When it comes to choosing the best in fish oils, you don't always get what you pay for.
There was a time when a cod liver oil was the prescription for whatever was ailing you. But concerns over polluted seas and toxins (like mercury and pesticides) retain-ed in fish livers led to a decline in the use of this dietary supplement. At the same time, some vegetable oils (particularly flaxseed oil) were identified as also being good sources of omega-3 fatty acids, so nutritionists began to 'prescribe' these instead.
Accumulating evidence, however, suggests that switching from fish oils, containing eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), to flaxseed oils, which contain alpha-linolenic acid (LNA, used by the body to make EPA and DHA), may not be as sound as first thought.
It has been found that, in elderly people, this process of converting LNA to EPA and DHA may not be as efficient as it should be (Am J Clin Nutr, 1991; 54: 438-63). Other studies have found that, even in healthy persons, the amount of LNA converted to EPA can be very low (Prostagl Leukotr EFAs, 2000; 63: 287-92). It is generally believed that around 14 per cent of LNA is converted to EPA. But, in one small study, only 0.2 per cent of the LNA in a flaxseed oil supplement was available to be converted to EPA compared with 23 per cent of the EPA in fish oil that was available to be converted to DHA (J Lipid Res, 2001; 42: 1257-65).
The inability of some individuals to met-abolise LNA may be one reason why supplementation with this fatty acid has been linked with higher rates of prostate cancer (J Natl Cancer Inst, 1993; 85: 1571-9; J Natl Cancer Inst, 1994; 86: 281-6; Int J Cancer, 1997; 71: 545-51). Research into LNA inhibition of other types of cancer cells has also proved inconclusive (Am J Clin Nutr, 1997; 66 [Suppl]: 998-1003S).
High levels of LNA have also been implicated in an increased risk of heart attack, and LNA is less effective than fish oil in reducing triglyceride levels (Am J Clin Nutr, 1997; 66: 591-8). In one study, heat attack victims not only had high levels of trans fatty acids, but also LNA and linoleic acid (LA) (Eur J Clin Nutr, 2000; 54: 618-25).
While proponents of flaxseed oil say that the improved condition of the skin often observed with flaxseed oil supplementation is a sign that it is working on the whole body, this could be a result of the phyto-estrogen content of the oil rather than a reflection of LNA activity.
In a diet already high in omega-6 fatty acids, flaxseed oil (which contains both omega-6 and -3) may also worsen the balance of omega-6 to omega-3 in the body. High levels of polyunsaturated fats (rich in omega-6) have been implicated in, among other things, increased rates of asthma. A recent study found that toddlers who consume large amounts of margarine and foods fried in vegetable oil are twice as likely to develop asthma (Thorax, 2001; 56: 589-95). And since the two types of fatty acids compete for the same metabolic enzymes, any increase in omega-6, particularly LA, may be detrimental to LNA metabolism (Am J Clin Nutr, 2000; 71: 179-88).
For these reasons, there is renewed interest in what we now recognise are the unique benefits of fish oils. Fish oil supplementation is beneficial for a range of inflammatory conditions such as Crohn's disease and rheumatoid arthritis (Gastroenterology, 1991; 100: A228; Arthritis Rheum, 1995; 38: 1107-14) as well as kidney diseases and chronic obstructive pulmonary diseases (N Engl J Med, 1994; 331: 1194- 9; J Am Dietet Assoc, 1997; 97: 5150-3: J Am Soc Nephrol, 1999; 10: 1772-7; N Engl J Med, 1994; 331: 228-33).
Omega-3 fatty acids can help Raynaud's disease, immune function and cardiac arrhythmias (Am J Med, 1989; 86: 158-64; Nutrition, 1998: 14: 627-33; J Nutr, 1997; 127: 383-93). Fish oil can prevent cancer in both humans and animals (Nutr Cancer, 1995; 24: 151-60; Lipids, 1986; 21: 285; J Natl Cancer Inst, 1985; 75: 959-62; J Am Coll Nutr, 1995; 14: 325), and several studies have reported low levels of omega-3 in people with depression (J Affect Disord, 1996; 38: 35-46; J Affect Disord, 1998; 48: 149- 55; Biol Psychiatry, 1998; 43: 315-9; Psychiatry Res, 1999; 85: 275-91).
But the news is not all good. While fish oils may appear healthful in the short-term, longer-term studies show a possible paradoxical effect. In 40 subjects given either a placebo or increasing doses of EPA and DHA, early results showed a rise in blood levels of both fatty acids, and a decline in harmful arachidonic acid and LA.
When the subjects were exposed to an oxidising agent at day 30, there was significantly less oxidation of fatty acids in those taking the highest EPA/DHA doses compared with placebo. By day 180, there was significantly more oxidative damage in those taking the highest doses of EPA/DHA.
The authors suggested that long-term use could lead to atherosclerosis (Am J Clin Nutr, 1996; 64: 297-304). Other data show an increase in atherosclerotic plaques over the long term (Arterioscler Thromb Vasc Biol, 1996; 16: 1197-202).
At this time, studies showing that fish oil supplements increase 'bad' LDL cholesterol also began to appear, though adding garlic to the mix appears to mitigate this (Am J Nutr, 1997; 65: 445-50; Altern Ther Health Med, 1997; 3: 108; J Natl Med Assoc, 1997; 89: 673-8). Other studies have shown that supplemental pectin (15 g/day) can have the same beneficial effect (Am J Clin Nutr, 1997; 66: 1183-7).
Fish oils can also lower blood levels of vitamin E (and other fats like retinol and beta-carotene) (Lipids, 1992; 27: 533-8; Am J Clin Nutr, 2000; 71 [Suppl]: 197-201S), so if you are taking it, you will need to add extra vitamin E to your regime. Studies show that 200 mg daily (around 100 IU) is sufficient to counteract the effect of fish oil supplementation (Am J Clin Nutr, 1993; 58: 98-102; Br J Nutr, 1992; 68: 163-73).
While many do benefit from fish oils, some, such as diabetics, may not as fish oils can worsen glucose control (J Diabetes Compl, 1996; 10: 280-7).
It is possible to get all the omega-3 we need from our diets. The US has no recommended daily amount (RDA) for DHA/EPA whereas, in the UK, the government recommends two portions of oily fish (salmon, mackerel, herring, sardines, albacore tuna, black cod or sablefish) a week. This provides around 2-3 g of fatty acids-equal to three or four 1000-mg fish oil capsules. (Organic grassfed animals, eggs from grainfed chickens, and wild game are also useful sources.) A weekly recommendation of 1.5 g of EPA/ DHA (through supplements) has also been made. Most of us take in substantially less.
One argument against fish oils is that they are prone to spoilage. Manufacturers try to bolster the fragility of fish oils by adding antioxidants like vitamin E. While not ideal, maintaining freshness is important since taking a supplement of rancid fish oil introduces free radicals, which can then damage molecules inside cells, including DNA.
To determine the freshness of our Road Test supplements, we examined the percentage of free fatty acids (FFAs) in each. In a fresh product, fatty acids cling together in a long chain but, as the product deteriorates, some of the 'links' break free. According to Pearson's Composition and Analysis of Foods , (9th edn, Longman Scientific and Technical, 1991), rancid oils are noticeable on tasting when the FFA content is 0.5-1.5 per cent. Unfortunately, fish oils have a fishy taste, which may obscure the taste of rancidity.
Producing higher concentrations of EPA/ DHA requires heat, which can increase FFA levels, and prolonged storage at room temperature is another contributory factor (so keep your fish oil supplements in the fridge to slow their deterioration).
Our Road Test also looked at whether the products contained the stated amount of active ingredients-in this case, EPA/ DHA. In a 1000-mg fish oil capsule (which refers to capsule weight), you would expect an average combined EPA/DHA content of 300 mg-180 mg of EPA and 120 mg of DHA. The good news: all of the capsules tested contained EPA/DHA to within 10 per cent of their declared amounts.
We also calculated value for money-and disproved the common belief that you always get what you pay for. We didn't test for toxic levels of mercury or pesticides. A study available online (Med Gen Med, 2001; 3: 20; www.medscape.com/viewarticle/ 408125) did look at mercury contamination of nine US brands of fish oil and found no detectable levels of mercury.
In contrast, a recent Irish survey of dioxin levels in European fish oil supplements was less reassuring (see box, p 3) so, where applicable, we also took this information into account in our assessments.
Finally, except for Higher Nature's product which claims on the label to come "from clean Arctic waters", the specific geographical sources of the fish used were not given.
Fish Oil Concentrate aaaa
Price: lb11.39 (60 softgels)
This product delivers the minimum daily requirement of EPA/DHA in a single capsule, so you only need to take one a day, as recommended on the label. Our test lab showed an EPA/DHA content of 195/133 mg, respectively, more than the 180/120 mg claimed on the label.
Also, with FFAs at less than 0.1 per cent, Solgar's fish oil has the lowest rancidity of all the products tested-quite an achievement given that it also had the lowest levels of natural vitamin E of all the products.
It is moderately expensive at 19 p per day, though some would argue that the peace of mind is worth it.
A note of caution: Solgar didn't do well in the Irish dioxin survey (see box, p 3). How-ever, those results were based on a different product and may not apply to this one.
Stable Fish Oil aaa
Price: lb7.50 (105 capsules)
Although apparently a good-value product, one capsule contains only 87/58 mg of EPA/ DHA, so you would need to take two or three capsules a day to reach the minimum RDA. In fact, the manufacturer recommends three to nine capsules daily.
But a couple of things made up for this potential drawback. This fish flesh oil was one of the freshest we tested. Using natural vitamin E as a preservative, it had a low rancidity rating (0.1 per cent FFAs). Also, this brand came out with a clean bill of health in the Irish dioxin study (see box, p 3).
If you were to take three capsules each day, this product would end up among the most expensive of our survey-setting you back 21 p/day. However, given its other virtues, some may feel that the reassurance is worth the cost and inconvenience.
Omega 3 Fish Oil aaa
Manufacturer: Higher Nature
Price: lb6.20 (90 capsules)
This one-a-day salmon-derived supplement delivers slightly less than its declared EPA/ DHA content (168/115 mg instead of 180/ 120 mg), but would still provide nearly all you need. To be sure, though, you may have to take two a day.
As for rancidity, its 0.3 per cent fatty acid level is encouraging (with no declared preservatives), but high enough to warrant caution. Look for a sell-by date that is a long way off to provide extra assurance. In the recent Irish toxicity study, this one also came out very low in dioxin and other potentially toxic waste.
As already mentioned, this was the only product to state that the product's source was "clean Arctic waters". Also, at just 7 p per capsule, this product-if absolutely fresh-was the best value for money, even if you ended up taking two a day.
Marine EPA Fish Oil aa
Price: lb5.65 (45 capsules)
Despite the word 'concentrate', this is a standard 1000-mg capsule with a declared 180/120 mg EPA/DHA content. But our lab found that each capsule contained slightly less (170/118 mg)-more likely due to the way the capsules are filled. Like Higher Nature's offering, this supplement delivers slightly less EPA/DHA than the RDA but, depending on your level of health and your diet, this may not be a problem.
If, however, you wanted to get your daily minimum EPA/DHA by supplements alone, you would need to take two capsules a day, raising the cost to 25 p per day-the most expensive of the lot. Also, even with added natural vitamin E, the sample we tested had crossed the threshold of 0.5 per cent FFAs, which could mean some rancidity.
High Potency aa
Price: lb10.50 (60 capsules)
This concentrated fish body oil product was one of the two most potent supplements in our sample. The manufacturer's recommended intake is one to three capsules daily, but one would be more than enough for most of us. The stated EPA/DHA content is 310/210 mg, but we found significantly more-364/ 272 mg-at a reasonable cost of 18 p per capsule.
But don't get too excited. With no declared preservative, this product also had the second highest rancidity level at 0.9 per cent-a disappointing finding in an otherwise good, if pricey, supplement.
Ultra Omega's aa
Manufacturer: Country Life
Price: lb12.25 (60 softgels)
This was the only supplement surveyed to have more DHA (by two and a half times) than EPA. Since the body can use EPA to make DHA, this may be particularly useful for those who suspect their fatty acid metabolism is faulty.
The label recommends two capsules a day to give you 500/200 mg of DHA/EPA (494/224 mg actual content). This product (which contains natural vitamin E) had a low rancidity rating of just 0.1 per cent.
One capsule a day would deliver nearly the total RDA of EPA/DHA (except in different proportions than most other supplements) needed by most people, though at a fairly high cost of 20 p per day. At the manufacturer's recommended level, this supplement is ridiculously expensive-nearly 41 p per day-with little extra benefit for the majority of consumers.
High Strength a
Cod Liver Oil
Manufacturer: Seven Seas
Price: lb5.29 (60 capsules)
Unlike many of the products in our sample, you can buy these supplements just about anywhere-healthfood shops, supermarkets and high-street chemists. Seven Seas is probably the best-known brand in the UK. Nevertheless, these capsules offer little in the way of EPA/DHA, with a stated combined content of 180 mg. Our lab found a total of 204 mg (112 mg EPA/92 mg DHA), slightly more than stated on the label, but less than you need in a one-a-day capsule.
Using a vitamin E preservative from a synthetic source, its FFA content of 0.4 per cent might be the beginnings of rancidity.
The label warns that exceeding the recommended dose is not a good idea (contrary to government guidelines), yet you would need to take two of these 'one-a-day' capsules to get what you need. This intake would cost 18 p per day, making this the fourth most expensive product of the eight we surveyed.
Mega EPA 1000 a
Price: lb7.05 (30 capsules)
Like the Lamberts high-potency supplement, this product provides two times the RDA for EPA/DHA-310/210 mg-and the amounts found by our lab were nearly identical at 303/218 mg. But BioCare's product is nearly 25 per cent more expensive than Lamberts'.
Also, this had the highest rancidity rating of all-1.5 per cent-in spite of relatively high amounts of natural vitamin E. It's not clear whether this was a problem of storage or a result of some particular process.
At 24 p per capsule, this is one of the most costly products we tested which, together with its lack of freshness, may represent poor value.
Liver oils versus flesh oils
Cod liver oil and fish oils are different. Oils extracted from fish liver (particularly cod liver oil) are good sources of vitamins A and D as well as useful amounts of EPA/DHA. Oils extracted from the flesh of fatty fish are also good sources of EPA/DHA, but lack significant levels of vitamins A and D.
Which you should take depends on what you are taking it for. In colder climates where sunshine is at a premium, fish liver oils may be an important source of life-giving, bone-building vitamins A and D. Studies of D supplementation in countries such as Sweden and Norway have shown this. However, if you are specifically treating heart or inflammatory diseases, a fish flesh oil would be a better choice.
The dioxin dilemma
Apart from rancidity, fish oils are associated with the problem of toxic waste that can accumulate in the liver and tissues of fatty fish. A recent study by the Food Safety Authority of Ireland (FSAI) examined 15 different fish oil capsules, most of which are also available in the UK, for the presence of dioxin. It found dioxin levels in two-thirds of them exceeding new EU safety limits (due to come into force in July 2002) for this highly toxic chemical.
Dioxin levels were highest in those products derived from fish liver oil. Indeed, the products with the highest levels of dioxin, polychlorinated biphenyl (PCB) and other contaminants were Quest's Polyunsaturated Cod Liver Oil, Solgar's Norwegian Cod Liver Oil and Boots' Cod Liver Oil. The one with the lowest level of toxins was Cardinova's Eskimo-3 Stable Fish Oil capsules. BioCare's Dri Celle Cod Liver Oil Powder and Higher Nature's Omega 3 Fish Oil capsules were also low in toxins.
The FSAI pointed out that the study was only a 'snapshot' and, given that the new directive hasn't yet come into force, it was not surprising that many of the products didn't meet the new standards. Nevertheless, it's worrying that a handful of the so-called quality brands were so high in dioxin-in some cases, five times over the new recommended safety limits. For consumers, the source and type of fish oil should be as important as the stability of the product-if they don't wish to add to the toxic burden of their body.