (red numbers) from the omega end of a polyunsaturated fatty acid that contains a double bond. Chemists (blue numbers) use reverse numbering from the carbonyl group.

Important omega-3 fatty acids in human nutrition are: a-linolenic acid (above) (18:3, ALA), eicosapentaenoic acid (20:5, EPA), and docosahexaenoic acid (22:6, DHA). These three polyunsaturates have either 3, 5 or 6 double bonds in a carbon chain of 18, 20 or 22 carbon atoms, respectively. All double bonds are in the cis-configuration, i.e. the two hydrogen atoms are on the same side of the double bond.

In Haliborange high DHA concentration Omega-3 fish oil (& Boots Smart Omega-3 Fish oil) each capsule contains 100mg DHA and 28mg EPA. Two capsules are recommended per day.

Mozaffarian say Intake of 250 mg/day of EPA and DHA appears sufficient for primary prevention (ie. 2 capsules of Haliborange or 10oz/week of canned tuna or equivalent) See Figure 2 & 6 top of page):-

Modest consumption of fish (eg, 1-2 servings/wk), especially
species higher in the n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), reduces risk of coronary death by 36% (95% confidence interval, 20%-50%; P .001) and total mortality by 17% (95% confidence interval, 0%-32%; P=.046) and may favorably affect other clinical outcomes. Intake of 250 mg/day of EPA and DHA appears sufficient for primary prevention.

What is the effect of Omega-3 fatty acids?
Omega-3 FA influence several cardiovascular risk factors and give altered membrane fluidity
and receptor responses following incorporation of (n-3 Poly Unsaturated Fatty Acids
n-3 PUFAs ) into cell membranes and direct binding of n-3 PUFAs to intracellular receptors regulating gene transcription. At typical dietary intakes, antiarrhythmic effects predominate, reducing risk of sudden death and CHD death within weeks by (1) modulation of myocardial sodium and calcium ion channels, reducing susceptibility to ischemia-induced arrhythmia and (2) reduced left ventricular workload and improved myocardial efficiency as a result of reduced heart rate, lower systemic vascular resistance, and improved diastolic filling.

n-3 PUFAs reduced total mortality by 17%. This can be compared to effects of statins on total mortality - a 15% reduction.

Avoidance of modest fish consumption due to confusion regarding risks and benefits could result in thousands of excess CHD deaths annually and suboptimal neurodevelopment in children.

No comments: